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Waterlogging and salinity in the Indus Plain

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Waterlogging and salinity in the Indus Plain some basic considerations
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Harvard University Center for Population Studies. Contribution
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Pakistan development review
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Dorfman, Robert.
Harvard School of Public Health -- Center for Population Studies
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[Cambridge Mass
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Center for Population Studies, Harvard University]
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English
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p. 331-370 : ; 25 cm.

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Waterlogging (Soils) -- Pakistan ( lcsh )
Salinity -- India -- West Pakistan ( lcsh )
Irrigation -- Pakistan ( lcsh )
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bibliography ( marcgt )
non-fiction ( marcgt )

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"Reprinted from The Pakistan Development Review, Vol. V, No. 3, 1965, pp. 331-370."
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Cover title.
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Contribution (Harvard School of Public Health. Center for Population Studies) ;
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by Robert Dorfman ... [et al.].

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Full Text
Dr. P. E. HILDEBRAND Ghief Economist 107* 0
Waterlogging and Salinity in the Indus
Plain: Some Basic Considerations
by
ROBERT DORFMAN, ROGER REVELLE, AND HAROLD THOMAS
-Comment by NAZIR AHMAD
-Comment by FRANK EATON
-Rejoinder by GHULAM MOHAMMAD
-:0:
Reprint from
THE
PAKISTAN DEVELOPMENT REVIEW
Quarterly Journal of
Pakistan Institute of Development Economics
Karachi (Pakistan)
Volume V-Autumn 1965-Number 3 *




Waterlogging and Salinity in the Indus Plain:
Some Basic Considerations
by
ROBERT DORFsAN, ROGER REVELLE, AND HAROLD THOMAS* INTRODUCTION
It takes more than ordinary presumption for a group of strangers to recommend changes in the efforts of a great nation to contend with a problem that goes to the very roots of its social structure and its livelihood. Yet we did just that in our Report on Land and Water Development in the Indus Plain[l]. We hoped our recommendations would be considered sympathetically and debated fully, that our sound suggestions would be adopted and our unsound ones forgiven. All this has been granted us, and more.
The months since the Panel's report was prepared have been eventful for the economic development of West Pakistan. It is hard to cast our minds back to the gloom that filled the atmosphere when the Panel was convened. Food production had been stagnant for the past several years, sem and thur were spreading through the most productive portions of the Plain, expensive efforts to control these twin menaces had been baffled. WAPDA knew, of course, that in principle tubewells could do the job, but there were more failures to report than successes. The yields of major crops were about what they had been five years before, and population growth was outstripping production.
Now many things are hopeful. The watertable has been pumped down to safe levels in large areas of the first experimental project. More than 2,000 government tubewells and perhaps 30,000 private tubewells are in operation. Fertilizer use is likely to treble in the course of the Second Five Year Plan. One does not debate stagnation any more.
This favorable turn of events has made parts of our report seem obsolete. Tasks we almost feared to suggest have proven easy. Resources we did not know existed have flowed abundantly. Some unforeseen difficulties have arisen, but, on the whole, the surprises have been happy ones. The danger now, indeed,
*Dr. Robert Dorfman is Professor of Economics and Member of the Faculty of Public Administration, Harvard University.
Dr. Roger Revelle is Richard Saltonstall Professor of Population Policy and Director of the Center for Population Studies, Harvard University. Mr. Harold A. Thomas, Jr. is Gordon McKay Professor of Civil and Sanitary Engineering and Member of the Faculty of Public Administration, Harvard University.




332 The Pakistan Development Review
is complacency-the premature conclusion that the programs already undertaken will suffice. They will not. The first positive steps have brought dramatic results because~ there was so much room for improvement in the cultivation of the Indus Plain. But fundamental shortcomings persist. There is still much hard work to be done. Just as our first message was one of hopefulness in a time of gloom, so now we want to offer some sober appraisals in a time of confidence.
One of the central themes of our report was interaction. We found that the agriculture of West Pakistan was be-set by numerous deficiencies. Efforts to correct any one of these could have only limited success, because the uncorrected shortcomings would still set a low ceiling to agricultural productivity. On the other hand, simultaneous measures to provide additional irrigation water; reclaim deteriorated land; supply chemical fertilizers, plant protection, and improved seeds; instruct farmers in the proper use of these materials and in modern agricultural methods; increase the ease and rapidity of loans to farmers; and improve marketing procedures and facilities-all concentrated on the same area-would be mutually supporting and would yield far greater increases in output than the same efforts scattered over different places. For these reasons we recommended the formation of the Land and Water Development Board and of local administrations, each responsible to the Board for supervising physical improvements and a number of agricultural programs in a single compact area. Because Pakistan has a limited supply of administrative resources, we recommended the strategy of starting project areas in succession, with development of no more than about a million acres being undertaken in any one year. We still adhere, in the main, to this broad concept. But now it appears that we overestimated some of the difficulties. Since the publication of our report, the farmers of West Pakistan have demonstrated more initiative and more willingness to adopt modern agricultural practices than we anticipated. This is indicated by the rapid spread of private tubowells-about 6,500 a yearand by the eager adoption of chemical fertilizers-usage increasing at about 20 per cent per year recently. Furthermore, it seems evident that the distribution of fertilizer, seeds, and other materials of agriculture can be accomplished efficiently through ordinary commercial channels. Thus, the agricultural administration can concentrate on providing water, agricultural advisory services, credit, and storage and marketing facilities, leaving the problems of distribution of agricultural materials and even some of the work of supplying irrigation water to private initiative. The resulting economies in the utilization of scarce administrative and technical manpawar may pe-rmit a considerable acceleration of the program.




Dorfman, Revelle and Thomas: Waterlogging and Salinity 333
A second theme implicit throughout the Panel report was integration-the hydrological problems of the Indus Plain can bast be handled on a unitary or "systems" basis. Three kinds of integration are involved.
1) The Plain as a whole and its water supply must be considered as a unit.
What is done to irrigate farm fields in former Punjab and Bahawalpur profoundly affects former Khairpur and Sind. The total water requirement for given cropping patterns and intensities in areas of given size throughout the Plain depends primarily on the potential evapotranspiration in these areas. It must be entered in any budget of irrigation water. But more important, because water in the Indus Plain is scarcer than arable land, is the total water supply from rivers and rain, and from surface and underground storage. We want to know the supplies (from both irrigation and effective rainfall), that can be made available during each month in each area at given levels of development of water structures. Comparisons need to be made of the social and economic costs and benefits of water developments in the Northern and Southern regions and their sub-regions. For each sub-region, with any given cropping pattern and intensity, the available water supplies will determine the size of the cropped area. The ultimate potential water supply for irrigation in the Plain as a whole is particularly significant, because it will fix the ultimate dimensions of the gross sown area, that is, the product of the cropping intensity times the net cultivated area. This must be the primary boundary condition in long range planning for agricultural development. The degree and speed of approach to this boundary condition are crucial for shorter range planning.
2) Irrigation water supplies fromt rivers and surface storage and from the underground reservoir should be managed as a single system. There is a marked seasonal variation in river flows, and a lack of concordance between these flows and the crop water requirements. At the same time, the unit costs of, surface storage are high, and good reservoir sites are scarce. Consequently, the proportion of river waters effectively usable for irrigation can be raised near to its potential level only if sufficient underground water supplies are also available, at the right times. Conversely, the full potential of the underground reservoir can be realized, and a high percentage of recovery of the seepage from canals, water courses, and field percolation attained, only if river waters are available at the right times and places for mixing with relatively salty or sodium-rich underground waters.
3) Supply and drainage of irrigation water should be closely integrated. To
maintain soil salinity and alkalinity control, a substantial fraction of the irrigation water applied to the fields must be drained off, either in conveyance channels or by percolation into the ground, and hence cannot be used consump-




334 The Pakistan Development Review
tively in evapotranspiration by the crops. To minimize this fraction, to postpone investments for drainage, conveyance channels, and to reduce the ultimate costs of drainage structures, it is necessary to use the underground reservoir as an integral component of the drainage system. Any ultimate tubewell system should be designed to accommodate both irrigation supply and drainage.
THE BUDGET OF IRRIGATION WATER
In a steady state, rivers and rainfall are the only sources of supply for water in the Indus Plain. While there are significant fluctuations from year to year, the average annual volume of river flow is about 136 MAF (million acre feet), and the "effective" rainfall perhaps another 10 MAF. Of the total, say 145 MAF, only about a third was available in 1960 for beneficial use by crops. A large part of the remaining two-thirds flowed to the sea unused during the months of the summer monsoon; a smaller part was lost in non-beneficial evapotranspiration from rivers, canals, and water courses. and their soggy banks, and from field ditches and edges. More than a third of the water diverted from the rivers into canals seeped into the ground, as did a small part of the river flows. A major fraction of the seepage was ultimately lost in non-beneficial evaporation from waterlogged and saline areas, where the watertable stood close to the surface.
A principal objective of water development in the Indus Plain is to contribute to increasing agricultural production by increasing the fraction of the total water supply that is beneficially used. Most of the beneficial use will be in evapotranspiration by crop plants, which. from the standpoint of water transfer behave much like little evaporating pans. But part of the beneficial use--ideally 10 to 15 per cent of the water applied to the fields-will be in achieving and maintaining a low salt content in the soil. This portion of the water will be used to wash away the salts already present or carried onto the fields with the irrigation water.
In the ultimate Water development, the water running to the sea will consist very largely of these irrigation return flows. They will be needed to carry salt off the fields and out of the Plain. The principal device for increasing the usable supplies will be water storage during the monsoon months, either in surface reservoirs or underground, and the use of this stored water during the remainder of the year. As much as possible of the seepage water will be recovered, chiefly by pumping from wells. Part of the seepage enters the ground in areas of high groundwater salinity such as characterize the Southern Zone. It will not be recoverable for beneficial use, and will have to be wasted to the sea or to desert




Dorfman, Revelle and Thomas: Waterlogging and Salinity 335
salt lagoons. Non-beneficial evapotranspiration losses will be minimized by careful water management, but these losses may actually be increased by surface storage.
Taking all factors into account, the Water and Power Development Authority of West Pakistan (WAPDA) has estimated that after construction of sufficient storage facilities, an average of some 114 MAF per year of river waters could ultimately be made available at the water courses leading to the farm fields[2]. The remaining 22 MAF would be lost, chiefly by non-beneficial evapotranspiration from reservoirs, link canals, rivers, irrigation canals, water courses, and from the border areas of all these various kinds of channels. WAPDA's estimate is based on an ultimate steady state in which only the averago annual water supplies from rivers and rain can be considered. The approach to such a steady state will inevitably be slow and expensive, because it involves very extensive construction of dams, conveyance channels, and other surface water structures. In the meantime, there is an overwhelming need to increase agricultural production in West Pakistan as quickly and inexpensively as possible. Although chemical fertilizers, improved seeds, and other production factors can contribute to this end, water is the key. Here, during the transition period, we can utilize one of the great natural resources of the earth-the enormous pool of fresh groundwater that underlies the Northern Zone of the Indus Plain, and is equal in volume to ten times the annual flow of the rivers.
In making up irrigation water budgets for this transition period, we can base our calculations either on the water requirements for an assumed cropping pattern, cropping intensity, and net cultivated area, or on the estimated supplies that can be made available at a particular time with a given level of expenditures for water development. A budget based on assumed crop requirements has the advantage that the water needed during each month can be calculated. A budget based on the anticipated availability of supplies can give only seasonal totals until a cropping pattern is specified, but it has the great merit that comparisons of different cropping patterns can be made and the economic optimum chosen.
A Water Budget Based on an Assumed Cropping Pattern
Table 1 gives an irrigation water budget based on requirements for assumed cropping patterns and intensities on a net cultivated area of 19.4 million acres in the Northern Zone, and 7 million acres in the Southern Zone. The budget is computed from data given in a report by Harza Engineering Company International, made in 1963 [31. The total irrigation requirement at the water courses is 108 MAF and the beneficial use on the fields (evapotranspiration by crops plus leaching) is 83 MAF.




336 The Pakistan Development Review
These water supplies are to be obtained by river diversions of 103 MAF at the canal heads and by pumping 36 MAF from tubewells. Only 72 MAF of the river diversions actually reach the water courses; the remainder is lost by seepage and by non-beneficial evapotranspiration. It is assumed that seepage into the ground from link and irrigation canals, water courses, and farm fields will balance the volume of water pumped. About 13 MAF of the diversions at canal heads are to be made possible by enlarging the canal system. All of the pumped water and nearly two-thirds of the canal water are to be used in the Northern Zone, with the result that about three-fourths of the total water supply is to be concentrated there.
In Table II we have computed from Harza's data the water budget by months. This table gives the interesting result that through careful coordination of tubawall and canal supplies it is possible, without enlarging the canals, to increase the beneficially usable river diversions during the kharif season by about the same amount as Harza calculates could be accomplished by canal enlargement.
Comparison of Different Budgets
In Table III, we have shown a comparison of the Harza "Programme" budget with that given in the Panel Report and with a budget for the Northern Zone computed from data given by Ghulam Mohammad[4]. The chief difference between our budget and Harza's is that ours was not based on crop requirements but on an estimate of the supplies that could be made available fairly quickly and with total expenditures much lower than those ultimately needed. We assumed construction of Tarbela and Mangla Dams to hold 12 MAF of live storage, and of a widespread grid of tubewells. These would be used to recover all possible recharge and to mine the aquifer in the Northern Zone down to a depth of about 100 feet. Another major difference is that we allocated much more water to the Southern Zone, both from canals and from tubewells. Finally, we attempted to work out a budget which would closely approach the ultimate potentialities of the river supplies in the Indus Plain, on the premise that the most rapid possible approach to the ultimate water potential offers the greatest opportunities for agricultural development and for economic and social progress. This premise receives some justification from the cost-benefit analysis of two alternative design schemes for the Northern Zone given in Chapter 7 of the Panel Report [1]. The first design involved the mining of the entire aquifer to a depth of 100 feet and provision of a firm water supply to 16.4 million acres under intensive cultivation. In the second design, the ultimate depth of the watertable was set at 50 feet; water would be pumped only at a rate sufficient to recover seepage losses in the distribution system and recharge from rivers and rain.




Dorfman, Revelle and Thomas Waterlogging and Salinity 337
While the second design entailed a much smaller investment in wells and would require considerably smaller power costs than the first, it had the marked disadvantage of providing water sufficient for the intensive development of only 11.6 million acres of cultivated land. This area is a great deal less than that occupied at the present time. Farming could be maintained over the present area only at the cost of a relatively low intensity of cultivation.
The first scheme was shown to be economically more efficient than the second when the discount rate was taken as 4 per cent per year. At this discount rate, the present value of the time stream of benefits and costs of the mining scheme was 8 per cent larger than that in which recharge only was pumped. Moreover at all other discount rates from 0 to 10 per cent per year the first scheme outranks the second. The ranking is insensitive to the discount rate and the Panel Plan with 100-foot mining and large scale tubewell development affords a 'better investment than the second scheme.
The opinion hasbeen expressed by some that the Panel Plan did not sufficiently take into account the difficulty that in mining over time the quality of groundwater will deteriorate due to the fact that salinity generallyincreases with depth. The Panel examined many hundreds of profiles of salinity and found that while this increase occurs in many places-indeed most places-the reverse is also true, and the average increase in salinity in 100 feet of depth was not large. Moreover, there are factors that operate to improve the quality of the groundwater over time. Several of the curves of salinity vs. time [1, Chapter 7J Figures 7.18 and 7.19 show a decrease in salinity after 30 years of operation. This decrease would have been even greater if the salt-flow model had been run under the plausible assumption that with a low watertable some of the salt leached below the root zone would be stored permanently in the soil pores above the watertable.
The Panel's principal argument for mining, however, did not rest upon the foregoing economic analysis. A more realistic but less quantifiable argument is that until a very large amount of surface storage is built, intensification of water use and cultivation can be accomplished in the Northern Zone only by mining or by greatly reducing the area of cultivated land. The latter would result in large social costs and perhaps monetary costs of resettlement and other adjustments.
Ghulam Mohammad's Budget for the Northern Zone[4]
A somewhat similar argument applies to the budget given by Ghulam Mohammad. Although he does not recommend a marked reduction in net cultivated area, his gross sown area in the Northern Zone would be much smaller than




338 The Pakistan Development Review
ours or Harza's and his cropping intensity lower. He assumes almost as much diversion of river waters at canal heads, but only 16 MAF of tubewell supplies, because he believes that about half the seepage water from canals and water courses, after mixing with the underground water, will be too salty or too sodium-rich to be usefully recovered by pumping. Although he does not mention the Southern Zone, by implicatin he allots it only a minor fraction of the canal diversions, since he states that his diversion scheme for the Northern Zone follows Harza's. He neglects non-beneficial evapotranspiration, but we have included this in recomputing his budget.
THE ROLE OF PUBLIC AND PRIVATE TUBEWELLS
At the time the Panel Report was written, the vigorous growth of privately installed and operated tubewells was not anticipated. About 30,000 such tubewells have now been installed, and they are making a significant contribution to the productivity of agriculture in West Pakistan. This contribution will grow as the private tubewells continue to be installed at a rate of several thousand units a year. The policy of the government in designing new SCARP and new public tubewell fields should, of course, take this development into account in order that the maximum benefit to the economy can be realized from the public and private tubewells together.
It must not be tho ought that this is simply a question of public versus private ownership. The public and the private tubewells differ from each other technologically and they will be operated in accordance with different principles and purposes. From the planner's point of view each is suitable for obtaining a somewhat different set of goals. The more appropriate mode for developing the underground water resources of any particular area will depend upon the conditions and problems prevalent in that area. The private tubewell owners have already recognized this. Although the private tubewells are quite widely dispersed throughout the irrigated region of the Plain they tend to be much more heavily concentrated in the upper regions of the doabs than elsewhere. We can make only a few tentative remarks on the four-way integration of public tub.wolls, private tubewells, canals, and drainage works, and feel that the situation must be watched closely and a sound policy developed in the light of experience. Our understanding of the operating characteristics of the private tubewells is especially deficient in spite of the excellent beginning that has been made by the two sample surveys of their operations, one conducted by Ghulam Mohammad [5] and the other by Harza Engineering Company International (6].
From a technical point of view the major differences between the two types of well are in capacity and depth. The public wells are designed for a capacity of from 3.5 to 4.5 cusecs (7 to 9 acre feet per day) and have a draft of from




Dorfman, Revelle and Thomas:- Waterlogging and Salinity 339
250 feet to 350 feet. They are intended to provide water to an area of 600 acres or more each. The private wells are much smaller. Typically their flows are from 1 to 1.25 cusecs (2 to 2.5 acre feet per day) and their drafts are typically about 100 feet. The usual practice is for the private wells to serve an area of approximately 60 acres, or 1/10 that of the public wells.
From an economic point of view, it is pertinent that the public wells are built with imported components for the most part, while the private wells use equipment of domestic manufacture. The private wells, therefore, economize on the use of foreign exchange and also contribute to the accumulation of domestic manufacturing capacity and experience.
It is evident that the larger public wells are more efficient technically than the private ones. As will b. discussed more fully in a later section the deeper draft of the large wells slows down the rate of salt build-up in the groundwater reservoir which is an inevitable result of the vertical drainage entailed by either system. The larger wells with their larger and more rugged pumps and motors, are also more efficient mechanically. It is very difficult to compare the costs of the two types of wells. Ghulam Mohammad has done so [7] and come to the conclusion that private wells can pump underground water more cheaply than government wells. This finding, however, should not be regarded as conelusive. The basic difficulty, aside from the fact that the government wells and the private ones are not in strictly comparable locations, is that different systems of accounts are used in computing the costs of the two systems of well. The cost accounts for government wells include charges for many items that the account for private wells omit, because the recorded cost for private wells incorporates only the out-of-pocket cost of the well owners. Costs of planning, supervision, and provision for contingencies, for example, are included in the government accounts but not in those for private wells, although the same economic functions must b. performed in both instances. A good justification can b- given for excluding the imputed costs of such functions from the estimate of the cost of private tub.wells. These exclusions do, however, impair the comparability of those costs with the cost of government wells. The government accounts include costs for draining saline effluent and for power transmission; private accounts do not. And there are many other similar items.
With these reservations in mind, we have tried, in Table IV, to place the costs of water pumped by private and government wells on a comparable basis, relying largely on Ghulam Mohammad's data. Costs of drainage are omitted; they would be somewhat larger for the private wells than for the government ones because the quality of the effluent would deteriorate more rapidly from the shallower wells. All costs for the provision of power are included in the




340 The Pakistan Development Review
charge of Rs. 0.08 par kwh, used for both types of installation. In other respects too the two systems have been put on as comparable a basis as possible, as the source notes indicate in detail.
The computation shows that water pumped by private tubewells costs about 8 per cent more than water pumped by government wells. In view of the inherent lack of precision of such a calculation this difference should not be taken seriously; to all intents and purposes the calculation indicates that the costs of water from the two types of well are approximately the same. It should be noted, however, that in Table IV we have assumed the same load factor for both types of well, approximately 25 per cent. This load factor accords with the recorded experience with private wells but the public wells in the SCARP have been operated at a load factor of about 60 per cent. If the more intensive use of government as compared with private wells should persist, then the government wells will show an appreciable economy in comparison with the operating costs of the private wells.
At any rate, such cost comparisons cannot be decisive, because, as remarked above, the private and the public wells serve different purposes in the overall development of the Indus Plain. Private wells have been used only for very local supplementation of the suppliesof canal water. Water provided by private tubewells is approximately four times as expensive as government canal water to the owner of the private well, and to a farmer who purchases from a private well owner, the discrepancy is even greater. Private wells will therefore be developed only in areas that have adequate supplies of high quality groundwater and they will be used mainly to fill in gaps in the supply of canal water. They have not been installed thus far in localities where the groundwater is too saline to be applied to the land without dilution with canal water. From the farmer's point of view the supply of government water from either wells or canals is less reliable than that of water provided by a locally owned tubewell and the government wells cannot be adapted as fiexibily to day by day changes in the local requirements for irrigation water. On the other hand, the government wells can be used for the dilution of saline groundwater, for reclamation of deteriorated lands, and for closely integrated management of both ground and surface water supplies.
The advantage of closely coordinating canal diversions and groundwater withdrawals can be seen from a simple calculation based on the data in Table 11. Suppose in the first instance that Mangla and Tarbela Dams are operating but that no tubewell water is available, and that the maximum amount of canal water available during any month in kharif is 12.4 MAF at the canal heads, or 8.7 MAF at the water courses, this being the maximum capacity of the canals.




Dorfman, Revelle and Thomas: Waterlogging and Salinity 341
This is only 65 per cent of the water requirement of 13.4 MAF in June, the critical month, so that under these conditions the entire program would aveh to be scaled down by 35 per cent. This scaled-down program would use only a total of 41 MAF of canal water at the water courses in kharif (59 MAF at the canal heads). On the other hand, if tubewells capable of providing 4.7 MAF per month (equivalent to a total well capacity of 80,000 cusecs) are available and suitably distributed over the cultivated area, then the required 13.4 MAF can be delivered to the water courses in June. The total delivery capacity of the canals can be utilised for irrigation from May through September, and 49. MAF of canal water can be delivered usefully to the water courses, corresponding to a diversion of 70 MAF at the canal heads. The tubewells not only supply 14 million acre feet in kharif but they make it possible to use 11 MAF of river water that would be wasted without them.
Similar calculations can be made for other assumed canal capacities, and they show in each case that the volume of beneficially usable river water during kharif can be increased by supplementing canal flows with sufficient pumping at the proper times. The same utilization of surface water could be attained by enlarging the canals. But by coordinating canal and tubewell operations, investments for enlarging and modifying the canal system can be minimized. Even more important, difficulties of silting and erosion, and of inadequate check structures on distributaries and water courses can be at least partly avoided. With the "regime" canals of the Indus Plain, these difficulties arise from large differences in canal flows during different months.
This calculation, naturally, somewhat overstates the case. An accurate computation would have to take account of the differing canal capacities and patterns of monthly irrigation requirements in the different canal systems, of the need for surface water to dilute saline groundwater, and of other complications. And, of course, perfect coordination cannot be attained. But the moral is clear that a closely integrated. operation of tubewells and canals greatly increases the efficiency with which surface supplies can be used. This close integration can be more easily attained where government wells are installed than where private ones are. But it may be possible to integrate private wells with the canal operations through wide dissemination of information about planned canal operations and economic pricing policies for both canal and tubewell water. Even before adequate well capacity is installed throughout the Northern Zone, sufficient capacity may ba developed in certain canal commands to test the scheme outlined in Table II, particularly the effectiveness of the incentives for the private operators.
One reason for the superior integration of government tubewells with canal operations is that this integration will require some changes from the historical




342 The Pakistan Development Review
patterns of canal diversions. It may be necessary or desirable to transfer surface supplies from one region to another, and to make good the transfers by additional pumping in areas underlain by high quality groundwater. These transfers will be more acceptable if reductions in surface water supplies are replaced by government-provided groundwater, but not if the deficit has to be made good by privately pumped groundwater, which, we have seen, is several times more expensive than canal water (see, for example [1, p. 280]).
Among the major benefits of the use of tubewells are the control of the level of the ground watertable and the reclamation of waterlogged and saline land. For these purposes government tubewells are much better adapted than private ones. The experience in SCARP I makes it clear that controlling the watertable requires coordinated operation of many tubewells covering a large area. Reclamation operations even when economically justifiable are not commercially attractive to private tubewell owners.
Private tubewell operations are also poorly adapted to exploiting the groundwater in regions where pools of poor quality water are interspersed among the good. If the level of the watertable is drawn down in regions underlain by high quality water to depths much below the average level, the neighbouring saline water is likely to infiltrate and to contaminate the remaining reservoir of sweet water. The long lives of some of the private tubewells indicate that this danger is not always present but it is clearly real in some places. Until accurate and detailed maps of groundwater quality can be made we must proceed with caution to avoid spoiling the underground water supplies.
Excessive lateral migration and mixing of saline with sweet groundwater can be prevented by operating all wells in a region as components of an integrated irrigation and drainage system, which is difficult when the wells are privately owned. On the other hand when problems of salinity control are likely to occur these problems may be intensified if the wells are operated by single farmer or small groups of farmers each pumping as much good quality water as he needs for his immediate use. Experience has been unsatisfactory in other countries when large numbers of privately owned and individually operated wells have been installed in regions where there are marked variations in the areal and vertical distribution of groundwater salinity.
The social effects of the private and public tubewells are also somewhat different. Water pumped by the government wells is available on the same terms to all farmers, while only the larger farmers, those operating farms of 25 acres or more, are likely to find it economical to install private tubewells. Small farmers can and do purchase tubewell water from the larger farmers, but the surveys available indicate that the prices are so high that the cost of




Dorfman, Revelle and Thomas: Waterlogging and Salinity 343
installing a private tubewell is amortized in a period of 2 or 3 years. Therefore, in regions developed by private tubewell owners the underground water supplies will benefit primarily the larger farmers. Ordinary market forces cannot be expected to moderate the price of private tubewell water to small farmers because each small farmer will be located in a position that can be served by at most one or two large tubewells. In this circumstance, it may be adviseable to regulate the price of private tubewell water just as the terms for farm tenancy are now regulated. This regulation should not be so stringent that it erodes substantially the incentive for the installation of private tubewells where they are appropriate.
This all adds up to a complicated mesh of considerations that cannot be resolved finally until we have more experience with the operation of the private wells. Tentatively it appears that the private wells, being more responsive to local day-by-day requirements, are preferable in areas where they can be installed and operated profitably, and where considerations of control of groundwater quality are not overriding. They are managerially simpler to operate and they mobilize resources of private management and capital the government cannot tap. But where land reclamation or groundwater quality control are commanding considerations,, and in areas from which surface water supplies should be diverted in the interests of overall economy, then the government tubewell developments are the method of choice. In the long run, there is also the question of coordinated operation of the canals and the tubewells in order to maxi-mi.ze the benefit from the high river flows of summer. We have suggested that it may be possible to do this with either private or public wells, but this should be tested. In any case, both sorts of wells have useful roles to play in the overall development of the Indus Plain.
QUALITY OF THE GROUNDWATER
Serious questions have been raised, most forcibly by Ghulam Mohammad [4], about the quality of the underground water in the former Punjab and Bahawalpur. These concern the salinity, or total salt concentration, of the water and the possibility of soil damage from an excessive sodium content in the presence of relatively high concentrations of carbonate and bicarbonate ions. Insufficient information exists to discuss such other problems as the potential hazards from boron, but we believe these are small.
Salinity
The Ground Water Development Organization ofthe IrrigationDepartment, and later the Water and Soil Investigation Division of the West Pakistan Water and Power Development Authority, made several thousand chemical analyses of water samples from nearly a thousand test holes, throughout 34 million




344 The Pakistan Development Review
acres of the Northern Zone. The total salt contents are summarized in Table V. We see that 16.3 million acres in the canal-irrigated regions of the former Punjab, and 2.0 million acres in canal regions of former Bahawalpur, overlie groundwaters with a salt content of less than 1000 ppm. These sweet water zones make up 70 per cent and 39 per cent, respectively, of the gross area in the canal-irrigated regions. Out of the entire 34 million acres, 21.2 million acres, over 62 per cent, have a salinity of less than 1000 ppm. There is no question that water in this salinity range can be used for irrigation, either directly or when suitably mixed with canal water. The area in the canal-irrigated regions underlain by this relatively high-quality water is close to the maximum net cultivated area, contemplated in Tables I and III for intensive cultivation.
To achieve the potentialities of the Indus Plain, it will be necessary to recapture as much seepage as possible from water courses, canals, and fields. Part of this seepage occurs in areas of salty groundwater. In the Panel Report, we assumed that groundwater with a salt content up to several thousand ppm could be used for irrigation if it is mixed with the river waters, which have a salinity of about 250 ppm. It is encouraging to note from Table V that less than 13 per cent of the entire Northern Zone is underlain by water with a salinity of more than 5000 ppm. In the canal irrigated regions, only 11 per cent of the gross area has a salinity in excess of 5000 ppm; 77 per cent has a salinity less than 2000 ppm.
In the Panel Report, we defined non-saline and saline areas as those underlain respectively by groundwater with a salinity less or more than 2000 ppm. The average salinity of water samples from the non-saline area (constituting 77 per cent of the canal region) is 750 ppm; the average for the saline area (constituting 23 per cent of the canal region) is 6000 ppm. The latter value is high because of the very high salinity of a few of the samples. If we consider instead the sizes of the areas overlying waters of different salinity, we can estimate, from Table V, that in half the saline area the groundwater has less than 50)0 ppm, averaging 3350 ppm. A good deal of this water in the "favorable" half of the saline area can be used for irrigation, if it is sufficiently diluted with canal water.
We conclude that over the Northern Zone the distribution of groundwater salinity is so favorable that extensive exploitation of nearly all the area of the underground aquifer is warranted. In order to do this safely, however, highly saline waters must be pumped from underground and carried out of the region, perhaps to desert salt lagoons.




Dorfman, Revelle and Thomas: Waterlogging and Salinity 345
Extent of Sodium Hazard In Mixtures of Tubewell and Canal Waters
The Panel became aware during its first visit to Pakistan of the sodium hazard associated with use of groundwater in some areas. In evaluating the suitability of water for irrigation, an important parameter is the potential extent of exchange of sodium ions between the water and the dispersed phase of the soils. Absorption of too many sodium ions by certain soil clay minerals can cause excessive swelling of the dispersed phase. This may drastically reduce te permeability and porosity of the soil and decrease or destroy its agricultural value. The amount of sodium absorption depends on two factors: i) the ratio of sodium ions to the square-root of one-half the sum of calcium and magnesium ions in the soil water-this is called the "Sodium Absorption Ratio" (SAR); ii) the chemical and mineralogical nature of the clay fraction of the soils.
The SAR of the soil water depends on the SAR of the applied irrigation water and on its content of bicarbonate and carbonate ions. The latter tend to precipitate calcium in the soil as CaCO3, and thereby to raise the SAR. In assessing the effect of bicarbonate and carbonate, the Panel used both the "residual" sodium carbonate (excess of carbonate and bicarbonate over calcium and magnesium in the applied water) and a new criterion developed by Dr. C. A. Bower, Director of the United States Salinity Laboratory at Riverside, California, and a member of the Panel. This criterion combines a modified Langlier index with the Sodium Absorption Ratio [8] to give a calculated "Exchangeable Sodium Percentage" (ESP).
'Clays may be divided into three groups that have markedly different tendencies to swell with absorption of sodium ions: 1) the kaolin group with a 1:1 lattice type; i) the hydrated mica group with a 2:1 lattice type; and iii) the montmorillonite or expanding lattice group with a 2:1 lattice type. Soils containing clays of the montmorillonite group (beidellite, saponite, etc.) have a large intramicellular surface and a strong tendency to expand when the soil water has a relatively high ESP. The kaolin minerals (kaolinite, nacrite, metahalloysite, etc.) and hydrated mica minerals (illite, chlorite, etc.) have fixed lattices and exhibit much smaller hydration and absorptive properties. Soil samples from the irrigated regions of West Pakistan that were examined by the Panel contain clays predominantly of the non-expanding type such as illite and chlorite. These soils tolerate larger concentrations of exchangeable sodium in irrigation water than soils containing montmorillonitic clays.
After collecting and examining field data available in 1961 relating to the chemical composition of soil and water, the Panel decided that we had insufficient information to establish the magnitude of the sodium hazard. Accord-




346 The Pakistan Development Review,
ingly, we arranged to carry out an investigation under Dr. Bower's guidance. During 1962 and 1963, chemical data from West Pakistan were sent to Riverside, and also to Cambridge, Massachusetts, for statistical analysis and evaluation. Dr. Bower carried forward a theoretical analysis of the various chemical processes at the soil-water interface that govern the uptake of sodium ions upon the clay lattice. This analysis was published by Bower and Maasland [8]. Maasland, Priest, and Malik [9] have summarized the results of the field and laboratory tests as well as the analytical studies.
In the water budget presented in Chapter 7 of the Panel Report, the predicated constraints pertaining to limiting mixing ratios of groundwater to surface water in the saline and non-saline areas were based on analyses of water from tubewells in the SCARP I project area and of water samples from elsewhere in the Northern Zone, made by the Water and Soils Investigation Division of WAPDA. The results are contained in items I C 7(a) and 7(c)(1)(2)(3) and (6) of the water budget. We estimated that in the non-saline areas of the former Panjab and former Bahawalpur the dilution ratio for one-third of the wells must be at least 1:1, while in the saline areas one-half the wells must have a dilution ratio of 2:1. These degrees of dilution were adequate to reduce the ESP to the range of 15 to 20 which we considered as generally safe for the soil types of the Northern Zone. As Maasland, Priest, and Malik show, reduction ,of the ESP to the commonly accepted "safe" range of 10-15 would require much higher dilution ratios. For example, in 40 per cent of the wells .in the non-saline area, 2.5 parts of canal water would be needed for 1 part of tubewell water. However, a reduction to this extent is probably not necessary with the mica-typa clays of former Punjab and Bahawalpur.
The Panel Report states the mixing ratios of canal to tubewell waters, as well as other design constraints based on groundwater salinity, in the form of inequalities, rather than eq"*ties, In the final solution (IC 7(e)) for the water budget, several of these containts were not binding. For example, if 77 per cent of the canal water is used in the non-saline area (see, Table III), the ratio of canal water to tubewell water at the water courses in the non-saline area is 70 per cent greater than that specified in the Report as a lower limit. In the saline area, if "skimming" wells can be used to recover canal seepage before it has become mixed with the salty underlying groundwaters, the salinities of the tubewell water may be lower than the calculated values.
The Panel Report contemplated that only 75 per cent of the area in the non-saline zone and 50 per cent of the area in the saline zone were to be cultivated. It should be possible to "pick and choose" favorable locations. In the non-saline zone, the groundwater over the best 75 per cent of the area may




Dorfman, Revelle and Thomas:w Waterlogging and Salinity 347
be expected to have a lower salinity and ESP than that predicated in the constraints of the water budget. As we showed above in discussing the distribution of salinity in the saline zone, the best half of this zone should overlie water with an average concentration of 3350 milligrams per litre.
On the basis of presently available water quality data, it is not possible to specify mixing ratios and irrigation rates or times in the various project areas with any degree of certainty, and the Panel made no attempt to do this. Any practical irrigation scheme depends on several factors. A water supply of a given salinity and alkalinity suitable for one soil type may be unsuitable for another. A given irrigation time or leaching rate appropriate for one blend of surface and groundwater may be inappropriate for another. A -program of water management for sugarcane may be unsatisfactory for pulses. It may be expected that practices will vary over a wide spectrum in the various canal commands and project areas of the Plain, depending upon local conditions. In the Northernmost, Zone, for example, the diluting effect of rainfall should be taken into consideration.
In spite of these uncertainties, the Panel Report did conclude, we believe reasonably, that integrated use of groundwater and canal water for irrigation can be safely undertaken throughout most of the cultivated area in former Punjab and Bahawalpur. Consequently, major investments to construct many large, deep tubewells are justified. In the following sections, further justifications for thigh conclusion are derived.
Salinity Control with Mixtures of Groundwater and Surface Water
The amount of irrigation water required to maximize crop production and control salination depends not only upon the consumptive use by crops but also upon the chemical quality of the water. The higher the salinity and/or the ratio of sodium ions to calcium and magnesium ions, the more water is needed. An extra amount, over and above the consumptive demands of the plants, must be allowed to percolate through the root zone. This will make it possible to maintain the concentration of salts in the soil water at a level such that growth will be sustained and excessive sodium absorption on the clay lattices will not occur. The critical period occurs at the end of the irrigation cycle just before watering, when the soil moisture is low and its salt concentration is high. The concentration at this time should be maintained at or below the tolerance level, which depends upon the particular crop and upon the type of soil. Two parameters are important in achieving salinity control i) the total depth of water applied per crop or per year; and fl) the irrigation time, that is, the period between waterings.




