EPA 430/9-74-006
             RETURN FLOWS
           Office of Water Program Operations
              Washington, D.C. 20460


             Arthur  L. Jenke,  Hydrologist

           Non-Point Source  Control  Branch

         Office of  Water Program Operations

           Environmental Protection  Agency
                     January,  1974
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price Jl.M

                     TABLE OF CONTENTS



ACKNOWLEDGEMENTS 	^...^	        viii

INTRODUCTION  	            1

     The Problem	            2


GENERAL	„	            7

     Irrigation Return Flow	            9

     Origin of Return Flow	           12

     Salt Accumulation in the Soil	           21


     Effect on Domestic Use	,	           24

     Effect on Agriculture	           26


     Colorado River Basin 	           33

     Upper Colorado River Basin Region 	           40

     Lower Colorado River Basin Region 	           45

     The Imperial Va,lley	           49

     The Coachella Valley	           55

     The Rio Grande Basin	           59

     Upper Rio Grande Basin	           59

     Middle Rio Grande Basin	•	           62

     Lower Rio Grande Basin	           64

     Pecos River Basin 	           67

     Central Valley Basin, California	           68

     Sacramento Valley 	           69

     Sacramento-San Joaquin Delta 	           69

     San Joaquin Valley	           72

     Yakima River Basin  	           75

     Snake River Basin 	           77

     Other Major Problem Areas  	           78


 *    Farm Water Delivery System  	           81

     Farm Water Management System	           93

     Water Application Methods	,	           96

     Surface Methods	           96

     Trickle and Drip Methods	           98

     Sprinkler Methods 	           99

     Subsurface Methods  	          100

     Minimum, Tillage 	          102

     Farm Water Removal  System  	          103

     Future Methods of Return Flow Control  	          107


     Technical	          110

     Institutional-Legal 	          113

GLOS SARY OF TERMS	          118

REFERENCES CITED 	          120

Cover Photograph:  Irrigated lettuce
in the Palo Verde  Valley,  California.
Water for the Palo Verde Project is
diverted from the  Colorado River.
Photo courtesy Bureau of Reclamation,
U.S. Dept.  of the Interior.


1.   Freeze protection afforded citrus nursery as a result
     of overnight irrigation in Florida.  Temperature was
     approximately 21 degrees fahrenheit for 8 hours.             10

2.   Destructive effect created by excessive amounts of
     tailwater being lost from irrigated field having too
     steep a grade for efficient irrigation.  Hudspeth            14
     County, Te xa s.

3.   Excessive amount of tailwater being lost from irrigated
     field.  Note water flowing across highway.  Hudspeth
     County, Texas.                                               15

4.   Considerable erosion caused by excessive irrigation on
     light sandy soil.  Gully depths are greater than two
     feet.  Near Caldwell, Idahq.                                 16

5.   Erosion caused by excessive irrigation.   San Diego
     County, California.                                          17

6.   Serious water erosion caused by excessive use of
     irrigation water on too steep slopes.  Approximately 75
     percent of the topsoil was lost in one irrigation,
     Fremont County, Wyoming.                                     18

7.   Irrigation waste water erosion on a cultivated field.
     Morrill County, Nebraska.                                    19

8.   Citrus grove abandoned as result of build up of salt in
     the soil.  Coachella Valley, California.                     21

9.   Salt damage to carrot crop, Coachella Valley,
     California.                                                  29

10.  Sugar beets growing sparsely along salt-encrusted
     ridges between irrigation furrows.  Irrigation water
     containing salts rose to the ridge surface through
     capillary action and evaporated, leaving the solids
     behind.  California.                                         30

11.  Salt buildup in soil results in extensive damage in
     this flax field as shown by the bare areas.  Imperial
     County, California.                                           31

12.  Aerial view of irrigated farmland southwest of Roll,
     Arizona.  Standing salty water and saline soils
     resulted in a less of approximately 1000 acres of
     crops.                                                        32

13.  Here high water table prevents removal of surface water
     after irrigation, resulting in ponding of water and
     drowning of crop.  Imperial Valley, California.               51

1U.  Tile, gravel and sights placed ahead of construction on
     an irrigated farm in the Imperial Valley, California.
     The tiling operation is engineered and constructed by
     the Imperial Irrigation District Engineering
     Department.                                                   53

15.  Typical discharge of tile drain designed to lower the
     water table beneath irrigated land.  Tile drainage
     commonly discharges into open collection ditches for
     ultimate disposal — in this instance into the Salton
     Sea.  Imperial Valley, California.                            54

16.  Grove of heavy-laden date palms near Indio, California
     in the Coachella Valley.  The Valley is one of a few
     areas in the United States where the date palm thrives.       57

17.  Seeding of presprouted rice using aircraft.                   70

18.  Application of pesticide by aerial crop spraying.             71

19.  Earthen water conveyance ditch being lined by spraying
     or "shooting" with concrete.  No reinforcement is used
     in this method.  Final County, Arizona.                       84

20.  Pouring concrete ditch with size 12 wire mesh being
     placed in the concrete.  This ditch is 34 inches deep
     with 1 to 1 side slopes.  Pueblo County, Colorado.            35

21.  The Delta B Canal, a large conveyance channel near
     Delta, Utah being  lined with plastic.  Two 32 foot
     plastic strips are being used to line the canal.              86

22.  A modern concrete-lined irrigation canal.  Note control
     gates which can be closed in order to regulate the flow
     of water into the desired channel.  The crop is
     alfalfa.  Installation is near Red Bluff, California.        87

23.  Steel mainline  (42 inch penstock) capable of delivering
     50 cubic feet per second of irrigation water to 3000
     acres of cropland.  Near Payette, Idaho.                     88

24.  Irrigation pipe being delivered by helicopter to site
     in mountainous terrain.  This 30 inch flume will
     deliver snow-melt runoff water directly to an open
     diversion ditch.  Near Gypsum, Colorado.                     89

25.  Earthen irrigation storage reservoir being lined with
     grout or "gunnite" reinforced with wire mesh.  Sealing
     the walls and floor of the structure virtually
     eliminates seepage.  San Diego County, California.           91

26.  Polyethylene lining being placed in large irrigation
     reservoir to render the water-holding facility
     impervious to leakage.  Riverside County, California.        -92

27.  On-farm irrigation tailwater return pit.  Intercepted
     water is recycled by pumping through a plastic pipeline
     to a concrete-lined ditch for reuse.  Near Pecos,
     Texas.                                                       106
     Significant Irrigation Areas in the Seventeen Western
     Conterminous  States.                                         37


     The information presented in this report has been drawn

from various sources.   The references cited represent a

worthwhile and useful  assemblage of publications on the

subject of irrigation return flow but is not intended to be

all-inclusive.  The Soil Conservation Service, USDA, and the

Bureau of Reclamation, USDI, have made a valuable

contribution in the form of both technical advice and

photographs of various aspects of problems associated with

irrigated agriculture and methods related to their solution.

