Paper 1103 IR 3
-.. Journal of the
S- \IRRIGATION AND DRAINAGE DIVISION
S' Proceedings of the American Society of Civil Engineers
S"SAFE YIELD" IN GROUND-WATER DEVELOPMENT,
REALITY OR ILLUSION?
Raphael G. Kazmann,1 M. ASCE
(Proc. Paper 1103)
Definitions of "safe yield" are critically examined and found wanting. The
effects of embodying such a term in laws controlling the utilization of ground
water are noted. An alternate, more feasible, approach to the problem of
ground-water control, based upon the functional utilization of aquifers is pro-
"Safe yield" or "perennial safe yield" are terms familiar to students of
ground water. The term 'safe yield" is apparently attributable to O. E.
Meinzer, who first used it in a paper published in 1920.2 It has since been
used in scientific literature and reports by governmental and private organi-
zations, and has found its way into the statute books of a number of states.
Said Meinzer, 'The safe yield of an underground reservoir is the practic-
able rate of withdrawing water from it perennially for human use."
This definition was unchallenged for about 20 years, although it does not
wholly satisfy many scientists and engineers simply because it is general. In
T certain respects it resembles the former speed limit in the State of Tennes-
see: "Please drive carefully." The speed limit was considered to have been
violated if any accident ensued. The law did not say anything about limiting
speed. In an attempt to reduce highway accidents the law has been changed
and a maximum speed set. Meinzer's definition, while clear, did not fix
limits to ground-water withdrawals and was not considered a satisfactory
ote: Discussion open until April 1, 1957. Paper 1103 is part of the copyrighted
Journal of the Irrigation and Drainage Division of the American Society of Civil
Engineers, Vol. 82, No. IR 3, November, 1956.
1. Cons. Engr., Stuttgart, Ark.
2. Meinze;,.O. E., Quantitative Methods of Estimating Ground-Water Sup-
plies: Bull. Geol. Soc. Amer., v. 31, no. 2, pp 329-338, 1920.
--------- ------------------~ ~~--
guide in deciding whether pumpage had exceeded the "safe yield.'
As pumping rates increased and the water -levels in ground-water basins
declined, Meinzer's definition was modified and made more specific. The
words "safe yield' came to mean an upper limiting pumping rate, the limit
being set, generally and ideally, by the pre-pumping steady-state flow in the
aquifer (assuming that such flow did occur). Attention and thought was then
directed to the phenomenon of ground-water replenishment, the so-called
"recharge" of aquifers.
The thought became current that the "safe yield" of an aquifer was surely
determinable in advance of ground-water development-or even after develop-
ment had begun.
By 1949 Meinzer's definition had been carefully reconsidered and "safe
yield" was redefined by a synonym "perennial yield': "The perennial yield
of the aquifer underlying an area of ground-water development has been re-
garded as the maximum rate at which water can be salvaged from the natural
discharge, or added to the recharge, or both ... In some reports the eco-
nomical pumping lift has been considered to be a factor in this definition,
however, the economics of recovery seem to be irrelevant to the determina-
tion of the quantity of water which an aquifer will yield and so are not con-
The Federal Government, in 1951, issued a circular on the water situation
in the United States, with special reference to ground water.4 In a special,
state-by-state summary, under a heading "Deficiencies in Information' there
is listed time and time again, "Safe yield of basin not known at present* or a
paraphrase of this statement.
Evidently the Federal Government has decided that for each ground water
basin there is a single, determinable figure which is the "safe yield" of the
basin and with only a reasonable extension of present efforts this "deficiency
in information" can be alleviated. Such an attitude has already had its effect
on the laws of a number of states and will undoubtedly influence the course of
future legislation in the field of water resource development.
However, in view of the fact that far more water is stored in waterbearing
formations than in all man-made reservoirs, it is imperative that basic tech-
nical concepts, and the legal consequences of these concepts, be examined
carefully and critically.