348 The Pakistan Development Review
The relations between the variables may be formulated as follows:Consider a soil column of unit surface area and a depth extending through the root zone to the drainage region.
Let Wr= the weight of water in the column when the soil moisture is at
field capacity, pounds per square foot;
W. the weight of water applied with each watering, pounds per square
foot;
E = the evapotranspiration rate, pounds per square foot per week;
T = the irrigation time (period between waterings), weeks;
Ca the salt concentration in the applied water;
Cr = the maximum permissible concentration in the soil water. The
magnitude of Cr is fixed by the type of crop (degree of salt tolerance) and/or the limiting value of the sodium absorption ratio
in the soil water for the particular soil being irrigated.
A = Wa/62.4T = the irrigation rate, feet per week;
R = the leaching ratio; the quantity of drainage'water as a fraction of
the amount of water applied.
After the soil has been irrigated for a period of time, the salt content in the soil will approach an equilibrium value with the increment of salt added during each cycle being balanced by the decrement of salt removed in drainage.
The amount of drainage water per cycle will be the excess of the water applied over that used consumptively. The leaching ratio therefore will be
R (W,7- M /w > 0 ................................................... (1)
With each application the soil is saturated and drainage occurs until the soil moisture reaches a level corresponding to field capacity. With good soils this process occurs in a time interval that is small compared to the irrigation time. The consumptive use during the irrigation time will be the product of this time and the evapotranspiration rate. The water remaining in the soil at the end of the cycle, therefore, will be,
W T =W f- ET > _0 ........................................................... (2)
If the system is managed so that the concentration of dissolved salts in the critical period at the end of the cycle has risen to the maximum permissible amount, the residual amount of salt remaining in the soil will be WTCT. When a salt balance is attained, the influx of salt will be balanced by the efflux to drainage. If it is assumed that the proportion of salt removed will be that of the drainage water to the total water after irrigation, then
WC -- [(W. E)(W.WT)1 (WTCT+W.C).




Dorfman, Revelle and Thomas: Waterlogging and Salinity 349
Using Equation (2) and solving for Ca,
C. (EW.- f .................................................. (3)
The maximum permissible salinity of the applied water may be formulated as
Ca =R(I-P) CT .......................................... (4)
where P =the proportion of available water used during each watering period. Equation (3) may also be written in the form
C. D,-ET/62.4 Df-ET/62.4
D., Df
where D = W./62.4 feet, and Df Wf/62.4 feet, represent respectively the depth of applied water and equivalent depth of water at field capacity.
To illustrate the use of the formulation, the following example is presented: (1) A surface water of good quality has been used successfully to irrigate land in accordance with a management scheme in which a depth of water of 0.65 feet is applied every four weeks to a soil in which the field capacity is 0.80 cubic feet per square foot (50 pounds per square foot). The evapotranspiration rate is 0.15 feet per week and the maximum permissible concentration of salt in the pore water is Cr.
From Equation (5)
C& 0.65 -0.15r .......................................... (6)
0.65 0.80
C, .0.0192 CT
(2) A tub.well field is constructed to supply additional water to increase the acreage under cultivation. The tubewells not only increase the total water supply, but they make possible greater flexibility in the timing of water applications. However, because of the concentration of salt and exchangeable sodium in the groundwater, it must be mixed with surface water to protect the soil and assure agricultural productivity equivalent to that obtained where surface water alone is used. What will be the maximum permissible concentration in the blended water supply in a management scheme in which the irrigation rate per season (or per year) is increased 25 per cent and the watering period reduced to 1.5 weeks? The value of D. will be (1.5/4) (0.65) (1.25) = 0.305 feet. Therefore from Equation (5),
Ca 0.305= 0.15(1.5) 0.80-,0.15(1.5) CT = 0.188 Cr ............ (7)
0.305 0.80




350 The Pakistan Development Review
Since the value Of CT is the same in both schemes, it follows that salinity concentration in the mixture of surface and groundwater of the second scheme can be 0. 188/0.0192 =9.8 times larger than that of the first scheme. If the surface water has a concentration of 200 milligrams per litre, then the concentration of the mixed waters can be 2000 milligrams per litre, corresponding to groundwater with a salinity of 3800 milligrams per litre mixed (or alternated with) an equal volume of surface water. Moreover, if the relative concentrations of sodium, calcium, magnesium, bicarbonate and carbonate are the same in the irrigation water used in both schemes, there will be no deterioration of the soil in the latter scheme.
In a subsequent section of this paper (see, Equation (11)) we show that the leaching ratio and hence the value of Ca/CT may be increased by increasing the pumping rate without affecting the other variables. It'is evident from the foregoing analysis that integration of canal and tubewell irrigation water supplies can incorporate a large element of flexibility in salinity and alkalinity control.
Effects of Government and Private Tubewrells on Salt Build-up and Drainage
The concept of a simple salt balance in a river basin was introduced a generation ago as a didactic device to illustrate underlying principles. Some elementary treatises on hydrology state that as an ideal a "favorable" balance should be maintained in which the efflux of salt from a region is not less than the influx. While this is patently desirable over a long span of time, it is far from being a valid design criterion that should be observed at all times, particularly in the first stages of a new era of investment in water resources. In our case a more rational criterion is to treat the vast aquifer of the northern plain as a primary resource to speed and sustain the economic development of West Pakistan. Hydraulic works for control of water and water quality should be installed in a carefully programmed sequence over a period of years. The optimal sequence may at different times entail a "favorable" salt balance in some regions, and an "unfavorable" balance in others. Decisions of this type can best be made using computer models for detailed simulation of project areas.
To maintain a salt balance, part of the irrigation water must be drained away from the region, and drainage channels must be constructed for this purpose. Drainage structures are expensive, and it will often be economically beneficial to postpone their construction for as long as possible. This can be accomplished in areas where both tubewell and canal waters are used for irrigation, if the salt is flushed out of the root zone and washed downward with recycled pumped water, to be stored underground. With typical private tubewells, which are usually only about 100 feet deep, the time interval before the underground




Dorfman, Revelle and Thomas Waterlogging and Salinity 351
water becomes so salty that drainage channels must be constructed will be relatively short, compared to the time available with typical "government" wells, which are usually about 250 feet deep.
Under some circumstances, early construction of drainage channels will be desirable, and in this case, when part of the irrigation water is drained off even in the early stages of development, the rate of increase of salt content in the underground water will be much slower than in the absence of drainage. Here also, the rate of build-up of groundwater salinity will be much less with deep governmentn" wells than with shallow private tubewells.
The following analysis, while not as versatile as the "salt-flow-model", presented in the Panel Report, shows the relationships involved. The system is assumed to be in a hydraulically steady state-the elevation of the watertable remains constant and inflows and outflows are balanced (see Figure 1)-but in an unsteady state as regards the salt content. This quantity initially may be larger or smaller than that in a steady state. The formulation shows the final concentration in the aquifer, the rate at which the system approaches salt equilibrium, and the significant design parameters. Let
Q: = inflow to irrigated area from canal system, acre feet per unit time; Qr = recharge from canal leakage and other sources, acre feet per unit time;
Q evapotranspiration rate, acre feet per unit time;
Qa =drainage flow, acre feet per unit time;
Q, =flow through tubewells, acre feet per unit time;
A = nrr2 = total area of well influence, acres or square feet; n is the
number of wells; r. is the radius of influence of a single well; and
2r. is the (approximate) well spacing, feet.
y =the proportion of total area cropped
yA =is the area under cultivation;
E =evapotranspiration rate, feet per unit time.
It is assumed that recharge and throughput are uniformly distributed over the aquifer. For a hydraulic balance over the entire system
Q + Qr'= Qe+ Qd ... .................. f .......................... (8)
where Qe = EyA = Enyr2 r ................................................... (9)
The irrigation supply derives from the canal system and the tubewells. The irrigation rate will be
Q0 + Qw Qd
_ = nyror.. .............................(10)




352 The Pakistan Development Review
The throughput including flow recycled from watercourse seepage will be
Q +Q. Eny7 > 0
and the leaching ratio (see, Equation (1)) will be
R Q +Q Q-d Enyr ......................... (11)
Q + Qw -Qd
Equation (11) shows that the leaching ratio may be increased by increasing Q, without changing any of the other variables. Accordingly, in Equation (4) an increase in Qw will increase the maximum value of the salt concentration of the mixed irrigation water supply. The flow in the well will include both the throughput and recharge. The salt carried into the groundwater in the throughput of the irrigation water and in seepage from the distribution system is assumed to be uniformly distributed over the area. The salt initially in the aquifer is assumed to be distributed uniformly throughout the groundwater. Under these assumptions and the further assumption that complete vertical mixing of the salt occurs during the travel to the well, the salt concentration will be the same in all parts of the groundwater and will increase everywhere at the same rate.
If the salt concentrations in the groundwater and in the canal water are denoted by C and C. respectively, then the weight of salt entering the groundwater during unit time will be
C. (Q. + Qr)+ C (Qw Qd)
and the amount leaving will be CQw. Therefore, the rate of increase of salt in the aquifer will be
dC C (Q, Qr) C(Q-Qd)--CQw
nSnr2h- dt- =.(,+Q
dC Cc (Qc + Qr)- C Qd
dt nS nr2h ................................. (12)
where S = the storage coefficient of the soil and h = effective depth of the well. Equation (12) may be integrated to give the following time-path for the salinity concentration in the groundwater:
C = [C. (Q. + Qr)/Qdl [1--exp (-Qdt/nSr2 h)) + C. exp (-Qdt/nS7r2h) .................. (13)
where C. is the initial salt concentration of the groundwater.




Dorfman, Revelle and Thomas. Waterlogging and Salinity 353
If the rate of drainage is very small or zero, Equation (13) may be written in the form of a linear equation in which the time rate of increase of the groundwater salinity is constant. The time required for the concentration to reach a specified maximum value Cm may be computed from the following equation.
___SAhl
t- (]C (Qc + Qr) (C.-CS) ................................................. (14)
Values of t for a range of soil salt contents from 0 to 50 tons/acre and for well depths of 50 to 250 feet are given in Table VI. In part I of this table, the initial salt concentration in the groundwater is taken as 500 mg/l; in part II, it is 750 mg/l. These values were chosen in order to keep well within the range of conditions where there is general agreement that tubewells can be used [4]. For privately operated tubewells, it will be difficult to attain an "optimum" mixing ratio of tubewell and canal waters. Hence Cm is taken as 1500 ppm. We have assumed that the volume of canal water plus river recharge is 3.3 acre feet/acre/year, C, is 250 ppm, and S is 0.25.
The times given above are those required for the average salinity in the groundwater layer which is supplying the well to reach 1500 ppm. As shown in the Panel Report, the time required for the well water to reach this salinity (after a brief initial period) will be somewhat longer than the above values, be cause thorough mixing does not occur in the aquifer. But the delay due to imperfect mixing will be short for shallow wells, and long for deep wells.
It is clear that relatively shallow tubewells without drainage channels to maintain a salt balance will become excessively salty in a few years, if they are used in areas where there is a significant initial salt accumulation in the soil. Within a few years after the tubewells are installed, channels will have to be constructed to carry away salty groundwater. If the salty water has a salinity of 1500 mg/l, the minimum amount of water that will need to be carried away will be 1/6th of the total canal supply, including that which enters the ground as recharge. Unless the conveyance channels are lined, about 25 per cent of the total water supply will have to be run into them, to make up for leakage. But part of this will, of course, be recovered by the wells. However, the 1/6th of the total supply that cannot be used will reduce the gross sown acreage.
Equation (14) and Table V give the time for salt build-up before surface drainage is installed. If soil drainage exists from the beginning, Equation (13) applies. The ultimate concentration in the groundwater will then be C. (Q. + Q, )/Qa. However, the time elapsed before a salt balance is attained may be very long. For example, if C, = 250 milligrams per litre and (Q, + Q )/Qd = 8,




354 The Pakistan Development Review
then the ultimate concentration will be 2000 milligrams per litre. If Qd/n n~ r02 = 0.25, S =0.25 and C, = 750 mg/i the salinity of the groundwater and the tubewell water at various times is given in Table VII for tubewell depths of 100 and 250 feet.
"Horizontal" versus "Vertical" Drainage
Any drainage system in an irrigated area must serve two purposes: i) removal of excess water and control of the elevation of the watertable; Ui) removal of saline water to prevent accumulation of salt in the soil. These objectives can be accomplished in one of two ways: i) by pumping water from underground and carrying part of the pumped water away from the region in conveyance channels; or, Ui) by allowing part of the irrigation water to percolate into a series of small ditches or porous tile pipes, which lead into larger "collector" and "main" drains. Such a "horizontal" system can be used to remove saline waters only if the watertable is sufficiently close to the surface to prevent a major part of the irrigation return flows from seeping out of the drains. The system is not effective for salinity control in a region where both ground and surface waters are being used for irrigation and the watertable is pumped down significantly below the bottom level of the drainage channels during part of the time. Wherever large numbers of tubewells, either public or private, are employed to supply part of the irrigation water, it will often be undesirable to keep the watertable high. Horizontal drainage structures will then have a limited usefulness, primarily to carry off flood waters.. In regions of highly saline underground water, tubewelis will not be employed to provide irrigation supplies, and either a horizontal system or a system of tubewells plus conveyance channels can be employed for drainage. Several factors should enter into the choice between these alternatives.
Horizontal drainage may be economical in certain regions of West Pakistan, particularly in parts of the Southern Zone, where conditions for vertical drainage are not satisfactory. In the Panel Report, however, we concluded that vertical drainage would be desirable in most areas of the Indus Plain.
The principal disadvantage of horizontal drainage is that it must operate with a relatively high watertable, and hence is incompatible with the use of tubewells to increase and stabilize the irrigation water supply. But other disadvantages must also be kept in mind.
1) A system of main drains and tile or open field drains is essentially a passive system. It is dependent upon gravity flow and once it is constructed it cannot easily be modified or revamped. The amount of water discharged through such a system depends upon the amount of water applied to the land it subtends, and the salt removed in drainage depends largely upon the salinity of the upper




Dorfmnan, Revelle and Thomas: Waterlogging and Salinity 355
layers of the groundwater. The flow in the main drains and laterals depends on seepage rates and these in turn depend upon the gradient of the watertable.
A vertical drainage system, on the other hand, is more flexible. The flow and sr,.linity of the mixed effluent of a set of tubewells can be controlled, and consequently, drainage can be carried out at any desired rate. This results both in a smaller investment in conveyance channels and in better salinity control, because salt can be returned to the rivers during periods of high runoff, or routed to salt
lagoons at times when the irrigation requirement is small.
Compared with vertical drainage, horizontal drainage systems are wasteful
of water. The salinity concentration of the drained water is likely to be smaller than with tubewell drainage and hence larger amounts of water must be carried
away in the drains.
2) In flat topography it is difficult to fit together efficiently a horizontal
drainage system with an intensive irrigation system. Crossings of conveyance lines of the two systems are unavoidable and are expensive. If the drainage is to be returned to the canals, pumps are required. The principal costs of horizontal drainage in the Indus Plain would be associated with pumps and with concrete control and access structures including weirs, gates, check stops,
bridges and pump sumps that cannot be built with unskilled labor.
3) Irrigated agriculture is most successful when it is most intensive, that is
when it is concentrated on a minimum land area. Open drain systems occupy a significant portion of the land area in and between the cultivated fields and hence cause the farming operations to be spread out on more land. While it is true that the supply of good land is greater than the supply of water throughout most of the Indus Plain, the layout of an extensive horizontal drainage system, which must conform to the topography and have a minimum number of inter sections with the distribution system, will extend and complicate the access routes to the fields. Farming operations are impeded when bridges must be
crossed.
* 4) Deep main drains and open field drains are difficult to maintain. Drainage works are sporadically impaired by flood damage and their efficiency is regularly reduced by growth of weeds. Flood damage to drains is inherently more
* serious than the damage to water distribution channels because of topography.
Unless pumps are used, artificial drainage must conform with natural drainage.
Consequently the drains must be adequate to handle storm runoff and must be repaired after the floods recede. Weed growth in drainage ditches is more abundant than in distribution channels because of lower flow velocity and greater nutrient supply. Maintenance of drains-removal of weeds and debris, channel realignment and repair of side slopes-is difficult and unpleasant work.- Even a
cow does not like to descend into the weedy morass of a malfunctioning drain.




356 The Pakistan Development Review
5) In semi-tropical climate the stagnant water and swampy reaches of open drains may constitute a public health hazard. The ditches afford a favorable environment for the growth of mosquitoes and snails. In other countries endemic and epidemic levels of morbidity from malaria and bilharziasis have been caused by horizontal drainage works that have not been properly maintained.
A Comment on Sub-irrigation
One of the arguments for a horizontal drainage system is that by keeping the watertable close to the surface a considerable fraction of the seepage from canals and water courses can be recovered by the crops through sub irrigation.
In the historical development of most irrigation projects it commonly happens that at one time or another enthusiasm is generated over the possibilities of sub-irrigation as a cheap method of water distribution. When such schemes are tried, however, they are usually found to have serious limitations. In some cases they have failed completely and caused serious land damage. In the United States, there have been two exceptions where sub-irrigation has proved to be more than a fad. One of these is in the San Luis Valley in Colorado, and the other in the Snake River Basin in Idaho. In both of these places the following favorable conditions obtain:
i) the slopes of the land and watertable are relatively steep so that stagnation does not occur; and
ii) the soil and subsoil are permeable (in the San Luis project the soil is almost a fine gravel, in Idaho the aquifer is a coarse-textured volcanic ash). Sub-irrigation at these sites has worked because it is possible to drain the soil thoroughly during the non-irrigation season. The soil is recharged in the spring; after the harvest the watertable is lowered and the salt carried away.
We conclude that sub-irrigation, as well as conventional horizontal drainage, might find limited application in certain localities of West Pakistan under special geological and hydrological conditions. Neither of these methods warrant much attention, however, in the primary scheme of water resource development in the Indus Plain.
CONCLUDING REMARKS
Agricultural production has shown heartening progress in the past two or three years, particularly in regions where traditional supplies of irrigation water have been enhanced either by government tubewells, as in SCARP I, or by private tubewells as in the upper part of Rechna Doab. Farmers have taken advantage of the improved water supplies with admirable alacrity. The trends in crop yields per acre and particularly in the intensity of cultivation both reflect




Dorfman, Revelle and Thomas: Waterlogging and Salinity 357'
this. There is every reason to expect that with the opening of new SCARPS and with the continued spread of private tubewells this progress will persist Nevertheless we must reiterate that insufficient water was not the only deficiency in the Indus Plain and the provision of more water is not the solution to the agricultural problem there. It is only the first step and, we hope, the catalyzing step in a movement toward thorough-going agricultural modernization. We do not have to spell out again the other measures that are urgently demanded; the report of the Commission on Food and Agriculture and our previous Report have covered these measures in ample detail. We need here only state our impression that insufficient attention is being given to the other need 's of agriculture in West Pakistan. Unless these other needs are met the ultimate results of all this effort will be disappointing. Yields will remain below world-wide averages, the ravages of insect and rodent pests will continue, and agricultural incomes will not advance as they should and must. The progress in the fields of agricultural extension, agricultural credit, seedstock improvement, and other directions has not been comparable to the progress made in improvements in water supply and in the use of fertilizer. We should like to conclude our review with an earnest plea that vigorous attention to these problems, admittedly difficult, be given the highest priority.
REFERENCES
1. White House-Department of Interior Panel on Waterlogging and
Salinity in West Pakistan, Report on Land and Water Development in the Induss Plain: (Washington, D.C.: The White House, January 1964).
2. Harza Engineering Company International, Programme for Water and
Power Development in West Pakistan through 1975. (Lahore: West
Pakistan Water and Power Development Authority, January 1964).
3. Harza Engineering Company International, A Programme for Water
and Power Development in West Pakistan 1963-75. Supporting Studies. An Appraisal of Resources and Potential Development. Chapter II: (Lahore:
Summer 1963)
4. Ghulam. Mohammad, "Waterlogging and Salinity in the Indus Plain:
A Critical Analysis of Some of the Major Conclusions of the Revelle
Report", Pakistan Development Review, Vol. IV, No. 3, Autumn 1964.
5. Ghulam. Mohammad, "Private Tubewell Development and Cropping Patterns in West Pakistan", Pakistan Development Review, Vol. V,
No.1, Spring 1965.




358 The Pakistan Development Review
6. Harza Engineering Company International, Reconnaissance Survey
of Private Tubewells. (Lahore: February 1965).
7. Ghulam Mohammad, "Some Strategic Problems in Agricultural Development in Pakistan", Pakistan Development Review, Vol. IV, No. 2,
Summer 1964.
8. Bower, C. A. and M. Maasland, "Sodium Hazard of Punjab Groundwaters", Symposium on Waterlogging and Salinity in West Pakistan.
(Lahore: West Pakistan Engineering Congress, October 1963).
9. Maasland, M. J. E. Priest and M. S. Malik, "Development of Ground
Water in the Indus Plains", Symposium on Waterlogging and Salinity in West Pakistan. (Lahore: West Pakistan Engineering Congress, October
1963).




Dorfman, Revelle and Thomas: Waterlogging and Salinity 359
TABLE 1
HARZA "PROGRAMME" IRRIGATION WATER BUDGET PART I: REQUIREMENTS
Northern Southern Total,
Indus
Zone Zone Plain
A. Assumed cultivated area (million acres)
1. Net cultivated area1 19.4 7.0 26.4
2. Gross sown area
a. Rabi 17.5 2.6 20.1
b. Kharif 11.6 4.9 16.5
c. Total 29.1 7.5 36.6
B. Irrigation water requirement (million acre-feet)
1. At water courses3
a. Rabi 36 9 45
b. Kharif 46 17 63
c. Annual 82 26 108
2. Beneficial use on fields (Evapotranspiration by
crops plus leaching)4
a. Rabi 28 7 35
b. Kharif 35 13 48
c. Annual 63 20 83
C. Depth of water used beneficially on fields (feet)
a. Rabis 1.6 2.7 1.7
b. Kharlf5 3.0 2.7 2.9
c. Annual 3.2 2.9 3.1
Source: Computed from data and assumptions in [3].
1 From [3, Table II-7].
2 Computed from cropping patterns in [3, Tables II-9 and II-10].
3 Computed from [3, Tables 1-11 and 11-12].
4 Values in B.1 multiplied by .765 (see text).
5 Values in B.2.a and B.2.b divided by corresponding values in A.2.a and A.2.b.
6 Values in B.2.c. divided by corresponding values in A.1.




360 The Pakistan Development Review
TABLE I (contd.)
HARZA "PROGRAMME" IRRIGATION WATER BUDGET PART II: SUPPLIES
Southern Total
Northern Southern Indus
Zone Zone Plain
A. From river diversions (million acre-feet)
1. At canal heads
a. Rabt 20 13 33
b. Kharif 46 24 70
c. Annual 66 37 103
2. At water courses
a. Rabi 14** 9t 23tt
b. Kharif 32** 17t 49tt
c. Annual 46** 26t 72*
B. From tubewells, at water courses (million acre-eet)2
a. Rabi 22 22
b. harlf 14 14
c. Annual 36*t 36*t
C. Total supplies at water courses (million acre-feet)t
a. Rabi 36 9 45
b. Kharif 46 17 63
c. Annual 82 26 108*t
1 Values at water courses (see A.2.), divided by 0.7.
2 Values in A.2 subtracted from corresponding values in C.
* 64.3 MAF [2, p. 28] plus 8 MAF [2, p. 29].
t From Part 1: Requirements, values in B.I.
ft From Table II.
** Total diversions for Indus Plain-diversions for Southern Zone.
*t [2, pp. 28-30]. 64.3 MAF average diversions at water courses with present canal system must be supplemented by 44 MAF to meet irrigation requirements. Of this amount, 8 MAF can be obtained by enlarging canals, the remainder can be provided by groundwater pumping and additional reservoirs.




Dorfman, Revelle and Thomas Waterlogging and Salinity 361
TABLE II
POSSIBLE AVERAGE MONTHLY WATER BUDGET IN THE INDUS PLAIN BASED ON HARZA "PROGRAMME" WITH PRESENTLY DESIGNED SURFACE STORAGE AND ASSUMED TUBEWELL AND CANAL CAPACITIES*
River and
At water courses At canal heads reservoir losses
Supplies I
Month Irri- -. Total River Changes Seepage
gation diver- flows in and eva- To sea
require- from from sions surface poration
ments canals wells storage
(1) (2) (3) (4) (5) (6) (7) (8) (9)
............... million acre-feet** ...............)
October 11.1 6.4 4.7 9.1 4.6 -4.6 0.1 0.0
November 7.0 3.0 4.0 4.3 3.1 -1.3 0.1 0.0
December 5.3 3.0 2.3 4.3 2.6 -1.8 0.1 0.0
January 7.0 3.0 4.0 4.3 2.7 -1.7 0.1 0.0
February 5.6 3.1 2.5 4.4 2.9 -1.6 0.1 0.0
March 8.8 4.1 4.7 5.8 5.0 --0.9 0.1 0.0
Rabt total 44.8 22.6 22.2 32.2 20.9 -11.9 0.6
April 7.4 5.7 1.7 8.1 8.2 0.0 0.1 0.0
May 12.9 8.7 4.2 12.4 14.2 0.0 02 1.6
June 13.4 8.7 4.7 12.4 22.4 0.0 3.0 7.4
July 10.7 8.7 2.0 12.4 30.7 +7.3 4.0 7.0
August 10.5 8.7 1.8 12.4 26.8 +4.7 4.0 5.7
September 8.7 8.7 0.0 12.4 12.4 --0.1 0.1 0.0
Kharif total 63.6 49.2 14.4 70.1 114.7 +11.9 11.4 21.7 Annual values 108.4 71.8 36.6 102.3 135.6 0.0 12.0 21.7
Assumptions: Live storage back of Mangla and Tarbela Dams = 12.0 MAF Canal capacity-12.4 MAF/month=207,000 second feet Tubewell capacity ; 4.7 MAF/month = 78,000 second feet. Annual losses from seepage and evaporation in rivers and reservoirs = 12.0 MAF [Harza, p. 291 states that 12 MAF are lost in natural river channels between the rim stations and diversion points. * Differences between corresponding values in Tables I and 2 are due to rounding.
Sources: Col. (2): Computed from [3, Tables II-1 I and II-12], combined with acreages and intensities of cultivation given in (3, Tables 11-7, 11-8 and 11-9]; see also our Table I. (sources continued on next page)




362 The Pakistan Development Review
Col. (3): Column (5) x 0.7.
Col. (4): Column (2) Column (3).
Col. (5): Maximum monthly canal diversions during kharif are limited by the assumed canal capacity of 12.4 MAF/month. Average monthly diversions during rabi are limited by the volume of water available in river flows plus surface storage; as Column (5) shows, this average is 5.4 MAF/month. With this limitation, the maximum monthly diversion during rabi is determined by the maximum difference between tubewell capacity and the irrigation requirement in any month. To minimize investment costs we have assumed that tubewell capacity is set by the amount of pumping needed in June-the month of highest irrigation requirement. This results in computed diversions of 9.1 MAF in October and only 4.3 MAF/month during November through January. Unless some canals are effectively non-perennial, the ratio between maximum and minimum canal flows of 12.4 to 4.3 may be too high to avoid difficulties of silting and erosion, and of inadequate check structures for gravity flow to water courses. These difficulties may exist even with a kharif-rabi ratio of 12.4/5.4
Col. (6): From [I, Table 1.2 and Figure 7.1].
Col. (7): Column (6)-[Column (5) + Column (8) + Column (9)].
Col. (8): River and reservoir losses from September through May are assumed to be principally by evapotranspiration. During June through August, evapotranspiration is greatly increased because of the spreading of the rivers in flood; in addition, there are major seepage losses during these months.
Col. (9): It may be possible to capture part of the runoff shown in this column through recharge of groundwater in the Southern Zone, provided additional tubewells are installed to pump out the aquifer near the Indus banks during the months of low flow.




Dorfman, Revelle and Thomas: Waterlogging and Salinity 363
TABLE III
COMPARISON OF AVERAGE ANNUAL IRRIGATION BUDGETS
Harza Ghulam
"Programme" Panel Mohammed
(1) (2) (3)
A. Cultivated area (million acres)
1. Net cultivated area
a. Northern Zone 19.4 17.05 15.8
b. Southern Zone 7.0 9.56 n.g.7
c. Total, Indus Plain 26.4 26.5 n.g.
2. Gross sown area 8
a. Northern Zone 29.1 28.4 20.7
b. Southern Zone 7.5 12.8 n.g.
c. Total, Indus Plain 36.6 41.2 n.g.
B. Cropping intensities (in per cent)9
a. Northern Zone 15010 167 13111
b. Southern Zone 10712 13513 n.g.
c. Indus Plain 139 159 n.g.
C. Irrigation water supplies (million acre-feet)
1. Diversions at canal heads
a. Northern Zone 66 4814 61
b. Southern Zone 37 44 n.g.
c. Total, Indus Plain 103 92 n.g.
2. Canal supplies at water courses
a. Northern Zone 46 3015 4316
b. Southern Zone 26 3817 n.g.
c. Total, Indus Plain 72 68 n.g.
3. Tubewell supplies at water courses
a. Northern Zone 36 4718 1619
b. Southern Zone 0 1120 n.g.
c. Total, Indus Plain 36 58 n.g.
-- -(continued)-




364 The Pakistan Development Review
TABLE III (contd.)
Harza Ghulam
"Programme" Panel Mohammed
(1) (2) (3)
4. Total supplies at water courses
a. Northern Zone 82 77 59
b. Southern Zone 26 49 n.g.
c. Total, Indus Plain 108 126 n.g.
5. Beneficial uses on fields: crop evapotranspiration plus leaching
a. Northern Zone 63 6122 4521
b. Southern Zone 20 3623 n.g.
c. Total, Indus Plain 83 97 n.g.
D. Annual depth of water used beneficially (feet)24
1. On net cultivated area
a. Northern Zone 3.2 3.6 2.8
b. Southern Zone 2.9 3.7 n.g.
c. Indus Plain 3.1 3.7 n.g.
2. On gross sown area
a. Northern Zone 2.2 2.2 2.2
b. Southern Zone 2.7 2.7 n.g.
c. Indus Plain 2.3 2.3 n.g.
E. Water losses from canals, water courses and
fields (million acre-feet)
1. Total seepage25
a. Northern Zone 29 2426 24
b. Southern Zone 14 1327 n.g
c. Total, Indus Plain 43 37 n.g.
2. Non-beneficial evapotranspiration28
a. Northern Zone 15 1029 12
b. Southern Zone 6 73o n.g.
c. Total, Indus Plain 21 17 n.g.
. .-.(continued)-




Dorfman, Revelle and Thomas: Waterlogging and Salinity 365
Sources: Col. (1) From Table I.
Col. (2) From data and computations in [1, Chapters 5 and 7, pp. 192193 and 269-284].
Col. (3): From [4, pp. 381-383].
4 Canal commanded area planted at least once during the year plus fallow.
5 In the Panel Report, the net cultivated acreage for the former Punjab and Bahawalpur is given as 16.4 MA, corresponding to "firm" canal diversions (4 out of 5 years) of 45 MAF. For comparison with Harza and Ghulam Mohammad we have used the Panel's average diversion of 48 MAF, which gives an increase of 3 per cent in the volume of water for beneficial use on crops. The net cultivated acreage is increased accordingly.
6 Mean of range of 9 to 11 MA.
7 n.g. not given.
9 Gross sown area= Net cultivated area x per cent cropping intensity/100.
9 In computing cropping intensity, Harza counts the acreage planted to sugarcane during both kharif and rabi: in the Panel Report, the sugar acreage is counted only once, in kharif. Here we have used the Harza procedure.
10 60 per cent in kharif and 90 per cent in rabi.
11 Per cent cropping intensity chosen to give same depth of water for beneficial use on the gross sown area (2.2 ft.) as in Column (1). 12 80 per cent in non-perennial area and 135 per cent in perennial area.
II Per cent cropping intensity chosen to give same depth of water for beneficial use on gross sown area (2.7 feet) as in Column (1). 14 Average canal diversions to former Punjab and Bahawalpur.
15 Seepage and non-beneficial evapotranspiration in canals are assumed to be 26 per cent and 12 per cent of canal head diversions, respectively. 16 Seepage and non-beneficial evapotranspiration in canals are assumed to be 24 per cent and 6 per cent of canal head diversions, respectively, following Harza.
17 Combined seepage and non-beneficial evapotranspiration in canals is assumed to be 13 per cent of canal head diversions. 18 41 MAF in the Panel's "non saline" area plus 6 MAF in the "saline"
area.




366 The Pakistan Development Review
19 12 MAF from canals, water courses and field seepage in Ghulam Mohammad's "non-saline area" and 4 MAF from "recharge from rain and river".
20 Total pumping at water courses required to provide 8 MAF of well water for beneficial use on farm fields (8/(1-.26) = 11 MAF).
21 Supplies at water courses-10 per cent losses in water courses and 15 per cent non-beneficial seepage plus evapotranspiration of water applied to fields. (.765 x water course supplies).
22 Supplies at water courses-20 per cent losses in water courses and farm fields.
23 Supplies at water courses-26 per cent losses in water courses and farm fields.
24 Beneficial use = evapotranspiration from crops or cultivated fields plus water required for leaching.
25 Except for Column (3), total seepage is assumed to be 37 per cent of diversions at canal heads plus 14 per cent of water pumped from tubewells.
26 35 per cent of diversions at canal heads plus 15 per cent of water pumped from tubewells.
27 26 per cent of diversions at canal heads plus 17 per cent of water pumped from tubewells.
28 Except for Column (3) non-beneficial evapotranspiration is assumed to be 16 per cent of diversions at canal heads plus 14 per cent of water pumped from tubewells.
29 15 per cent of diversions at canal headsplus 5 per cent of water pumped from tubewells.
30 13 per cent of canal head diversions plus 9 per cent of water pumped from tubewells.




Dorfman, Revele and Thomas: Waterlogging and Salinity 367
TABLE IV
COSTS OF WATER USING GOVERNMENT AND PRIVATE TUBEWELLS
(A) (B)
Item Government Private
tubewells tubewells
1. Direct construction cost (rupees) 51900 7800
2. Water distribution system and land (rupees) 3140
3. Net construction cost 47760 7800
4. Annual amortization factor (at 6 per cent) .0872 .1359
5. Annual charge (rupees) 4165 1060
6. Rate of flow (cusec) 3.9 1.25
7. Output per year. (2200 operating hours) (acre feet) 710 227
8. Capital charge per acre foot (rupees) 5.89 4.67
9. Operating cost per day (rupees) 11.06
10. Output per day, (acre feet) 0.826
11. Operating cost per acre foot (rupees) 10.80 13.38
12. Total cost per acre foot (rupees) 16.68 18.05
Sources: Rows 1, 2:1 [7, Table B-I].
Rows 3, 4, 5: Computed. 20-year economic life assumed for government tubewells, 10 years for private tubewells. Row 6: (7, Table B-I].
Rows 7, 8: Computed.
Row 9: [7, Table B-II].
Row 10: Computed.
Row 11: (A) from [1, Table 7.4, adjusted to power cost of Rs. 0.08 per Kw.hr].
(B) Computed.
Row 12: Row 8 + Row 17.




TABLE V
SALINITY OF GROUNDWATER IN NORTHERN ZONE _01
00
Area underlain by groundwater of indicated salinity
Salinity Former Punjab2 Former Bahawalpur3 Total
Canal Non-canal Canal Non-canal Canal Non-canal
regions regions4 regions regions regions regions Total
(.................................................. m illion acres...................................................)
Less than 500 ppm 9.9 0.1 1.2 11.1 0.1 11.2
500-1000 ppm 6.4 2.8 0.8 7.2 2.8 10.0
1000-2000 ppm 3.4 0.71
2000-3000 ppm 1.2 0.3 ) 1.1 0.4 7.0 1.5 8.5
3000-4000 ppm 0.6 0.1J
4000-5000 ppm 0.7
5000-10,000 ppm 1.0 1.3 0.7 2.3 0.7 3.0
10,000-20,000 ppm 0.2 0.6 0.4 0.8 0.4 1.2
More than 20,000 ppm 0.1 0.1 0.1
Total gross area 23.4 4.0 5.1 1.5 28.5 5.5 34.0
Culturable commanded area 15.2 3.5 18.7 18.7
(...............................................Per cent of gross area...............................................)
Less than 500 ppm 29.2 0.3 3.5 32.7 0.3 33.0
500-1000 ppm 18.8 8.2 2.4 21.2 8.2 29.4
1000-2000 ppm 10.0 2.1
2000-3000 ppm 3.5 0.9 3.2 1.2 20.6 4.5 25.1
3000-4000 ppm 1.8 0.3
4000-5000 ppm 2.1-j
5000-10,000 ppm 2.9 3.8 2.0 6.7 2.0 8.7
10,000--20,000 ppm 0.6 1.8 1.2 2.4 1.2 3.6
More than 20,000 ppm 0.3 0.3 0.3
68.9 11.8 15.0 4.4 83.9 16.2 100.1
Source: From (3, Table II-5, Chapter II. Irrigation Development in the Indus Plain].
1 Salinity as parts per million of total dissolved solids in groundwater samples at a depth of more than 100 feet.
2 Includes Thai, Chaj, Rechna and BariDoabs, but not Indus Right Bank areas.
3 Areas under command of Fordwah, Eastern Sadiquia, Quimpar, Bahaw canals, Plus 1.5 MA of "undeveloped" area
4 Includes 1.7 million acres in Gujrat Plain and Sialkot, where well irrigation is used, and 2.4 million acres of undeveloped and desert area in Thal Doab.
5 2.0 million acres commanded by the Panjnad Canal has been incompletely surveyed. According to Harza, about 50 per cent of this
area is believed underlain by water with less than 1000 ppm of salinity. Accordingly, we have distributed the Panjnad Canal area as follows : 0.5 million acres less than 500 ppm; 0.5 million acres, 500-1000 ppm; 0.3 million acres, 1000- 5000 ppm; 0.4 million acres, 5000-10000 ppm; 0.3 million acres; 10000-20000 ppm.