     Technical advice, comment, review and editing were

provided by personnel of the Non-Point Source Control

Branch, Office of Water Program Operations, and by personnel

of other elements of the Environmental Protection Agency.


     Irrigated agriculture has been practiced in arid and

semi-arid regions of the world since the beginning of man's

civilized history.  Supplementary irrigation during the

growing season is becoming increasingly commonplace in humid


     The earliest known records of man's attempt to raise

crops using artificial application of water are found in the

Middle East and North Africa.  The remains of wells,

underground collection systems, dams, reservoirs, terraced

irrigation works, catchment basins, aqueducts and conveyance

channels in the Middle East all indicate that the land once

supported a large population with an advanced knowledge of

irrigated agriculture.  Today, this once verdant land is

largely barren and non-productive as a result of salinity

buildup in once-fertile valleys, salt marsh development,

denudation of topsoil by aeolian and fluvial erosion, sand

dune encroachment, and general deterioration.

     Of the world's nations, China irrigates an  estimated

182,855,000 acres (74,001,100 hectares), India 93,000,000

acres(37,637,100 hectares)  and the United States

approximately 44,000,000 acres (17,807,000 hectares).

Irrigated agriculture is practiced on about 10 percent of

the cropped land of the United States and yields about 25

percent of the total national crop value.


     Irrigation is not without dilemmas.  Serious problems

of salinization and water-logging of land commonly result

from inferior or inefficient irrigation practices.  The

problem of excessive salinization is not necessarily

confined to soil.  Increases in salinity of waters receiving

irrigation return flows have been occurring at an alarming

rate in the United States during the past two decades.

Water pollution resulting from irrigated agriculture

originates from both non-point, or diffuse, and point

sources.  The impact of agricultural irrigation wastes,

including salinity, sedimentation, pesticides and nutrient

runoff and organic debris, on water quality degradation has

only been recognized fully in recent years.  This was due to

the gradual development of the problem.   Significant

increases in irrigated acreage since the termination of

World War II, along with increases in the use of pesticides

and fertilizers have focused attention on water quality

deterioration associated with irrigation practices.

     This report is devoted primarily to an objective

presentation of the nature and extent of water quality

deterioration created by the introduction of salinity into

the aquatic environment by irrigation return flows.   While

it deals primarily with salinity, or total solids, it

recognizes that sedimentation, nutrients, pesticides,

organic debris, and heavy metals, among others, contribute

significantly to the problem of water quality degradation

throughout the nation.  Water uses affected are municipal,

industrial, commercial, downstream agricultural and

recreational, all of whom receive water of ever-diminishing

quality.  Deep percolation of irrigation returns is causing

increasingly significant pollution of the ground water en-

vironment in many parts of the nation.


1.   Irrigation, the artificial application of water to the

land, can result in serious water pollution problems in the

aquatic environment wherever it is practiced.

2.   Numerous water quality changes may take place during

irrigation.  The magnitude and nature of these changes are

functions of mineralization, evaporation, transpiration, ion

exchange, solution, leaching and biochemical action.

3.   Surface runoff water from irrigated lands may be

expected to contain a mineral composition similar to that of

the applied water, with a significant increase in

pesticides, fertilizers, organic debris, soil particles,

colloids, heavy metals and other pollutants derived from

accidental or purposeful placement onto the land.

U.   Irrigation water which has moved through the soil  (deep

percolation) may become burdened with excessive dissolved

solids, and possibly a change in ionic composition.    The

water may also acquire soluble fractions of fertilizers such

as nitrates.  A reduction in insoluble nutrients, degradable

pesticides, oxidizable organics, pathogenic organisms and

bacteria can be expected.

5.   Degradation of water quality can be costly to the
consumer.  Adverse economic effects on municipal/ industrial
and commerical users often necessitates increased and
expensive treatment.  Agriculture frequently experiences
impaired crop yields and greater water use requirements.
Deep percolation, often required to leach salts below the
plant root zone, may introduce toxic levels of nitrates into
the aquifer.

6.   Improved and modernized on-the-farm water management
practices represent the most feasible approach to the
abatement or elimination of water quality degradation caused
by irrigation return flows.  An acceptable control program
includes the application of recognized technology at the
pollution source.  This is in harmony with the time-honored
concept that pollution be abated at the source rather than
by applying treatment to the contaminated waters.

7.   Demonstration and pilot control projects designed to improve
on-farm irrigation efficiency should be afforded high prioritv
in the overall effort to abate pollution created by irrigation

8.   Legal and institutional factors combine to constrain more
efficient water practices, particularly in the Western

United States.  The concepts and rules of the prior

appropriation doctrine, in which water quality is not

considered, are major deterrents to the implementation of a

sound water management technology.   A possible solution may

lie in the reinterpretation of the doctrine.

9.   A piecemeal approach to the water quality degradation

problem caused by irrigation return flows will be

ineffective.  (Only a basin-wide total control program will

prpduce acceptable and lasting results.

10.  There is a need for additional documentation of

pollution caused by irrigated agriculture throughout the

nation.  Records currently available too often involve only

those areas where salinity is already acute.  Frequently,

the modifying or diluting effects of ample water supplies

mask continuing increases in salinity.  Well-planned

monitoring and surveillance programs will direct immediate

attention to seemingly inconspicuous problem areas and allow

corrective measures to be applied.

11.  The best available irrigation and drainage management

methods, aimed at assuring a minimum generation of wastes,

should be incorporated into the initial planning and

development of all future irrigation projects.


     Irrigation is the artificial application of water to

land to supply and maintain optimum soil moisture necessary

for plant growth.  In arid and semi-arid regions of the

world, irrigation accounts for almost all of the life -

supporting water for agriculture whereas  in sub-humid and

some humid areas irrigation is supplementary and principally

used to maintain soil moisture during periods of drouth.

     The practice of irrigation was known to the peoples  of

ancient Egypt and Asia Minor.  Irrigation systems in that

part of the world are evident today.  This beginning was  in

arid and semi-arid lands similar to those in many parts of

the Western United States.  Increases in population created

concentrations in cities and villages and a reduction in  the

nomadic way of life.  This created increased crop demands

and irrigated agriculture was the method that could assure a

continuous food supply on a reasonably reliable basis.

Irrigation was, and is, a science of survival.  Successfully

practiced, it enabled man to survive drouths, support larger

populations, and expand territorially and culturally.