The Heart of the Matter
The basic' technical question is this: "For any given waterbearing forma-
tion, is it theoretically possible to determine a single specific figure which
can be termed the "safe yield' of the aquifer, without reference to the total
water resources of the region and adjacent regions?"
As point of departure, let us examine a definition of "safe yield" used bf
the Federal agency which has publicised and still uses the term, in view of
- the fact that it is a scientific agency and is not principally concerned with
3. Williams, C. C. and Lohman, S. W., Geology and Ground-Water Resources
of a Part of South Central Kansas: Geol. Surv. Kansas, Bull. 79, 1949,
4. McGuinness, C. L., The Water Situation in the United States with Special
Reference to Ground Water: Geol. Surv. (U. S. Dept. of Interior): Circ.
114, June 1951.
- ~ I
1. The transmissibility of the formation, combined with the maximum
available hydraulic gradient, might become too small to permit the necessary
rate of flow through the formation to the producing structure (or structures).
2. Even though enough water might flow to the structure at all times, the
quality of water throughout an aquifer is not necessarily the same. Concen-
tration of the withdrawal of water from a limited area might cause underlying
mineralized water to enter the structure, modifying water quality to the point
of being unusable-even though the "safe yield" of the aquifer were the fresh
water "safe yield."
In these two cases a perennial water output equal to the "safe yield' might
not be reached.
Now consider a situation wherein the natural recharge of the aquifer oc-
curs by seepage from a stream traversing the outcrop area of the aquifer.
The producing structures, designed for the "safe yield" of the aquifer (which
might be computed on the basis of the average transmissibility of the aquifer
and the average position and gradient of the piezometric surface before the
start of pumping) are located on the river bank next to the area of recharge.
In pumping af amount equal to the perennial "safe yield' of the aquifer, the
short distance between well and recharge area might require use of only a
small fraction of the available drawdown. Consequently, by increasing the
drawdown a steady-state output might be obtained in excess of the "safe yield"
of the aquifer, depending only upon the availability of water in the stream to
replensih the aquifer at the rate at which water is withdrawn. The Des
Moines infiltration gallery illustrates this situation admirably, having been
constructed in a thin aquifer next to a river and producing far more than the
original flow through the aquifer before the start of pumping.
It appears that our approximate definition cannot be used: for a single
aquifer it might give a value of "safe" water withdrawal that is.simultaneously
too high and too low l The.crux of the trouble seems to be that the engineering
P-ticabilityof accomplishing a rate of water withdrawal equal to the 'safe
engineering problems, construction methods, or the costs of operation of
structures. The last definition quoted will serve. It can be deduced that eco-
nomics, as shown by the definition, should be excluded from any definition of
Therefore, as a first approximation: "safe yield* is a term apparently
used to designate the quantity of water flowing through an aquifer before water
was first pumped from it. It can be taken for granted that if the pumping rate
from the aquifer does not exceed this figure such a rate of withdrawal may be
continued indefinitely. But can it?
Water may be withdrawn from an aquifer by means of a pump placed in a
suitable structure such as a well, infiltration gallery, or horizontal collector.
Is it, therefore, correct to state that if the structure (and for this purpose
any fixed number of wells may be considered one "structure") is designed
hydraulically to produce a quantity of water equal to the "safe yield" of the
aquifer and provided with suitable pumping equipment, the "safe yield' will
not be exceeded and the structure may be expected to continue to produce
water at this rate indefinitely?
There are a number of sound reasons why such a pumping rate might not
be continued indefinitely, even though it might be possible for an initial peri-
od. Let us consider two of these:
yield" has been excluded-and the practicability, which means economics,
was excluded on purpose I
The definition of "safe yield" should probably be modified: it is not mere
"observed data" but it requires that economics and engineering be considered.