Dorfman, Revelle and Thomas' Waterlogging and Salinity 369
TABLE VI
TIME OF BUILD-UP OF SALINITY IN UNDERGROUND WATER FOR TUBEWELLS OF DIFFERENT DEPTH
I. INITIAL GROUNDWATER SALINITY=500 PPM
FINAL GROUNDWATER SALINITY= 1500 PPM
Well Soil salt, tons/acre 0 10 20 30 40 50
depth
Feet Time in years to reach 1500 ppm in groundwater
50 15.1 6.3 0 0 0 0
100 30.2 21.4 12.5 3.7 0 0
150 45.5 36.7 27.8 18.9 10.0 1.1
200 60.5 51.6 42.7 33.8 25.1 16.0
250 75.6 66.9 57.9 48.4 40.6 48.4
II. INITIAL GROUNDWATER SALINITY =750 PPM
FINAL GROUNDWATER SALINITY = 1500 PPM
well Soil salt, tons/acre 0 10 20 30 40 50
depth
Feet Time in years to reach 1500 ppm in groundwater
50 11.3 2.5 0 0 0 0
100 22.7 13.8 5.0 0 0 0
150 34.1 25.2 16.4 7.5 0 0
200 45.4 36.4 27.6 18.7 10.0 0.9
250 56.7 48.0 39.2 30.4 21.6 12.5
TABLE VII
SALINITY OF TUBEWELL WATER AT DIFFERENT TIMES, WHEN
DRAINAGE SYSTEM IS INSTALLED AT THE BEGINNING OF PUMPING
Time in years 0 10 20 40 50 100 200 250
Salinity, ppm
Well depth, 100 feet 750 870 975 1165 1230 1540 1830 1895
Well depth, 250 feet 750 800 850 935 975 1165 1435 1540




370 The Pakistan Development Review
a
0
4-Y
zI
0
cl
c7-




Waterlogging and Salinity in the
Indus Plain: Comment
by
NAZIR AHMAD*
Mr. Ghulam Mohammad, Senior Research Economist of the Pakistan Institute of Development Economics, by publishing his critical analysis of the Revelle Report in Volume IV, No. 3 of the Pakistan Development Review [4] has done a great service to the country. A chance has, thus, been created to examine some of the recommendations for the solution of the problem as put forth by the Panel of scientists from America.
Ghulam Mohammad has summarised the major recommendations of the Revelle Report and then commented upon these, giving alternative suggestions. The main recommendations of the report are to install tubewells in the large agricultural regions of the Indus Plain. This suggestion is to supplement the insufficient diversion of the surface water and at the same time to effect the drainage of the land. Ghulam Mohammad has discussed the results of the. quality of groundwater, and has concluded, "that groundwater of the Indus Plain are charged with dangerous limits of bicarbonates and sodium contents and their indiscriminate utilization will make the soils alkaline and impermeable." In his opinion, tubewells should not be installed in areas where concentration of sodium or bicarbonates is very high.
Ghulam Mohammad has further put forth the financial workability of the deep open main drains combined with the open or tile field drains. As for water economy on drained land, the author is in favour of keeping a high level of groundwater to meet with a certain amount of crop requirements from sub-irrigation.
Ghulam Mohammad has cautioned against the indiscriminate use of groundwater on the land. At present, according to the Panel of scientists, the main problem is the insufficiency of water for sustained agriculture and lack of proper utilization of agricultural practices. For finding more water and to effect quick drainage, tubewells are suggested and for improvement
*Dr. Nazir Ahmad is the Principal Research Officer (physics) at the Irrigation Research Institute, Lahore.




372 The Pakistan Development Review
of agricultural yield, better management, better seeds, use of fertilizer, pest control, use of insecticide and such other measure, known to increase the yield, are suggested. The Panel has laid great stress on the agricultural aspect of the problem. Very little consideration is given to other means of drainage, on chemistry of soil and water and other hydrological and engineering considerations. Installation of tubewells, mining of accumulated groundwater, disposal ofs aline groundwater, salinity build-up in the aquifer, spacing of tubewells, etc., are the points discussed at length in-the report. The points missed are the long term success of this measure with respect to the type and design of tubewells, their life and durability, their working cost and results of mining on water requirements of crops, effect of pumping saline water and its disposal, interaction of the quality of pumped water with the type of soils generally in existence, etc.
Tubewells have Uneconomical Durability
This country has had more than fifty years' experience of installingtubewells in fine to medium sand formation of the Indus Plain which contains some small percentages of fines, such as silt and clay. Inspite of trials of many alternatives to develop a long-lasting tubewell, giving high economical yield, the solution has yet baffled success. Chocking of strainers and their incrustation is a majorproblem. Iron strainers have short lives in the soil and waterof this Plain; strainers of inert materials like cadmium, brass and copper were all tried and found to get incrusted. Trials with inert materials like wood, and coir string also did not stop the incrustation. Recent suggestions have been to install large diameter tubewells and use strainers with wide slits. This was tried with iron and brass strainers without much success. In case of SCARP 1, tubewells were installed with all precautions but these have started to misbehave in a short period of four years.
It was suggested that for an economical performance, high discharge capacity tubewell units may be installed. This brought in the use of turbine pumps replacing the centrifugal pumps of I to 2 cusecs capacity. The life of components of a turbine pump, however, is lower than a centrifugal pump (see, Table I) and components of a turbine pump are difficult to procure.
TABLE I
Estimated
Item useful life
Well and casing 20 years
Pump turbine bowl (about 50 per cent of cost of pump unit) 8 years
Column, etc. 16 years
Pump, centrifugal 16 years
Electric motor 25 years
Diesel engine 14 years
Source: [51.




Ahmad. Waterlogging and Salinity: Comment 373
This nullified the advantages of this suggestion. Pumping a high order discharge has some other serious disadvantages of quick incrustation, due to the movement of fine formation. The farmers in West Pakistan have found a solution to the incrustation. The solution is the low cost tubewells and their frequent replacement. A farmer's tubewell, to pump one to two cusecs, hardly costs one or two thousand dollars, so ihat within the life expectancy of the tubewells (assumed ten years), they not only recover the full capital invested within one or two years, but also make tremendous profits out of agricultural produce due to the large amount of available water. So far, the farmers do not know the advantages of multiple strainer tubewells. If they adopt this device by adding three or four strainers, 100 to 150 feet in length, 50 to 80 feet. apart, they can pump a high order discharge, even upto 3 or 4 cusecs and, at the same time they can prolong the life of the tubewells. Such a technique of multiple strainers has many other advantages not possible with a single strainer, turbinefitted tubewells. In Table II, pumping from multiple strainer tubewells with respect to power input and discharge is shown. In these tests, the pump capacity was only 2 cusecs and the strainers were very shallow, hardly 50 feet long with, 30 feet of blind pipe and were pumping from very fine sand (mean diameter 0.18 mm.). A longer strainer, installed in medium sand, worked by high capacity centrifugal pump, could yield a higher order of discharge.
TABLE II
Specific yield in
Depression Discharge, yield Power in
Strainer head in feet in cfs/per cfs/foot gpm/foot kwh
gallon
Niazbeg test
Single 21.50 0.98/441 0.045 20.2 7.50
Double 15.00 1.48/666 0.100 45.0 9.25
Triple 17.24 1.64/760 0.100 45.0. 9.40
Niazbeg
Single 21.20 1.43/653 0.068. 30.6 8.90
Double 18.97 1.73/778 0.091 41.0 9.50
Triple 16.13 .1.80/810 0.111 50.0 8.80
Kohali Distributary
Single 19.60 1.10/495 0.060 27.0 8.20
Double 17.25 1.58/711 0.087 39.1 8.84
Triple 17.48 1.70/765 0.100 45.0 9.05
Lahore Branch
Single 17.00 1.28/576 0.075 33.8 8.02
Double 15.00 1.72/774 0.112 50.4 9.20
Low Order Storage Coefficient of the Indus Formation
The Revelle Panel based their estimate of mining of groundwater on a high order of storage coefficient. Although extensive boring results were available which clearly showed the existence of clay lenses and existence of silty sand, yet




374 The Pakistan Development Review
while estimating the yield of groundwater, a storage coefficient for a high yielding sand formation was assumed. It was pointed out [11 to the Panel on the receipt of the first draft report in September 1962 that the storage coefficient assumed at 25 per cent should be reduced by half as within a depth of 100 feet from surface the soil crust and clay lenses constitute about 40 to 50 per cent of the formation, but the Panel scientists used 25 per cent as storage coefficient which gave higher results. The tubewells of SCARP 1 have demonstrated the fallacy of this assumption. The fall in the level of the watertable was found to be too quick when pumping the tubewells to their full capacity.
The Panal has assumed the total infiltration from the Punjab and Bahawalpur area as 20 million acre feet. The total amount of loss of water according to the Panel is 50 per cent of that released at the head. The seepage from canal and links is 35 per cent, the remaining 15 per cent being the evaporation and other losses.
Earlier estimate of Kennedy, Benton and Blench are shown in Table IlI below:
TABLE III
WATER LOSSES FROM CANAL DISTRIBUTION SYSTEM IN THE PUNJAB
Kennedy Benton Blench Khunger
Main canals 5 5 Seepage only
Branches 15 15
Sub-total 20 16.4 20 15.5
Distributaries 6 6.1 7 5.4
Water courses 21 20.2 20 6.5
Sub-total 27 26.3 27 11.9
Total 47 42.7 47 27.4
The Panel of scientists has attempted a confirmation on the basis of rise of groundwater as a result of infiltration from various sources. Taking the rise of groundwater per year equal to 1.5 feet and assuming a 25 per cent storage coefficient, they have estimated water accumulation in 30 million acres equal to 11.3 MAF (1.5 x .25x30= 11.3 MAF). Use of a figure of 1.5 feet rise with 25 per cent storage coefficient and without giving attention to the component of sub-soil flow, this figure is a poor proof.
It is proposed to pump 49.5 MAF of groundwater. This will constitute 20 MAF of seepage and 29.5 MAF to be drawn from the reservoir. The quantity of water to be mined is thus:




Ahnad: Waterlogging and Salinity: Comment 375
a) from good quality groundwater zone ... 24.2 MAF
b) from bad quality groundwater zone ... 5.3 MAF
Assuming 15 par cent of this water to be seeping back and assuming 25 per cent to be the storage coefficient, the depth of groundwater to be lowered to yield the required discharge will be:
24.2 0.85
Good quality groundwater zone = -- 3.58 feet
23 "0.25
5.30 0.85
Bad quality groundwater zone = 0.25 2.58 feet
As it is now established that the storage coefficient is about 12 to 14 per cent, the fall of groundwater per year to give the above yield will be doubled,' i.e., about 7.0 feet per year in good quality groundwater zone and about 5.0 feet in bad quality groundwater zone.
Defects while Pumping this Order of Water
If this programme of pumping is followed, a fall in the groundwater table of 7 feet per year is expected so that the watertable will be lowered down to 100 feet in 14 years. Let us examine this suggestion for SCARP 1. In this area, tubewells are installed in which the length of housing is 90 feet and the impeller of the turbine pumps are located about 70-75 feet below surface, i.e., about 60-65 feet below average watertable, at the time of the implementation of the scheme. These wells would pump 3 to 3.5 cusecs with an average depression head of 18 to 20 feet (see, Fig. 1).
If the mining is to be done as planned with a fall of 7 feet per year, the watertable will be below the impeller after 9 years of the operation. All the 2,000 tubewells of SCARP 1 will become useless if the groundwater is mined as proposed. The 3.0 cusecs discharge was started to be pumped with 20 feet of depression and 40 feet of water cushion. After five or six years, the cushion will be eliminated and water will be pumped by the depression alone. Working of the tubewells may become doubtful. If the conception of free surface opening on the discharge face as put forth by Peterson, Isrealson and Hansen holds [2], then the tubewell of SCARP 1 will stop working when the watertable goes down to 30-40 feet from its present level, i.e., after 4 to 5 years of the pumping to mining capacity. The 2,000 tubewells of SCARP installed to work for 40-50 years shall have to be scrapped much earlier than their assumed life.
If the watertable is to be taken down to 100 feet by tubewell pumping then the length of housing pipe needed is 160 to 170 feet with impellers located at 150 feet and the strainer starting below 170 feet. This design of tubewell is not being followed even in other SCARP areas.




376 The Pakistan Development Review
PUMP MOTOR
I----------------10.0 ORIGINAL IS.S.W.L. ORIGINAL GROUND SURFACE
I / PUMP HOUSING CASING
30.0 s
I 20.0
I
I GRAVEL SHROUDING
WATER SURFACE WELL WHEN PUMPING
BOWL ASSEMBLY
- -75
75
60 6,-0
CONCENTRIC REDUCER
.. 10 SLOTTED TUBEWELL CASING. 10 SLOTS ,kBY 2 TO 3TO PROVIDE 30 SQUARE INCHES 16
OF SLOTTED OPENING PER FOOT OF CASING
210
220 220 SEAL PLATE




Ahmad: Waterlogging and Salinity: Comment 377
Loss of Component of Sub-irrigation if Watertable is Lowered
When Ghulam Mohammad wrote his comments, the data on the amount of sub-irrigation was still preliminary.
Recently detailed studies [3] have been completed on sugarcane and cotton crops. The former can grow in high watertable and the later needs a deep watertable. These studies have shown that a considerable amount of the requirements of a crop is satisfied from the soil moisture if the watertable is high.
Puming Saline Water and its Disposal
The Panel's suggestion to export 3.9 MAF of water with 4000 ppm to lower regions and to make arrangement ultimately to arrange for the disposal of about one MAF of water of 10000 ppm by surface evaporation also needs careful consideration. During three or four summer months from May to August, water is sufficient in rivers to mix 4 MAF (about 5,500 cusecs) of water and cause no harm to ultimate increase of salts but during the remaining 8 months, the river discharges are low and mixing this order of saline water will have serious problems.
Again, to evaporate about one MAF of water we need an exposed surface of about 270 square miles as in this region about 5 cusecs ate evaporated from one square mile of the surface. The obvious course appears to be not to touch the saline water and to take such measures as to obtain the requirements without the mining of saline groundwater.
A Suggestion for the Solution of the Problem
The Panel has worked out that 58.8 MAF of water is to be made available at the fields. The present irrigation canal system diverts 48 MAF and makes available 24.3 MAF at the fields. The rest 34.5 MAF is to be pumped from the groundwater storage. This is to be made up of 20 MAF from seepage of canals and 14.5 MAF to be drawn from mining operation.
We know that during the 4 summer months from the beginning of May to the end of August, we have more river water supplies than we can utilize. Suppose we do not pump any groundwater during the 4 summer months. We can arrange our requirements from improved river diversion and further digging of canals. If we spread the pumping uniformly over the full year, then during the four summer months, we have to pump 11.2 MAF of water, During summer we have available water in our rivers. It needs arrangement to divert it on the land and during this period we can do without pumping. If we can succeed in this suggestion then we need only 23.3 MAF from groundwater for




378 The Pakistan Development Review
the next eight months. The source of this much water can be from seepage of the existing canal (20 MAF) and seepage from the new diversions. We can meet our requirements from the seepage only.
With a storage coefficient of 10 per cent a one foot rise of water in 30 million acres can store 3.0 MAF. During summer, canals run at full supply, temperature is high, and better saturated sub-soil connection exists, so that sufficient seepage is possible. High summer rainfall and high stages of rivers can also be a feeding source. We may take measures, to see that as much water infiltrates into the formation as possible. Other measures to feed the aquifer can be :
i) dam water in all drains by providing over-shot gates at proper places, il) dam water in all non-perennial canals by providing over-shot gates
at proper places and time,
iii) deepen all depressions and make their beds sandy and fill them with
water during summer,
iv) construct new canals and keep them full after flood season by
providing gates,
v) encourage extensive cultivation of rice,
vi) fill all village ponds, depressions, and lakes with water and adopt
measures to keep their bed pervious,
vii) encourage porous shingle beds in places where water can be diverted
to fill the formation.
These measures will feed the aquifer during the four summer months.
As soon as the rivers fall we shall start pumping intensively. We shall not only pump all the seepage but also mine the groundwater and take it down if need ba to the limit of pumping by centrifugal pumps. The average lowering may even exceed five feet. With the approach of summer, with more water in the rivers, the pumping may stop progressively and completely during the monsoon period to feed the aquifer, so that the mined zone is charged again with water. It is true that with the watertableat 10 or 15 feet. more evaporation or evapotranspiration loss occurs but the stoppage of pumping during summer, feeding from high stage river and heavy monsoon rainfall will all fill the aquifer emptied during dry months.
This system of management of water resources has many advantages. By this system we will
i) mine the groundwater equal to our requirements,
ii) use cheap and durable centrifugal pumps with low lift,




Ahmad: Waterlogging and Salinity: Comment 379
iii) use shallow multiple strainers to pump 2 to 4 cusecs from each unit
of pumping set.
iv) not pump saline groundwater as multiple strainers will be installed
to pump the top 70 to 100 feet of the aquifer,
v) replace the stagnant groundwater richly charged with carbonates
and bicarbonates as a result of action of root zone by fresh rain
water, rich in oxygen and most beneficial to crops,
vi) start fluctuating the groundwater which will rise during summer
and will fall by several feet during the remaining eight months, thus creating a system of natural drainage as exists along the flood plains,
vii) not pump saline groundwater, which would introduce the problem
of aquifer deterioration, nor have a problem of disposal of highly
saline water.
viii) water highly charged with carbonates and bicarbonates will be
replaced by rain infiltration, and the problem of conversion of normal soil into alkaline impermeable soils by use of bicarbonate
charged water will be remedied.
The financial aspect of these suggestions can further be examined but it is certain that when we have more summer supplies available, we should utilize them by ever-lasting canals, requiring little maintenance as against short lived tubewells with costly maintenance. Integration of the presently constructed storage at Mangla can be so incorporated as to reduce pumping. When we need winter supplies we may install cheap, shallow multiple tubewells. The efforts of the farmers can even be integrated to pump during winter both for drainage and for extra supplies.
These are the suggestions which can be applied in the Punjab and Bahawalpur or where significant pumpable good quality aquifer exists such as along the strip of the Indus in Sind or in Khairpur West or in Larkana-Shikarpur Districts. This suggestion is not workable for Ghulam Mohammad Barrage in general and the lower region of the Sukkur Barrage System adjoining the Ghulam Mohammad Barrage region having high watertable of a very highly saline nature. Here, we have to create good quality aquifer before tubewells can be installed. Tile and open drains are the solution and there is no doubt about the success of this type of drainage in that area.
In the end, it is admitted that Pakistan is much obliged to the American scientists which constituted the Panel for their great service to this country.




380 The Pakistan Development Review
They not only thoroughly studied the complicated problem in such a limited period but have suggested a solution. Their study of the problem will remain a source of guidance for generations to those who are to deal with the land and water problems of this country. To the scientists it has given new avenues to explore. Science progresses on new and novel ideas.
REFERENCES
1. Ahmad, Nazir, A Discussion on Hydrological Estimation of Water Resources
as Put Forth in Chapter VI of Kennedy Mission Report. Special Report
No. 255-Ph/ Seep.-53/63. (Lahore: Irrigation Research Institute, 1963).
2. Ahmad, Nazir and Mohammad Akram, Evapo-transpiration as A Function of
Depth to Watertable and Soils. Special Report No. 291-Ph/Soil. Ph.-7/65
(Lahore: Irrigation Research Institute, 1965).
3. Dean, F. Peterson, 0. W. Israelson and V. E. Hansen. Hydraulics of Wells.
Bulletin 35. (Logan: Utah State University, March 1952).
4. Ghulam Mohammad, "Waterlogging and Salinity in the Indus Plain- A Critical Analysis of Some of the Major Conclusions of the Revelle Report",
Pakistan Development Review, Vol. IV, No. 3, Autumn 1964.
5. United States Department of Agriculture, Soil Conservation Service, Irrigation Pumping Plants. Chapter 8. (Washington, D.C. United States Department of Agriculture).




Waterlogging and Salinity in the Indus Plain: Comment
by
FRANK M. EATON*
Not only does Ghulam Mohammad's contribution on waterlogging and salinity in the Indus Plain 151 reflect a wide understanding of the agricultural problems of Pakistan but the clarity of his presentation is commendable. My comments all have to do with water quality and drainage problems in this vast irrigated area with the future rather than the immediately present problems primarily in mind. I trust that all statements will be regarded as constructive rather than critical.
The changes now occurring with irrigation in the compositions of the initially high-quality canal waters of the Indus Plain as these waters become groundwaters, appear to be little different from the past changes which occurred more slowly but which are responsible for the diverse compositions of the present groundwaters. Many of these present-day groundwaters were left behind by the flood waters which deposited the valley alluvium. The flood waters left on the land surface underwent concentration by evapotranspiration with precipitations of CaCO3 and losses of Mg in the form of compounds of salica. As a result of these precipitations there were increases in the proportions of Na.
That little of the salt being left in the soils and groundwaters of Pakistan with irrigation is now being carried to the sea is indicated by the finding that a sample of the Indus River collected near Karachi in February 1953, when the discharge was very low, was only a little more saline than that of waters sampled near the upper head works [ 31. The Karachi sample was reported to have been about 80 per cent return flow from surface runoff and drainage from irrigated lands.
The fact that little of the salt brought onto the lands of the Indus Plain by the rivers and canals is being discharged into the sea, represents a major long-time threat to the permanency of the agriculture of West Pakistan unless a suitable means of disposing of the salt residues of these irrigation waters
*Dr. Frank M. Eaton is the Associate at the Agricultural Experiment Station, University of California, Riverside, California.




382 The Pakistan Development Review
is developed. History has repeatedly demonstrated that a permanent agriculture requires that the salts added to irrigated lands be balanced by a commensurate salt removal. The mere fact, however, that a "salt balance" is achieved may be meaningless if the balance exists only after the lands are too saline for a selfsupporting agriculture. Drainage facilities should be established before, rather than after, an agriculture is impoverished.
One automatically cringes at the thought of discharging saline drainages into the canals and rivers that are supporting downstream agricultures. The destruction of old agricultures to promote new ones can provide no mental comfort. The longevity of an agriculture which supports many millions of people should be viewed in terms of centuries rather than on the basis of an expedient which may suffice for only a limited number of years.
The Report on Land and Water Development in the Indus Plain [81 and the Panel's paper estimate that with recycling of the groundwater to supply additional irrigation water and at the same time prevent a further increase in waterlogging, the groundwaters will, with 10 to 50 years of pumping, have become too saline for further use.
The reports further recognize that the quality of the groundwaters underlying the Indus Plain are uneven: "... pools of poo rquality water are interspersed among the good." By the data presented for the Northern Plain, only one-third of the groundwater contains less than 500 ppm of total salt. A total of 38 per cent contains more than 1000 ppm of salt. The reports recognize that a disastrous infiltration of bad waters into the good will occur if the elevations of the good waters are reduced by pumping below the elevations of the bad. In other words, the idea is accepted that both the bad and good waters must be simultaneously pumped but the statement on how the bad waters should be disposed of is not very specific. It is suggested only that the bad waters might be discharged into lagoons or returned to the rivers during flood periods.
Two questions are raised by these proposals, particularly since the areas of bad waters will progressively expand during the 10 to 50 year periods of pumping until all waters are salinized. When the good waters are exhausted, Pakistan will again be dependent on canal waters. Neither the present nor future bad waters which require pumping will necessarily be adjacent to the rivers. The canals for distributing irrigation waters were designed for distribution only and it would appear to require much planning and construction of newdrainage works to carry away the discharges of widely scattered wells pumped only to protect the quality of the pools having good water. The problem of disposing of the saline groundwaters is recognized as one which will become




Eaton: Waterlogging and Salinity: Commrent 383
progressively more acute as pumping is continued. Eventually, there will be only limited sources of good groundwater which can be pumped and the disappearance of good waters will become more rapid if the bad waters are not pumped.
It seems important that decisions should be made now, rather than later, as to: i) who will pay for pumping the bad waters and, ii) how will they be disposed of?
Without pumping, the levels of all groundwaters will continue to rise into root zones in the future as they have risen in the past. Waterlogging of once fertile lands has been progressive in the past in Pakistan. Without a drainage system which is designed with the same care that the distributary system was designed, the problem of land abandonment will become more acute. As lands axe abandoned because of waterlogging and salinity, it is reasonable to believe that farmers will be no more able to pay for drainage systems in the future than they are at present or have been in the past.
The two reports which have been cited emphasize advantages of the vertical (pumping) drainage systems over horizontal systems. They point further to the difficult and high costs of integrating a drainage system with the distributary system. It may be true that it would be less costly to dispose of the saline drainages by pumps discharging into special canals than by a horizontal system but, if so, only with the provision that the government, or some other agency, would provide and operate the pumps and dig the canals that would dispose of the bad waters. When pumps no longer yield good waters, the agriculture of Pakistan will be in the same position that it was in before the present pumping episode was started.
Water Quality
The water quality statistics, employed by the Panel in its initial report and in response to the articles by Ghulam Mohammad, rely on salt concentrations expressed as parts per million of total salt. There is no summary of the percentages of high-sodium, high-bicarbonate groundwaters, or of the concentrations of calcium and magnesium relative to the concentrations of carbonates and bicarbonates. With values for these components in the groundwaters, it is possible to estimate the alkalinity hazards and the effects of the waters on soil permeability. From water analyses based on the concentrations of individual ions, it is possible to estimate the percentage of the applied water which must be passed through and out of the bottom of the root zone to carry salts away fast enough to permit yields 80 per cent as high as those possible on non-saline lands. Also, with these values it is possible to estimate




384 The Pakistan Development Review
the alnount of gypsum which should be applied to the water or to the land to prevent high alkalinity, serious soil impermeability, and the deficiencies of the calcium and magnesium required for normal growth. Knowledge of the existence of the alkali problem, both present and future, is indicated by the inclusion, in the paper by Dorfman, Revelle, and Thomas, of a discussion of the "sodium hazards". There were no statistics to indicate the magnitude of the problem represented by the composition of the groundwaters or of the proportion of the land which is now so high in sodium that leaching is too slow to be fully effective. No mention is made of the use of gypsum as a corrective.
On the basis of the old groundwater analyses, which the writer was able to find in Pakistan at the time of his three-month visit in 1952-1953, the problem of excess sodium and high alkalinity in soils and groundwaters impressed him as being serious and deserving of carefulattention. Since that visit, Hausenbuiller, et al [6, pp. 356-364] were similarly impressed and recommended applications of gypsum where needed. The writer recalls experimental data from the vicinity of Montgomery which demonstrated outstanding yield benefits from the use of gypsum. No practical substitute for the use of gypsum on high sodium alkali lands is known.
Ghulam Mohammad has reviewed [5, pp. 357-403], the now-available analyses of groundwaters of the Indus Plain. Even on the questionable assumption that 1.25 me./l of residual sodium carbonate may be safe (see, later discussion), the data show that the less saline waters are commonly so high in sodium and/or bicarbonate as to make their use hazardous unless they are mixed with canal water or treated with gypsum.
Private interests will undoubtedly avail themselves of the groundwaters of Pakistan by pumping only so long as the qualities of these waters permit profitable crops. When there is no longer a profit, the wells will be abandoned, after which the watertables will again rise. It seems doubtful at this stage that private funds will be available for the construction of the drainage system which should have been established when the distributary canals were constructed. The cost of a country-wide drainage system is so great that it seems doubtful that public agencies can now undertake it.
On-Farm Drainage
It was for the foregoing reason, and the foregoing reason only, that the writer in his FAO report [3] suggested a type of drainage system which he believed the farmers themselves could install and maintain. Such a system, although not ideal, may be the only recourse possible, now or in future, in many areas of Pakistan.




Eaton: Waterlogging and Salinity: Comment 385
Under ideal practice, saline drainages should discharge into the sea or into natural closed lakes or large land depressions. Horizontal drainage systems of large scale are expensive and, as noted in the reports cited, they seriously interfere with water-distributary systems.
The lands of Pakistan tend to be flat and for that reason, the drainage canals would have to be of large capacity and often augmented by pum ping to obtain the necessary discharges. Also to accommodate the necessary depths of field drains, the public canals would have to be deep.
As has been repeatedly noted by others, Pakistan has a great surplus of arable land in relation to its water supply. It is now apparent that the distributary system was designed to serve more land than could be cropped at any one time. It seems possible, if not probable, that the planners hoped thereby to at least slow down the rate of rise of the watertables, and thereby to postpone waterlogging. Over vast areas waterlogging has now become acute.
With the great excess of arable land, the writer believes that the cultivated acreages could appropriately be cut back to approach the land that can be served by canal or good-quality groundwaters. With such cut backs, there will be continuously idle lands that can be converted to evaporation flats-areas which are surrounded by low dikes or areas upon which the saline drainages can be spread by networks of furrows.
In the light of the effects of canal seepage and rainfall on rising watertables, in addition to the necessary leaching to remove existing salinity and to continuously remove the salts deposited in soils with irrigation, it is possible to estimate the required areas of the on-farm evaporation flats in relation to the area of the land irrigated. With knowledge of evaporation rates, leaching requirements, rainfall, and surface runoffs, such estimates become quite simple.
Under the evaporation-flat system, the farmer himself would install the field, drains (tiles or ditches) and the disposal ditches leading to his evaporation flat. Since the field and connecting drains should be installed to depths of upward to seven feet or more, small on-farm deep collecting sumps are necessary for the accumulation of the day-to-day drainage. Pumps, whether power or Persian wheel, are necessary for the discharge of drainage effluents from the sumps onto the evaporation flats.
The installation of on-farm evaporation flats is, of course, not an ideal substitute for country-wide drainage systems. But the method, as an alternative, is regarded by the writer as one of much promise under the existing




386 The Pakistan Development Review
circumstances and one which would p.-rmanently reverse the downward trend in production which has resulted from waterlogging and salinity.
Deep field and collecting drains should always serve the double purpose of disposing of saline wastes and of providing deep, well-aerated root zones.
Water Quality Evaluation
Tf a water is to be used for irrigation, it is deserving of a careful chemical analysis to make possible estimates of how it can be used most effectively. From analyses for each ion expressed in milligram equivalentsper liter (me./l), it is a simple matter to calculate leaching, or drainage, requirements and to estimate, also, the amount of gypsum which should be applied to maintain permeability and high production.
Ghulam Mohammad has pointed to a weakness in the Revelle Report in that emphasis was placed on total salinity with a neglect of the significance of bicarbonate in the precipitation of calcium and the resulting higher sodium percentages. He regards it as probable that many groundwaters which the Panel recommended as suitable for irrigation would result in low soil permeability and high alkalinity unless mixed with large quantities of canal water or used with heavy applications of gypsum. Because of insufficient canal water, the necessity of gypsum, and the costs of development, he recommends the elimination of tubewell installations over the Punjab and Bahawalpur, and undoubtedly elsewhere, except where sodium and bicarbonate concentrations are found to be low relative to calcium and magnesium. On the other hand, many waters that are now unsuitable for irrigation because of high bicarbonate can be successfully used by additions of gypsum. Reference will be made in a subsequent paragraph to the nature of the experimental evidence which led the Panel to regard 1.25 me./l of residual sodium carbonate in irrigation waters as "probably safe". Workable gypsum deposits are available in Pakistan and experimental evidence exists in Pakistan which shows that notable benefits of gypsum applications have resulted even in some of the canal-irrigated land. Hausenbuiller, et al [6, pp. 357-364] note that while power and machinery for mixing gypsum with water maybe expensive, applications of the finely powdered material directly to the land is practical.
Ghulam Mohammad refers to statements byHanson, Bower and Williams on advantages of maintaining subsurface waters within the lower root zone if care is taken to insure that adequate salinity control is exercised. Although it is true that water may be effectively stored in the deeper root zone, as in the polders of Holland where salinity is not usually a problem, the dangers of extending the concept to some of the irrigated lands of Pakistan are obvious.




Eaton: Waterlogging and Salinity Comment 387
If an irrigation water containing 10 units of chloride is used over a few years to produce a uniform 10 per cent of leaching, the leachate will contain 100 units of chloride; with 20 per cent of leaching, the leachate will contain 50 units of chloride; but with only 1 per cent of leaching there eventually will be 1000 units of chloride in the drainage. Drainage systems serve the double purpose of increasing the depth of aerated soil and of removing salt from the land. Plants take up more salt-relative to water uptake-as concentrations are increased and it is the salt in the plant that depresses growth.
Prior to my short visit to Pakistan in late 1952 and early 1953, I had spent a good bit. of time developing a set of simple equations for evaluating the quality of irrigation waters in the light of field and experimental responses. Those equations were included in my FAO report to Pakistan [3] and later published with the background information as Texas Agricultural Experiment Station Miscellaneous Bulletin 111, 1954. Since then a few minor simplifications and changes in constants have appeared to be advantageous.
Inasmuch- as CaSO4 added to a soil or water increases the SO4 content, one first computes the Ca requirement of the water and then adds I the required Ca to the sum of C1+ S04. For a number of plants, S04 has proven to be only half as toxic as Cl, equivalent for equivalent.
Calcium and Gypsum Requirements
The object here is to produce leachates with no more than 70 per cent Na.
Required Ca: me./l = sum of a, b, and c as shown below:
a) Ca+Mg needed, if any, so that the Na per cent will not exceed 70:
Na x 0.43 (Ca + Mg) Retain + or sign
b) Compensate for CaM+g that will probably be precipitated: (C03+HCO3) x 0.7
c) Compensate for the Ca + Mg in excess of Na that is removed from
the land by average crops: Add 0.5 me./l. This value is suggested for Pakistan because of the large amounts of forage which is carried into
the villages. Without such removals the value 0.3 me./1 is suitable.
Gypsum Equivalent of required Ca:
sum of a, b, and c X 234 =pounds of gypsum, if any, per acre foot of
water. (See, guide in Table I).
Leaching Requirements
RL = Leaching requirement
Sw = Salinity of the water expressed as Cl + SO4 + I- required Ca.
Mss = Mean soil solution concentration expressed as: Cl I -SO4 i.e., the average of the water and leachate.




388 The Pakistan Development Review
TABLE
GUIDE FOR COMPUTING THE LEACHING AND
Calculations (see
Calcium
Composition of water me./liter
(a) (b)
NaxO.43 C03 +HCO3
Water EC x -- '0 Minus x 0.7
No.** (10)6 Ca g Na C03 H C1
3 S4 CI (Ca+Mg)
1 52 0.21 0.12 0.19 0.00 0.34 0.05 0.16 -0.25 0.24
2 350 1.15 0.93 1.78 0.00 1.14 0.67 1.72 -1.315 0.798
3 420 2.35 0.75 1.39 0.00 2.94 0.98 0.56 -2.503 2.058
4 985 4.17 2.26 3.81 0.00 2.76 5.51 2.11 -4.80 1.93
5 789 0.24 0.02 7.28 0.00 2.39 2.48 2.47 2.87 1.67
6 2170 2.33 0.57 17.43 0.00 1.92 6.30 11.92 4.59 1.34
**Water sources: (1) San Joaquin River, California, (2) Gage Canal, Riverside, California, (3) California, (6) Well, Coachella Valley, California
*A mean soil solution (Mss) value of 30 is used for this calculation. tThis is the per cent of irrigation water applied which must be passed beyond the root zone to




Eaton: Waterlogging and Salinity: Comment 389
I
GYPSUM REQUIREMENTS OF IRRIGATION WATERS
formulas under text (pages 387-391) Appraisal
Requirement Leaching requirement Gypsum
-requirement Leaching
(c) (d) Sw= LR= (d)x 234= requireCrop Ca Require- Cl + ISO4 2xMss*-S Swx 100 lbs. Gyp./ac. ment
removal ment in me./1. + I required ft. water in
adjustment [(a) + (b)+(c)] calcium 2X(per cent) percentt
-____________ _____________ (per cent)
0.30 0.29 0.33 59.67 0.5 68.0 0.5
0.30 -0.21 2.10 57.90 3.6 None 3.6
(None)
0.30 -0.14 1.05 58.95 1.8 None 1.8
(None)
0.30 -2.57 4.86 55.14 8.8 None 8.8
(None)
0.30 4.84 6.13 53.87 11.4 1130.0 11.4
0.30 6.23 18.18 41.82 43.5 1460.0 43.5
Tracy Mendota Canal, California, (4) Colorado River, U.S.G.S. 1950, (5) Wel, Bakersfield,
keep salt from accumulating beyond levels consistent with good crop performance.