     There are approximately 44,000,000 acres (17,807,000

hectares)  of irrigated land in the United States.  About  90

percent is in the seventeen western conterminous states*-

The balance lies in humid and semi-humid states where there

is a need for supplemental irrigation during periods of

drouth.  Florida, for example, ranks tenth in the national

inventory with 1,490,000 irrigated acres (603,000 hectares).

The importance of irrigated agriculture to the national

economy is apparent when it is realized that irrigation is

practiced on about 10 percent of the nations cropland and

generates approximately 25 percent of the total crop value.

     Irrigated agriculture accounts for about 35 percent of

the total water withdrawn in the nation for off-channel uses

and approximately 85 percent of the total national water

consumption.  The national annual irrigation water

requirement, projected to 1980, is placed at 140,000,000

acre-feet (172,688, 600, 000 cubic meters) (1).  This water

will be supplied from both surface and ground water sources.

     The application of water to cropland under controlled

conditions has many advantages.  It enables the equitable

distribution of water-soluble fertilizers,   liquefied animal
*Those conterminous states located west of the eastern
boundaries of North Dakota, South Dakota, Nebraska, Kansas,
Oklahoma and Texas

wastes, and pesticides.  Crop cooling to ensure continued

growth, and frost protection are additional benefits  (Figure

1) .  Partial control of date of maturity and subsequent

early harvest of crops such as fruits, vegetables and

flowers may also be achieved through irrigation (2).

l£Ei2§tion Return Flow

     Of the total water applied during irrigation, as much

as 65 percent may be used consumptively.  This use includes

loss by direct evaporation from the soil plus transpiration

from plants.  Consumptively-used water is that discharged

into the atmosphere as vapor and is no longer available for

reuse within or by the existing system.  The balance of the

applied water, or about 35 percent, is termed irrigation

return flow and finds its way back into the surface or

subsurface hydrosystem.  Irrigation return flow then, is the

water diverted for irrigation which returns to the surface

stream or to the subsurface ground water environment  (3).

     The practice of irrigation necessarily degrades the

quality of applied water to some degree inasmuch as the

water is used consumptively.  Evaporation and transpiration

alone may concentrate dissolved minerals in the applied

water as much as 300 percent.  In addition to an increase in

salinity, the applied water may acquire sediments,


FIGURE 1. Freeze protection afforded citrus nursery
          as a result of overnight irrigation in Florida.
Temperature was approximately 27 degrees  farenheit
for 8 hours.  Photo Courtesy Soil Conservation Service,
U.S. Dept. of Agriculture.

pesticides, fertilizers, organic debris, heavy metals, trace

minerals, farm oils and greases, bacteria (including

pathogenic organisms), nematodes and other forms of

pollution.  Salinity, a major water pollutant, and its

effect on the aquatic environment, is addressed in this


     Salinity increases associated with return flows may be

brought about by both consumptive and non-consumptive uses

of applied water.  The principal constituents comprising

return flow salinity are the water-soluble compounds of

calcium, magnesium, sodium and potassium.  Minor amounts of

iron, aluminum, manganese and other cations may also be

involved.  The dominant anions in the compounds are

carbonates, bicarbonates, sulfates, and chlorides.  Any

combination of these cations, and anions form the salts or

"salinity" of irrigation return flows.

     A basic process by which irrigation return flow

elevates the salinity of a hydrologic system with which it

is in contact is termed salt loading.  This process

increases the total salt burden of the receiving waters by

adding salts.  A second process is concentration, in which

the salinity of a water body or hydrologic system is

increased by evaporation.  Evaporation merely reduces the

amount of water but does not reduce the total quantity of


dissolved salt.  Return flows may be aggravated by non-

associated sources of pollution as natural salt flows,

mining, and oil field operations.  Additional sources

including municipal, commercial and industrial waste

discharges, together with runoff from urban, construction,

highway and agricultural sources may augment return flow

     Return flows originate from both surface and subsurface

sources.  Surface sources include bypass water, tailwater

(wastewater) , and the incidental source, precipitation.

Bypass water is that diverted for irrigation but returned to

the source without having been applied to the land.

Tailwater is the excess remaining after an irrigation and is

hopefully retained in ditches or in ponds.  The subsurface

source is water which has percolated through the soil

profile.  This water finds its way either to the zone of

ground water saturation or to the stream through artificial

drains or by shallow diffuse seepage (non-point sources)

along the stream bank.

     Excessive application of irrigation water often results

in tailwater losses as shown in Figures 2 and 3.   If

movement of the runoff is excessive, serious erosion may

occur and valuable topsoil lost  (Figures 4-7)

     Runoff may have high turbidity imparted by sediment.

Eroded soil particles may transport adsorbed contaminants

such as pesticides, fertilizers, and organic material.

Tailwater is exposed to other pollutants and may contain

non-adsorbed pesticides that were applied directly to the

soil or washed from the plant by rainfall or sprinkler

irrigation.  Soluble fertilizers, soil amendments, animal

wastes and organic constituents may also be found among

tailwater pollutants.  Evaporation accounts for further

concentration of dissolved contituents.  Finally, excessive

application may cause a significant rise in temperature

resulting from storage in pools, canals, laterals and

ditches  (4) .

     Bypass water ordinarily acquires relatively little

additional contaminant inasmuch as it represents water

routed through conveyance canals and ditches and which is

returned directly to the stream without having been applied

to the land.  It too, is subject to concentration through

evaporation and may be consumptively used.



    FIGURE 2.  Destructive  effect created by excessive
              amount  of  tailwater  being lost  from field
    having too steep  a grade  for efficient irrigation.
    Hudspeth County,  Texas.   Photo courtesy Soil
    Conservation Service,  U.S.  Dept.  of Agriculture.


       -  x.4.
                          .  ,_ . -. r .
FIGURE 3.  Execessive amount of tailwater being lost
           from irrigated field.  Note water flowing
across highway.  Hudspeth County, Texas.  Photo cour-
tesy Soil Conservation Service, U.S. Dept. of Agricul-

*_    . ••«?«- -
                                                        ,  v;,  -
                                                      " '•  I '1.1
                                                          .'.'v  •
     FIGURE  U.  Considerable  erosion caused by excessive
                irrigation on light sandy soil.  Gully depths
     are greater than  two feet.   Near Caldwell, Idaho.  Photo
     courtesy Soil Conservation  Service, U.S. Dept. of

FIGURE 5.   Erosion caused by excessive irrigation.
           San Diego County, California.   Photo cour-
tesy soil Conservation Service, U.S. Dept. of Agriculture.