It may be legitimate, at this point, to speculate as to what procedure the
Federal Government has devised to produce a single "safe yield" figure for
each aquifer or 'ground-water basin' from its purely scientific and fact-
finding studies since, in 1955, with reference to ground water it has been pro-
posed, "That for the purpose of gaging water supplies and estimating the
perennial yields of underground basins a sufficient number of Federal obser-
vation wells be installed.'5
It seems evident that the determination of "safe yield' is far different
from measuring how much water flows in streams or what is the depth to
water in various parts of an aquifer.
The purely scientific approach of Meinzer's successors having failed, the
engineering approach remains:
"Safe yield is the annual extraction from a ground-water unit which will
not or does not (1) exceed the average annual recharge; (2) so lower the water
table that permissible cost of pumping is exceeded; or (3) so lower the water
table as to permit intrusion of water of undesirable quality.'6 A paraphrase
of this definition appeared in WATER, the Agriculture Yearbook for 1955.7
This definition includes "average annual recharge" and qualifies it by ex-
cluding highly mineralized water and making allowance for the "permissible
cost of pumping." Although this definition is highly useful in another connec-
tion, it leaves much to be desired as a usable definition of "safe yield."
For instance, a law based on achieving "safe yield" as defined above might
be slightly difficult to enforce: an administrator would have to decide upon
permissible pumping cost-and this cost might be much higher for an industry
or municipality than for a neighboring farmer irrigating wheat or cotton who
was pumping from the same aquifer. In addition, the "average annual re-
charge" must be determined, and this is a term possessing all of the weak-
nesses of the previous definition of "safe yield."
It may be legitimate to speculate how a State Engineer can proceed to find
a basis for controlling ground-water withdrawals using perennial "safe yield"
as his criterion, when he can't define it.
Yet, these definitions should not be dismissed lightly. They are the work
of thoughtful men, eminent in geology and engineering, who had much experi-
ence in ground water. The difficulties with the definitions are to be consid-
ered a warning that it is necessary to stop redefining "safe yield" and re-
examine the entire situation. But before doing this it is desirable to discuss
the effect of the "safe yield" doctrine on water-resource development.
5. Commission on Organization of the Executive Branch of the Government,
Task Force Report on Water Resources and Power: Vol. 3, p 1077, June,
6. Conkling, Harold, Utilization of Ground Water Storage in Stream System
Development: Trans. Am. Soc. Civ. Eng., Vol. III, pp 275-302, 1946.
7. Muckel, Dean C., Pumping Ground Water so as to Avoid Overdraft:
*Water," Yearbook of the Dept. of Agriculture, pp 294-5, 1955.
"Safe Yield" and the Doctrine of Appropriation
In the Western States, where water is limited in quantity and is particular-
ly valuable, more thought has been given to public policy in the field of water
control and utilization than anywhere else on earth. It may be fairly stated
that the doctrine of appropriation is becoming dominant in the West with re-
spect to the development of surface water. Efforts have been made to extend
this doctrine to cover utilization of ground water.
According to the Supreme Court,
"To appropriate water means to take and divert a specific quantity of water
therefrom (the watercourse-author's note) and to put it to beneficial use In
accordance with the laws of the state where such water is found, and by so do-
ing to acquire a right under such laws, a vested right to take and divert from
the same source and to use and consume the same quantity of water annually
As a rule, the first person to put water to beneficial use enjoys a superior
right, a priority, over any later, "junior," appropriators. Inherent in the
Supreme Court's definition is the "perpetual right" to divert water conferred
by the state upon the property owner. This implies that a determinable, eco-
nomic quantity of water will always be available, even though the total quanti-
ty available in any year may differ greatly from the quantity available during
.. Appropriators pumping directly from a stream have little difficulty In ap-
portioning the water according to the priority doctrine. When all available
water is required by senior appropriators, the junior appropriators either
have no water to pump or are prevented from pumping by a water master.
As more and more of the mean annual flow in a stream is appropriated, juni-
or developments become increasingly risky and expensive due to the increas-
ing possibility of economic failure of such developments during periods of
prolonged sub-normal stream flow.