390 The Pakistan Development Review
Sw X 100
RL=
2 x Mss-Sw
For annual plants of low salt tolerance Mss = 20
For annual plants of medium salt tolerance Mss. 30
For annual plants of high salt tolerance Mss 75
For standard water-quality comparisons, the use of Mss = 30 is suggested.
Comments on the Derivation of the Equations
The leaching requirement, RL, represents the percentage of the applied irrigation water which should be passed through and out of the root zone as leachate for the maintenance of yields averaging 80 per cent as high as on similar non-saline soil. If the equations, when converted to acre inches of leachate, for example, show that there should be five acre inches of leachate, this amount remains valid irrespective of whether the actual leaching is brought about by irrigation or by rainfall, i.e., the rainfall may produce the leaching but the acre inches of required leachate computed on the basis of the amount of irrigation water applied is not changed.
In the RL calculation, unreasonably high values result if either the electrical conductivity or sum-of-cations is substituted for Cl + -S04, because HCO3 would be included; HCO3 is not significantly accumulated by plants. But its presence as NaHCO3 depresses Ca and Mg accumulations. These ions, in ample amounts, are essential for good crop production. It is more economical to avoid the adverse effects of HCO3 by the use of gypsum than by extra leaching. In the instance of the Indus River at Sukkar on January 30, 1953 [3]. the leaching requirement by the present equations is 1.4 per cent. But on the basis of electrical conductance or sum of anions or cations, the requirement is found to be several times greater and unreasonably high.
The expression, in the Ca requirement equations, Na x 0.43 shows the amount of Ca + Mg needed for 70 per cent Na. If a water contains 5 me./l of Na then Na x 0.43 shows that 2.15 me./1 of Ca + Mg will be needed to give 70 per cent Na. The deficiency or excess from 2.15 is carried forward with the plus or minus sign in computing the Ca requirement: a+b+c.
The present Mss values (used in the denominator of the RL equation), are lower than those previously suggested because of experimental results [4, pp. 411-416] showing that chloride accumulates at root surfaces and gives rise to higher accumulations in plants on a soil than on a water culture even though the substrate concentrations are maintained at the same level.




Eaton: Waterlogging and Salinity: Comment 391
The extent of precipitation of CaCO3 in soils is a function of the CO2 partial pressure in the soil atmosphere and the concentrations of the reacting constituents. The latter are largely determined by leaching rates but estimates of C02 partial pressures in soils are difficult since they are dependent on the density in the soil of living and dead roots, their respiratory rates, and the freedom of gaseous exchange between the soil and the air above. The pH of soils measured in the laboratory after exposure to the atmosphere are usually much higher than when measured in place in the field.
Only a few good data are available on the proportion of the HCO3 in water supplies that are normally precipitated in soils. Among the best of these are the results presented by Pratt, et al. [7, pp. 185-192]. It was found that in the order of 50 per cent of all the HCO3 applied by an irrigation water with "88 per cent sodium possible" (i.e., Ca -2.43, Mg -0.76, Na 1.46, and HCO3 3.00 me.!l) was precipitated both in a .20-year lysimeter experiment and in an orchard irrigated for 38 years. In the foregoing "Ca requirement" equations use is made of Pratt's average value for loss of HCO3, i.e., 50 per cent, but in addition a 20 per cent allowance is made for the precipitation of Mg largely in the form of silica compounds, i.e., the value 0.7 x HCO3 is used in computing Ca + Mg requirements.
It is unfortunate that each of three extended (21 months to 4 years) and carefully conducted experiments on the significance of CO 3- HCO 3 in irrigation waters failed to take account of the importance of C02 partial pressures in the soil atmosphere on the extent of precipitation of CaCO3 (Wilcox, et al[9, pp. 259-2661); Babcock, et al [2, pp.155-164]; and Hausenbuiller, et al[6, pp. 357-364]. In each of these experiments the plants-respectively, Rhodes Grass, alfalfa, and Bermuda Grass-were grown in containers and irrigated with waters having various ratios of Ca' Na and HCO3: Cl. The oversight in the experimental designs is represented by the fact that the containers were not surrounded by densities of plants equal to those of the test plants in the containers. With the foregoing provision, lateral light would have been reduced and the top growths would have been more nearly proportional to soil area. But with the tops spreading out, the root densities must have been very high in the limited soil volumes (2, 32, and 5 gallons, respectively). The production of respiratory CO2 being somewhat proportional to root density, the precipitation of CaCO3 would, to a corresponding extent, have been inhibited by the high CO2 partial pressure, and the development of high ESP would have also been restricted. Babcock, et al. [ 2]make the observation that while little CaCO 3 precipitation occurred in their soils, it did occur in their collecting pans as the leachates came into equilibrium with the outside air.




392 The Pakistan Development Review
Hausenbuiller, et al (6] obtained a correlation coefficient of .984 between the residual Na2CO3 in 11 waters and the exchange sodium percentages found in the top eight inches of 11 soils and yet five of the waters contained less HCO3 than Ca + Mg. In accord with Pratt, et al. [7] much CaCO3 may be precipitated even though there is no residual Na2CO3 in the water. Pratt, et al. [7] found rather large increases in the ESP and pH values of the irrigated soils in both the lysimeter and field experiments.
REFERENCES
1. Asghar, A.G. and M.A. Hafeez Khan, "Behaviour of Saline-Alkaline Punjab
Soil Under Reclamation", Proceedings of Punjab Engineering Congress.
(Lahore Punjab Engineering Congress, 1955).
2. Babcock, K.L. et al., "A Study of the Effects of Irrigation Water Composition on Soil Properties", Hilgardia, 29(3), 1959, pp. 155-164.
3. Eaton, F.M. FAO Report No. 167 to the Government of Pakistan on Certain
Aspects of Salinity in Irrigated Soils. (Rome: FAO, September 1953).
4. -,--------- and J.E. Bernarelin, "Mass Flow and Salt Accumulation
by Plants on Water Verus Soil Culture", Soil Science, Vol. 97, No. 6, June
1963.
5. Ghulam Mohammad, "Waterlogging and Salinity in the Indus Plain: A
Critical Analysis of Some of the Major Conclusions of the Revelle Report",
Pakistan Development Review, Vol. IV, No. 3, Autumn 1964.
6. Hausenbiller, R.L., M.A. Haque and Abdul Wahab, "Some Effects of Irrigation Waters of Differing Quality on Soil Properties", Soil Science, Vol. 90,
1960.
7. Pratt, P.F., R.L. Branson and H.D. Chapman, "Effect of Crop, Fertilizer
and Leaching on Carbonate Precipitation and Sodium Accumulation in Soil",
VII International Soil Science Soc. Cong. Trans. 2, Vol. 11, 1960.
8. White House, Department of Interior Panel on Waterlogging and Salinity in
West Pakistan, Report on Land and Water Development in the Indus Plain.
(Washington D.C.: Suptt. Doc. January 1964).
9. Wilcox, L.V., G.Y. Blair and C.A. Bower, "Effect of bicarbonate on suitability of water for irrigation", Soil Science, Vol. 77, 1954.




Waterlogging and Salinity in the
Indus Plain: Rejoinder
by
GHULAM MOHAMMAD*
Most of the points raised by the Panel members, Drs. Roger Revelle, Harold Thomas and Robert Dorfman, have been answered in the comment by Dr. Frank M. Eaton. Dr. Nazir Ahmad has further elaborated some of the issues involved. The author will confine his remarks to two basic issues, namely, pumping of water for irrigation purposes in the non-saline high quality groundwater areas in the Northern Zone of the Indus Plain and provision of horizontal sub-surface drainage facilities in areas where the groundwaters are saline and unfit for irrigation use.
The author is happy to note that the Panel members acknowledge the significant contribution made by private tubewells to the productivity of agriculture in West Pakistan. The author agrees with the Panel members that private tubewells will be developed mainly in areas that have adequate supplies of high quality groundwater and not in areas where the groundwater is too saline to be applied to land without dilution with canal water.
Ina previous article, the author proposed that horizontal sub-surface drainage facilities should be provided in the saline groundwater areas [5, pp. 387-3951. The Panel members do not agree with this and propose instead deep tubewells for irrigation as well as for drainage purposes. They suggest that with the use of deep tubewells and canal water the salt be flushed out of the root zone and washed downward with recycled pumped water to be stored underground.
The Panel members consider that drainage structures are expensive, and argue that provision of drainage facilities should be postponed as long as possible (p. 350). The author considers thatthis is a dangerousrecommendation, As pointed out by Dr. Eaton (p. 382), the areas of bad waters will progressively expand during the next 10 to 50 years until all waters are salinized. With increasing salinity of groundwaters, agricultural production will progressively decline unless large scale drainage channels are constructed to remove part of the pumped waters out ot the area.
*The author is a Senior Research Economist at the Pakistan Institute of Development Economics. He is indebted to Dr. Bruce Glassburner, Senior Research Advisor, Mr. Keith Griffin, Research Adviser in the Institute and Mr. Carl Gotsch of the Harvard Advisory Group at Lahore for their valuable comments on the earlier draft. The author is grateful to Mr. Mohammad Ghaffar, Research Assistant, for assistance in computations. Responsibility for the views expressed and for any errors is entirely that of the author however.




394 The Pakistan Development Review
Dr. Eaton has raised two important questions on this issue (p. 383). He asks i) who will pay for pumping the bad waters and ii) how will these be disposed of?
As stated by Dr. Eaton, neither the government nor the farmers will be able to pay for the drainage structures when all the groundwaters have been salinized; certainly, they are better able to do so now when only part of the groundwaters are salinized.
It would be in the interest of Pakistan to install tubewells in the non-saline best quality groundwater areas only. These areas lie in the upper reaches of the Rechna, Chaj and Bari Doabs and along both sides of the rivers in the Punjab and Bahawalpur. Farmers are already installing tubewells in these areas. To keep the groundwater of these areas in good condition, Dr. Nazir Ahmad has suggested that the canal water supply to these areas should be increased during the summer season when there is excess water in the rivers. This would increase the infiltration of fresh water to the groundwater and in this way these areas could be kept fit for pumping for an almost indefinite period.
According to Harza Engineering Company International, the present river diversions into the West Pakistan canals are about 83 MAF per year, 48 MAF in the Northern Zone and 35 MAF in the Southern Zone [9, p. 39]. About 20 MAF of water is lost through seepage and evaporation in the rivers and about 61 MAF goes to the sea mainly during the summer season [9, p. 39]. It should be possible to divert some 10 MAF additional water to the non-saline groundwater areas out of the 61 MAF now going to the sea.
If the capacity of canals is increased and additional water is diverted onto these areas during the kharif season, the rabi water supply can be withdrawn from these areas. The farmers can install tubewells and meet the full need of the rabi crops by pumping groundwater. The rabi water removed from these areas can be diverted to saline groundwater areas in the lower reaches of the doabs where tubewells cannot be installed on account of high salinity.
In order to encourage the farmers to install tubewells in the non-saline groundwater areas, electricity should be provided to the whole of this area, and credit should be extended to the farmers for the purchase of tubewell materials.
In the remaining areas of the Punjab and Bahawalpur where groundwaters are relatively more saline, drainage facilities must be provided to remove the salt from the area. However, a basic problem of these areas is the deficiency of irrigation water. The capacity of the canals will have to be increased and addi-




Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 395
tional river water will have to be diverted on to these lands to meet the consumptive use requirements of crops and to leach down the salts. At the same time drainage channels will have to be constructed. As pointed out by Dr. Eaton, the drainage facilities must be provided before, rather than after, the agriculture is impoverished.
Saline Groundwater Areas
The most damaging recommendation in the Revelle Report was the proposal to pump water in the saline groundwater areas (having an average salinity of 6000 ppm), to mix it with canal water and to use the mixed water with an average salinity of 2000 ppm for irrigation purposes [18, p., 281]. The Panel members now consider (p. 344) that at least in half of the saline area the groundwater has a salinity of less than 5000 ppm, and this can be used for irrigation if it is sufficiently diluted with canal water. For justifying the use of this saline groundwater, the Panel members have developed a set of equations which are given on pages 348-350 of their paper.
Taking two examples, one with irrigation by canal water and the other with irrigation by mixed canal and tubewell water, the Panel members have shown (p. 350) that the salinity of the mixed water can be0.188/0.0192 =9.8 times larger than that of the canal water. Thus if the surfacewater has a salinity of 200 ppm, the concentration of the mixed water can be 2000 ppm, corresponding to a groundwater with a salinity of 3800 ppm, mixed with an equal quantity of canal water.
It appears that the Panel members obtained their result by making two incorrect assumptions: 1) The depth of irrigation water was taken as .65 feet (or 7.8 inches) and the interval of canal irrigation was taken as 4 weeks; 2) with 25 per cent increase in water supply with the installation of tubewells, the interval of irrigation of mixed water was reduced from 4 weeks to 1.5 weeks. The actual depth of irrigation in West Pakistan is 3 to 4 inches which is about one half of that assumed by the Panel members. The water is generally applied after 2 weeks. When irrigation supply is increased by 25 per cent, the interval of irrigation can be reduced from 2 weeks to 1.5 weeks, but not from 4 weeks to 1.5 weeks. If the example on page 349 is recalculated by taking depth of irrigation as 0.325 feet and interval of irrigation as 2 weeks, the salinity concentration of the mixed water would be 0.188/0.048 or 3.9 times that of canal water. If the salinity of canal water is 200 ppm, the salinity of mixed water can be 780 ppm, corresponding to a groundwater salinity of 1360 ppm when mixed with an equal quantity of canal water.




396 The Pakistan Development Review
To use mixed canal and tubewell water having a salinity of 780 ppm for crops of medium salt tolerance, about 18 per cent additional water will have to be provided for leaching purposes [18, p. 117]. This would mean that 30 per cent of the tubewell water will have to be pumped for leaching purposes onlyl. If on the other hand saline water containing as much as 3800 ppm is pumped and mixed with an equal quantity of canal water and mixed water having a salinity of 2000 ppm is used for irrigation as suggested by the Panel members, nearly 67 per cent of the mixed water would be required for leaching purposes with crops of medium salt tolerance [18, p. 117]. This means that about 80 per cent of the pumped water will have to be used for leaching purposes only2. In the case of crops of high salt tolerance such as cotton and barley, the leaching requirement will be about 25 per cent of the mixed water or about 40 per cent of the pumped water. Even with the provision of drainage and removal of 40 to 80 per cent of the pumped water as drainage water, there would be deterioration of land due to sodium damage and large quantities of gypsum will have to be provided to keep the soils in good condition.
Dr. Eaton has developed a method for estimating the amount of gypsum and the additional amount of water which should be applied to the land to prevent high alkalinity, serious soil impermeability and deficiencies of calcium and magnesium required for normal plant growth (see, pp. 387-391).
For saline groundwaters of the Northern Zone of the Indus Plain the author has calculated, from water analyses of Water and Soils Investigation Division of West Pakistan WAPDA [7; 15], the gypsum and leaching requirements for all groundwaters having a salinity between 3000 and 3900 ppm in the Chaj and Rechna Doabs according to Dr. Eaton's method. Calculations have been made for the undiluted groundwaters as well as for the groundwaters when mixed with an equal quantity of canal water. The results are summarized in Table I. For all groundwaters having an average salinity of 3500 to 3600 ppm, when mixed with an equal quantity of canal water the gypsum requirements (for the mixed waters having a salinity of 1800 to 1900 ppm) average about 3000 pounds per acre foot of mixed water in the Chaj Doab and about 2000 pounds per acre foot of mixed water in the Rechna Doab. The leaching requirement for crops of medium salt tolerance average about 75 per cent in the two doabs. This means that about 85 per cent of the pumped water will have to be used for leaching purposes only.
I Suppose 100 parts of canal water are used to mature one acre of crop. If 100 parts of tubewell water are mixed with the same, the total quantity becomes 200 but 36 parts of additional water is required for leaching purposes to mature 2 acres of crops. Thus canal water is increased to 118 parts and tubewell water to 118 parts. The 118 parts of canal water when used alone can mature 1.18 acres of crops. Therefore 118 parts of tubewell water mature 0.82 acres of crop and are thus equal to 82 parts of canal water. The remaining 36 parts of tubewell water or 30 per cent is used for leaching purposes.
2 Calculated as explained in footnote 1 above.




Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 397
TABLE I
GYPSUM AND LEACHING REQUIREMENTS OF GROUNDWATERS OF THE CHAJ AND RECHNA DOABS, UNDILUTED AND MIXED WITH CANAL WATER
FOR CROPS OF MEDIUM SALT TOLERANCE
Groundwater mixed
with canal waterb in
Undiluted groundwater equal proportion
Doab Salinity of Gypsum Leaching Gypsum Leaching
Well water ground requirements require- requirements requirenumbera per acre ments per acre ments
foot of foot of
water water
(1) (2) (3) (4) (5) (6) (7)
Cha (ppm) (pounds) (per cent) (pounds) (per cent)
Chaj
C.26 3,000 4,951 343 2,370 67
C.39 3,530 10,144 410 4,975 70
C.42 3,500 3,398 838 1,596 84
C.43 3,580 4,797 384 2,291 68
C.50 3,580 5,316 2,551 127
C.62 3,790 8,702 458 4,280 73
C.63 3,790 5,373 479 2,581 73
C.64 3,910 6,512 2,717 3,617 107
CTLD.14 3,690 4,848 493 2,434 75
CTLZ.38 3,030 5,162 447 2,476 73
CTLZ.48 3,000 8,955 182 4,373 50
CTLZ.50 3,700 10,245 282 5,015 63
CTLZ.53 3,650 4,708 2,246 121
CTLZ.55 3,000 4,572 305 2,179 63
CTW.31 3,400 7,888 291 3,838 62
Average 3,477 3,070 77
Rechna RTLF.17 3,780 3,496 2,226 1,645 95
RTLG.15 3,450 4,844 419 2,312 70
RTLZ.28 3,260 7,495 167 3,648 48
RTLZ.30 3,630 3,393 328 1,589 65
RTLZ.31 3,800 4,530 459 2,167 72
RTLZ.32 3,680 3,868 1,074 1,828 88
RTLZ.33 3,370 nil 321 nil 64
RTLZ.47 3,560 nil 199 nil 52
RTW.28 3,910 1,884 1,132 835 82
RTW.54 3,970 3,945 4,445 1,748 101
RTW.53 3,940 669 321 229 64
R.11 3,990 6,575 700 3,189 81
R.14 3,750 6,573 259 3,178 59
R.15 3,600 5,304 550 2,548 76
RCC.30 3,580 9,287 347 4,535 66
Average 3,685 1,963 72
Notes: a) Well numbers as given by the Water and Sources: Columns (2) and (3):
Soils Investigation Division of WAPDA Chaj Doab [7, Tables 2
in their publications [7; 15]. and 3]
b) Assuming Jhelum and Chenab river water Rechna Doab [15, Tables
at Trimmu containing 208 ppm [16, p. B-6] 2 & 3].
Columns (4) to (7): Calculated
according to Dr. Eaton's
method (see, Table I on
pp. 388-389).




398 The Pakistan Development Review
For consumptive use requirement of 4.0 acre feet per acre, the leaching requirement will be about 3.0 acre feet per acre and the total water requirements would be about 7.0 acre feet per acre. The gypsum requirements for these waters would be about 10 tons per acre per year in the Chaj Doab and about 6 tons per acre per year in the Rechna Doab. The cost of gypsum is estimated as 70 rupees per ton delivered in the West Pakistan villages. For use of the saline groundwaters, even when mixed with canal water, about 400 to 700 rupees per acre would have to be spent on gypsum every year. It is clear that on account of extremely high gypsum requirements these waters cannot be used for irrigation even when about 85 per cent of the pumped water has to be used for leaching purposes and only about 15 per cent contributes to the consumptive use requirements of crops.
It may be stated that above calculations are based on the experimental work carried out in the south-western United States and in some other countries. When similar experimental work is carried out in the Chaj and Rechna Doabs, the actual gypsum requirements may be found to be somewhat different. However they are not likely to be so different as to make the use of soduim-rich saline waters having more than 3000 ppm as economic.
As previously suggested by the author [5], but most forcefully put by Dr. Eaton, provision of horizontal sub-surface drainage is the only solution for the saline groundwater areas of West Pakistan. A basic requirement for the use of horizontal sub-surface drainage is the provision of additional river water to these areas. A programme for increasing the capacity of canals to divert additional river water and installation of horizontal drainage should therefore be initiated immediately for these areas.
The canal water supply is not likely to be adequate for all the culturable canal commanded areas. It is, therefore, essential that canal water should be used on the best agricultural areas already under irrigation. Out of the total canal commanded area of about 32.8 million acres, there are some 1.5 million acres of highly saline uncultivated or abandoned lands in the Punjab and Bahawalpur and about 1.4 million acres in Sind [17, pp. 18 and 23]. The West Pakistan WAPDA and Irrigation Department are engaged in the reclamation of these soils. As will be clear from Table VI (page 369) in the report by Panel members, installation of tubewells in the highly saline soils would cause the good groundwaters to deteriorate 35 years earlier than installation of tubewells in non-saline soils. It is therefore essential that no tubewells should be installed in the highly saline soils even when these lie in good groundwater areas. Tubewells installed in the non-saline soils would draw down the watertable under




Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 399
the saline soils also and the groundwater would thus be used on good soils. Similarly no canal water should be used for the reclamation of these areas or for the development of any other uncultivated lands. All canal waters as well as all tubewell waters from the high quality groundwater areas should be used only on the best agricultural lands already under cultivation.
Horizontal versus Vertical Drainage
The Panel members have enumerated 5 disadvantages of the horizontal drainage system on pages 354 to 356 of their paper and have concluded that horizontal drainage does not "warrant much attention.. .in the primary scheme of water resources development in the Indus Plain".
The first objection of the Panel members to horizontal drainage is that salt removed in the drainage depends largely upon the salinity of the upper layers of groundwater. The author considers this to be the principal advantage rather than the disadvantage of the horizontal drainage system. It is easier to dispose of salt removed from 7 to 10 feet of the soilprofile and the upper groundwater than it is to dispose of the salt removed from 250 feet of the soil profile. In this connection Mr. Arthur Pillsbury, Professorof Irrigationand Engineering, University of California at Los Angeles, and Consultant to the Land and Water Development DivisionofFAO, has stated that "the zone ofconcentration of ground wateristhe root zone, and that the most efficient point to separate degraded waters, before they become diluted is immediately below the root zone" [14, p. 81. Professor Pillsbury considers that this separation can be done efficiently only with horizontal sub-surface drainage facilities [14, p. 81 and that pumping of groundwater is completely inefficient for drainage alone [14, p. 6]. According to Professor Pillsbury many vertical drainage schemes were started in the southwestern part of the United States beginning in the early 1920's but at present there is not a single "drainage" well operating where the water is not used to help irrigate the overlying land or is used to satisfy downstream water rights. Professor Pillsbury further. states that where saline waters are being pumped an extreme corrosion and incurstation (all italics ours) problem with the well and pump appear to be inevitable [14, p. 6].
Another point raised by the Panel members is that vertical drainage results in a "smaller investment in conveyance channels and better salinity control because salt can be returned to the rivers during periods of high run off or routed to salt lagoons at times when irrigation requirement is small."
As the idea of drainage tubewells pumping into rivers during "periods of high run off" has been recommended by the Panel members as well as by Tipton and Kalmbach, Inc. Consultants to WAPDA, it is necessary to examine it in




400 The Pakistan Development Review
detail. By 1970, the entire flow of the Sutlej, Beas and Ravi Rivers (designated as the Eastern Rivers in the Indus Water Treaty) will be diverted by India and there will be no period of high run off in these rivers. No saline tubewell waters can, therefore, be returned into the Sutlej and Ravi Rivers.
The same would be the condition of Chenab and Jhelum Rivers after a few years. According to Mr. S. S. Kirmani, Chief Engineer, Indus Basin Projects, West Pakistan WAPDA, "After the completion of the Indus Project, most of the flows of the Jhelum and Chenab Rivers will be fully used in the existing irrigation system and for the replacement of the irrigation uses on the Eastern Rivers" [11, p. 247J. The Chenab and Jhelum Rivers will have a surplus of only 2 to 3 MAF which will consist of erratic and infrequent flood peaks of only a few days duration.
No drainage tubewell waters from any part of the Punjab can therefore be returned to any river during the "period of high run off" because there will be no period of high run off after 1975. If canal capacity is increased and more river water is diverted on to lands as suggested earlier in this paper, there may not be any period of high run off after 1970.
The Indus is the only river in which some 35 MAF will continue to flow to the sea during the period of high run off but topography does not permit drains in any area in the Punjab part of the Indus Plain to outfall to the Indus River. Drainage waters from the lower part of the Bahawalpur and Sind could be returned to the Indus during the period of high run off, but that would damage the agriculture in Lower Sind, slowly but certainly. As pointed out by Dr. Eaton (p. 382), the longevity of agriculture which supports many millions of people should be viewed in terms of centuries rather than on the basis of an expedient which may suffice for only a limited number of years. Alexander Karpov has pointed out there are millions of acres in North Africa and Western Asia where great cultures once flourished. At present nothing is left but sand dunes, salt marshes and eroded landscapes [10, p. 2271. The proposals of Panel members and of Tipton and Kalmbach would similarly convert the Indus Valley agricultural areas into barren salty lands.
The Panel members have also proposed disposal of saline pumped waters into desert lagoons. This is possible for Bahawalpur and parts of Sind, but unfortunately there are no desert lagoons in the Rechna and Chaj Doabs where large quantities of pumped waters from the highly saline groundwater areas of these doabs could be disposed off. The conclusion is therefore inescapable that there is no place for disposalof pumped water from the highly saline groundwater areas inthe Punjab. These must remain where theyare. Salt from theupper 7to 10




Ghulani Mohammad: Waterlogging and Salinity: Rejoinder 401
feet of the soil profile only should be removed by horizontal drainage. This would be small and can be disposed of in on-farm evaporation flats as suggested Dr. Eaton (pp. 384-385) or in larger evaporation flats at the lower end of each doab as previously suggested by the author [5, pp. 394-95].
The Revelle Report also reconmmended "the use of salt tolerant crops" in areas where saline groundwaters are to be used (18. p. 991. Tipton and Kalmbach are again proposing "basic changes in the agriculture" of West Pakistan and the introduction of "new crops" in saline groundwater areas. The author would like to point out that introduction of "new crops" does not lessen the soil salinity brought on the land by the saline waters. The people of the Tigris-Euphrates Valley tried this method to stave off the effect of salt; they replaced wheat with barley, which is more salt tolerant. That helped temporarily, but the salt content continued to increase and the civilization declined and passed away [10, p. 2411. The same thing would happen to West Pakistan if it tried to introduce new salt tolerant crops proposed by the Panel members and by Tipton and Kaimbach, instead of solving the basic problem of the removal of salt from the irrigated areas by the provision of horizontal sub-surface drainage facilities.
The second objection of the Panel members regarding flat topography and cost of horizontal drains has been- discussed at length by the author in a previous issue of this Review [5, pp. 388-3941. Calculations made by Dr. Mushtaq Ahmad, Director, irrigation Research Institute, Lahore, indicate that the natural slope of the country is more than adequate for the slopes required for seepage drains in West Pakistan [13, pp. 10-561.
The third objection of the Panel members is that open drain systems occupy a significant portion of land area inbetween the cultivated fields and hence cause the farming operation to be spread out on more land. This objection is not valid for West Pakistan, where the canals have already been laid out. Actually, in a considerable part of the Punjab, shallow main drains have already been constructed. Mr. C. R. Maierhofer, Chief, Division of Drainage and Groundwater Engineering of the United States Bureau of Reclamation, considers that deep drains should be constructed where these shallow drains are located [12, p. 14].
The fourth objection of the Panel members that deep main drains and open field drains are difficult to maintain is somewhat more telling. For this reason, field drains are generally covered. The cost of maintenance of tile drains is very low [12, p. 161. The large collector drains and main drains are generally open. They have to be maintained in efficient condition just as canals are main-




402 The Pakistan Development Review
tained in efficient condition. The removal of weeds and debris and repair of side slopes is far more economical than the operation, maintenance, and .frequent replacement of corroded and incrusted tubewells in saline groundwater areas in any country of the world, but more so in a country like Pakistan where labour is underemployed and unemployed.
The fifth objection of the Panel members regarding the public health hazard of stagnant water and swampy reaches of open drains would be valid only if the drains were not properly maintained. There is no point in constructing the drains if these are not to be properly maintained. When properly maintained there is no public health hazard.
Role of Public and Private Tubewells
The Panel members consider that government tubewells are better than private tubewells for the following reasons:
1) Government tubewells are somewhat more economical than private
tubewells (pp. 339-340 and Table IV).
2) Government tubewells can be more easily integrated with canal
operations than private tubewells (pp. 340-341).
3) Government tubewells can be used for reclamation of saline soils and
the underground reservoir can be used for storage of salt flushed out
of root zone (pp. 342 and 350).
4) Government tubewells are better adapted for the exploitation of poor
quality and sodium-rich groundwaters which can be used by mixing
with Canal water (p. 342).
5) Givernment tubewells are better adapted for control of lateral migration of salinity. (p. 342).
6) Government tubewells are better than private tubewells on account
of their social effects (pp. 342-343).
The author considers that it is not necessary to have government tubewells for any of the above reasons:
1) In calculating the cost of pumping water from government and private tubewells, the Panel members have used full cost of the private tubewells but only part of the cost of government tubewells. The total cost of a private tubewell (of 1.25 cusec capacity) to the economy was estimated as 7,800 rupees by the author, whereas cost of the government tubewell (of 3.9 cusec capacity) to the economy was estimated as 79,700 rupees by WAPDA [4, p. 255]. In Table IV of their paper, the cost of project preparation, cost of equipment required for drilling government tubewells, cost of government staff, fee to be paid to the contractors engaged after international bidding, contingencies, and interest




Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 403
during the period of construction all amounting to 27,800 rupees for each 3.9 cusec tubewell have been ignored by the Panel members. Furthermore, the life of government tubewell has been taken as double that of private tubewells for which there is no justification [4, pp. 238-391. (see also, Table I on p. 372).
The author has included the full cost of government tubewells and recalculated cost of pumping water in Table IV of the report of the Panel members, assuming life of both tubewells to be 10 years. On this assumption the cost of pumping water from government tubewells comes out to be 44 per cent higher than private tubewells when the load factor is assumed as 25 per cent. However, government tubewells have been worked on a load factor of over 50 per cent. If this is adopted, the cost of pumping water from government tubewells is equal to that from private tubewells.
2) There is no reason why farmers will not integrate the working of private tubewells with the working of canals. Already the farmers of Gujranwala and Sialkot districts where canal water is supplied only during the kharif season are integrating the working of private tubewells with the canal water and have attained the highest intensity of cropping [6, p. 261. It is simple: the moment, the canal is closed, the farmers switch on the tubewells. Dissemination of information about canal closures is good but is not absolutely necessary.
3) As already pointed out, all canal water and tubewell water should be used on the best agricultural lands already under cultivation and not on reclamation of highly saline soils. Such reclamation by government tubewells will only deteriorate the quality of groundwater by adding salts leached down from the soil profile.
4) As previously stated saline and sodium-rich groundwaters should not be pumped at all. They would increase water supply but would cause deterioration of soil and reduce the total agricultural production in the country.
5) The centrifugal pumps used by the farmers have a maximum draw down of about 20 to 25 feet. With private tubewells located in the upper reaches of the doabs and lowering the watertable to about 20 feet, and with drains lowering the watertable to about 7 to 10 feet in the saline areas, there is no danger of contamination of non-saline groundwaters with infiltration from saline groundwater areas. On the other hand, there would be some danger with government tubewells pumping water to 100 feet depth in non-saline areas and to 50 feet depth in the saline areas as proposed by the Panel members.
6) In all areas where an adequate number of tubewells has been installed, the price charged by tubewell owners varies from 2.5 to 3.5 rupees per hour




404 The Pakistan Development Review
whereas the cost of operation of tubewells comes to about 1.2 to 2.6 rupees per hour [6, pp. 17-181. With additional tubewells being installed every year, the price charged by owners is being reduced year by year. No government regulation on the price of tubewell water, as proposed by the Panel members, is necessary.
Some of the major points in favour of private tubewells are the following: First, the private tubewells mobilize domestic resources and thus increase the total size of the development programme to that extent. A greater increase in agricultural production in West Pakistan would result if the farmer's resources are used for installation of tubewells and government resources are used for increasing the fertilizer manufacturing capacity and for electric transmission and distribution facilities than if government resources are used for drilling of tubewells. Secondly, foreign exchange required for private tubewells is very small whereas the foreign exchange component of government tubewells approximates 58 per cent of the total cost.3. If an appropriate "shadow price", say 7 rupees to a dollar is used for foreign exchange, the cost of government tubewells increases by approximately 27 per cent. The cost of pumping water from government tubewells then becomes 67 per cent higher than those from private tubewells when the load factor is the same. When government tubewells work twice the number of hours compared to private tubewells, the cost of pumping water is 14 per cent higher in these when foreign exchange is appropriately valued. Thirdly, private tubewells contribute to the development of local industry such as diesel engines, electric motors, drilling rigs, and other manufacturing capacity. The government tubewells damage the established manufacturing industries by importing the same equipment, goods and services from abroad. Finally, the private tubewells not only mobilize domestic resources but also develop a strong class of highly energetic farmers who act as leaders in modernizing agriculture in the country. The government tubewells depend upon tied foreign loans obtained with high rates of interest, increase the foreign debt of the country and stifle the energetic class of farmers by destroying their previously installed tubewells and installing expensive government tubewells instead.
Concluding Remarks
The system of tubewell installation for irrigation and drainage purposes as recommended by the Revelle Panel and by Tipton and Kalmbach and that being followed by West Pakistan WAPDA is a temporary expedient and a self-destruc3 Total cost of tubewells (excluding electrification and drainage facilities) in SCARP 3 is estimated as 123.5 million rupees, out of which 71.8 million rupees (15.1 million dollars) are required in foreign exchange for equipment, goods and services that must be imported [16, p. 481.




Ghulam Mohammad. Waterlogging and Salinity: Rejoinder 405
tive system. The saline groundwaters being pumped or proposed to be pumped can neither be used in the same area nor can they be passed on to downstream users without acceptance of ultimate desolation. The salts must be removed from the irrigated areas by a permanent horizontal sub-surface drainage system and the saline waste disposed of in evaporation flats in the Upper Indus Plain and conveyed to the sea through special canals in the Lower Indus Plain.
A basic problem in the irrigated agriculture of West Pakistan is the deficiency of water supply to meet the consumptive use requirements of crops and to leach down the salts. This deficiency is being made good by the farmers in the non-saline groundwater areas with the installation of private tubewells. The government must increase the capacity of canals and divert additional river water on to the best agricultural lands in the saline groundwater areas and initiate a programme for the construction of subsurface drainage facilities.
Reclamation of saline soils even in high quality groundwater areas would cause the groundwater to become unfit for use due to leaching down of salts. No canal or tubewell water should therefore be used for such reclamation. Similarly no canal or tubewell water should be used for the development of marginal lands and all available water supplies should be used on the best agricultural lands already under cultivation.
REFERENCES
I. Asghar A.G. and Nazir Ahmad, "Drainage or Irrigated Soils in Arid Regions", Proceedings of the Punjab Engineering Congress, Vol. XXXIX, 1955.
2. Ahmed, Nazir, and Mohammad Akram, Evapo-Transpiration as a Function of Depth to Watertable and Soils. (Lahore: Irrigation Research Institute, 1965).
3. Bower, C.A., and M. Maasland, "Sodium Hazard of Punjab Groundwaters"
Symposium on Waterlogging and Salinity in West Pakistan. (Lahore: West
Pakistan Engineering Congress, October 1963).
4. Ghulam Mohammad, "Some Strategic Problems in Agricultural Development in Pakistan", Pakistan Development Review, Vol. IV, No. 2, Summer
1964.
5. "Waterlogging and Salinity in the Indus Plain: A
Critical Analysis of Some of the Major Conclusions of the Revelle
Report", Pakistan Development Review, Vol. IV, No. 3, Autumn 1964.




406 The Pakistan Development Review
6. "Private Tubewell Development and Cropping
Pattern in West Pakistan", Pakistan Development Review, Vol. V, No. 1,
Spring 1965.
7. Gilani, Maqsood Ali Shah, and Abdul Hamid, Quality of Ground Water, Chaj Doab. Mimeographed. (Lahore: Water and Soils Investigation Division, West Pakistan WAPDA, August 1960).
8. Greenmen D.W., W.V. Swarzenski and G.D. Bennet, The Groundwater Hydrology of the Punjab. (Lahore: Water and Soil Investigation Division,
West Pakistan WAPDA, 1963).
9. Harza Engineering Company International, Programme for Water andPower Development in West Pakistan Through 1975. (Lahore: Harza Engineering
Company, January 1964).
10. Karpov, Alexander V., "Indus Valley-West Pakistan's Life Line", Journal
of the Hydraulics Division, (Proceedings of the American Society of Civil
Engineers), Vol. 90, No. HY 1, January 1964.
11. Kirmani, S.S., "Indus Valley, West Pakistan's Life Line' Discussion", Journal of the Hydraulics Division, (Proceedings of the American Society
of Civil Engineers), Vol. 90, No. HY 5 September 1964.
12. Maierhofer, C.R., Report on Drainage Requirements For Irrigated Areas of West Pakistan. Mimeographed. (Denvor. Tipton and Kalmbach Inc.,
April 1957).
13. Mushtaq Ahmad and Abdur Reluhman ,"Design of Alluvial Channels As Influenced by Sediment Charge", Proceedings of West Pakistan Engineering
Congress, 1962. (Lahore: West Pakistan Engineering Congress, 1962).
14. Pillsbury, Arthur F., Principles in the Utilization of Flood Plains.
Paper presented at the Seminar on waterlogging and Salinity sponsored by FAO and the Government of Pakistan. Lahore, November 1964.
Mimeographed. (Rome: FAO 1965).
15. Shamsi, R.A. and Abdul Hamid, Quality of Groundwater, Rechna Doab, Mimeographed. (Lahore Water and Soils Investigation Division, West
Pakistan WAPDA, August 1960).
16. Tipton and Kalmbach, Feasibility Reporton Salinity ControlandReclamation Project Number 3, Lower Thal Doab. (Denvor Tipton and Kalmbach, April
1963).