                                                        ' ~

                  c;_ -
:.:,/^X  -"*4A''
'• "-»"*V%»f "^S-'
   -  •.'"^•**x"'- _",
    •  ' -   - *v •••*f^..
     FIGURE 6.   Serious water  erosion caused by excessive use
                of irrigation  water on too steep slopes.
     Approximately 75 percent  of  the topsoil was lost  in  one
     irrigation.  Fremont County,  Wyoming.  Photo courtesy
     Soil Conservation Service, U.S. Dept. of Agriculture.

FIGURE 7.  Irrigation waste water erosion on a culti-
           vated field.  Morrill County, Nebraska.
Photo courtesy Soil Conservation Service, U.S. Dept. of

     The applied water which percolates into the subsurface
plays the major role in the life-sustaining drama of the
irrigation event.  Normally, it is also the greatest
contributor to pollution in return flows.  A part of the
water is stored in the root zone where it is used
consumptively by crops.  The plant uses the pure-water
fraction of root-zone moisture and the remainder is left
with an elevated mineral (salt)  and soluble nutrient
concentration.  That water not retained in the root zone may
continue to percolate downward,  continuously acting as a
mineral solvent or leaching agent.  It may then move
laterally to seepage areas, be collected by artificial
drains, or ultimately find its way into the ground water
system.  The percolating fraction of applied water increases
the concentration of salinity in the return flow.  This
increase is inevitable and is an inherent part of the
irrigation scheme that must be recognized by agriculturist,
hydrologist, engineer and environmentalist alike.  The
concentration of mineral salts in irrigation return flow
from both leaching and evapotranspiration may range from
three to ten times that of the applied water.

§§i£ Accumulation in the Soil

     The introduction of irrigation into the field of

agriculture on a large scale has had the effect of diverting

salt to the soil.  This is salt that, in previous years, had

been dedicated by nature to the oceans.  Through irrigation,

salt is being intercepted enroute to its time-honored

destination, placed upon and through the soil mantle,

concentrated by evapotranspiration and leaching, and

returned to the stream.  This series of events may take

place many times in a single river basin or stream prior to

discharge.  Each use results in increased concentration and

the cumulative effect is the magnification of a normal salt

content several times that expected under non-irrigating

waterway conditions (5).

     Accumulations of salt in irrigated soil must be avoided

inasmuch as the land would soon become too saline to support

plant life.  If normal rainfall cannot flush the salt from

the root zone, excess water must be applied during regular

seasonal irrigations to prevent buildup.  The excess

represents the "leaching requirement" necessary to prevent

salt accumulation above a prescribed level.  Failure to

maintain the level can become a limiting factor to further

agricultural development in a given area.  The increased

application of water to achieve a proper leaching


requirement could result in waterlogging the land.  The

imbalance, if it occurs can be corrected by providing

adequate drainage.  Returns collected in drainage systems

may be highly saline.

     The degradation of water quality caused by increased

salinity may have far-reaching, accumulative effects on

subsequent beneficial use.  The use to which water is put

determines the level of quality required.  A particular

quality may have a detrimental effect on a specific use.

High quality water is required for municipal use and for

many industrial purposes.  The effects of moderate increases

in salinity on the well-being of adult aquatic animals may

be minimal.  However, spawning of certain fish species may

be impaired by salinities in the range of 500 milligrams per

liter, or even less.  Ascertaining water quality

requirements for aquatic life may be difficult inasmuch as

different species vary widely in their tolerence to salinity

and other dissolved substances during various life stages.

For other uses salinity levels can be moderately high and

not be particularly detrimental.  Among these are water

skiing, swimming, boating and hydroelectric power generation

and some commerical applications.

     Water is ordinarily categorized in terms of its

suitability for municipal, industrial, agricultural, and

recreational uses.  Some specialized industrial uses such as

pharmaceutical, food processing, textile manufacturing, and


laundering are often particularly sensitive to specific

dissolved elements in very low concentrations.   The

projected industrial growth and expansion of any area or

municipality may be limited by the quality qf the available

water supply.  Industries critically examine additional

costs involved in treatment necessary to upgrade water

quality at prospective plantsites.  These secondary costs

may be an important factor in determining the establishment

of highly desirable industries in areas that are otherwise

ideally situated with repsect to terrain, fuel, labor,

climate and accessibility.
          Domestic Use
     The use of water that is of direct personal concern to

the domestic consumer includes drinking,  food preparation,

laundering and personal hygiene among the most important.

Water high in dissolved solids may damage ornamental shrubs,

trees and lawns.  It can also be detrimental to water- us ing

home appliances.  Water high in calcium and magnesium salts,

termed "hard",  can cause scaling in hot-water heaters,

pipes, boilers, air-conditioning equipment and significantly

shorten their life.  The salts of calcium and magnesium,

unless eliminated by softening,  leaves scums, crusts,  curds

and rings on household utensils and fixtures  They also

cause yellowing of fabrics and toughen vegetables during


cooking.  Hard water requires excessive amounts of soap and

detergent, adding appreciably to household expense.  If the

water contains excessive chlorides and sulfates, corrosion

may replace scaling as the undersirable mechanism.  Salts of

these ions are more difficult and more expensive to control.

     The U.S. Department of Health, Education and Welfare,

Public Health Service, has published standards applicable to

drinking water and water supply systems used by public carriers

and other subject to Federal quarantine regulations.  The recom-

mended upper limit of total dissolved solids is placed at 500

parts per million (6).  The National Technical Advisory Sub-

committee on Public Water Supplies in its report to the Secretary

of the Interior, has expanded upon the Public Health Service's

Regulations with respect to drinking water standards.  The

Subcommittee prepared an in-depth review and reported its findings

and recommendations regarding water quality for Recreation and

Aesthetics; Public Water Supplies; Fish, Other Aquatic Life and

Wildlife; Agricultural uses including Farmstead Water Supplies,

Livestock and Irrigation; and Industry  (7).

     A severe municipal water salinity problem caused by

irrigation return flows recently occurred in the Lower

Colorado River.  Saline water in an aquifer underlying the

We11ton-Mohawk Irrigation District near Yuma, Arizona is

drained by a series of large-capacity wells drilled to

control the water table (8).   The discharged effluent

greatly increased the salinity of the Colorado River at

Yuma.  The company that supplied domestic water to the city

had to abandon its intake structures in the river and obtain

potable water by diversion at Imperial Dam, approximately 15

miles upstream.  Downstream users in Mexico, however, had no

alternative source of supply and the salinity of the

Colorado River flowing into Mexico is the subject of

international negotiations (9).

Effect on Agriculture

     Salinity created by irrigation generates additional

problems for the downstream user.  Saline water may increase

the salinity of the root zone environment of the soil.

