IRRI TION PRINCIPLES
ORSON W. ISRAELSEN, Ph.D.
Emertus Prfesor, Civil and Irrigation Engineering
VAUGH$ E. HANSEN, Ph.D.
Director, Ejlneering Experiment Station
UTAH STATE L iToy., OAN, UTAH
New York I
It.;~ :r 9' .-,
SAFE YIELDS FROM GROUNDWATER RESERVOIRS 25
Loweringthe ground-water levels increases the pumping lift and makes
the water so obtained increasingly expensive. In some areas shortages
have become msfiently acute to justify curtailed use.
2.12 RECHARGING 'Rd i-WATER RESER OIRS
Critical shortages of underground water due to limited natural
recharge, small Astrage capacity, and overuse have stimulated efforts
to recharge groumd-water reservoirs with surface waters. Flbod flows
which would otherwise have been lost are diverted andapplied to the
land, thus provide inwater to seep into underground rebrevoirs Wfiter
flow of streams, sewage, and industrial water may also le utilised to
excellent advantage for recharging these reservoirs. Full conserva-
tion and use of available water supplies requires an integrated use of
surface and sub-surface waters and storage facilities.
Systematic loading of land surfaces overlying or dinitg into
underground resrvoire is a reognzised. method of Water storage.
Usually the water; Is spread over the.land to expedite ihfiltrdaion into
the soilaIdlpercblatiodh downwrd to the ground water. .iguhe 2.5
shows a tyjftal anyoi Idi fan with. rook dams to. etard fbod
low in ter;aeed, eausmng intattiontto recharge a griund-water
basin. R drin dikes, ffii&f'iAthl Z;i upVriteff fatb.rm
ponds, c hWrn in 'ig. 2.6, from w~1i h the water pe. latest into the
ground-warter. eservowt to be stored until needed for irrigation.
Infiltration hasibeen increased by using organic resides and grasses
to conditioE grodd surfaces to prolonged periods of submergence.
Grasses appear to maintain a more pliable and open condition bn soil
surfaces than do presently used soil conditioners, particularly where
the sediment. content of the water is considerable. High infiltration
rates during the techarging operation are essential.
A less coinmon method of reharging utilizes shafts, pit, trenches,
or wells to convey water to the gravel and rock materials underground.
The Peoria recharge pit (Suter, 1956) has been very successful in
obtaining an infiltration sufficient to absorb 35 to 41 ofs per acre
(70 to 80 feet depth per day) by using .pea gravel as a filter. When
sand is used the rate is only 9 efs per acre. Suter emphasises from
the results of the Peoria pit thai, since many unexpected facts have
been observed which are not as predicted, recharging operations still
offer a wide field for research.
2.13 SAFE YIELDS FROM GROUND-WATER RESERVOIRS
Early withdrawals of ground water were based upon water needs
and costs. Serious lowering of the water level (or pressure) brought
alarm and resulted in attempts to define "safe yield." Demands from
e to more
d with the
.rol is well
still in its
AFTER SAFE YIELDS FROM GROUNDWATER RESERVOIRS 27
Fig. 26 Soil placed against upper face of dikes retards flow of water through
them and encourages ponding of water from crest of lower dike to toe of dike
next above. (USD.A. Tech. Bu 578.)
adjacent water users resulted in many courts restricting water use
to the extent that the level (or pressure) of the water in the aquifer is
maintained. In essence, these court decisions guarantee not only the
right of the user to the water, but also the mechanical energy repre-
sented by the elevation of water in the well. Ground-water resources
cannot be effectively utilized if the natural water levels and pressures
have to be maintained. Usually only a small fraction of the available
water can be withdrawn under these restrictions. For full utilization
of surface and sub-surface water resources, ground-water levels and
pressures must be lowered during periods of drought or periods of
limited surface supplies and elevated by recharging the reservoirs
during periods of water surplus.
In some areas where recharging possibilities are limited, the con-
cept of "mining" the water is being accepted as a necessary an -
desirable procedure. Water is being considered, therefore, in the same
category as other natural resources-resources which may be expended
in the interest of current development
An outstanding example of this philosophy exists in the Central
Mount Valley development in Galifornia. Depletion of the ground water was
i1 light not only permitted, but encouraged, by some of the more progressive
>m left irrigation leaders. The plan was to utilize the "mined" water to build
storm a strong taxable economy which could support the later development
SOURCES AND STORAGE OF IRRIGATION WATER CHANGES IN
and transportation of distant waters to areas of the valley which
would develop a water shortage. This plan of ultimate development
and integration of water resources of the state is now being imple-
mented, and supplemental waters are being diverted and stored in the
ground-water reserves which were seriously depleted.
With the development of new techniques of exploration for ground
water, with increasing control and understanding of weather, and
with decreasing cost of mechanical energy incident to the atomic age,
water supplies can be made available to areas of shortage which at
the present time appear to be impractical. Therefore, the definition
of "safe-yield" is changing and will continue to change as economic
and technological conditions change. Certainly, surplus and reclaimed
surface waters cannot be stored in sub-surface reservoirs until ca-
pacities are created in these reservoirs by withdrawal of existing
Safe-yield also implies a wise balance where excessive and un-
economical pumping lifts are not imposed, nor serious deterioration
in water quality permitted. It is important to consider "safe-yield"
in the light of total water resources: surface and sub-surface, devel-
oped and potential.
2.14 FEASIBILITY OF GROUND-WATER DEVELOPMENT
Undue lowering of ground water results in higher pumping lifts
and sometimes prohibitive pumping costs. Wells may need to be
deepened and pumps; lowered in order to obtain sufficient quantities
of water. The extent of irrigation pumping from ground-water
supplies should therefore be determined on the basis of thorough,
long-time investigations of the quantity of annual inflow or recharge
to ground-water streams, basins, or reservoirs.
Essential decisions concerning development of ground-water sup-
plies for irrigation can be made after checking "yes" or "no" on
twelve important points, listed in the following questionnaire. The
answers shown are generally considered as indicating that ground-
water supplies can be developed satisfactorily.
A. Availability, quality, and depth of water:
1. Is a plentiful supply of water available?
2. Is water of the right quality available to per-
mit production of the desired crops?
3. Is water available at a depth that will permit
B. Trend of
4. Is thi
5. Is it i
6. Is it
7. Is dt
C. Legal or
8. Do tl
9. Is tl
D. Cost of
E. Land re
11. Is t
12. Is t!
can be she