Ghulam Mohammad: Waterlogging and Salinity Rejoinder 407
17. West Pakistan WAPDA, Summary of Basic Report on Waterlogging and
Salinity in West Pakistan. Prepared for the Seminar on Waterlogging and Salinity sponsored by FAO and Government of Pakistan. Mimeographed
(Rome: FAO, 1964).
18. White House-Department of Interior Panel on Waterlogging and Salinity
in West Pakistan, Report on Land and Water Development in the Indus Plain. (Washington, D.C.: Supdt. Doc. January 1964). This report is referred to as the Revelle Report in this paper




Printed at the Inter Services Press Ltd., 17, Near Napier Barracks P.O., Karachi-4.




Full Text

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Waterlogging and Salinity in the Indus Plain: Some Basic Considerations by ROBERT DORFsAN, ROGER REVELLE, AND HAROLD THOMAS* INTRODUCTION It takes more than ordinary presumption for a group of strangers to recommend changes in the efforts of a great nation to contend with a problem that goes to the very roots of its social structure and its livelihood. Yet we did just that in our Report on Land and Water Development in the Indus Plain[l]. We hoped our recommendations would be considered sympathetically and debated fully, that our sound suggestions would be adopted and our unsound ones forgiven. All this has been granted us, and more. The months since the Panel's report was prepared have been eventful for the economic development of West Pakistan. It is hard to cast our minds back to the gloom that filled the atmosphere when the Panel was convened. Food production had been stagnant for the past several years, sem and thur were spreading through the most productive portions of the Plain, expensive efforts to control these twin menaces had been baffled. WAPDA knew, of course, that in principle tubewells could do the job, but there were more failures to report than successes. The yields of major crops were about what they had been five years before, and population growth was outstripping production. Now many things are hopeful. The watertable has been pumped down to safe levels in large areas of the first experimental project. More than 2,000 government tubewells and perhaps 30,000 private tubewells are in operation. Fertilizer use is likely to treble in the course of the Second Five Year Plan. One does not debate stagnation any more. This favorable turn of events has made parts of our report seem obsolete. Tasks we almost feared to suggest have proven easy. Resources we did not know existed have flowed abundantly. Some unforeseen difficulties have arisen, but, on the whole, the surprises have been happy ones. The danger now, indeed, *Dr. Robert Dorfman is Professor of Economics and Member of the Faculty of Public Administration, Harvard University. Dr. Roger Revelle is Richard Saltonstall Professor of Population Policy and Director of the Center for Population Studies, Harvard University. Mr. Harold A. Thomas, Jr. is Gordon McKay Professor of Civil and Sanitary Engineering and Member of the Faculty of Public Administration, Harvard University.



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Dorfman, Revelle and Thomas. Waterlogging and Salinity 353 If the rate of drainage is very small or zero, Equation (13) may be written in the form of a linear equation in which the time rate of increase of the groundwater salinity is constant. The time required for the concentration to reach a specified maximum value Cm may be computed from the following equation. ___SAhl t(]C (Qc + Qr) (C.-CS) ................................................. (14) Values of t for a range of soil salt contents from 0 to 50 tons/acre and for well depths of 50 to 250 feet are given in Table VI. In part I of this table, the initial salt concentration in the groundwater is taken as 500 mg/l; in part II, it is 750 mg/l. These values were chosen in order to keep well within the range of conditions where there is general agreement that tubewells can be used [4]. For privately operated tubewells, it will be difficult to attain an "optimum" mixing ratio of tubewell and canal waters. Hence Cm is taken as 1500 ppm. We have assumed that the volume of canal water plus river recharge is 3.3 acre feet/acre/year, C, is 250 ppm, and S is 0.25. The times given above are those required for the average salinity in the groundwater layer which is supplying the well to reach 1500 ppm. As shown in the Panel Report, the time required for the well water to reach this salinity (after a brief initial period) will be somewhat longer than the above values, be cause thorough mixing does not occur in the aquifer. But the delay due to imperfect mixing will be short for shallow wells, and long for deep wells. It is clear that relatively shallow tubewells without drainage channels to maintain a salt balance will become excessively salty in a few years, if they are used in areas where there is a significant initial salt accumulation in the soil. Within a few years after the tubewells are installed, channels will have to be constructed to carry away salty groundwater. If the salty water has a salinity of 1500 mg/l, the minimum amount of water that will need to be carried away will be 1/6th of the total canal supply, including that which enters the ground as recharge. Unless the conveyance channels are lined, about 25 per cent of the total water supply will have to be run into them, to make up for leakage. But part of this will, of course, be recovered by the wells. However, the 1/6th of the total supply that cannot be used will reduce the gross sown acreage. Equation (14) and Table V give the time for salt build-up before surface drainage is installed. If soil drainage exists from the beginning, Equation (13) applies. The ultimate concentration in the groundwater will then be C. (Q. + Q, )/Qa. However, the time elapsed before a salt balance is attained may be very long. For example, if C, = 250 milligrams per litre and (Q, + Q )/Qd = 8,



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Ghulani Mohammad: Waterlogging and Salinity: Rejoinder 401 feet of the soil profile only should be removed by horizontal drainage. This would be small and can be disposed of in on-farm evaporation flats as suggested Dr. Eaton (pp. 384-385) or in larger evaporation flats at the lower end of each doab as previously suggested by the author [5, pp. 394-95]. The Revelle Report also reconmmended "the use of salt tolerant crops" in areas where saline groundwaters are to be used (18. p. 991. Tipton and Kalmbach are again proposing "basic changes in the agriculture" of West Pakistan and the introduction of "new crops" in saline groundwater areas. The author would like to point out that introduction of "new crops" does not lessen the soil salinity brought on the land by the saline waters. The people of the Tigris-Euphrates Valley tried this method to stave off the effect of salt; they replaced wheat with barley, which is more salt tolerant. That helped temporarily, but the salt content continued to increase and the civilization declined and passed away [10, p. 2411. The same thing would happen to West Pakistan if it tried to introduce new salt tolerant crops proposed by the Panel members and by Tipton and Kaimbach, instead of solving the basic problem of the removal of salt from the irrigated areas by the provision of horizontal sub-surface drainage facilities. The second objection of the Panel members regarding flat topography and cost of horizontal drains has beendiscussed at length by the author in a previous issue of this Review [5, pp. 388-3941. Calculations made by Dr. Mushtaq Ahmad, Director, irrigation Research Institute, Lahore, indicate that the natural slope of the country is more than adequate for the slopes required for seepage drains in West Pakistan [13, pp. 10-561. The third objection of the Panel members is that open drain systems occupy a significant portion of land area inbetween the cultivated fields and hence cause the farming operation to be spread out on more land. This objection is not valid for West Pakistan, where the canals have already been laid out. Actually, in a considerable part of the Punjab, shallow main drains have already been constructed. Mr. C. R. Maierhofer, Chief, Division of Drainage and Groundwater Engineering of the United States Bureau of Reclamation, considers that deep drains should be constructed where these shallow drains are located [12, p. 14]. The fourth objection of the Panel members that deep main drains and open field drains are difficult to maintain is somewhat more telling. For this reason, field drains are generally covered. The cost of maintenance of tile drains is very low [12, p. 161. The large collector drains and main drains are generally open. They have to be maintained in efficient condition just as canals are main-



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354 The Pakistan Development Review then the ultimate concentration will be 2000 milligrams per litre. If Qd/n n~ r02 = 0.25, S =0.25 and C, = 750 mg/i the salinity of the groundwater and the tubewell water at various times is given in Table VII for tubewell depths of 100 and 250 feet. "Horizontal" versus "Vertical" Drainage Any drainage system in an irrigated area must serve two purposes: i) removal of excess water and control of the elevation of the watertable; Ui) removal of saline water to prevent accumulation of salt in the soil. These objectives can be accomplished in one of two ways: i) by pumping water from underground and carrying part of the pumped water away from the region in conveyance channels; or, Ui) by allowing part of the irrigation water to percolate into a series of small ditches or porous tile pipes, which lead into larger "collector" and "main" drains. Such a "horizontal" system can be used to remove saline waters only if the watertable is sufficiently close to the surface to prevent a major part of the irrigation return flows from seeping out of the drains. The system is not effective for salinity control in a region where both ground and surface waters are being used for irrigation and the watertable is pumped down significantly below the bottom level of the drainage channels during part of the time. Wherever large numbers of tubewells, either public or private, are employed to supply part of the irrigation water, it will often be undesirable to keep the watertable high. Horizontal drainage structures will then have a limited usefulness, primarily to carry off flood waters.. In regions of highly saline underground water, tubewelis will not be employed to provide irrigation supplies, and either a horizontal system or a system of tubewells plus conveyance channels can be employed for drainage. Several factors should enter into the choice between these alternatives. Horizontal drainage may be economical in certain regions of West Pakistan, particularly in parts of the Southern Zone, where conditions for vertical drainage are not satisfactory. In the Panel Report, however, we concluded that vertical drainage would be desirable in most areas of the Indus Plain. The principal disadvantage of horizontal drainage is that it must operate with a relatively high watertable, and hence is incompatible with the use of tubewells to increase and stabilize the irrigation water supply. But other disadvantages must also be kept in mind. 1) A system of main drains and tile or open field drains is essentially a passive system. It is dependent upon gravity flow and once it is constructed it cannot easily be modified or revamped. The amount of water discharged through such a system depends upon the amount of water applied to the land it subtends, and the salt removed in drainage depends largely upon the salinity of the upper



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Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 397 TABLE I GYPSUM AND LEACHING REQUIREMENTS OF GROUNDWATERS OF THE CHAJ AND RECHNA DOABS, UNDILUTED AND MIXED WITH CANAL WATER FOR CROPS OF MEDIUM SALT TOLERANCE Groundwater mixed with canal waterb in Undiluted groundwater equal proportion Doab Salinity of Gypsum Leaching Gypsum Leaching Well water ground requirements requirerequirements requirenumbera per acre ments per acre ments foot of foot of water water (1) (2) (3) (4) (5) (6) (7) Cha (ppm) (pounds) (per cent) (pounds) (per cent) Chaj C.26 3,000 4,951 343 2,370 67 C.39 3,530 10,144 410 4,975 70 C.42 3,500 3,398 838 1,596 84 C.43 3,580 4,797 384 2,291 68 C.50 3,580 5,316 -2,551 127 C.62 3,790 8,702 458 4,280 73 C.63 3,790 5,373 479 2,581 73 C.64 3,910 6,512 2,717 3,617 107 CTLD.14 3,690 4,848 493 2,434 75 CTLZ.38 3,030 5,162 447 2,476 73 CTLZ.48 3,000 8,955 182 4,373 50 CTLZ.50 3,700 10,245 282 5,015 63 CTLZ.53 3,650 4,708 -2,246 121 CTLZ.55 3,000 4,572 305 2,179 63 CTW.31 3,400 7,888 291 3,838 62 Average 3,477 3,070 77 Rechna RTLF.17 3,780 3,496 2,226 1,645 95 RTLG.15 3,450 4,844 419 2,312 70 RTLZ.28 3,260 7,495 167 3,648 48 RTLZ.30 3,630 3,393 328 1,589 65 RTLZ.31 3,800 4,530 459 2,167 72 RTLZ.32 3,680 3,868 1,074 1,828 88 RTLZ.33 3,370 nil 321 nil 64 RTLZ.47 3,560 nil 199 nil 52 RTW.28 3,910 1,884 1,132 835 82 RTW.54 3,970 3,945 4,445 1,748 101 RTW.53 3,940 669 321 229 64 R.11 3,990 6,575 700 3,189 81 R.14 3,750 6,573 259 3,178 59 R.15 3,600 5,304 550 2,548 76 RCC.30 3,580 9,287 347 4,535 66 Average 3,685 1,963 72 Notes: a) Well numbers as given by the Water and Sources: Columns (2) and (3): Soils Investigation Division of WAPDA Chaj Doab [7, Tables 2 in their publications [7; 15]. and 3] b) Assuming Jhelum and Chenab river water Rechna Doab [15, Tables at Trimmu containing 208 ppm [16, p. B-6] 2 & 3]. Columns (4) to (7): Calculated according to Dr. Eaton's method (see, Table I on pp. 388-389).



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Dorfman, Revelle and Thomas Waterlogging and Salinity 351 water becomes so salty that drainage channels must be constructed will be relatively short, compared to the time available with typical "government" wells, which are usually about 250 feet deep. Under some circumstances, early construction of drainage channels will be desirable, and in this case, when part of the irrigation water is drained off even in the early stages of development, the rate of increase of salt content in the underground water will be much slower than in the absence of drainage. Here also, the rate of build-up of groundwater salinity will be much less with deep governmentn" wells than with shallow private tubewells. The following analysis, while not as versatile as the "salt-flow-model", presented in the Panel Report, shows the relationships involved. The system is assumed to be in a hydraulically steady state-the elevation of the watertable remains constant and inflows and outflows are balanced (see Figure 1)-but in an unsteady state as regards the salt content. This quantity initially may be larger or smaller than that in a steady state. The formulation shows the final concentration in the aquifer, the rate at which the system approaches salt equilibrium, and the significant design parameters. Let Q: = inflow to irrigated area from canal system, acre feet per unit time; Qr = recharge from canal leakage and other sources, acre feet per unit time; Q evapotranspiration rate, acre feet per unit time; Qa =drainage flow, acre feet per unit time; Q, =flow through tubewells, acre feet per unit time; A = nrr2 = total area of well influence, acres or square feet; n is the number of wells; r. is the radius of influence of a single well; and 2r. is the (approximate) well spacing, feet. y =the proportion of total area cropped yA =is the area under cultivation; E =evapotranspiration rate, feet per unit time. It is assumed that recharge and throughput are uniformly distributed over the aquifer. For a hydraulic balance over the entire system Q + Qr'= Qe+ Qd ... .................. f .......................... (8) where Qe = EyA = Enyr2 r ................................................... (9) The irrigation supply derives from the canal system and the tubewells. The irrigation rate will be Q0 + Qw -Qd = nyror.. .............................(10)



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356 The Pakistan Development Review 5) In semi-tropical climate the stagnant water and swampy reaches of open drains may constitute a public health hazard. The ditches afford a favorable environment for the growth of mosquitoes and snails. In other countries endemic and epidemic levels of morbidity from malaria and bilharziasis have been caused by horizontal drainage works that have not been properly maintained. A Comment on Sub-irrigation One of the arguments for a horizontal drainage system is that by keeping the watertable close to the surface a considerable fraction of the seepage from canals and water courses can be recovered by the crops through sub irrigation. In the historical development of most irrigation projects it commonly happens that at one time or another enthusiasm is generated over the possibilities of sub-irrigation as a cheap method of water distribution. When such schemes are tried, however, they are usually found to have serious limitations. In some cases they have failed completely and caused serious land damage. In the United States, there have been two exceptions where sub-irrigation has proved to be more than a fad. One of these is in the San Luis Valley in Colorado, and the other in the Snake River Basin in Idaho. In both of these places the following favorable conditions obtain: i) the slopes of the land and watertable are relatively steep so that stagnation does not occur; and ii) the soil and subsoil are permeable (in the San Luis project the soil is almost a fine gravel, in Idaho the aquifer is a coarse-textured volcanic ash). Sub-irrigation at these sites has worked because it is possible to drain the soil thoroughly during the non-irrigation season. The soil is recharged in the spring; after the harvest the watertable is lowered and the salt carried away. We conclude that sub-irrigation, as well as conventional horizontal drainage, might find limited application in certain localities of West Pakistan under special geological and hydrological conditions. Neither of these methods warrant much attention, however, in the primary scheme of water resource development in the Indus Plain. CONCLUDING REMARKS Agricultural production has shown heartening progress in the past two or three years, particularly in regions where traditional supplies of irrigation water have been enhanced either by government tubewells, as in SCARP I, or by private tubewells as in the upper part of Rechna Doab. Farmers have taken advantage of the improved water supplies with admirable alacrity. The trends in crop yields per acre and particularly in the intensity of cultivation both reflect



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Eaton: Waterlogging and Salinity: Comment 385 Under ideal practice, saline drainages should discharge into the sea or into natural closed lakes or large land depressions. Horizontal drainage systems of large scale are expensive and, as noted in the reports cited, they seriously interfere with water-distributary systems. The lands of Pakistan tend to be flat and for that reason, the drainage canals would have to be of large capacity and often augmented by pum ping to obtain the necessary discharges. Also to accommodate the necessary depths of field drains, the public canals would have to be deep. As has been repeatedly noted by others, Pakistan has a great surplus of arable land in relation to its water supply. It is now apparent that the distributary system was designed to serve more land than could be cropped at any one time. It seems possible, if not probable, that the planners hoped thereby to at least slow down the rate of rise of the watertables, and thereby to postpone waterlogging. Over vast areas waterlogging has now become acute. With the great excess of arable land, the writer believes that the cultivated acreages could appropriately be cut back to approach the land that can be served by canal or good-quality groundwaters. With such cut backs, there will be continuously idle lands that can be converted to evaporation flats-areas which are surrounded by low dikes or areas upon which the saline drainages can be spread by networks of furrows. In the light of the effects of canal seepage and rainfall on rising watertables, in addition to the necessary leaching to remove existing salinity and to continuously remove the salts deposited in soils with irrigation, it is possible to estimate the required areas of the on-farm evaporation flats in relation to the area of the land irrigated. With knowledge of evaporation rates, leaching requirements, rainfall, and surface runoffs, such estimates become quite simple. Under the evaporation-flat system, the farmer himself would install the field, drains (tiles or ditches) and the disposal ditches leading to his evaporation flat. Since the field and connecting drains should be installed to depths of upward to seven feet or more, small on-farm deep collecting sumps are necessary for the accumulation of the day-to-day drainage. Pumps, whether power or Persian wheel, are necessary for the discharge of drainage effluents from the sumps onto the evaporation flats. The installation of on-farm evaporation flats is, of course, not an ideal substitute for country-wide drainage systems. But the method, as an alternative, is regarded by the writer as one of much promise under the existing



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342 The Pakistan Development Review patterns of canal diversions. It may be necessary or desirable to transfer surface supplies from one region to another, and to make good the transfers by additional pumping in areas underlain by high quality groundwater. These transfers will be more acceptable if reductions in surface water supplies are replaced by government-provided groundwater, but not if the deficit has to be made good by privately pumped groundwater, which, we have seen, is several times more expensive than canal water (see, for example [1, p. 280]). Among the major benefits of the use of tubewells are the control of the level of the ground watertable and the reclamation of waterlogged and saline land. For these purposes government tubewells are much better adapted than private ones. The experience in SCARP I makes it clear that controlling the watertable requires coordinated operation of many tubewells covering a large area. Reclamation operations even when economically justifiable are not commercially attractive to private tubewell owners. Private tubewell operations are also poorly adapted to exploiting the groundwater in regions where pools of poor quality water are interspersed among the good. If the level of the watertable is drawn down in regions underlain by high quality water to depths much below the average level, the neighbouring saline water is likely to infiltrate and to contaminate the remaining reservoir of sweet water. The long lives of some of the private tubewells indicate that this danger is not always present but it is clearly real in some places. Until accurate and detailed maps of groundwater quality can be made we must proceed with caution to avoid spoiling the underground water supplies. Excessive lateral migration and mixing of saline with sweet groundwater can be prevented by operating all wells in a region as components of an integrated irrigation and drainage system, which is difficult when the wells are privately owned. On the other hand when problems of salinity control are likely to occur these problems may be intensified if the wells are operated by single farmer or small groups of farmers each pumping as much good quality water as he needs for his immediate use. Experience has been unsatisfactory in other countries when large numbers of privately owned and individually operated wells have been installed in regions where there are marked variations in the areal and vertical distribution of groundwater salinity. The social effects of the private and public tubewells are also somewhat different. Water pumped by the government wells is available on the same terms to all farmers, while only the larger farmers, those operating farms of 25 acres or more, are likely to find it economical to install private tubewells. Small farmers can and do purchase tubewell water from the larger farmers, but the surveys available indicate that the prices are so high that the cost of



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338 The Pakistan Development Review ours or Harza's and his cropping intensity lower. He assumes almost as much diversion of river waters at canal heads, but only 16 MAF of tubewell supplies, because he believes that about half the seepage water from canals and water courses, after mixing with the underground water, will be too salty or too sodium-rich to be usefully recovered by pumping. Although he does not mention the Southern Zone, by implicatin he allots it only a minor fraction of the canal diversions, since he states that his diversion scheme for the Northern Zone follows Harza's. He neglects non-beneficial evapotranspiration, but we have included this in recomputing his budget. THE ROLE OF PUBLIC AND PRIVATE TUBEWELLS At the time the Panel Report was written, the vigorous growth of privately installed and operated tubewells was not anticipated. About 30,000 such tubewells have now been installed, and they are making a significant contribution to the productivity of agriculture in West Pakistan. This contribution will grow as the private tubewells continue to be installed at a rate of several thousand units a year. The policy of the government in designing new SCARP and new public tubewell fields should, of course, take this development into account in order that the maximum benefit to the economy can be realized from the public and private tubewells together. It must not be tho ought that this is simply a question of public versus private ownership. The public and the private tubewells differ from each other technologically and they will be operated in accordance with different principles and purposes. From the planner's point of view each is suitable for obtaining a somewhat different set of goals. The more appropriate mode for developing the underground water resources of any particular area will depend upon the conditions and problems prevalent in that area. The private tubewell owners have already recognized this. Although the private tubewells are quite widely dispersed throughout the irrigated region of the Plain they tend to be much more heavily concentrated in the upper regions of the doabs than elsewhere. We can make only a few tentative remarks on the four-way integration of public tub.wolls, private tubewells, canals, and drainage works, and feel that the situation must be watched closely and a sound policy developed in the light of experience. Our understanding of the operating characteristics of the private tubewells is especially deficient in spite of the excellent beginning that has been made by the two sample surveys of their operations, one conducted by Ghulam Mohammad [5] and the other by Harza Engineering Company International (6]. From a technical point of view the major differences between the two types of well are in capacity and depth. The public wells are designed for a capacity of from 3.5 to 4.5 cusecs (7 to 9 acre feet per day) and have a draft of from



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350 The Pakistan Development Review Since the value Of CT is the same in both schemes, it follows that salinity concentration in the mixture of surface and groundwater of the second scheme can be 0. 188/0.0192 =9.8 times larger than that of the first scheme. If the surface water has a concentration of 200 milligrams per litre, then the concentration of the mixed waters can be 2000 milligrams per litre, corresponding to groundwater with a salinity of 3800 milligrams per litre mixed (or alternated with) an equal volume of surface water. Moreover, if the relative concentrations of sodium, calcium, magnesium, bicarbonate and carbonate are the same in the irrigation water used in both schemes, there will be no deterioration of the soil in the latter scheme. In a subsequent section of this paper (see, Equation (11)) we show that the leaching ratio and hence the value of Ca/CT may be increased by increasing the pumping rate without affecting the other variables. It'is evident from the foregoing analysis that integration of canal and tubewell irrigation water supplies can incorporate a large element of flexibility in salinity and alkalinity control. Effects of Government and Private Tubewrells on Salt Build-up and Drainage The concept of a simple salt balance in a river basin was introduced a generation ago as a didactic device to illustrate underlying principles. Some elementary treatises on hydrology state that as an ideal a "favorable" balance should be maintained in which the efflux of salt from a region is not less than the influx. While this is patently desirable over a long span of time, it is far from being a valid design criterion that should be observed at all times, particularly in the first stages of a new era of investment in water resources. In our case a more rational criterion is to treat the vast aquifer of the northern plain as a primary resource to speed and sustain the economic development of West Pakistan. Hydraulic works for control of water and water quality should be installed in a carefully programmed sequence over a period of years. The optimal sequence may at different times entail a "favorable" salt balance in some regions, and an "unfavorable" balance in others. Decisions of this type can best be made using computer models for detailed simulation of project areas. To maintain a salt balance, part of the irrigation water must be drained away from the region, and drainage channels must be constructed for this purpose. Drainage structures are expensive, and it will often be economically beneficial to postpone their construction for as long as possible. This can be accomplished in areas where both tubewell and canal waters are used for irrigation, if the salt is flushed out of the root zone and washed downward with recycled pumped water, to be stored underground. With typical private tubewells, which are usually only about 100 feet deep, the time interval before the underground



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 365 Sources: Col. (1) From Table I. Col. (2) From data and computations in [1, Chapters 5 and 7, pp. 192193 and 269-284]. Col. (3): From [4, pp. 381-383]. 4 Canal commanded area planted at least once during the year plus fallow. 5 In the Panel Report, the net cultivated acreage for the former Punjab and Bahawalpur is given as 16.4 MA, corresponding to "firm" canal diversions (4 out of 5 years) of 45 MAF. For comparison with Harza and Ghulam Mohammad we have used the Panel's average diversion of 48 MAF, which gives an increase of 3 per cent in the volume of water for beneficial use on crops. The net cultivated acreage is increased accordingly. 6 Mean of range of 9 to 11 MA. 7 n.g. -not given. 9 Gross sown area= Net cultivated area x per cent cropping intensity/100. 9 In computing cropping intensity, Harza counts the acreage planted to sugarcane during both kharif and rabi: in the Panel Report, the sugar acreage is counted only once, in kharif. Here we have used the Harza procedure. 10 60 per cent in kharif and 90 per cent in rabi. 11 Per cent cropping intensity chosen to give same depth of water for beneficial use on the gross sown area (2.2 ft.) as in Column (1). 12 80 per cent in non-perennial area and 135 per cent in perennial area. II Per cent cropping intensity chosen to give same depth of water for beneficial use on gross sown area (2.7 feet) as in Column (1). 14 Average canal diversions to former Punjab and Bahawalpur. 15 Seepage and non-beneficial evapotranspiration in canals are assumed to be 26 per cent and 12 per cent of canal head diversions, respectively. 16 Seepage and non-beneficial evapotranspiration in canals are assumed to be 24 per cent and 6 per cent of canal head diversions, respectively, following Harza. 17 Combined seepage and non-beneficial evapotranspiration in canals is assumed to be 13 per cent of canal head diversions. 18 41 MAF in the Panel's "non saline" area plus 6 MAF in the "saline" area.



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404 The Pakistan Development Review whereas the cost of operation of tubewells comes to about 1.2 to 2.6 rupees per hour [6, pp. 17-181. With additional tubewells being installed every year, the price charged by owners is being reduced year by year. No government regulation on the price of tubewell water, as proposed by the Panel members, is necessary. Some of the major points in favour of private tubewells are the following: First, the private tubewells mobilize domestic resources and thus increase the total size of the development programme to that extent. A greater increase in agricultural production in West Pakistan would result if the farmer's resources are used for installation of tubewells and government resources are used for increasing the fertilizer manufacturing capacity and for electric transmission and distribution facilities than if government resources are used for drilling of tubewells. Secondly, foreign exchange required for private tubewells is very small whereas the foreign exchange component of government tubewells approximates 58 per cent of the total cost.3.If an appropriate "shadow price", say 7 rupees to a dollar is used for foreign exchange, the cost of government tubewells increases by approximately 27 per cent. The cost of pumping water from government tubewells then becomes 67 per cent higher than those from private tubewells when the load factor is the same. When government tubewells work twice the number of hours compared to private tubewells, the cost of pumping water is 14 per cent higher in these when foreign exchange is appropriately valued. Thirdly, private tubewells contribute to the development of local industry such as diesel engines, electric motors, drilling rigs, and other manufacturing capacity. The government tubewells damage the established manufacturing industries by importing the same equipment, goods and services from abroad. Finally, the private tubewells not only mobilize domestic resources but also develop a strong class of highly energetic farmers who act as leaders in modernizing agriculture in the country. The government tubewells depend upon tied foreign loans obtained with high rates of interest, increase the foreign debt of the country and stifle the energetic class of farmers by destroying their previously installed tubewells and installing expensive government tubewells instead. Concluding Remarks The system of tubewell installation for irrigation and drainage purposes as recommended by the Revelle Panel and by Tipton and Kalmbach and that being followed by West Pakistan WAPDA is a temporary expedient and a self-destruc3 Total cost of tubewells (excluding electrification and drainage facilities) in SCARP 3 is estimated as 123.5 million rupees, out of which 71.8 million rupees (15.1 million dollars) are required in foreign exchange for equipment, goods and services that must be imported [16, p. 481.



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 357' this. There is every reason to expect that with the opening of new SCARPS and with the continued spread of private tubewells this progress will persist Nevertheless we must reiterate that insufficient water was not the only deficiency in the Indus Plain and the provision of more water is not the solution to the agricultural problem there. It is only the first step and, we hope, the catalyzing step in a movement toward thorough-going agricultural modernization. We do not have to spell out again the other measures that are urgently demanded; the report of the Commission on Food and Agriculture and our previous Report have covered these measures in ample detail. We need here only state our impression that insufficient attention is being given to the other need 's of agriculture in West Pakistan. Unless these other needs are met the ultimate results of all this effort will be disappointing. Yields will remain below world-wide averages, the ravages of insect and rodent pests will continue, and agricultural incomes will not advance as they should and must. The progress in the fields of agricultural extension, agricultural credit, seedstock improvement, and other directions has not been comparable to the progress made in improvements in water supply and in the use of fertilizer. We should like to conclude our review with an earnest plea that vigorous attention to these problems, admittedly difficult, be given the highest priority. REFERENCES 1. White House-Department of Interior Panel on Waterlogging and Salinity in West Pakistan, Report on Land and Water Development in the Induss Plain: (Washington, D.C.: The White House, January 1964). 2. Harza Engineering Company International, Programme for Water and Power Development in West Pakistan through 1975. (Lahore: West Pakistan Water and Power Development Authority, January 1964). 3. Harza Engineering Company International, A Programme for Water and Power Development in West Pakistan 1963-75. Supporting Studies. An Appraisal of Resources and Potential Development. Chapter II: (Lahore: Summer 1963) 4. Ghulam. Mohammad, "Waterlogging and Salinity in the Indus Plain: A Critical Analysis of Some of the Major Conclusions of the Revelle Report", Pakistan Development Review, Vol. IV, No. 3, Autumn 1964. 5. Ghulam. Mohammad, "Private Tubewell Development and Cropping Patterns in West Pakistan", Pakistan Development Review, Vol. V, No.1, Spring 1965.



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380 The Pakistan Development Review They not only thoroughly studied the complicated problem in such a limited period but have suggested a solution. Their study of the problem will remain a source of guidance for generations to those who are to deal with the land and water problems of this country. To the scientists it has given new avenues to explore. Science progresses on new and novel ideas. REFERENCES 1. Ahmad, Nazir, A Discussion on Hydrological Estimation of Water Resources as Put Forth in Chapter VI of Kennedy Mission Report. Special Report No. 255-Ph/ Seep.-53/63. (Lahore: Irrigation Research Institute, 1963). 2. Ahmad, Nazir and Mohammad Akram, Evapo-transpiration as A Function of Depth to Watertable and Soils. Special Report No. 291-Ph/Soil. Ph.-7/65 (Lahore: Irrigation Research Institute, 1965). 3. Dean, F. Peterson, 0. W. Israelson and V. E. Hansen. Hydraulics of Wells. Bulletin 35. (Logan: Utah State University, March 1952). 4. Ghulam Mohammad, "Waterlogging and Salinity in the Indus PlainA Critical Analysis of Some of the Major Conclusions of the Revelle Report", Pakistan Development Review, Vol. IV, No. 3, Autumn 1964. 5. United States Department of Agriculture, Soil Conservation Service, Irrigation Pumping Plants. Chapter 8. (Washington, D.C. United States Department of Agriculture).



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344 The Pakistan Development Review acres of the Northern Zone. The total salt contents are summarized in Table V. We see that 16.3 million acres in the canal-irrigated regions of the former Punjab, and 2.0 million acres in canal regions of former Bahawalpur, overlie groundwaters with a salt content of less than 1000 ppm. These sweet water zones make up 70 per cent and 39 per cent, respectively, of the gross area in the canal-irrigated regions. Out of the entire 34 million acres, 21.2 million acres, over 62 per cent, have a salinity of less than 1000 ppm. There is no question that water in this salinity range can be used for irrigation, either directly or when suitably mixed with canal water. The area in the canal-irrigated regions underlain by this relatively high-quality water is close to the maximum net cultivated area, contemplated in Tables I and III for intensive cultivation. To achieve the potentialities of the Indus Plain, it will be necessary to recapture as much seepage as possible from water courses, canals, and fields. Part of this seepage occurs in areas of salty groundwater. In the Panel Report, we assumed that groundwater with a salt content up to several thousand ppm could be used for irrigation if it is mixed with the river waters, which have a salinity of about 250 ppm. It is encouraging to note from Table V that less than 13 per cent of the entire Northern Zone is underlain by water with a salinity of more than 5000 ppm. In the canal irrigated regions, only 11 per cent of the gross area has a salinity in excess of 5000 ppm; 77 per cent has a salinity less than 2000 ppm. In the Panel Report, we defined non-saline and saline areas as those underlain respectively by groundwater with a salinity less or more than 2000 ppm. The average salinity of water samples from the non-saline area (constituting 77 per cent of the canal region) is 750 ppm; the average for the saline area (constituting 23 per cent of the canal region) is 6000 ppm. The latter value is high because of the very high salinity of a few of the samples. If we consider instead the sizes of the areas overlying waters of different salinity, we can estimate, from Table V, that in half the saline area the groundwater has less than 50)0 ppm, averaging 3350 ppm. A good deal of this water in the "favorable" half of the saline area can be used for irrigation, if it is sufficiently diluted with canal water. We conclude that over the Northern Zone the distribution of groundwater salinity is so favorable that extensive exploitation of nearly all the area of the underground aquifer is warranted. In order to do this safely, however, highly saline waters must be pumped from underground and carried out of the region, perhaps to desert salt lagoons.



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Dorfman, Revelle and Thomas Waterlogging and Salinity 337 While the second design entailed a much smaller investment in wells and would require considerably smaller power costs than the first, it had the marked disadvantage of providing water sufficient for the intensive development of only 11.6 million acres of cultivated land. This area is a great deal less than that occupied at the present time. Farming could be maintained over the present area only at the cost of a relatively low intensity of cultivation. The first scheme was shown to be economically more efficient than the second when the discount rate was taken as 4 per cent per year. At this discount rate, the present value of the time stream of benefits and costs of the mining scheme was 8 per cent larger than that in which recharge only was pumped. Moreover at all other discount rates from 0 to 10 per cent per year the first scheme outranks the second. The ranking is insensitive to the discount rate and the Panel Plan with 100-foot mining and large scale tubewell development affords a 'better investment than the second scheme. The opinion hasbeen expressed by some that the Panel Plan did not sufficiently take into account the difficulty that in mining over time the quality of groundwater will deteriorate due to the fact that salinity generallyincreases with depth. The Panel examined many hundreds of profiles of salinity and found that while this increase occurs in many places-indeed most places-the reverse is also true, and the average increase in salinity in 100 feet of depth was not large. Moreover, there are factors that operate to improve the quality of the groundwater over time. Several of the curves of salinity vs. time [1, Chapter 7J Figures 7.18 and 7.19 show a decrease in salinity after 30 years of operation. This decrease would have been even greater if the salt-flow model had been run under the plausible assumption that with a low watertable some of the salt leached below the root zone would be stored permanently in the soil pores above the watertable. The Panel's principal argument for mining, however, did not rest upon the foregoing economic analysis. A more realistic but less quantifiable argument is that until a very large amount of surface storage is built, intensification of water use and cultivation can be accomplished in the Northern Zone only by mining or by greatly reducing the area of cultivated land. The latter would result in large social costs and perhaps monetary costs of resettlement and other adjustments. Ghulam Mohammad's Budget for the Northern Zone[4] A somewhat similar argument applies to the budget given by Ghulam Mohammad. Although he does not recommend a marked reduction in net cultivated area, his gross sown area in the Northern Zone would be much smaller than



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TABLE V SALINITY OF GROUNDWATER IN NORTHERN ZONE _01 00 Area underlain by groundwater of indicated salinity Salinity Former Punjab2 Former Bahawalpur3 Total Canal Non-canal Canal Non-canal Canal Non-canal regions regions4 regions regions regions regions Total (.................................................. m illion acres...................................................) Less than 500 ppm 9.9 0.1 1.2 -11.1 0.1 11.2 500-1000 ppm 6.4 2.8 0.8 -7.2 2.8 10.0 1000-2000 ppm 3.4 0.71 2000-3000 ppm 1.2 0.3 ) 1.1 0.4 7.0 1.5 8.5 3000-4000 ppm 0.6 0.1J 4000-5000 ppm 0.7 5000-10,000 ppm 1.0 -1.3 0.7 2.3 0.7 3.0 10,000-20,000 ppm 0.2 -0.6 0.4 0.8 0.4 1.2 More than 20,000 ppm ---0.1 -0.1 0.1 Total gross area 23.4 4.0 5.1 1.5 28.5 5.5 34.0 Culturable commanded area 15.2 -3.5 -18.7 -18.7 (...............................................Per cent of gross area...............................................) Less than 500 ppm 29.2 0.3 3.5 -32.7 0.3 33.0 500-1000 ppm 18.8 8.2 2.4 -21.2 8.2 29.4 1000-2000 ppm 10.0 2.1 2000-3000 ppm 3.5 0.9 3.2 1.2 20.6 4.5 25.1 3000-4000 ppm 1.8 0.3 4000-5000 ppm 2.1-j 5000-10,000 ppm 2.9 -3.8 2.0 6.7 2.0 8.7 10,000--20,000 ppm 0.6 -1.8 1.2 2.4 1.2 3.6 More than 20,000 ppm --0.3 -0.3 -0.3 68.9 11.8 15.0 4.4 83.9 16.2 100.1 Source: From (3, Table II-5, Chapter II. Irrigation Development in the Indus Plain]. 1 Salinity as parts per million of total dissolved solids in groundwater samples at a depth of more than 100 feet. 2 Includes Thai, Chaj, Rechna and BariDoabs, but not Indus Right Bank areas. 3 Areas under command of Fordwah, Eastern Sadiquia, Quimpar, Bahaw canals, Plus 1.5 MA of "undeveloped" area 4 Includes 1.7 million acres in Gujrat Plain and Sialkot, where well irrigation is used, and 2.4 million acres of undeveloped and desert area in Thal Doab. 5 2.0 million acres commanded by the Panjnad Canal has been incompletely surveyed. According to Harza, about 50 per cent of this area is believed underlain by water with less than 1000 ppm of salinity. Accordingly, we have distributed the Panjnad Canal area as follows : 0.5 million acres less than 500 ppm; 0.5 million acres, 500-1000 ppm; 0.3 million acres, 10005000 ppm; 0.4 million acres, 5000-10000 ppm; 0.3 million acres; 10000-20000 ppm.