Elevation of soil salinity may inhibit seed germination,

reduce crop yields and prevent the growing of crops having

low salt tolerances.  In extreme instances, salt buildup may

even cause the removal of land from agricultural production

(Figure 8).  Production of vegetable crops having low salt

                                   .  ;
                                                  -. -.-.'.
FIGURE 8. Citrus grove abandoned as a result of
          build up of salt in the soil.
Coachella Valley, California.  Photo courtesy
Bureau of Reclamation, U.S. Department of the

tolerances such as celery, beans, lettuce, carrots and

cabbage, together with melons and practically all citrus

fruits could be greatly reduced by soil salinity buildup

(Figure 9) .  These are high-value crops which contribute

substantially to the economic well-being of the grower.

Other money crops such as sugar beets and flax have suffered

damage from excessive soil-salinity (Figures 10 and 11).

Water quality criteria for irrigation and general

agricultural purposes have been developed by the Federal

Salinity Laboratory Staff (10).  These cover a wide range

and are closely interrelated with soil texture, infiltration

rate, drainage, climate and crop salt tolerance.

     As the salinity of applied water increases, a larger

quantity is ordinarily needed to prevent salt buildup in the

root zone.   In some soils continued irrigations using

limited amounts of water — only that necessary to maintain

field capacity -- will invarably induce salt concentration.

The buildup can progress to the stage where it adversely

affects the surface and greatly inhibits plant growth,

creates large "kill" areas and may ultimately result in the

abandonment of much land  (Figure 12).

     Many soils in their natural (virgin)  environment are

highly mineralized and may be either sodic or saline.  Sodic

FIGURE 9. Salt damage to carrot crop, Coachella
          Valley California.  Photo courtesy
Bureau of Reclamation, U.S.  Dept.  of the Interior.

FIGURE 10.     Sugar beets growing sparsely along
               salt-encrusted ridges between ir-
rigation furrows.  Irrigation water containing salts
rose to the ridge surface through capillary action
and evaporated, leaving the solids behind.
Photo courtesy Dept.  of Water Resources, State of

FIGURE 11.  Salt buildup in soil results in exten-
            sive damage in this flax field as shown
by the bare areas.  Imperial County, California.
Photo courtesy Soil Conservation Service, U.S. Dept.
of Agriculture.

FIGURE 12.  Aerial view of irrigated farmland south-
            west of Roll, Arizona.  Standing salty
water and saline soils resulted in a loss of approx-
imately 1000 acres of crops.  Photo courtesy Bureau
of Reclamation, U.S. Dept. of the Interior.

soils have a high exchangeable sodium ion content whereas

saline soils may contain excessive concentrations of soluble

salts other than, or in addition to, exchangeable sodium.

Both soil types require special management practices,

particularly when irrigated and subject to leaching,

inasmuch as the high concentrations of mineral constituents

impair their productivity  (10).  Leachates from these soils

may contribute significantly to return flow salinity.  It is

estimated that salt-affected soils comprise about 28 percent

of all irrigated acreage in the Western states.

     Excess water applied to the land to control root zone

salt must be removed or the land may become waterlogged as

the water table rises.  Measures to control the elevation of

the ground water table require drainage systems which in

turn requires high capital investments on the part of the

irrigator.  An example is the region in southern California

served by the Imperial Irrigation District and covering

553,000 acres (223,800 hectares).  Facilities to drain

saline irrigation return flows in the Imperial Valley have

required the construction of approximately 1375 miles (2210

kilometers)  of open drainage ditches and nearly 18,000 miles

(28,960 kilometers)  of subsurface drainage tile in an effort

to maintain a favorable salinity balance in the soil (11).

Current capital costs to install subsurface tile average

$2450 per mile.   The elaborate drainage system, designed to


maintain a favorable salt balance in the root zone, is

needed because of a predominance of clay and heavy loam

soils which impede downward percolation of water and

encourage salt buildup in the shallow zone.  Estimated

capital costs of pipe or tile drainage systems ranges from

$150 to more than $100 per acre, depending on the depth and

spacing of the pipe (12).  Avoidance of soil salinity

buildup and potential reduction of crop yields obviously

requires large capital outlays by the irrigator.

     Philosophically, detriments associated with water

degradation are fundamentally economic.  Any increase in

salinity results in an economic penalty inasmuch as

additional water is required for equivalent benefit (13).
     If water is degraded, the user must either apply more

water to the field to maintain crop yield or use the same

amount of water and risk a decrease in yield.  If more water

is required for leaching or to maintain salt balance, the

cost of water rises, installation of artificial drains may

be necessary, soluble fertilizer requirements may be

increased, labor costs may rise, and the danger of soil

damage resulting from sodium hazard may increase,   if

additional water is not available, the irrigator may have to

turn to more salt-tolerant crops.  In any event, the loss is

an economic one.

     Direct adverse effects to the plant from increased

salinity are;  reduction in osmotic action, decreasing water

uptake capability, and possible adverse metabolic reaction

with resultant toxicity.  Indirect adverse effects may

include impairment of surrounding soil structure. This in

turn may reduce permeability, porosity, and water

infiltration capability.


     Water quality problems of some type and magnitude exist

in every irrigated area of the nation.  These vary both in

intensity and kind of pollutant involved.  The most severe

return flow problems are found in the conterminous Western

States   (See Plate I).  Soils in these arid and semi-arid

regions are ordinarily high in residual mineral salts

inasmuch as they have not been subjected to extensive

leaching by rainfall or snowmelt as have those in the more

humid parts of the nation.  The soil profile developed in

sub-humid and humid regions is thick and relatively free of

readily-soluble minerals.

     There are several areas in the United States

categorized by agricultural, soil, irrigation and ecological

authorities as those in which water quality problems

associated with irrigation return flows are serious.

     The Colorado River Basin probably contains more major

salinity problem areas than any other in the nation.  It is

closely followed by the Imperial and Coachella Valley of

Southern California, the Rio Grande Basin of New Mexico,

Texas and Mexico, and the great Central Valley of California
which contains the agriculturally important San Joaquin and

                                    IN THE
Yaklma River Valley^
                                                       NORTH DAKOTA
 San Joaquln Valley
   Coachella Valley

     Salton Sea

   Imperial Valle
            Lower Colorado River Basin    Rlncon-Mesllla Valley
                                                             Lower Rio Grande Valley
           PLATE I

Sacramento Valleys.  These , together with several

additional, but less serious, areas are reviewed.
     The Colorado River heads on the east slope of Mt.