Appropriation doctrine could be applied directly to ground-water withdraw-
als if-if the source of ground water were completely independent of precipi-
tation, evaporation, and runoff. Under such circumstances it might be pos-
sible to determine the annual contribution of the ground-water basin and this
would be in addition to all flows measured elsewhere. Hydrologic fact con-
tradicts the postulated condition:
A particle of water can be part of the surface-water body, infiltrate into an
aquifer, be pumped out for irrigation or sanitary purposes, reach a stream as
return flow or sewage, and repeat the cycle several times before either being
evaporated or reaching the sea.
Consumptive use of surface-water that prevents it from reaching the out-
crop of an aquifer and becoming part of the ground-water supply would inter-
fere with the appropriative rights of ground-water users. Conversely, the
increased recharge to an aquifer due to the operation of wells (next to a
stream, for example) might adversely affect the rights of appropriators of
surface water by diminishing the stream flow.
Thus, the concept of a "safe yield" of-aquifers, independent of considera-
tions of regional hydrology, cannot be reconciled with the doctrine of appro-
priation. All water pumped from the ground must be replaced by water
8. Arizona vs. California, 238 U. S. 423 (1931).
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1103-6 IR 3
coming from the land surface if a perennial water supply is to be obtained
from the ground. If all surface runoff in the area overlying an aquifer has
been appropriated, a perennial supply cannot be obtained from the ground,
Nevertheless the built-in difficulties found in "safe-yield" legislation do
not come to light immediately after the passage of the law. For example, on-
ly within the past five years has the New Mexico ground-water law, passed in
1931, been challenged for the reason that a ground-water basin cannot be ad-
ministered on the basis of appropriation or the impariment of existing
rights.9 Additional litigation along the same lines may be expected in the
The Role of Aquifers
How, then, is the problem of ground-water conservation and development
to be solved within the framework of the present development of surface wa-
Consideration should first be directed to the composition and structure of
waterbearing formations, their functions, and the limitations of each function.
An aquifer is a volume of the earth's mantle containing water. This
volume of material is sufficiently permeable that water can move through it
under the action of gravity and from it water can be withdrawn at useful rates
by properly designed structures. An aquifer composed of unconsolidated ma-
terial such as sand, or sand and gravel, functions as a natural "filter plant,'
a 'pipe line,' and a "reservoir.' In certain rock formations, such as caver-
nous limestone or highly fractured basalt, the filter plant function may be
partially or entirely lacking. The discussion of aquifers as filter plants does
not apply to such rock aquifers.
Aquifers as Filter Plants
The exposed area of an aquifer which is composed of granular materials
acts as a natural filter to remove all suspended matter and pathogenic or-
ganisms from the surface water which passes through it into the ground.
Sometimes this area becomes clogged and recharge is rejected. Sometimes
the aquifer is brimful of water and recharge is also rejected. When, for one
reason or another, conditions favorable to recharge occur, the aquifer re-
sumes its function as a natural filtration plant.
--It is by virtue of this property of aquifers that ground water reaching wells
is free of suspended matter and pathogenic organisms. This phenomenon of
safe water from an aquifer composed of granular materials has been ob-
served even when the aquifer is traversed and recharged by highly polluted
streams, as in the industrial East. Even organic tastes and odors are lacking
in the ground water, even though the source may contain them in full mea-
sure. It has been suggested that an act of bio-filtration occurs in the re-
charge area of the aquifer: that the aquifer functions not only as a rapid sand
filter, but also as a bio-filtration plant.
The capacity of an aquifer to act as a filter plant is not constant throughout
9. Thomas, H. E., Water Rights in Areas of Ground-Water Mining: Geol.
Surv. (U. S. Dept. of Interior) Circ. 347, Washington, 1955, p. 10.
the year. It depends on the head, temperature, velocity, and silt content of
the water, the design, location, construction and operation of the water-
producing structures, and other, less important factors. However, the prob-,
able minimum yield of a well field constructed in or near a recharge area
can be computed to the required degree of accuracy after the proper engi-
neering exploration and hydrologic studies have been accomplished. The eco-
nomics of water development play an important part in determining the "firm*
yield of the system.