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Dorfman, Revelle and Thomas:Waterlogging and Salinity 339 250 feet to 350 feet. They are intended to provide water to an area of 600 acres or more each. The private wells are much smaller. Typically their flows are from 1 to 1.25 cusecs (2 to 2.5 acre feet per day) and their drafts are typically about 100 feet. The usual practice is for the private wells to serve an area of approximately 60 acres, or 1/10 that of the public wells. From an economic point of view, it is pertinent that the public wells are built with imported components for the most part, while the private wells use equipment of domestic manufacture. The private wells, therefore, economize on the use of foreign exchange and also contribute to the accumulation of domestic manufacturing capacity and experience. It is evident that the larger public wells are more efficient technically than the private ones. As will b. discussed more fully in a later section the deeper draft of the large wells slows down the rate of salt build-up in the groundwater reservoir which is an inevitable result of the vertical drainage entailed by either system. The larger wells with their larger and more rugged pumps and motors, are also more efficient mechanically. It is very difficult to compare the costs of the two types of wells. Ghulam Mohammad has done so [7] and come to the conclusion that private wells can pump underground water more cheaply than government wells. This finding, however, should not be regarded as conelusive. The basic difficulty, aside from the fact that the government wells and the private ones are not in strictly comparable locations, is that different systems of accounts are used in computing the costs of the two systems of well. The cost accounts for government wells include charges for many items that the account for private wells omit, because the recorded cost for private wells incorporates only the out-of-pocket cost of the well owners. Costs of planning, supervision, and provision for contingencies, for example, are included in the government accounts but not in those for private wells, although the same economic functions must b. performed in both instances. A good justification can bgiven for excluding the imputed costs of such functions from the estimate of the cost of private tub.wells. These exclusions do, however, impair the comparability of those costs with the cost of government wells. The government accounts include costs for draining saline effluent and for power transmission; private accounts do not. And there are many other similar items. With these reservations in mind, we have tried, in Table IV, to place the costs of water pumped by private and government wells on a comparable basis, relying largely on Ghulam Mohammad's data. Costs of drainage are omitted; they would be somewhat larger for the private wells than for the government ones because the quality of the effluent would deteriorate more rapidly from the shallower wells. All costs for the provision of power are included in the



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340 The Pakistan Development Review charge of Rs. 0.08 par kwh, used for both types of installation. In other respects too the two systems have been put on as comparable a basis as possible, as the source notes indicate in detail. The computation shows that water pumped by private tubewells costs about 8 per cent more than water pumped by government wells. In view of the inherent lack of precision of such a calculation this difference should not be taken seriously; to all intents and purposes the calculation indicates that the costs of water from the two types of well are approximately the same. It should be noted, however, that in Table IV we have assumed the same load factor for both types of well, approximately 25 per cent. This load factor accords with the recorded experience with private wells but the public wells in the SCARP have been operated at a load factor of about 60 per cent. If the more intensive use of government as compared with private wells should persist, then the government wells will show an appreciable economy in comparison with the operating costs of the private wells. At any rate, such cost comparisons cannot be decisive, because, as remarked above, the private and the public wells serve different purposes in the overall development of the Indus Plain. Private wells have been used only for very local supplementation of the suppliesof canal water. Water provided by private tubewells is approximately four times as expensive as government canal water to the owner of the private well, and to a farmer who purchases from a private well owner, the discrepancy is even greater. Private wells will therefore be developed only in areas that have adequate supplies of high quality groundwater and they will be used mainly to fill in gaps in the supply of canal water. They have not been installed thus far in localities where the groundwater is too saline to be applied to the land without dilution with canal water. From the farmer's point of view the supply of government water from either wells or canals is less reliable than that of water provided by a locally owned tubewell and the government wells cannot be adapted as fiexibily to day by day changes in the local requirements for irrigation water. On the other hand, the government wells can be used for the dilution of saline groundwater, for reclamation of deteriorated lands, and for closely integrated management of both ground and surface water supplies. The advantage of closely coordinating canal diversions and groundwater withdrawals can be seen from a simple calculation based on the data in Table 11. Suppose in the first instance that Mangla and Tarbela Dams are operating but that no tubewell water is available, and that the maximum amount of canal water available during any month in kharif is 12.4 MAF at the canal heads, or 8.7 MAF at the water courses, this being the maximum capacity of the canals.



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Dorfman, Revelle and Thomas' Waterlogging and Salinity 369 TABLE VI TIME OF BUILD-UP OF SALINITY IN UNDERGROUND WATER FOR TUBEWELLS OF DIFFERENT DEPTH I. INITIAL GROUNDWATER SALINITY=500 PPM FINAL GROUNDWATER SALINITY= 1500 PPM Well Soil salt, tons/acre 0 10 20 30 40 50 depth Feet Time in years to reach 1500 ppm in groundwater 50 15.1 6.3 0 0 0 0 100 30.2 21.4 12.5 3.7 0 0 150 45.5 36.7 27.8 18.9 10.0 1.1 200 60.5 51.6 42.7 33.8 25.1 16.0 250 75.6 66.9 57.9 48.4 40.6 48.4 II. INITIAL GROUNDWATER SALINITY =750 PPM FINAL GROUNDWATER SALINITY = 1500 PPM well Soil salt, tons/acre 0 10 20 30 40 50 depth Feet Time in years to reach 1500 ppm in groundwater 50 11.3 2.5 0 0 0 0 100 22.7 13.8 5.0 0 0 0 150 34.1 25.2 16.4 7.5 0 0 200 45.4 36.4 27.6 18.7 10.0 0.9 250 56.7 48.0 39.2 30.4 21.6 12.5 TABLE VII SALINITY OF TUBEWELL WATER AT DIFFERENT TIMES, WHEN DRAINAGE SYSTEM IS INSTALLED AT THE BEGINNING OF PUMPING Time in years 0 10 20 40 50 100 200 250 Salinity, ppm Well depth, 100 feet 750 870 975 1165 1230 1540 1830 1895 Well depth, 250 feet 750 800 850 935 975 1165 1435 1540



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400 The Pakistan Development Review detail. By 1970, the entire flow of the Sutlej, Beas and Ravi Rivers (designated as the Eastern Rivers in the Indus Water Treaty) will be diverted by India and there will be no period of high run off in these rivers. No saline tubewell waters can, therefore, be returned into the Sutlej and Ravi Rivers. The same would be the condition of Chenab and Jhelum Rivers after a few years. According to Mr. S. S. Kirmani, Chief Engineer, Indus Basin Projects, West Pakistan WAPDA, "After the completion of the Indus Project, most of the flows of the Jhelum and Chenab Rivers will be fully used in the existing irrigation system and for the replacement of the irrigation uses on the Eastern Rivers" [11, p. 247J. The Chenab and Jhelum Rivers will have a surplus of only 2 to 3 MAF which will consist of erratic and infrequent flood peaks of only a few days duration. No drainage tubewell waters from any part of the Punjab can therefore be returned to any river during the "period of high run off" because there will be no period of high run off after 1975. If canal capacity is increased and more river water is diverted on to lands as suggested earlier in this paper, there may not be any period of high run off after 1970. The Indus is the only river in which some 35 MAF will continue to flow to the sea during the period of high run off but topography does not permit drains in any area in the Punjab part of the Indus Plain to outfall to the Indus River. Drainage waters from the lower part of the Bahawalpur and Sind could be returned to the Indus during the period of high run off, but that would damage the agriculture in Lower Sind, slowly but certainly. As pointed out by Dr. Eaton (p. 382), the longevity of agriculture which supports many millions of people should be viewed in terms of centuries rather than on the basis of an expedient which may suffice for only a limited number of years. Alexander Karpov has pointed out there are millions of acres in North Africa and Western Asia where great cultures once flourished. At present nothing is left but sand dunes, salt marshes and eroded landscapes [10, p. 2271. The proposals of Panel members and of Tipton and Kalmbach would similarly convert the Indus Valley agricultural areas into barren salty lands. The Panel members have also proposed disposal of saline pumped waters into desert lagoons. This is possible for Bahawalpur and parts of Sind, but unfortunately there are no desert lagoons in the Rechna and Chaj Doabs where large quantities of pumped waters from the highly saline groundwater areas of these doabs could be disposed off. The conclusion is therefore inescapable that there is no place for disposalof pumped water from the highly saline groundwater areas inthe Punjab. These must remain where theyare. Salt from theupper 7to 10



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Ahmad: Waterlogging and Salinity: Comment 377 Loss of Component of Sub-irrigation if Watertable is Lowered When Ghulam Mohammad wrote his comments, the data on the amount of sub-irrigation was still preliminary. Recently detailed studies [3] have been completed on sugarcane and cotton crops. The former can grow in high watertable and the later needs a deep watertable. These studies have shown that a considerable amount of the requirements of a crop is satisfied from the soil moisture if the watertable is high. Puming Saline Water and its Disposal The Panel's suggestion to export 3.9 MAF of water with 4000 ppm to lower regions and to make arrangement ultimately to arrange for the disposal of about one MAF of water of 10000 ppm by surface evaporation also needs careful consideration. During three or four summer months from May to August, water is sufficient in rivers to mix 4 MAF (about 5,500 cusecs) of water and cause no harm to ultimate increase of salts but during the remaining 8 months, the river discharges are low and mixing this order of saline water will have serious problems. Again, to evaporate about one MAF of water we need an exposed surface of about 270 square miles as in this region about 5 cusecs ate evaporated from one square mile of the surface. The obvious course appears to be not to touch the saline water and to take such measures as to obtain the requirements without the mining of saline groundwater. A Suggestion for the Solution of the Problem The Panel has worked out that 58.8 MAF of water is to be made available at the fields. The present irrigation canal system diverts 48 MAF and makes available 24.3 MAF at the fields. The rest 34.5 MAF is to be pumped from the groundwater storage. This is to be made up of 20 MAF from seepage of canals and 14.5 MAF to be drawn from mining operation. We know that during the 4 summer months from the beginning of May to the end of August, we have more river water supplies than we can utilize. Suppose we do not pump any groundwater during the 4 summer months. We can arrange our requirements from improved river diversion and further digging of canals. If we spread the pumping uniformly over the full year, then during the four summer months, we have to pump 11.2 MAF of water, During summer we have available water in our rivers. It needs arrangement to divert it on the land and during this period we can do without pumping. If we can succeed in this suggestion then we need only 23.3 MAF from groundwater for



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332 The Pakistan Development Review is complacency-the premature conclusion that the programs already undertaken will suffice. They will not. The first positive steps have brought dramatic results because~ there was so much room for improvement in the cultivation of the Indus Plain. But fundamental shortcomings persist. There is still much hard work to be done. Just as our first message was one of hopefulness in a time of gloom, so now we want to offer some sober appraisals in a time of confidence. One of the central themes of our report was interaction. We found that the agriculture of West Pakistan was be-set by numerous deficiencies. Efforts to correct any one of these could have only limited success, because the uncorrected shortcomings would still set a low ceiling to agricultural productivity. On the other hand, simultaneous measures to provide additional irrigation water; reclaim deteriorated land; supply chemical fertilizers, plant protection, and improved seeds; instruct farmers in the proper use of these materials and in modern agricultural methods; increase the ease and rapidity of loans to farmers; and improve marketing procedures and facilities-all concentrated on the same area-would be mutually supporting and would yield far greater increases in output than the same efforts scattered over different places. For these reasons we recommended the formation of the Land and Water Development Board and of local administrations, each responsible to the Board for supervising physical improvements and a number of agricultural programs in a single compact area. Because Pakistan has a limited supply of administrative resources, we recommended the strategy of starting project areas in succession, with development of no more than about a million acres being undertaken in any one year. We still adhere, in the main, to this broad concept. But now it appears that we overestimated some of the difficulties. Since the publication of our report, the farmers of West Pakistan have demonstrated more initiative and more willingness to adopt modern agricultural practices than we anticipated. This is indicated by the rapid spread of private tubowells-about 6,500 a yearand by the eager adoption of chemical fertilizers-usage increasing at about 20 per cent per year recently. Furthermore, it seems evident that the distribution of fertilizer, seeds, and other materials of agriculture can be accomplished efficiently through ordinary commercial channels. Thus, the agricultural administration can concentrate on providing water, agricultural advisory services, credit, and storage and marketing facilities, leaving the problems of distribution of agricultural materials and even some of the work of supplying irrigation water to private initiative. The resulting economies in the utilization of scarce administrative and technical manpawar may pe-rmit a considerable acceleration of the program.



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•Ahmad: Waterlogging and Salinity: Comment 379 iii) use shallow multiple strainers to pump 2 to 4 cusecs from each unit of pumping set. iv) not pump saline groundwater as multiple strainers will be installed to pump the top 70 to 100 feet of the aquifer, v) replace the stagnant groundwater richly charged with carbonates and bicarbonates as a result of action of root zone by fresh rain water, rich in oxygen and most beneficial to crops, vi) start fluctuating the groundwater which will rise during summer and will fall by several feet during the remaining eight months, thus creating a system of natural drainage as exists along the flood plains, vii) not pump saline groundwater, which would introduce the problem of aquifer deterioration, nor have a problem of disposal of highly saline water. viii) water highly charged with carbonates and bicarbonates will be replaced by rain infiltration, and the problem of conversion of normal soil into alkaline impermeable soils by use of bicarbonate charged water will be remedied. The financial aspect of these suggestions can further be examined but it is certain that when we have more summer supplies available, we should utilize them by ever-lasting canals, requiring little maintenance as against short lived tubewells with costly maintenance. Integration of the presently constructed storage at Mangla can be so incorporated as to reduce pumping. When we need winter supplies we may install cheap, shallow multiple tubewells. The efforts of the farmers can even be integrated to pump during winter both for drainage and for extra supplies. These are the suggestions which can be applied in the Punjab and Bahawalpur or where significant pumpable good quality aquifer exists such as along the strip of the Indus in Sind or in Khairpur West or in Larkana-Shikarpur Districts. This suggestion is not workable for Ghulam Mohammad Barrage in general and the lower region of the Sukkur Barrage System adjoining the Ghulam Mohammad Barrage region having high watertable of a very highly saline nature. Here, we have to create good quality aquifer before tubewells can be installed. Tile and open drains are the solution and there is no doubt about the success of this type of drainage in that area. In the end, it is admitted that Pakistan is much obliged to the American scientists which constituted the Panel for their great service to this country.



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358 The Pakistan Development Review 6. Harza Engineering Company International, Reconnaissance Survey of Private Tubewells. (Lahore: February 1965). 7. Ghulam Mohammad, "Some Strategic Problems in Agricultural Development in Pakistan", Pakistan Development Review, Vol. IV, No. 2, Summer 1964. 8. Bower, C. A. and M. Maasland, "Sodium Hazard of Punjab Groundwaters", Symposium on Waterlogging and Salinity in West Pakistan. (Lahore: West Pakistan Engineering Congress, October 1963). 9. Maasland, M. J. E. Priest and M. S. Malik, "Development of Ground Water in the Indus Plains", Symposium on Waterlogging and Salinity in West Pakistan. (Lahore: West Pakistan Engineering Congress, October 1963).



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390 The Pakistan Development Review Sw X 100 RL= 2 x Mss-Sw For annual plants of low salt tolerance Mss = 20 For annual plants of medium salt tolerance Mss. 30 For annual plants of high salt tolerance Mss 75 For standard water-quality comparisons, the use of Mss = 30 is suggested. Comments on the Derivation of the Equations The leaching requirement, RL, represents the percentage of the applied irrigation water which should be passed through and out of the root zone as leachate for the maintenance of yields averaging 80 per cent as high as on similar non-saline soil. If the equations, when converted to acre inches of leachate, for example, show that there should be five acre inches of leachate, this amount remains valid irrespective of whether the actual leaching is brought about by irrigation or by rainfall, i.e., the rainfall may produce the leaching but the acre inches of required leachate computed on the basis of the amount of irrigation water applied is not changed. In the RL calculation, unreasonably high values result if either the electrical conductivity or sum-of-cations is substituted for Cl + -S04, because HCO3 would be included; HCO3 is not significantly accumulated by plants. But its presence as NaHCO3 depresses Ca and Mg accumulations. These ions, in ample amounts, are essential for good crop production. It is more economical to avoid the adverse effects of HCO3 by the use of gypsum than by extra leaching. In the instance of the Indus River at Sukkar on January 30, 1953 [3]. the leaching requirement by the present equations is 1.4 per cent. But on the basis of electrical conductance or sum of anions or cations, the requirement is found to be several times greater and unreasonably high. The expression, in the Ca requirement equations, Na x 0.43 shows the amount of Ca + Mg needed for 70 per cent Na. If a water contains 5 me./l of Na then Na x 0.43 shows that 2.15 me./1 of Ca + Mg will be needed to give 70 per cent Na. The deficiency or excess from 2.15 is carried forward with the plus or minus sign in computing the Ca requirement: a+b+c. The present Mss values (used in the denominator of the RL equation), are lower than those previously suggested because of experimental results [4, pp. 411-416] showing that chloride accumulates at root surfaces and gives rise to higher accumulations in plants on a soil than on a water culture even though the substrate concentrations are maintained at the same level.



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394 The Pakistan Development Review Dr. Eaton has raised two important questions on this issue (p. 383). He asks i) who will pay for pumping the bad waters and ii) how will these be disposed of? As stated by Dr. Eaton, neither the government nor the farmers will be able to pay for the drainage structures when all the groundwaters have been salinized; certainly, they are better able to do so now when only part of the groundwaters are salinized. It would be in the interest of Pakistan to install tubewells in the non-saline best quality groundwater areas only. These areas lie in the upper reaches of the Rechna, Chaj and Bari Doabs and along both sides of the rivers in the Punjab and Bahawalpur. Farmers are already installing tubewells in these areas. To keep the groundwater of these areas in good condition, Dr. Nazir Ahmad has suggested that the canal water supply to these areas should be increased during the summer season when there is excess water in the rivers. This would increase the infiltration of fresh water to the groundwater and in this way these areas could be kept fit for pumping for an almost indefinite period. According to Harza Engineering Company International, the present river diversions into the West Pakistan canals are about 83 MAF per year, 48 MAF in the Northern Zone and 35 MAF in the Southern Zone [9, p. 39]. About 20 MAF of water is lost through seepage and evaporation in the rivers and about 61 MAF goes to the sea mainly during the summer season [9, p. 39]. It should be possible to divert some 10 MAF additional water to the non-saline groundwater areas out of the 61 MAF now going to the sea. If the capacity of canals is increased and additional water is diverted onto these areas during the kharif season, the rabi water supply can be withdrawn from these areas. The farmers can install tubewells and meet the full need of the rabi crops by pumping groundwater. The rabi water removed from these areas can be diverted to saline groundwater areas in the lower reaches of the doabs where tubewells cannot be installed on account of high salinity. In order to encourage the farmers to install tubewells in the non-saline groundwater areas, electricity should be provided to the whole of this area, and credit should be extended to the farmers for the purchase of tubewell materials. In the remaining areas of the Punjab and Bahawalpur where groundwaters are relatively more saline, drainage facilities must be provided to remove the salt from the area. However, a basic problem of these areas is the deficiency of irrigation water. The capacity of the canals will have to be increased and addi-



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Ahnad: Waterlogging and Salinity: Comment 375 a) from good quality groundwater zone ... 24.2 MAF b) from bad quality groundwater zone ... 5.3 MAF Assuming 15 par cent of this water to be seeping back and assuming 25 per cent to be the storage coefficient, the depth of groundwater to be lowered to yield the required discharge will be: 24.2 0.85 Good quality groundwater zone = -3.58 feet 23 "0.25 5.30 0.85 Bad quality groundwater zone = 0.25 -2.58 feet As it is now established that the storage coefficient is about 12 to 14 per cent, the fall of groundwater per year to give the above yield will be doubled,' i.e., about 7.0 feet per year in good quality groundwater zone and about 5.0 feet in bad quality groundwater zone. Defects while Pumping this Order of Water If this programme of pumping is followed, a fall in the groundwater table of 7 feet per year is expected so that the watertable will be lowered down to 100 feet in 14 years. Let us examine this suggestion for SCARP 1. In this area, tubewells are installed in which the length of housing is 90 feet and the impeller of the turbine pumps are located about 70-75 feet below surface, i.e., about 60-65 feet below average watertable, at the time of the implementation of the scheme. These wells would pump 3 to 3.5 cusecs with an average depression head of 18 to 20 feet (see, Fig. 1). If the mining is to be done as planned with a fall of 7 feet per year, the watertable will be below the impeller after 9 years of the operation. All the 2,000 tubewells of SCARP 1 will become useless if the groundwater is mined as proposed. The 3.0 cusecs discharge was started to be pumped with 20 feet of depression and 40 feet of water cushion. After five or six years, the cushion will be eliminated and water will be pumped by the depression alone. Working of the tubewells may become doubtful. If the conception of free surface opening on the discharge face as put forth by Peterson, Isrealson and Hansen holds [2], then the tubewell of SCARP 1 will stop working when the watertable goes down to 30-40 feet from its present level, i.e., after 4 to 5 years of the pumping to mining capacity. The 2,000 tubewells of SCARP installed to work for 40-50 years shall have to be scrapped much earlier than their assumed life. If the watertable is to be taken down to 100 feet by tubewell pumping then the length of housing pipe needed is 160 to 170 feet with impellers located at 150 feet and the strainer starting below 170 feet. This design of tubewell is not being followed even in other SCARP areas.



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384 The Pakistan Development Review the alnount of gypsum which should be applied to the water or to the land to prevent high alkalinity, serious soil impermeability, and the deficiencies of the calcium and magnesium required for normal growth. Knowledge of the existence of the alkali problem, both present and future, is indicated by the inclusion, in the paper by Dorfman, Revelle, and Thomas, of a discussion of the "sodium hazards". There were no statistics to indicate the magnitude of the problem represented by the composition of the groundwaters or of the proportion of the land which is now so high in sodium that leaching is too slow to be fully effective. No mention is made of the use of gypsum as a corrective. On the basis of the old groundwater analyses, which the writer was able to find in Pakistan at the time of his three-month visit in 1952-1953, the problem of excess sodium and high alkalinity in soils and groundwaters impressed him as being serious and deserving of carefulattention. Since that visit, Hausenbuiller, et al [6, pp. 356-364] were similarly impressed and recommended applications of gypsum where needed. The writer recalls experimental data from the vicinity of Montgomery which demonstrated outstanding yield benefits from the use of gypsum. No practical substitute for the use of gypsum on high sodium alkali lands is known. Ghulam Mohammad has reviewed [5, pp. 357-403], the now-available analyses of groundwaters of the Indus Plain. Even on the questionable assumption that 1.25 me./l of residual sodium carbonate may be safe (see, later discussion), the data show that the less saline waters are commonly so high in sodium and/or bicarbonate as to make their use hazardous unless they are mixed with canal water or treated with gypsum. Private interests will undoubtedly avail themselves of the groundwaters of Pakistan by pumping only so long as the qualities of these waters permit profitable crops. When there is no longer a profit, the wells will be abandoned, after which the watertables will again rise. It seems doubtful at this stage that private funds will be available for the construction of the drainage system which should have been established when the distributary canals were constructed. The cost of a country-wide drainage system is so great that it seems doubtful that public agencies can now undertake it. On-Farm Drainage It was for the foregoing reason, and the foregoing reason only, that the writer in his FAO report [3] suggested a type of drainage system which he believed the farmers themselves could install and maintain. Such a system, although not ideal, may be the only recourse possible, now or in future, in many areas of Pakistan.



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Waterlogging and Salinity in the Indus Plain: Comment by FRANK M. EATON* Not only does Ghulam Mohammad's contribution on waterlogging and salinity in the Indus Plain 151 reflect a wide understanding of the agricultural problems of Pakistan but the clarity of his presentation is commendable. My comments all have to do with water quality and drainage problems in this vast irrigated area with the future rather than the immediately present problems primarily in mind. I trust that all statements will be regarded as constructive rather than critical. The changes now occurring with irrigation in the compositions of the initially high-quality canal waters of the Indus Plain as these waters become groundwaters, appear to be little different from the past changes which occurred more slowly but which are responsible for the diverse compositions of the present groundwaters. Many of these present-day groundwaters were left behind by the flood waters which deposited the valley alluvium. The flood waters left on the land surface underwent concentration by evapotranspiration with precipitations of CaCO3 and losses of Mg in the form of compounds of salica. As a result of these precipitations there were increases in the proportions of Na. That little of the salt being left in the soils and groundwaters of Pakistan with irrigation is now being carried to the sea is indicated by the finding that a sample of the Indus River collected near Karachi in February 1953, when the discharge was very low, was only a little more saline than that of waters sampled near the upper head works [ 31. The Karachi sample was reported to have been about 80 per cent return flow from surface runoff and drainage from irrigated lands. The fact that little of the salt brought onto the lands of the Indus Plain by the rivers and canals is being discharged into the sea, represents a major long-time threat to the permanency of the agriculture of West Pakistan unless a suitable means of disposing of the salt residues of these irrigation waters *Dr. Frank M. Eaton is the Associate at the Agricultural Experiment Station, University of California, Riverside, California.



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Dorfmnan, Revelle and Thomas: Waterlogging and Salinity 355 layers of the groundwater. The flow in the main drains and laterals depends on seepage rates and these in turn depend upon the gradient of the watertable. A vertical drainage system, on the other hand, is more flexible. The flow and sr,.linity of the mixed effluent of a set of tubewells can be controlled, and consequently, drainage can be carried out at any desired rate. This results both in a smaller investment in conveyance channels and in better salinity control, because salt can be returned to the rivers during periods of high runoff, or routed to salt lagoons at times when the irrigation requirement is small. Compared with vertical drainage, horizontal drainage systems are wasteful of water. The salinity concentration of the drained water is likely to be smaller than with tubewell drainage and hence larger amounts of water must be carried away in the drains. 2) In flat topography it is difficult to fit together efficiently a horizontal drainage system with an intensive irrigation system. Crossings of conveyance lines of the two systems are unavoidable and are expensive. If the drainage is to be returned to the canals, pumps are required. The principal costs of horizontal drainage in the Indus Plain would be associated with pumps and with concrete control and access structures including weirs, gates, check stops, bridges and pump sumps that cannot be built with unskilled labor. 3) Irrigated agriculture is most successful when it is most intensive, that is when it is concentrated on a minimum land area. Open drain systems occupy a significant portion of the land area in and between the cultivated fields and hence cause the farming operations to be spread out on more land. While it is true that the supply of good land is greater than the supply of water throughout most of the Indus Plain, the layout of an extensive horizontal drainage system, which must conform to the topography and have a minimum number of inter sections with the distribution system, will extend and complicate the access routes to the fields. Farming operations are impeded when bridges must be crossed. 4) Deep main drains and open field drains are difficult to maintain. Drainage works are sporadically impaired by flood damage and their efficiency is regularly reduced by growth of weeds. Flood damage to drains is inherently more serious than the damage to water distribution channels because of topography. Unless pumps are used, artificial drainage must conform with natural drainage. Consequently the drains must be adequate to handle storm runoff and must be repaired after the floods recede. Weed growth in drainage ditches is more abundant than in distribution channels because of lower flow velocity and greater nutrient supply. Maintenance of drains-removal of weeds and debris, channel realignment and repair of side slopes-is difficult and unpleasant work.Even a cow does not like to descend into the weedy morass of a malfunctioning drain.



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362 The Pakistan Development Review Col. (3): Column (5) x 0.7. Col. (4): Column (2) -Column (3). Col. (5): Maximum monthly canal diversions during kharif are limited by the assumed canal capacity of 12.4 MAF/month. Average monthly diversions during rabi are limited by the volume of water available in river flows plus surface storage; as Column (5) shows, this average is 5.4 MAF/month. With this limitation, the maximum monthly diversion during rabi is determined by the maximum difference between tubewell capacity and the irrigation requirement in any month. To minimize investment costs we have assumed that tubewell capacity is set by the amount of pumping needed in June-the month of highest irrigation requirement. This results in computed diversions of 9.1 MAF in October and only 4.3 MAF/month during November through January. Unless some canals are effectively non-perennial, the ratio between maximum and minimum canal flows of 12.4 to 4.3 may be too high to avoid difficulties of silting and erosion, and of inadequate check structures for gravity flow to water courses. These difficulties may exist even with a kharif-rabi ratio of 12.4/5.4 Col. (6): From [I, Table 1.2 and Figure 7.1]. Col. (7): Column (6)-[Column (5) + Column (8) + Column (9)]. Col. (8): River and reservoir losses from September through May are assumed to be principally by evapotranspiration. During June through August, evapotranspiration is greatly increased because of the spreading of the rivers in flood; in addition, there are major seepage losses during these months. Col. (9): It may be possible to capture part of the runoff shown in this column through recharge of groundwater in the Southern Zone, provided additional tubewells are installed to pump out the aquifer near the Indus banks during the months of low flow.



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372 The Pakistan Development Review of agricultural yield, better management, better seeds, use of fertilizer, pest control, use of insecticide and such other measure, known to increase the yield, are suggested. The Panel has laid great stress on the agricultural aspect of the problem. Very little consideration is given to other means of drainage, on chemistry of soil and water and other hydrological and engineering considerations. Installation of tubewells, mining of accumulated groundwater, disposal ofs aline groundwater, salinity build-up in the aquifer, spacing of tubewells, etc., are the points discussed at length in-the report. The points missed are the long term success of this measure with respect to the type and design of tubewells, their life and durability, their working cost and results of mining on water requirements of crops, effect of pumping saline water and its disposal, interaction of the quality of pumped water with the type of soils generally in existence, etc. Tubewells have Uneconomical Durability This country has had more than fifty years' experience of installingtubewells in fine to medium sand formation of the Indus Plain which contains some small percentages of fines, such as silt and clay. Inspite of trials of many alternatives to develop a long-lasting tubewell, giving high economical yield, the solution has yet baffled success. Chocking of strainers and their incrustation is a majorproblem. Iron strainers have short lives in the soil and waterof this Plain; strainers of inert materials like cadmium, brass and copper were all tried and found to get incrusted. Trials with inert materials like wood, and coir string also did not stop the incrustation. Recent suggestions have been to install large diameter tubewells and use strainers with wide slits. This was tried with iron and brass strainers without much success. In case of SCARP 1, tubewells were installed with all precautions but these have started to misbehave in a short period of four years. It was suggested that for an economical performance, high discharge capacity tubewell units may be installed. This brought in the use of turbine pumps replacing the centrifugal pumps of I to 2 cusecs capacity. The life of components of a turbine pump, however, is lower than a centrifugal pump (see, Table I) and components of a turbine pump are difficult to procure. TABLE I Estimated Item useful life Well and casing 20 years Pump turbine bowl (about 50 per cent of cost of pump unit) 8 years Column, etc. 16 years Pump, centrifugal 16 years Electric motor 25 years Diesel engine 14 years Source: [51.



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Waterlogging and Salinity in the Indus Plain: Comment by NAZIR AHMAD* Mr. Ghulam Mohammad, Senior Research Economist of the Pakistan Institute of Development Economics, by publishing his critical analysis of the Revelle Report in Volume IV, No. 3 of the Pakistan Development Review [4] has done a great service to the country. A chance has, thus, been created to examine some of the recommendations for the solution of the problem as put forth by the Panel of scientists from America. Ghulam Mohammad has summarised the major recommendations of the Revelle Report and then commented upon these, giving alternative suggestions. The main recommendations of the report are to install tubewells in the large agricultural regions of the Indus Plain. This suggestion is to supplement the insufficient diversion of the surface water and at the same time to effect the drainage of the land. Ghulam Mohammad has discussed the results of the. quality of groundwater, and has concluded, "that groundwater of the Indus Plain are charged with dangerous limits of bicarbonates and sodium contents and their indiscriminate utilization will make the soils alkaline and impermeable." In his opinion, tubewells should not be installed in areas where concentration of sodium or bicarbonates is very high. Ghulam Mohammad has further put forth the financial workability of the deep open main drains combined with the open or tile field drains. As for water economy on drained land, the author is in favour of keeping a high level of groundwater to meet with a certain amount of crop requirements from sub-irrigation. Ghulam Mohammad has cautioned against the indiscriminate use of groundwater on the land. At present, according to the Panel of scientists, the main problem is the insufficiency of water for sustained agriculture and lack of proper utilization of agricultural practices. For finding more water and to effect quick drainage, tubewells are suggested and for improvement *Dr. Nazir Ahmad is the Principal Research Officer (physics) at the Irrigation Research Institute, Lahore.



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352 The Pakistan Development Review The throughput including flow recycled from watercourse seepage will be Q +Q. --Eny7 > 0 and the leaching ratio (see, Equation (1)) will be R Q +Q -Q-d Enyr ......................... (11) Q + Qw -Qd Equation (11) shows that the leaching ratio may be increased by increasing Q, without changing any of the other variables. Accordingly, in Equation (4) an increase in Qw will increase the maximum value of the salt concentration of the mixed irrigation water supply. The flow in the well will include both the throughput and recharge. The salt carried into the groundwater in the throughput of the irrigation water and in seepage from the distribution system is assumed to be uniformly distributed over the area. The salt initially in the aquifer is assumed to be distributed uniformly throughout the groundwater. Under these assumptions and the further assumption that complete vertical mixing of the salt occurs during the travel to the well, the salt concentration will be the same in all parts of the groundwater and will increase everywhere at the same rate. If the salt concentrations in the groundwater and in the canal water are denoted by C and C. respectively, then the weight of salt entering the groundwater during unit time will be C. (Q. + Qr)+ C (Qw -Qd) and the amount leaving will be CQw. Therefore, the rate of increase of salt in the aquifer will be dC C (Q, Qr) C(Q-Qd)--CQw nSnr2hdt=.(,+Q dC Cc (Qc + Qr)C Qd dt nS nr2h ................................. (12) where S = the storage coefficient of the soil and h = effective depth of the well. Equation (12) may be integrated to give the following time-path for the salinity concentration in the groundwater: C = [C. (Q. + Qr)/Qdl [1--exp (-Qdt/nSr2 h)) + C. exp (-Qdt/nS7r2h) .................. (13) where C. is the initial salt concentration of the groundwater.



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Ghulam Mohammad: Waterlogging and Salinity Rejoinder 407 17. West Pakistan WAPDA, Summary of Basic Report on Waterlogging and Salinity in West Pakistan. Prepared for the Seminar on Waterlogging and Salinity sponsored by FAO and Government of Pakistan. Mimeographed (Rome: FAO, 1964). 18. White House-Department of Interior Panel on Waterlogging and Salinity in West Pakistan, Report on Land and Water Development in the Indus Plain. (Washington, D.C.: Supdt. Doc. January 1964). This report is referred to as the Revelle Report in this paper



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Ghulam Mohammad. Waterlogging and Salinity: Rejoinder 405 tive system. The saline groundwaters being pumped or proposed to be pumped can neither be used in the same area nor can they be passed on to downstream users without acceptance of ultimate desolation. The salts must be removed from the irrigated areas by a permanent horizontal sub-surface drainage system and the saline waste disposed of in evaporation flats in the Upper Indus Plain and conveyed to the sea through special canals in the Lower Indus Plain. A basic problem in the irrigated agriculture of West Pakistan is the deficiency of water supply to meet the consumptive use requirements of crops and to leach down the salts. This deficiency is being made good by the farmers in the non-saline groundwater areas with the installation of private tubewells. The government must increase the capacity of canals and divert additional river water on to the best agricultural lands in the saline groundwater areas and initiate a programme for the construction of subsurface drainage facilities. Reclamation of saline soils even in high quality groundwater areas would cause the groundwater to become unfit for use due to leaching down of salts. No canal or tubewell water should therefore be used for such reclamation. Similarly no canal or tubewell water should be used for the development of marginal lands and all available water supplies should be used on the best agricultural lands already under cultivation. REFERENCES I. Asghar A.G. and Nazir Ahmad, "Drainage or Irrigated Soils in Arid Regions", Proceedings of the Punjab Engineering Congress, Vol. XXXIX, 1955. 2. Ahmed, Nazir, and Mohammad Akram, Evapo-Transpiration as a Function of Depth to Watertable and Soils. (Lahore: Irrigation Research Institute, 1965). 3. Bower, C.A., and M. Maasland, "Sodium Hazard of Punjab Groundwaters" Symposium on Waterlogging and Salinity in West Pakistan. (Lahore: West Pakistan Engineering Congress, October 1963). 4. Ghulam Mohammad, "Some Strategic Problems in Agricultural Development in Pakistan", Pakistan Development Review, Vol. IV, No. 2, Summer 1964. 5. "Waterlogging and Salinity in the Indus Plain: A Critical Analysis of Some of the Major Conclusions of the Revelle Report", Pakistan Development Review, Vol. IV, No. 3, Autumn 1964.