Richthofen in the northwest part of the Rocky Mountain

National Park, about 70 miles (113 kilometers) northwest of

Denver.  The river then flows west by south into the Gulf of

California 1450 miles  (2330 kilometers)  distant.  The

Colorado and its tributaries drain an area of approximately

255,000 square miles (582,750 square kilometers) or about

one-twelfth of the area of the conterminous United States.

It is unique among the great waterways of the world in that

its flow is completely "captured" by a series of large

reservoirs.  Among these are Lake Havasu, Mohave, Mead,

Powell, Flaming Gorge, Fontenelle, Navajo, Morrow Point and

Blue Mesa  (14).  The most acute problem facing future

development of water resources in the Colorado River Basin

is salinity.

     The basin is divided into an Upper and Lower Region by

the Colorado River Compact of 1922.  The Upper Region

contains 113,496 square miles (293,955 square kilometers)

located upstream from Lee Ferry, Arizona.  Irrigated

agriculture, a major industry,  utilized 1,621,500 acres


(656,220 hectares) of farmland in 1965 of which 99 oercent

were irrigated entirely from surface sources - the balance

being supplied by ground water (15).

     The total annual dissolved solids load  (salinity)

reaching Lee Ferry, Arizona, during the period 1941-1966 is

placed at 8,155,000 tons  (7,398,000 metric tons).   Of this

amount, the estimated loads contributed by irrigated

agriculture ranged from 1,995,000 to 3,320,000 tons

(1,809,800 to 3,011,800 metric tons).  This  range,

representing a variance of 24 to 41 percent  of the total

salt load points out a need to develop more  accurate

prediction of salinity caused by irrigation  return flows

(16) .  It is further estimated that nearly 90 percent of the

total relative salt load from irrigated agriculture in the

entire Basin originates in the Upper Region.

     The balance of the salinity in the River at Lee Ferry

is attributed to natural sources.  These are both non-point

or diffuse, and point.  The diffuse sources  in both the

Upper and Lower Basin are the most significant.

     The Lower Colorado River Basin Region lies downstream

from the Lee Ferry division point and contains 141,137

square miles (365,545 square kilometers).  Approximately

1,200,000 acres (485,640 hectares) of Lower  Basin farmland


were irrigated in 1965 under both organized irrigation

systems and privately- owned wells pumping from river

aquifers.  Of the total, approximately 895,000 acres

 (362,210 hectares) were located in the important Gila River

Subregion  (17) .

     It is estimated that only 12 percent Of the total

relative salt load from irrigated agriculture in the entire

Colorado River Basin originates in the lower portion.
      Colorado River Basin Region
     The Grand Valley irrigated agriculture area located in

the valley of the Colorado River both upstream and

downstream from its confluence with the Gunnison River in

western Colorado is the most serious salinity problem area

in the Upper Basin.  Deep percolation from excessive amounts

of applied water, plus leakage from old canal and ditch

distribution systems in the Valley reaches the underlying

saline aquifer developed over the highly mineralized Mancos

Shale of Cretaceous Age.  The excess water has elevated the

ground water table to the point where a substantial amount

of base flow is introduced into the Colorado River Channel.

This has added significantly to the salt load of the river.

The excessive amount of salt represents that dissolved from

the highly saline shale beds.  It is estimated that 88,000


irrigated acres  (35,315 hectares) in the Grand Valley

contribute about 8 tons of salt  per acre per year or a total

of 704,000 tons  (638,655 metric  tons) annually to the Upper

Basin.  This is an estimated 18  percent of the total

irrigated agriculture salt load  of the entire Colorado River

Basin!  (13).

     Deterioration of water quality in the Grand Valley

increased to the point where it  became the target of several

special investigations funded, in part, by the Environmental

Protection Agency.  Recent valley-wide land-use studies

indicated that almost 30 percent of the available

agricultural acreage in the valley has become unproductive

due to high water table and attendant salinity problems  (18,

19, 20,21) .

     Another major area of salinity created by irrigation

return flows is the Gunnison River - Uncompahgre River

Valley System in western Colorado south of Grand Valley.

The Uncompahgre Valley contains  6,000 acres  (2430 hectares)

of irrigable land from which the salt yield is placed at an

estimated 4.5 tons per acre per  year or a total contribution

of 27,000 tons (24,495 metric tons) annually.  The valley of

the Gunnison River and its tributaries contain 167.000 acres

(67,585 hectares) of irrigated land, most of which is

underlain by the highly mineralized  (gypsiferous)  Mancos

shale and yields and average of  6.7 tons of salt per acre


per year, or an annual total of 1,118,900 tons (1,015,045

metric tons) .  The significance of applying irrigation water

to soils derived from highly mineralized bedrock becomes

readily apparent.  The Gunnison-Uncompahgre complex accounts

for an estimated 29 percent of the total irrigation-

associated salt load of the entire Colorado River Basin.

The salt load of the combined irrigated area of the Grand

Valley and Gunnison-Uncompahgre Basins totals 47 percent or

almost one-half of the salt load from irrigated areas in the

entire Colorado River Basin.  Their combined yearly salt

contribution to the Colorado River is about 1,850,000 tons

(1,678,000 metric tons).

     Additional return flow problem areas in the Upper Basin

are located in the Green River Subbasin.  Relative salt

loads from irrigated agriculture in the Subbasin contribute

an estimated 32 percent of the total salt load of the entire

Colorado River Basin.  The Green River is the largest

tributary of the Colorado and drains parts of Wyoming,

Colorado and Utah.  The river and its tributaries contain

numerous irrigated valleys, several of which have

significant salinity problems associated with irrigated

agriculture.  Among the more important areas having return

flow problems are the Big Sandy Creek Basin in southwestern

Wyoming together with Ashley Valley and Duchesne Valley,both

in eastern Utah.


     The Big Sandy Creek Basin contains an irrigated area of

approximately 13,000 acres  (5260 hectares) underlain by

highly gypsiferous, relatively soluble, sedimentary rocks

which, upon weathering, form the soils that support

agriculture in the basin.   Irrigation return flows

contribute an estimated 5.6 tons (5.08 metric tons) of salt

per acre per year or a total of 73,000 tons (66,225 metric

tons) per year to the Green River System.

     Ashley Valley, located in northeastern Utah, also

referred to as the Vernal Unit Area, has long been

identified with water quality deterioration imparted by

irrigation return flow salinity.  The approximate 20,000

acres  (8,094 hectares) of irrigated land in the Valley

contributed an annual salt  load of 4.2 tons (3.8 metric

tons) per acre during the period of June 1965 to May 1966 or

a total of 84,000 tons (76,205 metric tons) to the Green

River.  The predominant ion is sulfate leached from

gypsiferous soils.  The Ashley Valley-Vernal locale, while

relatively small in areal extent, is intensely saline and

has been the subject of recent studies funded by the

Environmental Protection Agency and the Bureau of

Reclamation (22,23).