It has been pointed out elsewhere, that in the East, where streams are
highly polluted, the filter-plant function of aquifers is of great economic im-
portance.10 The use of water for sanitary and industrial purposes places a
value on clean water, even though there is no shortage of sediment laden, pol-
luted surface water. In the West the emphasis is primarily on the availability
of water. The presence of sediment and microorganisms in water are of
minor economic importance when the water is used for irrigation.
Let it be noted that since the yield of the "filter plant' is importantly
changed by rainfall, runoff, and water temperature, its maximum utilization
depends on the magnitude of available storage to permit this variable output
to be averaged over a period of time.
Aquifers as Pipe Lines
Although the use of aquifers as pipe lines (to convey water from the re-
charge area to the well field) has been of great economic importance in the
past, it is likely that in the future the importance of this function will de-
crease. A pipe line full of sand is not an efficient vehicle for transporting
water over long distances, even though the pipe line may be an aquifer extend-
ing over many hundreds of square miles and may be hundreds of feet in thick-
ness. This is particularly true in areas of intensive ground-water develop-
ment, where use as a pipe line may well conflict with other uses of the
For example, under a gradient of 20 feet per mile, an 18-inch concrete
pipe will transmit about 5 million gallons of water a day. Under the same
gradient it requires an aquifer one mile wide, 75 feet thick, with a perme-
ability of 3,400 gpd/sq ft to move the same quantity. Aquifers are inefficient
pipe lines for the long distance transport of water, although, for distributing
water over relatively short distances there is much to be said in their favor.
The writer's experience would seem to indicate that the maximum distance
that an aquifer should serve as a pipe line is about two miles. In areas of in-
tensive ground-water pumpage this maximum may be too high.
The foregoing discussion contains important implications regarding the
need for ground-water recharge in or near the area of pumpage: from an en-
gineering viewpoint artificial recharge is necessary whenever a well field is
located at a great distance from the area of natural recharge.. Where direct
recharge from the land surface is impossible, due to the existence of clay
layers between the surface and the aquifer (as in the Grand Prairie Region of
Arkansas and many parts of the Central Valley of California), artificial re-
charge through man-made structures is essential.
0-" Kazmann, R. G., The Role of Aquifers in Water Supply: Trans. Am.
Geophys. Union, v. 32, pp 227-230, Washington, 1951.
i _~_____~*_~ 1-111
-2~~Uy~u~ ---- r IE
Aquifers as Reservoirs
Many ground-water problems originate because of erroneous conclusions
reached as a result of short-period observation of the operation of wells in
depleting, or failing to deplete substantially, the enormous quantity of water
stored in aquifers. Many aquifers are essentially vast, closed reservoirs
which are analogous, on a large scale, to petroleum reservoirs. There is no
merit in discussion the "perennial yield" or "safe yield" of such an aquifer.
No one uses the term relative to an oil-bearing formation, yet many reports
have been written (by the writer, among others) purporting to determine the
-"safe yield" of closed aquifers. In oil fields the rate of withdrawal and well
spacing are subject to regulation because these factors determine to a large
extent the maximum total output from the reservoir. But no one acts or
thinks as though a perennial supply or oil were available, no matter how vast
the oil-bearing structure. We all know and accept the fact that a limited,
though large, quantity of oil may be obtained from a given area. This fact is
even recognized in the Federal tax laws by the much-debated "depletion
It is probably due to the limited popular understanding of the tremendous
quantities of water stored in our major aquifers, combined with a misappre-
S hension as to how, and how fast, ground-water replenishment occurs, that the
S renewability of our water resources, as evidenced by the perennial flow of
streams, has been embodied in the ground-water laws of several states.