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406 The Pakistan Development Review 6. "Private Tubewell Development and Cropping Pattern in West Pakistan", Pakistan Development Review, Vol. V, No. 1, Spring 1965. 7. Gilani, Maqsood Ali Shah, and Abdul Hamid, Quality of Ground Water, Chaj Doab. Mimeographed. (Lahore: Water and Soils Investigation Division, West Pakistan WAPDA, August 1960). 8. Greenmen D.W., W.V. Swarzenski and G.D. Bennet, The Groundwater Hydrology of the Punjab. (Lahore: Water and Soil Investigation Division, West Pakistan WAPDA, 1963). 9. Harza Engineering Company International, Programme for Water andPower Development in West Pakistan Through 1975. (Lahore: Harza Engineering Company, January 1964). 10. Karpov, Alexander V., "Indus Valley-West Pakistan's Life Line", Journal of the Hydraulics Division, (Proceedings of the American Society of Civil Engineers), Vol. 90, No. HY 1, January 1964. 11. Kirmani, S.S., "Indus Valley, West Pakistan's Life Line' Discussion", Journal of the Hydraulics Division, (Proceedings of the American Society of Civil Engineers), Vol. 90, No. HY 5 September 1964. 12. Maierhofer, C.R., Report on Drainage Requirements For Irrigated Areas of West Pakistan. Mimeographed. (Denvor. Tipton and Kalmbach Inc., April 1957). 13. Mushtaq Ahmad and Abdur Reluhman ,"Design of Alluvial Channels As Influenced by Sediment Charge", Proceedings of West Pakistan Engineering Congress, 1962. (Lahore: West Pakistan Engineering Congress, 1962). 14. Pillsbury, Arthur F., Principles in the Utilization of Flood Plains. Paper presented at the Seminar on waterlogging and Salinity sponsored by FAO and the Government of Pakistan. Lahore, November 1964. Mimeographed. (Rome: FAO 1965). 15. Shamsi, R.A. and Abdul Hamid, Quality of Groundwater, Rechna Doab, Mimeographed. (Lahore Water and Soils Investigation Division, West Pakistan WAPDA, August 1960). 16. Tipton and Kalmbach, Feasibility Reporton Salinity ControlandReclamation Project Number 3, Lower Thal Doab. (Denvor Tipton and Kalmbach, April 1963).



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Eaton: Waterlogging and Salinity: Commrent 383 progressively more acute as pumping is continued. Eventually, there will be only limited sources of good groundwater which can be pumped and the disappearance of good waters will become more rapid if the bad waters are not pumped. It seems important that decisions should be made now, rather than later, as to: i) who will pay for pumping the bad waters and, ii) how will they be disposed of? Without pumping, the levels of all groundwaters will continue to rise into root zones in the future as they have risen in the past. Waterlogging of once fertile lands has been progressive in the past in Pakistan. Without a drainage system which is designed with the same care that the distributary system was designed, the problem of land abandonment will become more acute. As lands axe abandoned because of waterlogging and salinity, it is reasonable to believe that farmers will be no more able to pay for drainage systems in the future than they are at present or have been in the past. The two reports which have been cited emphasize advantages of the vertical (pumping) drainage systems over horizontal systems. They point further to the difficult and high costs of integrating a drainage system with the distributary system. It may be true that it would be less costly to dispose of the saline drainages by pumps discharging into special canals than by a horizontal system but, if so, only with the provision that the government, or some other agency, would provide and operate the pumps and dig the canals that would dispose of the bad waters. When pumps no longer yield good waters, the agriculture of Pakistan will be in the same position that it was in before the present pumping episode was started. Water Quality The water quality statistics, employed by the Panel in its initial report and in response to the articles by Ghulam Mohammad, rely on salt concentrations expressed as parts per million of total salt. There is no summary of the percentages of high-sodium, high-bicarbonate groundwaters, or of the concentrations of calcium and magnesium relative to the concentrations of carbonates and bicarbonates. With values for these components in the groundwaters, it is possible to estimate the alkalinity hazards and the effects of the waters on soil permeability. From water analyses based on the concentrations of individual ions, it is possible to estimate the percentage of the applied water which must be passed through and out of the bottom of the root zone to carry salts away fast enough to permit yields 80 per cent as high as those possible on non-saline lands. Also, with these values it is possible to estimate



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Ahmad. Waterlogging and Salinity: Comment 373 This nullified the advantages of this suggestion. Pumping a high order discharge has some other serious disadvantages of quick incrustation, due to the movement of fine formation. The farmers in West Pakistan have found a solution to the incrustation. The solution is the low cost tubewells and their frequent replacement. A farmer's tubewell, to pump one to two cusecs, hardly costs one or two thousand dollars, so ihat within the life expectancy of the tubewells (assumed ten years), they not only recover the full capital invested within one or two years, but also make tremendous profits out of agricultural produce due to the large amount of available water. So far, the farmers do not know the advantages of multiple strainer tubewells. If they adopt this device by adding three or four strainers, 100 to 150 feet in length, 50 to 80 feet. apart, they can pump a high order discharge, even upto 3 or 4 cusecs and, at the same time they can prolong the life of the tubewells. Such a technique of multiple strainers has many other advantages not possible with a single strainer, turbinefitted tubewells. In Table II, pumping from multiple strainer tubewells with respect to power input and discharge is shown. In these tests, the pump capacity was only 2 cusecs and the strainers were very shallow, hardly 50 feet long with, 30 feet of blind pipe and were pumping from very fine sand (mean diameter 0.18 mm.). A longer strainer, installed in medium sand, worked by high capacity centrifugal pump, could yield a higher order of discharge. TABLE II Specific yield in Depression Discharge, -yield Power in Strainer head in feet in cfs/per cfs/foot gpm/foot kwh gallon Niazbeg test Single 21.50 0.98/441 0.045 20.2 7.50 Double 15.00 1.48/666 0.100 45.0 9.25 Triple 17.24 1.64/760 0.100 45.0. 9.40 Niazbeg Single 21.20 1.43/653 0.068. 30.6 8.90 Double 18.97 1.73/778 0.091 41.0 9.50 Triple 16.13 .1.80/810 0.111 50.0 8.80 Kohali Distributary Single 19.60 1.10/495 0.060 27.0 8.20 Double 17.25 1.58/711 0.087 39.1 8.84 Triple 17.48 1.70/765 0.100 45.0 9.05 Lahore Branch Single 17.00 1.28/576 0.075 33.8 8.02 Double 15.00 1.72/774 0.112 50.4 9.20 Low Order Storage Coefficient of the Indus Formation The Revelle Panel based their estimate of mining of groundwater on a high order of storage coefficient. Although extensive boring results were available which clearly showed the existence of clay lenses and existence of silty sand, yet



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364 The Pakistan Development Review TABLE III (contd.) Harza Ghulam "Programme" Panel Mohammed (1) (2) (3) 4. Total supplies at water courses a. Northern Zone 82 77 59 b. Southern Zone 26 49 n.g. c. Total, Indus Plain 108 126 n.g. 5. Beneficial uses on fields: crop evapotranspiration plus leaching a. Northern Zone 63 6122 4521 b. Southern Zone 20 3623 n.g. c. Total, Indus Plain 83 97 n.g. D. Annual depth of water used beneficially (feet)24 1. On net cultivated area a. Northern Zone 3.2 3.6 2.8 b. Southern Zone 2.9 3.7 n.g. c. Indus Plain 3.1 3.7 n.g. 2. On gross sown area a. Northern Zone 2.2 2.2 2.2 b. Southern Zone 2.7 2.7 n.g. c. Indus Plain 2.3 2.3 n.g. E. Water losses from canals, water courses and fields (million acre-feet) 1. Total seepage25 a. Northern Zone 29 2426 24 b. Southern Zone 14 1327 n.g c. Total, Indus Plain 43 37 n.g. 2. Non-beneficial evapotranspiration28 a. Northern Zone 15 1029 12 b. Southern Zone 6 73o n.g. c. Total, Indus Plain 21 17 n.g. ..-.(continued)-



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336 The Pakistan Development Review These water supplies are to be obtained by river diversions of 103 MAF at the canal heads and by pumping 36 MAF from tubewells. Only 72 MAF of the river diversions actually reach the water courses; the remainder is lost by seepage and by non-beneficial evapotranspiration. It is assumed that seepage into the ground from link and irrigation canals, water courses, and farm fields will balance the volume of water pumped. About 13 MAF of the diversions at canal heads are to be made possible by enlarging the canal system. All of the pumped water and nearly two-thirds of the canal water are to be used in the Northern Zone, with the result that about three-fourths of the total water supply is to be concentrated there. In Table II we have computed from Harza's data the water budget by months. This table gives the interesting result that through careful coordination of tubawall and canal supplies it is possible, without enlarging the canals, to increase the beneficially usable river diversions during the kharif season by about the same amount as Harza calculates could be accomplished by canal enlargement. Comparison of Different Budgets In Table III, we have shown a comparison of the Harza "Programme" budget with that given in the Panel Report and with a budget for the Northern Zone computed from data given by Ghulam Mohammad[4]. The chief difference between our budget and Harza's is that ours was not based on crop requirements but on an estimate of the supplies that could be made available fairly quickly and with total expenditures much lower than those ultimately needed. We assumed construction of Tarbela and Mangla Dams to hold 12 MAF of live storage, and of a widespread grid of tubewells. These would be used to recover all possible recharge and to mine the aquifer in the Northern Zone down to a depth of about 100 feet. Another major difference is that we allocated much more water to the Southern Zone, both from canals and from tubewells. Finally, we attempted to work out a budget which would closely approach the ultimate potentialities of the river supplies in the Indus Plain, on the premise that the most rapid possible approach to the ultimate water potential offers the greatest opportunities for agricultural development and for economic and social progress. This premise receives some justification from the cost-benefit analysis of two alternative design schemes for the Northern Zone given in Chapter 7 of the Panel Report [1]. The first design involved the mining of the entire aquifer to a depth of 100 feet and provision of a firm water supply to 16.4 million acres under intensive cultivation. In the second design, the ultimate depth of the watertable was set at 50 feet; water would be pumped only at a rate sufficient to recover seepage losses in the distribution system and recharge from rivers and rain.



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388 The Pakistan Development Review TABLE GUIDE FOR COMPUTING THE LEACHING AND Calculations (see Calcium Composition of water me./liter (a) (b) NaxO.43 C03 +HCO3 Water EC x ---'0 -Minus x 0.7 No.** (10)6 Ca g Na C03 H C1 3 S4 CI (Ca+Mg) 1 52 0.21 0.12 0.19 0.00 0.34 0.05 0.16 -0.25 0.24 2 350 1.15 0.93 1.78 0.00 1.14 0.67 1.72 -1.315 0.798 3 420 2.35 0.75 1.39 0.00 2.94 0.98 0.56 -2.503 2.058 4 985 4.17 2.26 3.81 0.00 2.76 5.51 2.11 -4.80 1.93 5 789 0.24 0.02 7.28 0.00 2.39 2.48 2.47 2.87 1.67 6 2170 2.33 0.57 17.43 0.00 1.92 6.30 11.92 4.59 1.34 **Water sources: (1) San Joaquin River, California, (2) Gage Canal, Riverside, California, (3) California, (6) Well, Coachella Valley, California *A mean soil solution (Mss) value of 30 is used for this calculation. tThis is the per cent of irrigation water applied which must be passed beyond the root zone to



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Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 395 tional river water will have to be diverted on to these lands to meet the consumptive use requirements of crops and to leach down the salts. At the same time drainage channels will have to be constructed. As pointed out by Dr. Eaton, the drainage facilities must be provided before, rather than after, the agriculture is impoverished. Saline Groundwater Areas The most damaging recommendation in the Revelle Report was the proposal to pump water in the saline groundwater areas (having an average salinity of 6000 ppm), to mix it with canal water and to use the mixed water with an average salinity of 2000 ppm for irrigation purposes [18, p., 281]. The Panel members now consider (p. 344) that at least in half of the saline area the groundwater has a salinity of less than 5000 ppm, and this can be used for irrigation if it is sufficiently diluted with canal water. For justifying the use of this saline groundwater, the Panel members have developed a set of equations which are given on pages 348-350 of their paper. Taking two examples, one with irrigation by canal water and the other with irrigation by mixed canal and tubewell water, the Panel members have shown (p. 350) that the salinity of the mixed water can be0.188/0.0192 =9.8 times larger than that of the canal water. Thus if the surfacewater has a salinity of 200 ppm, the concentration of the mixed water can be 2000 ppm, corresponding to a groundwater with a salinity of 3800 ppm, mixed with an equal quantity of canal water. It appears that the Panel members obtained their result by making two incorrect assumptions: 1) The depth of irrigation water was taken as .65 feet (or 7.8 inches) and the interval of canal irrigation was taken as 4 weeks; 2) with 25 per cent increase in water supply with the installation of tubewells, the interval of irrigation of mixed water was reduced from 4 weeks to 1.5 weeks. The actual depth of irrigation in West Pakistan is 3 to 4 inches which is about one half of that assumed by the Panel members. The water is generally applied after 2 weeks. When irrigation supply is increased by 25 per cent, the interval of irrigation can be reduced from 2 weeks to 1.5 weeks, but not from 4 weeks to 1.5 weeks. If the example on page 349 is recalculated by taking depth of irrigation as 0.325 feet and interval of irrigation as 2 weeks, the salinity concentration of the mixed water would be 0.188/0.048 or 3.9 times that of canal water. If the salinity of canal water is 200 ppm, the salinity of mixed water can be 780 ppm, corresponding to a groundwater salinity of 1360 ppm when mixed with an equal quantity of canal water.



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334 The Pakistan Development Review tively in evapotranspiration by the crops. To minimize this fraction, to postpone investments for drainage, conveyance channels, and to reduce the ultimate costs of drainage structures, it is necessary to use the underground reservoir as an integral component of the drainage system. Any ultimate tubewell system should be designed to accommodate both irrigation supply and drainage. THE BUDGET OF IRRIGATION WATER In a steady state, rivers and rainfall are the only sources of supply for water in the Indus Plain. While there are significant fluctuations from year to year, the average annual volume of river flow is about 136 MAF (million acre feet), and the "effective" rainfall perhaps another 10 MAF. Of the total, say 145 MAF, only about a third was available in 1960 for beneficial use by crops. A large part of the remaining two-thirds flowed to the sea unused during the months of the summer monsoon; a smaller part was lost in non-beneficial evapotranspiration from rivers, canals, and water courses. and their soggy banks, and from field ditches and edges. More than a third of the water diverted from the rivers into canals seeped into the ground, as did a small part of the river flows. A major fraction of the seepage was ultimately lost in non-beneficial evaporation from waterlogged and saline areas, where the watertable stood close to the surface. A principal objective of water development in the Indus Plain is to contribute to increasing agricultural production by increasing the fraction of the total water supply that is beneficially used. Most of the beneficial use will be in evapotranspiration by crop plants, which. from the standpoint of water transfer behave much like little evaporating pans. But part of the beneficial use--ideally 10 to 15 per cent of the water applied to the fields-will be in achieving and maintaining a low salt content in the soil. This portion of the water will be used to wash away the salts already present or carried onto the fields with the irrigation water. In the ultimate Water development, the water running to the sea will consist very largely of these irrigation return flows. They will be needed to carry salt off the fields and out of the Plain. The principal device for increasing the usable supplies will be water storage during the monsoon months, either in surface reservoirs or underground, and the use of this stored water during the remainder of the year. As much as possible of the seepage water will be recovered, chiefly by pumping from wells. Part of the seepage enters the ground in areas of high groundwater salinity such as characterize the Southern Zone. It will not be recoverable for beneficial use, and will have to be wasted to the sea or to desert



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 363 TABLE III COMPARISON OF AVERAGE ANNUAL IRRIGATION BUDGETS Harza Ghulam "Programme" Panel Mohammed (1) (2) (3) A. Cultivated area (million acres) 1. Net cultivated area a. Northern Zone 19.4 17.05 15.8 b. Southern Zone 7.0 9.56 n.g.7 c. Total, Indus Plain 26.4 26.5 n.g. 2. Gross sown area 8 a. Northern Zone 29.1 28.4 20.7 b. Southern Zone 7.5 12.8 n.g. c. Total, Indus Plain 36.6 41.2 n.g. B. Cropping intensities (in per cent)9 a. Northern Zone 15010 167 13111 b. Southern Zone 10712 13513 n.g. c. Indus Plain 139 159 n.g. C. Irrigation water supplies (million acre-feet) 1. Diversions at canal heads a. Northern Zone 66 4814 61 b. Southern Zone 37 44 n.g. c. Total, Indus Plain 103 92 n.g. 2. Canal supplies at water courses a. Northern Zone 46 3015 4316 b. Southern Zone 26 3817 n.g. c. Total, Indus Plain 72 68 n.g. 3. Tubewell supplies at water courses a. Northern Zone 36 4718 1619 b. Southern Zone 0 1120 n.g. c. Total, Indus Plain 36 58 n.g. --(continued)-



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Dorfman, Revelle and Thomas:w Waterlogging and Salinity 347 be expected to have a lower salinity and ESP than that predicated in the constraints of the water budget. As we showed above in discussing the distribution of salinity in the saline zone, the best half of this zone should overlie water with an average concentration of 3350 milligrams per litre. On the basis of presently available water quality data, it is not possible to specify mixing ratios and irrigation rates or times in the various project areas with any degree of certainty, and the Panel made no attempt to do this. Any practical irrigation scheme depends on several factors. A water supply of a given salinity and alkalinity suitable for one soil type may be unsuitable for another. A given irrigation time or leaching rate appropriate for one blend of surface and groundwater may be inappropriate for another. A -program of water management for sugarcane may be unsatisfactory for pulses. It may be expected that practices will vary over a wide spectrum in the various canal commands and project areas of the Plain, depending upon local conditions. In the Northernmost, Zone, for example, the diluting effect of rainfall should be taken into consideration. In spite of these uncertainties, the Panel Report did conclude, we believe reasonably, that integrated use of groundwater and canal water for irrigation can be safely undertaken throughout most of the cultivated area in former Punjab and Bahawalpur. Consequently, major investments to construct many large, deep tubewells are justified. In the following sections, further justifications for thigh conclusion are derived. Salinity Control with Mixtures of Groundwater and Surface Water The amount of irrigation water required to maximize crop production and control salination depends not only upon the consumptive use by crops but also upon the chemical quality of the water. The higher the salinity and/or the ratio of sodium ions to calcium and magnesium ions, the more water is needed. An extra amount, over and above the consumptive demands of the plants, must be allowed to percolate through the root zone. This will make it possible to maintain the concentration of salts in the soil water at a level such that growth will be sustained and excessive sodium absorption on the clay lattices will not occur. The critical period occurs at the end of the irrigation cycle just before watering, when the soil moisture is low and its salt concentration is high. The concentration at this time should be maintained at or below the tolerance level, which depends upon the particular crop and upon the type of soil. Two parameters are important in achieving salinity control i) the total depth of water applied per crop or per year; and fl) the irrigation time, that is, the period between waterings.



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346 The Pakistan Development Review, ingly, we arranged to carry out an investigation under Dr. Bower's guidance. During 1962 and 1963, chemical data from West Pakistan were sent to Riverside, and also to Cambridge, Massachusetts, for statistical analysis and evaluation. Dr. Bower carried forward a theoretical analysis of the various chemical processes at the soil-water interface that govern the uptake of sodium ions upon the clay lattice. This analysis was published by Bower and Maasland [8]. Maasland, Priest, and Malik [9] have summarized the results of the field and laboratory tests as well as the analytical studies. In the water budget presented in Chapter 7 of the Panel Report, the predicated constraints pertaining to limiting mixing ratios of groundwater to surface water in the saline and non-saline areas were based on analyses of water from tubewells in the SCARP I project area and of water samples from elsewhere in the Northern Zone, made by the Water and Soils Investigation Division of WAPDA. The results are contained in items I C 7(a) and 7(c)(1)(2)(3) and (6) of the water budget. We estimated that in the non-saline areas of the former Panjab and former Bahawalpur the dilution ratio for one-third of the wells must be at least 1:1, while in the saline areas one-half the wells must have a dilution ratio of 2:1. These degrees of dilution were adequate to reduce the ESP to the range of 15 to 20 which we considered as generally safe for the soil types of the Northern Zone. As Maasland, Priest, and Malik show, reduction ,of the ESP to the commonly accepted "safe" range of 10-15 would require much higher dilution ratios. For example, in 40 per cent of the wells .in the non-saline area, 2.5 parts of canal water would be needed for 1 part of tubewell water. However, a reduction to this extent is probably not necessary with the mica-typa clays of former Punjab and Bahawalpur. The Panel Report states the mixing ratios of canal to tubewell waters, as well as other design constraints based on groundwater salinity, in the form of inequalities, rather than eq"*ties, In the final solution (IC 7(e)) for the water budget, several of these containts were not binding. For example, if 77 per cent of the canal water is used in the non-saline area (see, Table III), the ratio of canal water to tubewell water at the water courses in the non-saline area is 70 per cent greater than that specified in the Report as a lower limit. In the saline area, if "skimming" wells can be used to recover canal seepage before it has become mixed with the salty underlying groundwaters, the salinities of the tubewell water may be lower than the calculated values. The Panel Report contemplated that only 75 per cent of the area in the non-saline zone and 50 per cent of the area in the saline zone were to be cultivated. It should be possible to "pick and choose" favorable locations. In the non-saline zone, the groundwater over the best 75 per cent of the area may



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Eaton: Waterlogging and Salinity Comment 387 If an irrigation water containing 10 units of chloride is used over a few years to produce a uniform 10 per cent of leaching, the leachate will contain 100 units of chloride; with 20 per cent of leaching, the leachate will contain 50 units of chloride; but with only 1 per cent of leaching there eventually will be 1000 units of chloride in the drainage. Drainage systems serve the double purpose of increasing the depth of aerated soil and of removing salt from the land. Plants take up more salt-relative to water uptake-as concentrations are increased and it is the salt in the plant that depresses growth. Prior to my short visit to Pakistan in late 1952 and early 1953, I had spent a good bit. of time developing a set of simple equations for evaluating the quality of irrigation waters in the light of field and experimental responses. Those equations were included in my FAO report to Pakistan [3] and later published with the background information as Texas Agricultural Experiment Station Miscellaneous Bulletin 111, 1954. Since then a few minor simplifications and changes in constants have appeared to be advantageous. Inasmuchas CaSO4 added to a soil or water increases the SO4 content, one first computes the Ca requirement of the water and then adds I the required Ca to the sum of C1+ S04.For a number of plants, S04 has proven to be only half as toxic as Cl, equivalent for equivalent. Calcium and Gypsum Requirements The object here is to produce leachates with no more than 70 per cent Na. Required Ca: me./l = sum of a, b, and c as shown below: a) Ca+Mg needed, if any, so that the Na per cent will not exceed 70: Na x 0.43 -(Ca + Mg) Retain + or -sign b) Compensate for CaM+g that will probably be precipitated: (C03+HCO3) x 0.7 c) Compensate for the Ca + Mg in excess of Na that is removed from the land by average crops: Add 0.5 me./l. This value is suggested for Pakistan because of the large amounts of forage which is carried into the villages. Without such removals the value 0.3 me./1 is suitable. Gypsum Equivalent of required Ca: sum of a, b, and c X 234 =pounds of gypsum, if any, per acre foot of water. (See, guide in Table I). Leaching Requirements RL = Leaching requirement Sw = Salinity of the water expressed as Cl + SO4 + Irequired Ca. Mss = Mean soil solution concentration expressed as: Cl I -SO4 i.e., the average of the water and leachate.



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370 The Pakistan Development Review a 0 4-Y zI 0 cl c7-



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348 The Pakistan Development Review The relations between the variables may be formulated as follows:Consider a soil column of unit surface area and a depth extending through the root zone to the drainage region. Let Wr= the weight of water in the column when the soil moisture is at field capacity, pounds per square foot; W. -the weight of water applied with each watering, pounds per square foot; E = the evapotranspiration rate, pounds per square foot per week; T = the irrigation time (period between waterings), weeks; Ca -the salt concentration in the applied water; Cr = the maximum permissible concentration in the soil water. The magnitude of Cr is fixed by the type of crop (degree of salt tolerance) and/or the limiting value of the sodium absorption ratio in the soil water for the particular soil being irrigated. A = Wa/62.4T = the irrigation rate, feet per week; R = the leaching ratio; the quantity of drainage'water as a fraction of the amount of water applied. After the soil has been irrigated for a period of time, the salt content in the soil will approach an equilibrium value with the increment of salt added during each cycle being balanced by the decrement of salt removed in drainage. The amount of drainage water per cycle will be the excess of the water applied over that used consumptively. The leaching ratio therefore will be R -(W,7M /w .> 0 ................................................... (1) With each application the soil is saturated and drainage occurs until the soil moisture reaches a level corresponding to field capacity. With good soils this process occurs in a time interval that is small compared to the irrigation time. The consumptive use during the irrigation time will be the product of this time and the evapotranspiration rate. The water remaining in the soil at the end of the cycle, therefore, will be, W T =W fET > _0 ........................................................... (2) If the system is managed so that the concentration of dissolved salts in the critical period at the end of the cycle has risen to the maximum permissible amount, the residual amount of salt remaining in the soil will be WTCT. When a salt balance is attained, the influx of salt will be balanced by the efflux to drainage. If it is assumed that the proportion of salt removed will be that of the drainage water to the total water after irrigation, then WC -[(W. -E)(W.WT)1 (WTCT+W.C).



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Dorfman, Revele and Thomas: Waterlogging and Salinity 367 TABLE IV COSTS OF WATER USING GOVERNMENT AND PRIVATE TUBEWELLS (A) (B) Item Government Private tubewells tubewells 1. Direct construction cost (rupees) 51900 7800 2. Water distribution system and land (rupees) 3140 3. Net construction cost 47760 7800 4. Annual amortization factor (at 6 per cent) .0872 .1359 5. Annual charge (rupees) 4165 1060 6. Rate of flow (cusec) 3.9 1.25 7. Output per year. (2200 operating hours) (acre feet) 710 227 8. Capital charge per acre foot (rupees) 5.89 4.67 9. Operating cost per day (rupees) -11.06 10. Output per day, (acre feet) -0.826 11. Operating cost per acre foot (rupees) 10.80 13.38 12. Total cost per acre foot (rupees) 16.68 18.05 Sources: Rows 1, 2:1 [7, Table B-I]. Rows 3, 4, 5: Computed. 20-year economic life assumed for government tubewells, 10 years for private tubewells. Row 6: (7, Table B-I]. Rows 7, 8: Computed. Row 9: [7, Table B-II]. Row 10: Computed. Row 11: (A) from [1, Table 7.4, adjusted to power cost of Rs. 0.08 per Kw.hr]. (B) Computed. Row 12: Row 8 + Row 17.



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Dr. P. E. HILDEBRAND Ghief Economist 107* 0 Waterlogging and Salinity in the Indus Plain: Some Basic Considerations by ROBERT DORFMAN, ROGER REVELLE, AND HAROLD THOMAS -Comment by NAZIR AHMAD -Comment by FRANK EATON -Rejoinder by GHULAM MOHAMMAD -:0: Reprint from THE PAKISTAN DEVELOPMENT REVIEW Quarterly Journal of Pakistan Institute of Development Economics Karachi (Pakistan) Volume V-Autumn 1965-Number 3



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Waterlogging and Salinity in the Indus Plain: Rejoinder by GHULAM MOHAMMAD* Most of the points raised by the Panel members, Drs. Roger Revelle, Harold Thomas and Robert Dorfman, have been answered in the comment by Dr. Frank M. Eaton. Dr. Nazir Ahmad has further elaborated some of the issues involved. The author will confine his remarks to two basic issues, namely, pumping of water for irrigation purposes in the non-saline high quality groundwater areas in the Northern Zone of the Indus Plain and provision of horizontal sub-surface drainage facilities in areas where the groundwaters are saline and unfit for irrigation use. The author is happy to note that the Panel members acknowledge the significant contribution made by private tubewells to the productivity of agriculture in West Pakistan. The author agrees with the Panel members that private tubewells will be developed mainly in areas that have adequate supplies of high quality groundwater and not in areas where the groundwater is too saline to be applied to land without dilution with canal water. Ina previous article, the author proposed that horizontal sub-surface drainage facilities should be provided in the saline groundwater areas [5, pp. 387-3951. The Panel members do not agree with this and propose instead deep tubewells for irrigation as well as for drainage purposes. They suggest that with the use of deep tubewells and canal water the salt be flushed out of the root zone and washed downward with recycled pumped water to be stored underground. The Panel members consider that drainage structures are expensive, and argue that provision of drainage facilities should be postponed as long as possible (p. 350). The author considers thatthis is a dangerousrecommendation, As pointed out by Dr. Eaton (p. 382), the areas of bad waters will progressively expand during the next 10 to 50 years until all waters are salinized. With increasing salinity of groundwaters, agricultural production will progressively decline unless large scale drainage channels are constructed to remove part of the pumped waters out ot the area. *The author is a Senior Research Economist at the Pakistan Institute of Development Economics. He is indebted to Dr. Bruce Glassburner, Senior Research Advisor, Mr. Keith Griffin, Research Adviser in the Institute and Mr. Carl Gotsch of the Harvard Advisory Group at Lahore for their valuable comments on the earlier draft. The author is grateful to Mr. Mohammad Ghaffar, Research Assistant, for assistance in computations. Responsibility for the views expressed and for any errors is entirely that of the author however.



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374 The Pakistan Development Review while estimating the yield of groundwater, a storage coefficient for a high yielding sand formation was assumed. It was pointed out [11 to the Panel on the receipt of the first draft report in September 1962 that the storage coefficient assumed at 25 per cent should be reduced by half as within a depth of 100 feet from surface the soil crust and clay lenses constitute about 40 to 50 per cent of the formation, but the Panel scientists used 25 per cent as storage coefficient which gave higher results. The tubewells of SCARP 1 have demonstrated the fallacy of this assumption. The fall in the level of the watertable was found to be too quick when pumping the tubewells to their full capacity. The Panal has assumed the total infiltration from the Punjab and Bahawalpur area as 20 million acre feet. The total amount of loss of water according to the Panel is 50 per cent of that released at the head. The seepage from canal and links is 35 per cent, the remaining 15 per cent being the evaporation and other losses. Earlier estimate of Kennedy, Benton and Blench are shown in Table IlI below: TABLE III WATER LOSSES FROM CANAL DISTRIBUTION SYSTEM IN THE PUNJAB Kennedy Benton Blench Khunger Main canals 5 -5 Seepage only Branches 15 -15 Sub-total 20 16.4 20 15.5 Distributaries 6 6.1 7 5.4 Water courses 21 20.2 20 6.5 Sub-total 27 26.3 27 11.9 Total 47 42.7 47 27.4 The Panel of scientists has attempted a confirmation on the basis of rise of groundwater as a result of infiltration from various sources. Taking the rise of groundwater per year equal to 1.5 feet and assuming a 25 per cent storage coefficient, they have estimated water accumulation in 30 million acres equal to 11.3 MAF (1.5 x .25x30= 11.3 MAF). Use of a figure of 1.5 feet rise with 25 per cent storage coefficient and without giving attention to the component of sub-soil flow, this figure is a poor proof. It is proposed to pump 49.5 MAF of groundwater. This will constitute 20 MAF of seepage and 29.5 MAF to be drawn from the reservoir. The quantity of water to be mined is thus:



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392 The Pakistan Development Review Hausenbuiller, et al (6] obtained a correlation coefficient of .984 between the residual Na2CO3 in 11 waters and the exchange sodium percentages found in the top eight inches of 11 soils and yet five of the waters contained less HCO3 than Ca + Mg. In accord with Pratt, et al. [7] much CaCO3 may be precipitated even though there is no residual Na2CO3 in the water. Pratt, et al. [7] found rather large increases in the ESP and pH values of the irrigated soils in both the lysimeter and field experiments. REFERENCES 1. Asghar, A.G. and M.A. Hafeez Khan, "Behaviour of Saline-Alkaline Punjab Soil Under Reclamation", Proceedings of Punjab Engineering Congress. (Lahore Punjab Engineering Congress, 1955). 2. Babcock, K.L. et al., "A Study of the Effects of Irrigation Water Composition on Soil Properties", Hilgardia, 29(3), 1959, pp. 155-164. 3. Eaton, F.M. FAO Report No. 167 to the Government of Pakistan on Certain Aspects of Salinity in Irrigated Soils. (Rome: FAO, September 1953). 4. -,--------and J.E. Bernarelin, "Mass Flow and Salt Accumulation by Plants on Water Verus Soil Culture", Soil Science, Vol. 97, No. 6, June 1963. 5. Ghulam Mohammad, "Waterlogging and Salinity in the Indus Plain: A Critical Analysis of Some of the Major Conclusions of the Revelle Report", Pakistan Development Review, Vol. IV, No. 3, Autumn 1964. 6. Hausenbiller, R.L., M.A. Haque and Abdul Wahab, "Some Effects of Irrigation Waters of Differing Quality on Soil Properties", Soil Science, Vol. 90, 1960. 7. Pratt, P.F., R.L. Branson and H.D. Chapman, "Effect of Crop, Fertilizer and Leaching on Carbonate Precipitation and Sodium Accumulation in Soil", VII International Soil Science Soc. Cong. Trans. 2, Vol. 11, 1960. 8. White House, Department of Interior Panel on Waterlogging and Salinity in West Pakistan, Report on Land and Water Development in the Indus Plain. (Washington D.C.: Suptt. Doc. January 1964). 9. Wilcox, L.V., G.Y. Blair and C.A. Bower, "Effect of bicarbonate on suitability of water for irrigation", Soil Science, Vol. 77, 1954.