     The Duchesne area of northeastern Utah contains 166,000

acres (67,180 hectares)  of  irrigated land, mostly


concentrated in the valleys of the Uinta and Duchesne River

and their tributaries.  Return flows contribute an estimated

three tons of salt per acre per year or about 498,000 tons

(451,775 metric tons)  annually to the Green River System.

     Irrigation in the Price River Valley cf northeastern

Utah, located about 60 miles (97 kilometers) southeast of

Provo^ is developed in soils derived from the Mancos shale.

Approximately 20,000 acres (8100 hectares)  are under

irrigation and the total salt load attributed to return flow

could be as great as 8.5 tons (7.7 metric tons)  per acre per

year or 170,000 tons  (154,220 metric tons)  annually.

Difficulty has been experienced in attempting to establish

the total quantity of salt assignable to return flows in the

Valley.  The contribution of naturally-occurring salinity in

the area of ground water is known to be sizeable.  Both

irrigation returns and ground water in the Valley owe their

excessive salt pickup to leaching of soils developed upon

the Mancos shale.  The Mancos is an excellent example of an

off-repeated condition in arid lands in which a rock

formation, usually shale, is a valley-builder capable of

yielding gentle topgraphy well-suited to irrigated

agriculture but is at the same time capable of severely

degrading the quality of water applied to its weathered    *

mantle (soil).

Lower Colorado River Basin Region

     Significant increases in salinity in the Lower Colorado

River mainstem occur in its reaches upstream from Imperial

Dam.  This dam represents the southernmost point of

diversion of Colorado River water for irrigation in the

United States.  Principal increases in salinity involving

return flows originate in the Parker Valley, nearly all of

which lies within the Colorado River Indian Reservation.

The valley contains about 110,000 acres  (44,517 hectares)  of

river flood plain of which 31,700 acres  (12,830 hectares)

were irrigated in 1962.  The Reservation has unused water

rights sufficient to irrigate  an additional 67,500 acres

(27,320 hectares) which, if developed, will create a further

increase in the total amount of dissolved solids in the

downstream reaches of the river.  The projected increase

will be the result of salt concentration by stream depletion


     The Palo Verde Irrigation District located in the Palo

Verde Valley immediately downstream from the Colorado River

Indian Reservation contains approximately 85,000 acres

(34,400 hectares) under irrigation.  The district

contributes a salt load of about two tons per acre per year

to the mainstem.  Much of this is groundwater salinity

currently being withdrawn through deepened existing drains.


     The Colorado River emerges from mountainous terrain

fourteen miles upstream from Yuma, Arizona and is joined by

the Gila River.  The floodplain immediately below the

junction is an important irrigated area.  It widens

downstream from Yuma and merges with the Colorado River

delta system, a vast arable plain, which extends westward to

the Salton Sea Basin and south to  the Gulf of California

(8).  Agriculture, the mainstay of the area's economy is

made possible by irrigation with Colorado River water

diverted at the Imperial Dam located 26 miles (42

kilometers) upstream from the Northern International

Boundary with Mexico.  This great diversion point supplies

the Yuma, Gila and Wellton-Mohawk irrigated areas in Arizona

and the Imperial and Coachella Valleys in California through

two major conveyances — the Gila Gravity Main Canal into

Arizona and the All-American  Canal into California.  The

total annual diversion of water from the Imperial Dam into

the canals is approximately 6,000,000 acre-feet

(7,400,940,000 cubic meters).  Water is also released at

Imperial Dam for delivery to Mexico under provisions of the

1944 Treaty with that country.  Summarizing, most of the

Colorado River water used in the United States is diverted

at the Imperial Dam.

     The major irrigation return flow salinity problem in

the Lower Colorado region is that created by ground water


pumped to control water levels beneath the Wellton-Mohawk

Irrigation District in the Gila River Valley.  The pumped

water  was originally discharged into the Colorado River

downstream from Imperial Dam.  Past irrigation during the

early part of the century used ground water pumped from an

aquifer underlying Wellton-Mohawk and eventually increased

the salinity of the water to the point where it was no

longer usable.  The increase in salinity is a classic

example of the combined effect of continued evapotran-

spiration of the applied water plus deep percolation of the

remainder (irrigation returns) to the aquifer from which it

was withdrawn.  The irrigation water was, in essence,

continuously recycled.  Inauguration of the Gila Project

revived irrigation in the Gila Valley.  Subsequent

application of Colorado River water diverted at Imperial Dam

elevated the water table and the Wellton-Mohawk area became

waterlogged.  Land reclamation required much larger

quantities of water than were originally anticipated.  High

capacity withdrawal wells were drilled, beginning in 1955,

to control ground water levels.  The quality of the effluent

discharged into the Gila River underwent severe

deterioration during the summer of 1961.  During that year

returns from more than 60 wells in the Wellton-Mohawk Valley

were discharged into a wastewater conveyance channel  (the

Wellton-Mohawk Main Outlet Drain) which emptied into the

Gila River.   The problem was aggravated by greatly increased


pumping rates and the development of additional wells.  The

result was an alarming elevation of salinity in the Colorado

River immediately north of the international boundary.  The

salinity trend has since reversed and the quality of

We11ton-Mohawk drainage has shown steady improvement.  It

reached a maximum of 6,000 parts per million total dissolved

solids in 1961, then decreased to an average of 4,620 ppm

during the water year 1966 and to 4,100 ppm in 1969 (9,12).

     The control of salinity of Colorado River water

reaching Mexico has been the subject of international

discussion and negotiation.  Initial control measures

designed to reduce the salinity included the release of

additional water at Imperial Dam to provide dilution; the

elimination of several highly saline drainage wells in the

Wellton-Mohawk Project; and the construction of a concrete-

lined conveyance channel to divert undesirable saline

drainage to the Colorado River immediately downstream from

Mexico's Morelos Dam.  Morelos dam is the point of diversion

of water for irrigation in Mexico's Mexicali Valley, a

southward extension of the Imperial Valley.  The concrete-

lined conveyance channel was constructed in fulfillment of a

formal international agreement with Mexico and was placed in

service on November 16,1965.  While the primary function of

the channel is to divert saline returns downstream of the

Morelos Dam,  provision is made for directing the flow into


the Colorado River either upstream from or downstream from

the dam if requested by Mexico.

The Imperial Valley

     The Imperial Valley of California, located south of the

Salton Sea is a broad, flat plain flanked by low, barren

mountain ranges and is a part of an elongated desert valley

extending northward from the Gulf of California.