These laws try to limit the pumpage of ground water to the "safe yield" of
ground-water basins. But unless surface water is available to replace the
ground water that has been pumped and is used for that purpose, it is unsound
public policy to discuss the "safe yield" of a water-bearing formation.
The preceding statements should not be interpreted to mean that ground-
water reservoirs are of no importance in connection with the conservation
and use of our water resources. Such reservoirs are essential in the con-
servation of our water resources. They make possible the utilization of flood
waters far beyond the potentialities of surface reservoir sites. The water
stored in them is not subject to evaporation loss and the reservoir area is not
removed from productive use. Moreover, most of our major aquifers under-
lie areas of human habitation and agricultural activity such as upland plains,
river valleys, and coastal plains. The storage of surplus surface water un-
der or near the areas of water use has manifest advantages (two of which
.have been pointed out). The principal drawbacks are, (1) the impossibility of
generating electric power from water stored beneath the surface of the
ground and (2) the impossibility of using the stored water directly for recre-
ational purposes. However, as a counterbalancing factor, the increasing use
of atomic energy in modern civilization has made the storage of water in
aquifers of increased importance: such stored water is not subject to direct
contamination by radioactive fallout and, by virtue.of dilution and the slow
movement of water within aquifers, even if the recharge-water is contami-
nated, radioactive decay has time to occur and an important amount of dilu-
tion also occurs before the water is pumped out and used. As a rule, water
stored in aquifers is safe water.
In utilizing aquifers as storage reservoirs, it should be emphasized that a
reservoir must be filled as well as emptied-and if the replenishment is neg-
ligible or non-existent, no perennial right to withdraw water should be grant-
ed since the available water supply is not perennial.
S It is becoming evident that the technical breakthrough most needed at this
time in the field of ground water is a generally applicable method of artificial
recharge which will use raw surface water that is either untreated or has re-
ceived an absolute minimum of treatment. Without such a breakthrough we
cannot p operly utilize our aquifers as ground-water reservoirs.
An amusing summary of the present status of recharge was given at the
"Water for Texas" conference in 1955. It was reported on page 26 of the
Water Log, November, 1955:
"There were also discussions on recharge, the least known phase of
ground-water development. It seems that the best method of recharge is
accidental recharge. The few attempts at artificial recharge have met with
many problems such as.silting up of the wells, insufficient pressure, limited
transmissibility of sand strata, organisms that multiply in air and clog wells,
What are the prospects of achieving a technical breakthrough in the field
of artificial recharge? The prospects are good. The problem is one of engi-
neering, not science. Engineering development is needed to reduce the cost
of artificial recharge to a point far below its present level. For instance, the
use of completely filtered river water has been entirely successful in re-
charging depleted aquifers through wells and horizontal collectors. Artificial
recharge during and after the war years was successfully accomplished with
the use of filtered City water in Louisville and Cincinnati. However, the cost
of the water was high. More recent experiments in the Los Angeles area,
utilizing the treated effluent from a sewage plant, have been entirely success-
ful. The mathematics and hydraulic theory have been found to be adequate:
it is now a question of engineering technique and cost. Estimates have been
made which seem to indicate that a properly designed development project -in
the field of artificial recharge, to utilize surface water which had a minimum
of treatment, or no treatment at all, would cost between $500,000 and
$1,000,000 for the needed exhaustive tests on structure prototypes. There is
every reason to believe that an economic method of artificial recharge
through structures will be achieved within the next few years. Such a devel-
opment would enable the nation to fully utilize aquifers as storage reservoirs
and make possible great advances in the field of water conservation.
Legislation provides the framework for the development of our water re-,
sources. It must be broad enough to include present nd potential technical
In most of the West the doctrine of appropriation has been adopted for the
development of our surface-water resources. The writer has no doubt that
this doctrine can be successfully extended to include ground water, although I
its equitable application will involve complex matters of geology and engi-
eering, far removed from the relatively simple matter of flow measurement
and control of water, in open channels or closed conduits. The doctrine will
be more easily applied in areas where unappropriated surface water is
1103-10 IR 3 November, 1956
available and in areas where "safe yield" or an equivalent phrase on ground
water use is not presently incorporated in the law.