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376 The Pakistan Development Review PUMP MOTOR I----------------10.0 ORIGINAL IS.S.W.L. ORIGINAL GROUND SURFACE I / PUMP HOUSING CASING 30.0 s I 20.0 I I GRAVEL SHROUDING WATER SURFACE WELL WHEN PUMPING BOWL ASSEMBLY --75 75 60 6,-0 CONCENTRIC REDUCER .. 10 SLOTTED TUBEWELL CASING. 10 SLOTS ,kBY 2 TO 3TO PROVIDE 30 SQUARE INCHES 16 OF SLOTTED OPENING PER FOOT OF CASING 210 220 220 SEAL PLATE



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402 The Pakistan Development Review tained in efficient condition. The removal of weeds and debris and repair of side slopes is far more economical than the operation, maintenance, and .frequent replacement of corroded and incrusted tubewells in saline groundwater areas in any country of the world, but more so in a country like Pakistan where labour is underemployed and unemployed. The fifth objection of the Panel members regarding the public health hazard of stagnant water and swampy reaches of open drains would be valid only if the drains were not properly maintained. There is no point in constructing the drains if these are not to be properly maintained. When properly maintained there is no public health hazard. Role of Public and Private Tubewells The Panel members consider that government tubewells are better than private tubewells for the following reasons: 1) Government tubewells are somewhat more economical than private tubewells (pp. 339-340 and Table IV). 2) Government tubewells can be more easily integrated with canal operations than private tubewells (pp. 340-341). 3) Government tubewells can be used for reclamation of saline soils and the underground reservoir can be used for storage of salt flushed out of root zone (pp. 342 and 350). 4) Government tubewells are better adapted for the exploitation of poor quality and sodium-rich groundwaters which can be used by mixing with Canal water (p. 342). 5) Givernment tubewells are better adapted for control of lateral migration of salinity. (p. 342). 6) Government tubewells are better than private tubewells on account of their social effects (pp. 342-343). The author considers that it is not necessary to have government tubewells for any of the above reasons: 1) In calculating the cost of pumping water from government and private tubewells, the Panel members have used full cost of the private tubewells but only part of the cost of government tubewells. The total cost of a private tubewell (of 1.25 cusec capacity) to the economy was estimated as 7,800 rupees by the author, whereas cost of the government tubewell (of 3.9 cusec capacity) to the economy was estimated as 79,700 rupees by WAPDA [4, p. 255]. In Table IV of their paper, the cost of project preparation, cost of equipment required for drilling government tubewells, cost of government staff, fee to be paid to the contractors engaged after international bidding, contingencies, and interest



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378 The Pakistan Development Review the next eight months. The source of this much water can be from seepage of the existing canal (20 MAF) and seepage from the new diversions. We can meet our requirements from the seepage only. With a storage coefficient of 10 per cent a one foot rise of water in 30 million acres can store 3.0 MAF. During summer, canals run at full supply, temperature is high, and better saturated sub-soil connection exists, so that sufficient seepage is possible. High summer rainfall and high stages of rivers can also be a feeding source. We may take measures, to see that as much water infiltrates into the formation as possible. Other measures to feed the aquifer can be : i) dam water in all drains by providing over-shot gates at proper places, il) dam water in all non-perennial canals by providing over-shot gates at proper places and time, iii) deepen all depressions and make their beds sandy and fill them with water during summer, iv) construct new canals and keep them full after flood season by providing gates, v) encourage extensive cultivation of rice, vi) fill all village ponds, depressions, and lakes with water and adopt measures to keep their bed pervious, vii) encourage porous shingle beds in places where water can be diverted to fill the formation. These measures will feed the aquifer during the four summer months. As soon as the rivers fall we shall start pumping intensively. We shall not only pump all the seepage but also mine the groundwater and take it down if need ba to the limit of pumping by centrifugal pumps. The average lowering may even exceed five feet. With the approach of summer, with more water in the rivers, the pumping may stop progressively and completely during the monsoon period to feed the aquifer, so that the mined zone is charged again with water. It is true that with the watertableat 10 or 15 feet. more evaporation or evapotranspiration loss occurs but the stoppage of pumping during summer, feeding from high stage river and heavy monsoon rainfall will all fill the aquifer emptied during dry months. This system of management of water resources has many advantages. By this system we will i) mine the groundwater equal to our requirements, ii) use cheap and durable centrifugal pumps with low lift,



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Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 399 the saline soils also and the groundwater would thus be used on good soils. Similarly no canal water should be used for the reclamation of these areas or for the development of any other uncultivated lands. All canal waters as well as all tubewell waters from the high quality groundwater areas should be used only on the best agricultural lands already under cultivation. Horizontal versus Vertical Drainage The Panel members have enumerated 5 disadvantages of the horizontal drainage system on pages 354 to 356 of their paper and have concluded that horizontal drainage does not "warrant much attention.. .in the primary scheme of water resources development in the Indus Plain". The first objection of the Panel members to horizontal drainage is that salt removed in the drainage depends largely upon the salinity of the upper layers of groundwater. The author considers this to be the principal advantage rather than the disadvantage of the horizontal drainage system. It is easier to dispose of salt removed from 7 to 10 feet of the soilprofile and the upper groundwater than it is to dispose of the salt removed from 250 feet of the soil profile. In this connection Mr. Arthur Pillsbury, Professorof Irrigationand Engineering, University of California at Los Angeles, and Consultant to the Land and Water Development DivisionofFAO, has stated that "the zone ofconcentration of ground wateristhe root zone, and that the most efficient point to separate degraded waters, before they become diluted is immediately below the root zone" [14, p. 81. Professor Pillsbury considers that this separation can be done efficiently only with horizontal sub-surface drainage facilities [14, p. 81 and that pumping of groundwater is completely inefficient for drainage alone [14, p. 6]. According to Professor Pillsbury many vertical drainage schemes were started in the southwestern part of the United States beginning in the early 1920's but at present there is not a single "drainage" well operating where the water is not used to help irrigate the overlying land or is used to satisfy downstream water rights. Professor Pillsbury further. states that where saline waters are being pumped an extreme corrosion and incurstation (all italics ours) problem with the well and pump appear to be inevitable [14, p. 6]. Another point raised by the Panel members is that vertical drainage results in a "smaller investment in conveyance channels and better salinity control because salt can be returned to the rivers during periods of high run off or routed to salt lagoons at times when irrigation requirement is small." As the idea of drainage tubewells pumping into rivers during "periods of high run off" has been recommended by the Panel members as well as by Tipton and Kalmbach, Inc. Consultants to WAPDA, it is necessary to examine it in



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 345 Extent of Sodium Hazard In Mixtures of Tubewell and Canal Waters The Panel became aware during its first visit to Pakistan of the sodium hazard associated with use of groundwater in some areas. In evaluating the suitability of water for irrigation, an important parameter is the potential extent of exchange of sodium ions between the water and the dispersed phase of the soils. Absorption of too many sodium ions by certain soil clay minerals can cause excessive swelling of the dispersed phase. This may drastically reduce te permeability and porosity of the soil and decrease or destroy its agricultural value. The amount of sodium absorption depends on two factors: i) the ratio of sodium ions to the square-root of one-half the sum of calcium and magnesium ions in the soil water-this is called the "Sodium Absorption Ratio" (SAR); ii) the chemical and mineralogical nature of the clay fraction of the soils. The SAR of the soil water depends on the SAR of the applied irrigation water and on its content of bicarbonate and carbonate ions. The latter tend to precipitate calcium in the soil as CaCO3, and thereby to raise the SAR. In assessing the effect of bicarbonate and carbonate, the Panel used both the "residual" sodium carbonate (excess of carbonate and bicarbonate over calcium and magnesium in the applied water) and a new criterion developed by Dr. C. A. Bower, Director of the United States Salinity Laboratory at Riverside, California, and a member of the Panel. This criterion combines a modified Langlier index with the Sodium Absorption Ratio [8] to give a calculated "Exchangeable Sodium Percentage" (ESP). 'Clays may be divided into three groups that have markedly different tendencies to swell with absorption of sodium ions: 1) the kaolin group with a 1:1 lattice type; i) the hydrated mica group with a 2:1 lattice type; and iii) the montmorillonite or expanding lattice group with a 2:1 lattice type. Soils containing clays of the montmorillonite group (beidellite, saponite, etc.) have a large intramicellular surface and a strong tendency to expand when the soil water has a relatively high ESP. The kaolin minerals (kaolinite, nacrite, metahalloysite, etc.) and hydrated mica minerals (illite, chlorite, etc.) have fixed lattices and exhibit much smaller hydration and absorptive properties. Soil samples from the irrigated regions of West Pakistan that were examined by the Panel contain clays predominantly of the non-expanding type such as illite and chlorite. These soils tolerate larger concentrations of exchangeable sodium in irrigation water than soils containing montmorillonitic clays. After collecting and examining field data available in 1961 relating to the chemical composition of soil and water, the Panel decided that we had insufficient information to establish the magnitude of the sodium hazard. Accord-



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396 The Pakistan Development Review To use mixed canal and tubewell water having a salinity of 780 ppm for crops of medium salt tolerance, about 18 per cent additional water will have to be provided for leaching purposes [18, p. 117]. This would mean that 30 per cent of the tubewell water will have to be pumped for leaching purposes onlyl. If on the other hand saline water containing as much as 3800 ppm is pumped and mixed with an equal quantity of canal water and mixed water having a salinity of 2000 ppm is used for irrigation as suggested by the Panel members, nearly 67 per cent of the mixed water would be required for leaching purposes with crops of medium salt tolerance [18, p. 117]. This means that about 80 per cent of the pumped water will have to be used for leaching purposes only2.In the case of crops of high salt tolerance such as cotton and barley, the leaching requirement will be about 25 per cent of the mixed water or about 40 per cent of the pumped water. Even with the provision of drainage and removal of 40 to 80 per cent of the pumped water as drainage water, there would be deterioration of land due to sodium damage and large quantities of gypsum will have to be provided to keep the soils in good condition. Dr. Eaton has developed a method for estimating the amount of gypsum and the additional amount of water which should be applied to the land to prevent high alkalinity, serious soil impermeability and deficiencies of calcium and magnesium required for normal plant growth (see, pp. 387-391). For saline groundwaters of the Northern Zone of the Indus Plain the author has calculated, from water analyses of Water and Soils Investigation Division of West Pakistan WAPDA [7; 15], the gypsum and leaching requirements for all groundwaters having a salinity between 3000 and 3900 ppm in the Chaj and Rechna Doabs according to Dr. Eaton's method. Calculations have been made for the undiluted groundwaters as well as for the groundwaters when mixed with an equal quantity of canal water. The results are summarized in Table I. For all groundwaters having an average salinity of 3500 to 3600 ppm, when mixed with an equal quantity of canal water the gypsum requirements (for the mixed waters having a salinity of 1800 to 1900 ppm) average about 3000 pounds per acre foot of mixed water in the Chaj Doab and about 2000 pounds per acre foot of mixed water in the Rechna Doab. The leaching requirement for crops of medium salt tolerance average about 75 per cent in the two doabs. This means that about 85 per cent of the pumped water will have to be used for leaching purposes only. I Suppose 100 parts of canal water are used to mature one acre of crop. If 100 parts of tubewell water are mixed with the same, the total quantity becomes 200 but 36 parts of additional water is required for leaching purposes to mature 2 acres of crops. Thus canal water is increased to 118 parts and tubewell water to 118 parts. The 118 parts of canal water when used alone can mature 1.18 acres of crops. Therefore 118 parts of tubewell water mature 0.82 acres of crop and are thus equal to 82 parts of canal water. The remaining 36 parts of tubewell water or 30 per cent is used for leaching purposes. 2Calculated as explained in footnote 1 above.



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Ghulam Mohammad: Waterlogging and Salinity: Rejoinder 403 during the period of construction all amounting to 27,800 rupees for each 3.9 cusec tubewell have been ignored by the Panel members. Furthermore, the life of government tubewell has been taken as double that of private tubewells for which there is no justification [4, pp. 238-391. (see also, Table I on p. 372). The author has included the full cost of government tubewells and recalculated cost of pumping water in Table IV of the report of the Panel members, assuming life of both tubewells to be 10 years. On this assumption the cost of pumping water from government tubewells comes out to be 44 per cent higher than private tubewells when the load factor is assumed as 25 per cent. However, government tubewells have been worked on a load factor of over 50 per cent. If this is adopted, the cost of pumping water from government tubewells is equal to that from private tubewells. 2) There is no reason why farmers will not integrate the working of private tubewells with the working of canals. Already the farmers of Gujranwala and Sialkot districts where canal water is supplied only during the kharif season are integrating the working of private tubewells with the canal water and have attained the highest intensity of cropping [6, p. 261. It is simple: the moment, the canal is closed, the farmers switch on the tubewells. Dissemination of information about canal closures is good but is not absolutely necessary. 3) As already pointed out, all canal water and tubewell water should be used on the best agricultural lands already under cultivation and not on reclamation of highly saline soils. Such reclamation by government tubewells will only deteriorate the quality of groundwater by adding salts leached down from the soil profile. 4) As previously stated saline and sodium-rich groundwaters should not be pumped at all. They would increase water supply but would cause deterioration of soil and reduce the total agricultural production in the country. 5) The centrifugal pumps used by the farmers have a maximum draw down of about 20 to 25 feet. With private tubewells located in the upper reaches of the doabs and lowering the watertable to about 20 feet, and with drains lowering the watertable to about 7 to 10 feet in the saline areas, there is no danger of contamination of non-saline groundwaters with infiltration from saline groundwater areas. On the other hand, there would be some danger with government tubewells pumping water to 100 feet depth in non-saline areas and to 50 feet depth in the saline areas as proposed by the Panel members. 6) In all areas where an adequate number of tubewells has been installed, the price charged by tubewell owners varies from 2.5 to 3.5 rupees per hour



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Dorfman, Revelle and Thomas Waterlogging and Salinity 361 TABLE II POSSIBLE AVERAGE MONTHLY WATER BUDGET IN THE INDUS PLAIN BASED ON HARZA "PROGRAMME" WITH PRESENTLY DESIGNED SURFACE STORAGE AND ASSUMED TUBEWELL AND CANAL CAPACITIES* River and At water courses At canal heads reservoir losses Supplies I Month Irri..-. Total River Changes Seepage gation diverflows in and evaTo sea requirefrom from sions surface poration ments canals wells storage (1) (2) (3) (4) (5) (6) (7) (8) (9) ............... million acre-feet** ...............) October 11.1 6.4 4.7 9.1 4.6 -4.6 0.1 0.0 November 7.0 3.0 4.0 4.3 3.1 -1.3 0.1 0.0 December 5.3 3.0 2.3 4.3 2.6 -1.8 0.1 0.0 January 7.0 3.0 4.0 4.3 2.7 -1.7 0.1 0.0 February 5.6 3.1 2.5 4.4 2.9 -1.6 0.1 0.0 March 8.8 4.1 4.7 5.8 5.0 --0.9 0.1 0.0 Rabt total 44.8 22.6 22.2 32.2 20.9 -11.9 0.6 April 7.4 5.7 1.7 8.1 8.2 0.0 0.1 0.0 May 12.9 8.7 4.2 12.4 14.2 0.0 02 1.6 June 13.4 8.7 4.7 12.4 22.4 0.0 3.0 7.4 July 10.7 8.7 2.0 12.4 30.7 +7.3 4.0 7.0 August 10.5 8.7 1.8 12.4 26.8 +4.7 4.0 5.7 September 8.7 8.7 0.0 12.4 12.4 --0.1 0.1 0.0 Kharif total 63.6 49.2 14.4 70.1 114.7 +11.9 11.4 21.7 Annual values 108.4 71.8 36.6 102.3 135.6 0.0 12.0 21.7 Assumptions: Live storage back of Mangla and Tarbela Dams = 12.0 MAF Canal capacity-12.4 MAF/month=207,000 second feet Tubewell capacity ; 4.7 MAF/month = 78,000 second feet. Annual losses from seepage and evaporation in rivers and reservoirs = 12.0 MAF [Harza, p. 291 states that 12 MAF are lost in natural river channels between the rim stations and diversion points. •* Differences between corresponding values in Tables I and 2 are due to rounding. Sources: Col. (2): Computed from [3, Tables II-1 I and II-12], combined with acreages and intensities of cultivation given in (3, Tables 11-7, 11-8 and 11-9]; see also our Table I. (sources continued on next page)



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 341 This is only 65 per cent of the water requirement of 13.4 MAF in June, the critical month, so that under these conditions the entire program would aveh to be scaled down by 35 per cent. This scaled-down program would use only a total of 41 MAF of canal water at the water courses in kharif (59 MAF at the canal heads). On the other hand, if tubewells capable of providing 4.7 MAF per month (equivalent to a total well capacity of 80,000 cusecs) are available and suitably distributed over the cultivated area, then the required 13.4 MAF can be delivered to the water courses in June. The total delivery capacity of the canals can be utilised for irrigation from May through September, and 49. MAF of canal water can be delivered usefully to the water courses, corresponding to a diversion of 70 MAF at the canal heads. The tubewells not only supply 14 million acre feet in kharif but they make it possible to use 11 MAF of river water that would be wasted without them. Similar calculations can be made for other assumed canal capacities, and they show in each case that the volume of beneficially usable river water during kharif can be increased by supplementing canal flows with sufficient pumping at the proper times. The same utilization of surface water could be attained by enlarging the canals. But by coordinating canal and tubewell operations, investments for enlarging and modifying the canal system can be minimized. Even more important, difficulties of silting and erosion, and of inadequate check structures on distributaries and water courses can be at least partly avoided. With the "regime" canals of the Indus Plain, these difficulties arise from large differences in canal flows during different months. This calculation, naturally, somewhat overstates the case. An accurate computation would have to take account of the differing canal capacities and patterns of monthly irrigation requirements in the different canal systems, of the need for surface water to dilute saline groundwater, and of other complications. And, of course, perfect coordination cannot be attained. But the moral is clear that a closely integrated. operation of tubewells and canals greatly increases the efficiency with which surface supplies can be used. This close integration can be more easily attained where government wells are installed than where private ones are. But it may be possible to integrate private wells with the canal operations through wide dissemination of information about planned canal operations and economic pricing policies for both canal and tubewell water. Even before adequate well capacity is installed throughout the Northern Zone, sufficient capacity may ba developed in certain canal commands to test the scheme outlined in Table II, particularly the effectiveness of the incentives for the private operators. One reason for the superior integration of government tubewells with canal operations is that this integration will require some changes from the historical



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 349 Using Equation (2) and solving for Ca, C. (EW.f ................................................... (3) The maximum permissible salinity of the applied water may be formulated as Ca =R(I-P) CT .......................................... (4) where P =the proportion of available water used during each watering period. Equation (3) may also be written in the form C. D,-ET/62.4 Df-ET/62.4 D., Df where D = W./62.4 feet, and Df Wf/62.4 feet, represent respectively the depth of applied water and equivalent depth of water at field capacity. To illustrate the use of the formulation, the following example is presented: (1) A surface water of good quality has been used successfully to irrigate land in accordance with a management scheme in which a depth of water of 0.65 feet is applied every four weeks to a soil in which the field capacity is 0.80 cubic feet per square foot (50 pounds per square foot). The evapotranspiration rate is 0.15 feet per week and the maximum permissible concentration of salt in the pore water is Cr. From Equation (5) C& 0.65 -0.15r .......................................... (6) 0.65 0.80 C, .0.0192 CT (2) A tub.well field is constructed to supply additional water to increase the acreage under cultivation. The tubewells not only increase the total water supply, but they make possible greater flexibility in the timing of water applications. However, because of the concentration of salt and exchangeable sodium in the groundwater, it must be mixed with surface water to protect the soil and assure agricultural productivity equivalent to that obtained where surface water alone is used. What will be the maximum permissible concentration in the blended water supply in a management scheme in which the irrigation rate per season (or per year) is increased 25 per cent and the watering period reduced to 1.5 weeks? The value of D. will be (1.5/4) (0.65) (1.25) = 0.305 feet. Therefore from Equation (5), Ca 0.305= 0.15(1.5) .0.80-,0.15(1.5) CT = 0.188 Cr ............ (7) 0.305 0.80



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398 The Pakistan Development Review For consumptive use requirement of 4.0 acre feet per acre, the leaching requirement will be about 3.0 acre feet per acre and the total water requirements would be about 7.0 acre feet per acre. The gypsum requirements for these waters would be about 10 tons per acre per year in the Chaj Doab and about 6 tons per acre per year in the Rechna Doab. The cost of gypsum is estimated as 70 rupees per ton delivered in the West Pakistan villages. For use of the saline groundwaters, even when mixed with canal water, about 400 to 700 rupees per acre would have to be spent on gypsum every year. It is clear that on account of extremely high gypsum requirements these waters cannot be used for irrigation even when about 85 per cent of the pumped water has to be used for leaching purposes and only about 15 per cent contributes to the consumptive use requirements of crops. It may be stated that above calculations are based on the experimental work carried out in the south-western United States and in some other countries. When similar experimental work is carried out in the Chaj and Rechna Doabs, the actual gypsum requirements may be found to be somewhat different. However they are not likely to be so different as to make the use of soduim-rich saline waters having more than 3000 ppm as economic. As previously suggested by the author [5], but most forcefully put by Dr. Eaton, provision of horizontal sub-surface drainage is the only solution for the saline groundwater areas of West Pakistan. A basic requirement for the use of horizontal sub-surface drainage is the provision of additional river water to these areas. A programme for increasing the capacity of canals to divert additional river water and installation of horizontal drainage should therefore be initiated immediately for these areas. The canal water supply is not likely to be adequate for all the culturable canal commanded areas. It is, therefore, essential that canal water should be used on the best agricultural areas already under irrigation. Out of the total canal commanded area of about 32.8 million acres, there are some 1.5 million acres of highly saline uncultivated or abandoned lands in the Punjab and Bahawalpur and about 1.4 million acres in Sind [17, pp. 18 and 23]. The West Pakistan WAPDA and Irrigation Department are engaged in the reclamation of these soils. As will be clear from Table VI (page 369) in the report by Panel members, installation of tubewells in the highly saline soils would cause the good groundwaters to deteriorate 35 years earlier than installation of tubewells in non-saline soils. It is therefore essential that no tubewells should be installed in the highly saline soils even when these lie in good groundwater areas. Tubewells installed in the non-saline soils would draw down the watertable under



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360 The Pakistan Development Review TABLE I (contd.) HARZA "PROGRAMME" IRRIGATION WATER BUDGET PART II: SUPPLIES Southern Total Northern Southern Indus Zone Zone Plain A. From river diversions (million acre-feet) 1. At canal heads a. Rabt 20 13 33 b. Kharif 46 24 70 c. Annual 66 37 103 2. At water courses a. Rabi 14** 9t 23tt b. Kharif 32** 17t 49tt c. Annual 46** 26t 72* B. From tubewells, at water courses (million acre-eet)2 a. Rabi 22 -22 b. harlf 14 -14 c. Annual 36*t -36*t C. Total supplies at water courses (million acre-feet)t a. Rabi 36 9 45 b. Kharif 46 17 63 c. Annual 82 26 108*t 1 Values at water courses (see A.2.), divided by 0.7. 2 Values in A.2 subtracted from corresponding values in C. 64.3 MAF [2, p. 28] plus 8 MAF [2, p. 29]. t From Part 1: Requirements, values in B.I. ft From Table II. ** Total diversions for Indus Plain-diversions for Southern Zone. *t [2, pp. 28-30]. 64.3 MAF average diversions at water courses with present canal system must be supplemented by 44 MAF to meet irrigation requirements. Of this amount, 8 MAF can be obtained by enlarging canals, the remainder can be provided by groundwater pumping and additional reservoirs.



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 335 salt lagoons. Non-beneficial evapotranspiration losses will be minimized by careful water management, but these losses may actually be increased by surface storage. Taking all factors into account, the Water and Power Development Authority of West Pakistan (WAPDA) has estimated that after construction of sufficient storage facilities, an average of some 114 MAF per year of river waters could ultimately be made available at the water courses leading to the farm fields[2]. The remaining 22 MAF would be lost, chiefly by non-beneficial evapotranspiration from reservoirs, link canals, rivers, irrigation canals, water courses, and from the border areas of all these various kinds of channels. WAPDA's estimate is based on an ultimate steady state in which only the averago annual water supplies from rivers and rain can be considered. The approach to such a steady state will inevitably be slow and expensive, because it involves very extensive construction of dams, conveyance channels, and other surface water structures. In the meantime, there is an overwhelming need to increase agricultural production in West Pakistan as quickly and inexpensively as possible. Although chemical fertilizers, improved seeds, and other production factors can contribute to this end, water is the key. Here, during the transition period, we can utilize one of the great natural resources of the earth-the enormous pool of fresh groundwater that underlies the Northern Zone of the Indus Plain, and is equal in volume to ten times the annual flow of the rivers. In making up irrigation water budgets for this transition period, we can base our calculations either on the water requirements for an assumed cropping pattern, cropping intensity, and net cultivated area, or on the estimated supplies that can be made available at a particular time with a given level of expenditures for water development. A budget based on assumed crop requirements has the advantage that the water needed during each month can be calculated. A budget based on the anticipated availability of supplies can give only seasonal totals until a cropping pattern is specified, but it has the great merit that comparisons of different cropping patterns can be made and the economic optimum chosen. A Water Budget Based on an Assumed Cropping Pattern Table 1 gives an irrigation water budget based on requirements for assumed cropping patterns and intensities on a net cultivated area of 19.4 million acres in the Northern Zone, and 7 million acres in the Southern Zone. The budget is computed from data given in a report by Harza Engineering Company International, made in 1963 [31. The total irrigation requirement at the water courses is 108 MAF and the beneficial use on the fields (evapotranspiration by crops plus leaching) is 83 MAF.



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 343 installing a private tubewell is amortized in a period of 2 or 3 years. Therefore, in regions developed by private tubewell owners the underground water supplies will benefit primarily the larger farmers. Ordinary market forces cannot be expected to moderate the price of private tubewell water to small farmers because each small farmer will be located in a position that can be served by at most one or two large tubewells. In this circumstance, it may be adviseable to regulate the price of private tubewell water just as the terms for farm tenancy are now regulated. This regulation should not be so stringent that it erodes substantially the incentive for the installation of private tubewells where they are appropriate. This all adds up to a complicated mesh of considerations that cannot be resolved finally until we have more experience with the operation of the private wells. Tentatively it appears that the private wells, being more responsive to local day-by-day requirements, are preferable in areas where they can be installed and operated profitably, and where considerations of control of groundwater quality are not overriding. They are managerially simpler to operate and they mobilize resources of private management and capital the government cannot tap. But where land reclamation or groundwater quality control are commanding considerations,, and in areas from which surface water supplies should be diverted in the interests of overall economy, then the government tubewell developments are the method of choice. In the long run, there is also the question of coordinated operation of the canals and the tubewells in order to maxi-mi.ze the benefit from the high river flows of summer. We have suggested that it may be possible to do this with either private or public wells, but this should be tested. In any case, both sorts of wells have useful roles to play in the overall development of the Indus Plain. QUALITY OF THE GROUNDWATER Serious questions have been raised, most forcibly by Ghulam Mohammad [4], about the quality of the underground water in the former Punjab and Bahawalpur. These concern the salinity, or total salt concentration, of the water and the possibility of soil damage from an excessive sodium content in the presence of relatively high concentrations of carbonate and bicarbonate ions. Insufficient information exists to discuss such other problems as the potential hazards from boron, but we believe these are small. Salinity The Ground Water Development Organization ofthe IrrigationDepartment, and later the Water and Soil Investigation Division of the West Pakistan Water and Power Development Authority, made several thousand chemical analyses of water samples from nearly a thousand test holes, throughout 34 million



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Eaton: Waterlogging and Salinity: Comment 391 The extent of precipitation of CaCO3 in soils is a function of the CO2 partial pressure in the soil atmosphere and the concentrations of the reacting constituents. The latter are largely determined by leaching rates but estimates of C02 partial pressures in soils are difficult since they are dependent on the density in the soil of living and dead roots, their respiratory rates, and the freedom of gaseous exchange between the soil and the air above. The pH of soils measured in the laboratory after exposure to the atmosphere are usually much higher than when measured in place in the field. Only a few good data are available on the proportion of the HCO3 in water supplies that are normally precipitated in soils. Among the best of these are the results presented by Pratt, et al. [7, pp. 185-192]. It was found that in the order of 50 per cent of all the HCO3 applied by an irrigation water with "88 per cent sodium possible" (i.e., Ca -2.43, Mg -0.76, Na -1.46, and HCO3 -3.00 me.!l) was precipitated both in a .20-year lysimeter experiment and in an orchard irrigated for 38 years. In the foregoing "Ca requirement" equations use is made of Pratt's average value for loss of HCO3, i.e., 50 per cent, but in addition a 20 per cent allowance is made for the precipitation of Mg largely in the form of silica compounds, i.e., the value 0.7 x HCO3 is used in computing Ca + Mg requirements. It is unfortunate that each of three extended (21 months to 4 years) and carefully conducted experiments on the significance of CO 3HCO 3 in irrigation waters failed to take account of the importance of C02 partial pressures in the soil atmosphere on the extent of precipitation of CaCO3 (Wilcox, et al[9, pp. 259-2661); Babcock, et al [2, pp.155-164]; and Hausenbuiller, et al[6, pp. 357-364]. In each of these experiments the plants-respectively, Rhodes Grass, alfalfa, and Bermuda Grass-were grown in containers and irrigated with waters having various ratios of Ca' Na and HCO3: Cl. The oversight in the experimental designs is represented by the fact that the containers were not surrounded by densities of plants equal to those of the test plants in the containers. With the foregoing provision, lateral light would have been reduced and the top growths would have been more nearly proportional to soil area. But with the tops spreading out, the root densities must have been very high in the limited soil volumes (2, 32, and 5 gallons, respectively). The production of respiratory CO2 being somewhat proportional to root density, the precipitation of CaCO3 would, to a corresponding extent, have been inhibited by the high CO2 partial pressure, and the development of high ESP would have also been restricted. Babcock, et al. [ 2]make the observation that while little CaCO 3 precipitation occurred in their soils, it did occur in their collecting pans as the leachates came into equilibrium with the outside air.



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382 The Pakistan Development Review is developed. History has repeatedly demonstrated that a permanent agriculture requires that the salts added to irrigated lands be balanced by a commensurate salt removal. The mere fact, however, that a "salt balance" is achieved may be meaningless if the balance exists only after the lands are too saline for a selfsupporting agriculture. Drainage facilities should be established before, rather than after, an agriculture is impoverished. One automatically cringes at the thought of discharging saline drainages into the canals and rivers that are supporting downstream agricultures. The destruction of old agricultures to promote new ones can provide no mental comfort. The longevity of an agriculture which supports many millions of people should be viewed in terms of centuries rather than on the basis of an expedient which may suffice for only a limited number of years. The Report on Land and Water Development in the Indus Plain [81 and the Panel's paper estimate that with recycling of the groundwater to supply additional irrigation water and at the same time prevent a further increase in waterlogging, the groundwaters will, with 10 to 50 years of pumping, have become too saline for further use. The reports further recognize that the quality of the groundwaters underlying the Indus Plain are uneven: "... pools of poo rquality water are interspersed among the good." By the data presented for the Northern Plain, only one-third of the groundwater contains less than 500 ppm of total salt. A total of 38 per cent contains more than 1000 ppm of salt. The reports recognize that a disastrous infiltration of bad waters into the good will occur if the elevations of the good waters are reduced by pumping below the elevations of the bad. In other words, the idea is accepted that both the bad and good waters must be simultaneously pumped but the statement on how the bad waters should be disposed of is not very specific. It is suggested only that the bad waters might be discharged into lagoons or returned to the rivers during flood periods. Two questions are raised by these proposals, particularly since the areas of bad waters will progressively expand during the 10 to 50 year periods of pumping until all waters are salinized. When the good waters are exhausted, Pakistan will again be dependent on canal waters. Neither the present nor future bad waters which require pumping will necessarily be adjacent to the rivers. The canals for distributing irrigation waters were designed for distribution only and it would appear to require much planning and construction of newdrainage works to carry away the discharges of widely scattered wells pumped only to protect the quality of the pools having good water. The problem of disposing of the saline groundwaters is recognized as one which will become



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 333 A second theme implicit throughout the Panel report was integration-the hydrological problems of the Indus Plain can bast be handled on a unitary or "systems" basis. Three kinds of integration are involved. 1) The Plain as a whole and its water supply must be considered as a unit. What is done to irrigate farm fields in former Punjab and Bahawalpur profoundly affects former Khairpur and Sind. The total water requirement for given cropping patterns and intensities in areas of given size throughout the Plain depends primarily on the potential evapotranspiration in these areas. It must be entered in any budget of irrigation water. But more important, because water in the Indus Plain is scarcer than arable land, is the total water supply from rivers and rain, and from surface and underground storage. We want to know the supplies (from both irrigation and effective rainfall), that can be made available during each month in each area at given levels of development of water structures. Comparisons need to be made of the social and economic costs and benefits of water developments in the Northern and Southern regions and their sub-regions. For each sub-region, with any given cropping pattern and intensity, the available water supplies will determine the size of the cropped area. The ultimate potential water supply for irrigation in the Plain as a whole is particularly significant, because it will fix the ultimate dimensions of the gross sown area, that is, the product of the cropping intensity times the net cultivated area. This must be the primary boundary condition in long range planning for agricultural development. The degree and speed of approach to this boundary condition are crucial for shorter range planning. 2) Irrigation water supplies fromt rivers and surface storage and from the underground reservoir should be managed as a single system. There is a marked seasonal variation in river flows, and a lack of concordance between these flows and the crop water requirements. At the same time, the unit costs of, surface storage are high, and good reservoir sites are scarce. Consequently, the proportion of river waters effectively usable for irrigation can be raised near to its potential level only if sufficient underground water supplies are also available, at the right times. Conversely, the full potential of the underground reservoir can be realized, and a high percentage of recovery of the seepage from canals, water courses, and field percolation attained, only if river waters are available at the right times and places for mixing with relatively salty or sodium-rich underground waters. 3) Supply and drainage of irrigation water should be closely integrated. To maintain soil salinity and alkalinity control, a substantial fraction of the irrigation water applied to the fields must be drained off, either in conveyance channels or by percolation into the ground, and hence cannot be used consump-



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Dorfman, Revelle and Thomas: Waterlogging and Salinity 359 TABLE 1 HARZA "PROGRAMME" IRRIGATION WATER BUDGET PART I: REQUIREMENTS Northern Southern Total, Indus Zone Zone Plain A. Assumed cultivated area (million acres) 1. Net cultivated area1 19.4 7.0 26.4 2. Gross sown area a. Rabi 17.5 2.6 20.1 b. Kharif 11.6 4.9 16.5 c. Total 29.1 7.5 36.6 B. Irrigation water requirement (million acre-feet) 1. At water courses3 a. Rabi 36 9 45 b. Kharif 46 17 63 c. Annual 82 26 108 2. Beneficial use on fields (Evapotranspiration by crops plus leaching)4 a. Rabi 28 7 35 b. Kharif 35 13 48 c. Annual 63 20 83 C. Depth of water used beneficially on fields (feet) a. Rabis 1.6 2.7 1.7 b. Kharlf5 3.0 2.7 2.9 c. Annual 3.2 2.9 3.1 Source: Computed from data and assumptions in [3]. 1 From [3, Table II-7]. 2 Computed from cropping patterns in [3, Tables II-9 and II-10]. 3 Computed from [3, Tables 1-11 and 11-12]. 4 Values in B.1 multiplied by .765 (see text). 5 Values in B.2.a and B.2.b divided by corresponding values in A.2.a and A.2.b. 6 Values in B.2.c. divided by corresponding values in A.1.



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366 The Pakistan Development Review 19 12 MAF from canals, water courses and field seepage in Ghulam Mohammad's "non-saline area" and 4 MAF from "recharge from rain and river". 20 Total pumping at water courses required to provide 8 MAF of well water for beneficial use on farm fields (8/(1-.26) = 11 MAF). 21 Supplies at water courses-10 per cent losses in water courses and 15 per cent non-beneficial seepage plus evapotranspiration of water applied to fields. (.765 x water course supplies). 22 Supplies at water courses-20 per cent losses in water courses and farm fields. 23 Supplies at water courses-26 per cent losses in water courses and farm fields. 24 Beneficial use = evapotranspiration from crops or cultivated fields plus water required for leaching. 25 Except for Column (3), total seepage is assumed to be 37 per cent of diversions at canal heads plus 14 per cent of water pumped from tubewells. 26 35 per cent of diversions at canal heads plus 15 per cent of water pumped from tubewells. 27 26 per cent of diversions at canal heads plus 17 per cent of water pumped from tubewells. 28 Except for Column (3) non-beneficial evapotranspiration is assumed to be 16 per cent of diversions at canal heads plus 14 per cent of water pumped from tubewells. 29 15 per cent of diversions at canal headsplus 5 per cent of water pumped from tubewells. 30 13 per cent of canal head diversions plus 9 per cent of water pumped from tubewells.



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386 The Pakistan Development Review circumstances and one which would p.-rmanently reverse the downward trend in production which has resulted from waterlogging and salinity. Deep field and collecting drains should always serve the double purpose of disposing of saline wastes and of providing deep, well-aerated root zones. Water Quality Evaluation Tf a water is to be used for irrigation, it is deserving of a careful chemical analysis to make possible estimates of how it can be used most effectively. From analyses for each ion expressed in milligram equivalentsper liter (me./l), it is a simple matter to calculate leaching, or drainage, requirements and to estimate, also, the amount of gypsum which should be applied to maintain permeability and high production. Ghulam Mohammad has pointed to a weakness in the Revelle Report in that emphasis was placed on total salinity with a neglect of the significance of bicarbonate in the precipitation of calcium and the resulting higher sodium percentages. He regards it as probable that many groundwaters which the Panel recommended as suitable for irrigation would result in low soil permeability and high alkalinity unless mixed with large quantities of canal water or used with heavy applications of gypsum. Because of insufficient canal water, the necessity of gypsum, and the costs of development, he recommends the elimination of tubewell installations over the Punjab and Bahawalpur, and undoubtedly elsewhere, except where sodium and bicarbonate concentrations are found to be low relative to calcium and magnesium. On the other hand, many waters that are now unsuitable for irrigation because of high bicarbonate can be successfully used by additions of gypsum. Reference will be made in a subsequent paragraph to the nature of the experimental evidence which led the Panel to regard 1.25 me./l of residual sodium carbonate in irrigation waters as "probably safe". Workable gypsum deposits are available in Pakistan and experimental evidence exists in Pakistan which shows that notable benefits of gypsum applications have resulted even in some of the canal-irrigated land. Hausenbuiller, et al [6, pp. 357-364] note that while power and machinery for mixing gypsum with water maybe expensive, applications of the finely powdered material directly to the land is practical. Ghulam Mohammad refers to statements byHanson, Bower and Williams on advantages of maintaining subsurface waters within the lower root zone if care is taken to insure that adequate salinity control is exercised. Although it is true that water may be effectively stored in the deeper root zone, as in the polders of Holland where salinity is not usually a problem, the dangers of extending the concept to some of the irrigated lands of Pakistan are obvious.



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Eaton: Waterlogging and Salinity: Comment 389 I GYPSUM REQUIREMENTS OF IRRIGATION WATERS formulas under text (pages 387-391) Appraisal Requirement Leaching requirement Gypsum -requirement Leaching (c) (d) Sw= LR= (d)x 234= requireCrop Ca RequireCl + ISO4 2xMss*-S Swx 100 lbs. Gyp./ac. ment removal ment in me./1. + I required ft. water in adjustment [(a) + (b)+(c)] calcium 2X(per cent) percentt -____________ _____________ (per cent) 0.30 0.29 0.33 59.67 0.5 68.0 0.5 0.30 -0.21 2.10 57.90 3.6 None 3.6 (None) 0.30 -0.14 1.05 58.95 1.8 None 1.8 (None) 0.30 -2.57 4.86 55.14 8.8 None 8.8 (None) 0.30 4.84 6.13 53.87 11.4 1130.0 11.4 0.30 6.23 18.18 41.82 43.5 1460.0 43.5 Tracy Mendota Canal, California, (4) Colorado River, U.S.G.S. 1950, (5) Wel, Bakersfield, keep salt from accumulating beyond levels consistent with good crop performance.