On the assumption that the water law in a State is based on the doctrine of
appropriation, what are the elements that must be included in water control
legislation applicable to ground water?
First, legislation should be passed defining the recharge of aquifers as a
beneficial use of water and authorizing the creation of water districts for the
purpose of ground-water recharge. These Districts would be formed on the
initiative of local users of ground water and the District would have the right
to appropriate water (or buy It) for the purpose of recharge. Organization of
the District would be similar to the organization of an irrigation or drainage
district. The District would have the necessary power to collect operating
funds and to insure that the average annual extraction from the aquifer or
aquifers within the District did not (1) exceed the average annual recharge,
(2) so lower the piezometric surface that the permissible cost of pumping was
exceeded, and (3) so lower the piezometric surface as to permit the intrusion
of water of undesirable quality. Despite minor modification the reader will
recognize the engineering definition quoted previously with respect to "safe
Secondly, existing water law would be extended to ground-water withdraw-
S als. All areas of ground-water pumpage would be classified in one of two
S categories: areas of "mining" or areas of 'perennial yield." The distin-
guishing characteristic would be the availability and utilization of surface
water for accidental or artificial recharge.
In areas of ground-water mining, well drilling and pumping would be unre-
stricted. However, some attention might be given to the desirability of es-
tablishing a minimum well spacing in order to insure that water could be re-
covered in economic quantities for the maximum period of time. All areas of
ground-water development might automatically be classed as mining areas
unless it could be shown that unappropriated surface water was available for
recharge, in quantity sufficient to balance the withdrawals, and the aquifer
was currently being replenished within a predetermined distance of the water-
Areas of "mining" which had been organized as Districts would become
"perennial yield" areas and would appropriate surface water on an equal
basis with other surface-water users and would be obligated to construct,
maintain, and utilize structures for artificial recharge. Within the District,
well owners would receive secondary appropriative rights: these rights
would be contingent upon the continued recharge of surface water to the aqui-
fer. There would be no senior or junior appropriators within a District: the
stored water within the aquifer would make it possible to put all appropria-
tors on the same level of priority. Within the District there would probably
be no restriction upon the drilling of wells, although the total quantity of water
pumped during a period of years by an appropriator might be limited.
Within the boundaries of the District, outside of the area of "perennial
yield," there would be established a "buffer zone" to minimize the possibility
of capture of any substantial quantity of recharge water by wells whose output
was not replaced by surface water obtained through the District's appropria-
tive right. The area of the buffer zone might be fixed by administrative
authority. The buffer zone is made necessary by the fact that it would be
possible to establish a "perennial yield" area in a portion of an extensive
aquifer from which, in another area, it might be desirable to mine water. It
should be mentioned that there are several technical devices available to
make the buffer zone effective in preventing loss of ground water to wells
outside the area of "perennial yield."
Before concluding this brief discussion of proposed legislation, legislation
which might replace present ground-water law which requires the pumpage
from an aquifer to be limited to the "safe yield," it is necessary to make
brief mention of the "watercourse problem." The 'watercourse problem"
was aptly defined by Harold Thomas in 1951 as the . result from pump-
ing wells alongrrivers, where the ground water is so closely related to the
water in the stream that pumping from wells depletes the stream flow. Di-
versions from the stream for various purposes may increase the amount of
ground water at one place and reduce it at another.*11
It will be necessary to classify such areas of "accidental recharge" as
perennial yield areas. Well owners in such areas would be required to or-
ganize themselves into Districts in order to receive an appropriative right'
on an equal basis with other diverters of surface water-or would have to
stop operating their wells. However, since recharge would be "accidental"
it will be necessary for such Districts to equalize stream flow above and be-
low the area of accidental recharge in accordance with their appropriative
rights. Such Districts might also have to undertake operations of artificial
recharge. It is likely that the most complex problems in the equitable ad-
ministration of ground-water legislation will be encountered where water-
Scourse problems are found.
All of these situations, and additional ones, must be carefully considered
before reaching conclusions and embodying them in legislation. Inherently,
however, in contrast to present laws based on "safe yield" doctrine, it will be
possible for workable legislation to be passed. Useful decisions can be
made on the basis of the approach outlined previously, decisions that do not
contradict the facts of hydrogeology.
It can be concluded that much of the presently existing body of ground-
water law, law that is predicated on determining the "safe yield and annual
recharge" (as in Oklahoma), will be found to be administratively unworkable,
inequitable, and an obstacle that prevents society from achieving maximum
water conservation and development. This conclusion rests on the fact that
the concept of "safe yield" is a fallacious one.
It may also be concluded that much of the existing ground-water law will
have to be rewritten to eliminate the concept of "safe yield" and to bring laws
into accord with the facts of hydrogeology before real progress can be
achieved in the conservation and development of our water resources through
the use of aquifers. The cautious approach by most state legislatures in the
field of ground-water law seems to have been fully justified.
Future legislation concerning ground water should be based on appropria-
tion doctrine and applied with proper consideration for present techniques
and probable futureadvances in the field of ground-water engineering. In
particular, consideration should be given to the possibility of a technical
11. Thomas, H. E., Conservation of Ground Water: McGraw Hill, New York,
1951, p. 7.
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its -,,-I -- ------- ----------------------------- -------------
breakthrough on the field of artificial recharge.. Legislation should be writ-
ten broadly enough to take advantage of this development when it occurs. ___
Finally, every effort should be made by professionals in the field of hy- JTor f tl
drogeology to remove the concept of "safe yield" from legislation, to elimi- urn
S nate it as an objective of ground-water studies, and to restudy all reports IRRIGATION AND DRAINAGE DIVISION
purporting to fix such a figure with the object of revising and reissuing such
reports more in accord with determinable fact. Proceedings of the American Society of Civil Engineers
EVAPORATION FROM FREE WATER SURFACES AT HIGH ALTITUDES1
Harry F. Blaney,2 M. ASCE
(Proc. Paper 1104)
In western United States, evaporation losses from reservoirs and lakes at
high altitudes are of importance as an element affecting the net water supply
available for irrigation crops, production of power, and municipal and indus-
trial purposes. Except in unusual instances, evaporation cannot be measured
directly from large water areas. Thus, it is common practice to measure
evaporation from pans and use coefficients to reduce pan evaporation to lake
evaporation. At high altitudes it is seldom possible to measure evaporation
during the winter months because the water in the pans freezes. This paper
presents data on evaporation in several western states and develops a method
of estimating monthly evaporation for the entire year from temperature and
SThe storage of stream flow from mountain watersheds in reservoirs has
made possible the development of much of the irrigated agriculture of the
West. These reservoirs help to prevent floods, conserve a water supply that
otherwise night be wasted, and make possible the production of power. The
importance of a knowledge of water lost through evaporation to the efficient
design and later operation of the works involved in.a water-supply project
has long been recognized by engineers.
There are very few instances where evaporation can be measured directly
from lakes or reservoirs because of the unknown elements of supply; such as,
'to: Discussion open until April 1, 1957. Paper 1104 is part of the copyrighted
Journal of the Irrigation and Drainage Division of the American Society of Civil
Engineers, Vol. 82, No. m 3, November, 1956.
1. Presented at a Regional Meeting of the ASCE, Irriga. and Drainage Div.,
September 8, 1955,.Denver, Colo.
2. Prin. Irrig. Eng., Western Soil and Water Management Section, Soil and
Water Conservation Research Branch, Agricultural Research Service,
U. S.D.A., Los Angeles, Calif.
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IR 3 November, 1956