Physiographically, it is a segment of the Colorado River

delta fan tributary to the Salton Sea Basin (24).  The

valley is a closed depression and represents the southern

part of the bed of ancient Lake Cahuilla.  Most of its area

is below sea level.

     The Imperial Valley is one of the most intensively

irrigated areas in the world.  Agricultural production

depends entirely on water supplied from the Colorado River

through the Ail-American Canal.  The average annual rainfall

in the region is about 3 inches (7.6 centimeters).

Approximately 475,000 acres (192,250 hectares)  were

irrigated in 1971, yielding a gross value of agricultural

products in excess of $300,000,000.

     The control of salt buildup in Imperial Valley soils

caused  by consumptive use of irrigation water requires

continual leaching and carefully controlled irrigation

management practices, particularly with respect to amount,

frequency and methods of water application.  The physical

and chemical properties of the soils require additonal

management practices to prevent salt accumulation in the

plant root zone.  The salts in the soil lend themselves

readily to leaching, and are composed principally of the

chlorides and sulfates of sodium, calcium and magnesium.

     About 50 years ago it became apparent that drainage of

the valley soils was grossly inadequate.  A rapidly rising

water table along with an alarming increase in ground water

salinity combined to seriously affect crop productivity.

Figure 13 illustrates land and crop damage associated with

high water tables in the Valley.  The Imperial Irrigation

District initiated the installation of a series of open

drainage ditches to depress the water table and conduct

returns to the Salton Sea.  Construction of a tile drainage

system to augment the surface drainage network and further

remove accumulated saline ground waters that threatened to

waterlog the valley began as early as 1929.  Today there are

17,834 miles (28,695 kilometers)  of tile drains serving more

than 377,000 irrigated acres (152,570 hectares)  in the

valley.   The type of tile drain used in the valley and the




FIGURE 13.  Here high water table prevents removal of
            surface water after irrigation, resulting
in ponding of water and drowning of crop.   Imperial
Valley, California.  Photo courtesy Soil Conservation
Service, U.S. Dept. of Agriculture.

method of discharge of collected irrigation return flows

into conveyance ditches are shown in Figures 14 and 15.

     It is necessary to earmark about 20 percent of the

total irrigation water diverted to the Imperial Valley for

root zone leaching in order to achieve a condition wherein

the total annual quantity of salts removed is somewhat

greater than the total annual quantity introduced.  Also, as

the salinty of the source water, diverted from the Colorado

River increases, the leaching requirement Will have to be

increased (27).  Salt balance in Valley soils was initially

achieved in 1946 and has been maintained continuously.

     Furrow irrigation is the water-application technique

used almost entirely in the Imperial Valley because of the

low infiltration rates and elevated soil salinities*  The

more versatile and efficient sprinkler methods are seldom

used due to the relatively high concentration of salt in the

applied water coupled with the very high summer

temperatures.  Rapid drying of saline water on the leaf

surface leaves a toxic concentration of salt and often

results in the death of the foliage (27).

     Irrigation return flows from the Imperial Valley amount

to approximately 900,000 acre-feet (1,110,140,000 cubic

meters)per year, all of which is discharged into the Salton


FIGURE 11.  Tile, gravel and sights placed ahead of
            construction on an irrigated farm in the
Imperial Valley, California.  The tiling operation is
engineered and constructed by the Imperial Irrigation
District Engineering Department.  Photo courtesy Soil
Conservation Service, U.S. Dept. of Agriculture.

   FIGURE 15.  Typical discharge of tile drain designed to
               lower the water table beneath irrigated land.
   Tile drainage commonly discharges into open collection
   ditches for ultimate disposal — in this instance into
   the Salton Sea.   Imperial Valley, California.  Photo
   courtesy Soil Conservation Service U.S. Dept. of Agriculture.

Sea and represents 90 percent of the total annual inflow

into that body.
The^Coachella Valley
     Irrigation return flow problems in the Coachella Valley

are similar to those in the Imperial Valley.  The Coachella

Valley is an intermontane, linear depression located

immediately north of the Salton Sea and represents the

northern part of the elongate alluvial limb of the Colorado

Desert which extends northwestward from the Gulf of

California.  A portion of the Valley is located within the

downstream segment of the Whitewater River Basin and is

flanked by the Little San Bernardino Mountains on the

northeast and the Santa Rosa Mountains on the southwest.

The southern part of the Valley is the bed of ancient Lake

Cahuilla which now contains the recently-formed Salton Sea*.
*The present Salton Sea was formed during 1905-1907 when more
than 16,000,000 acre-feet  (19,735,840,000 cubic meters) of
Colorado River water poured through several breaches in the
river levee system and flowed westward into the Salton

     Coachella Valley is one of the few areas in the United

States where select date palms can be successfully grown.

An experimental station was established by the government in

1904 to study and develop date palm culture in this country.

Choice date palm varieties were imported from Egypt and

Algeria and irrigated groves established (24).  The

production of dates now represents an important aspect of

the economy of the Valley.  (Figure 16).

     Ground water resources were developed early in the

agricultural history of the Coachella Valley.   As water

levels declined, Colorado River water was imported into the

area, beginning in 1948, through the Coachella Branch of the

All-Americah Canal.  The availability of ample water,

accompanied by expanded irrigation activity, resulted in the

development of a shallow, perched ground water body.  The

installation of tile drainage designed to combat the high

water table began in 1950 and continues.  More than half of

the 60,000 irrigated acres (24,280 hectares) in the valley

which overlie areas of restricted ground water movement have

been tiled.   Salt balance studies indicate that the annual

tonnage of salt in the return flows exceeds that applied

during irrigation (28) .  The leaching fraction of the

Coachella Valley is approximately 30 percent.   Continued  .

high water requirements for leaching will have to be


FIGURE 16.     Grove of heavy-laden date palms near
          Indio, California in the Coachella Valley.
The Valley is one of the few areas in the United States
where the date palm thrives.  Photo courtesy Bureau
of  Reclamation, U.S. Dept. of the Interior.

maintained.  Return flows from the Valley amount to about

100,000 acre-feet (123,349,000 cubic meters)  annually and

are discharged into the Salton Sea.

     Irrigation return flows from the combined Coachella and

Imperial Valleys literally control the quantity, quality,

and related problems of the Salton Sea inasmuch as the total

annual inflow into this body of water is composed almost

entirely of irrigation returns.  Saltwater sport fish were

introduced into the Salton Sea when its salinity reached

approximately 35,000 ppm or that of the oceans.  Its

salinity is currently about 37,000 ppm and rising, which

means that sport fishing and associated recreation may soon

terminate if the salinity increase is not arrested.

Reduction of salinity can be accomplished by augmentation

with fresh or low-salinity water.  This, in turn would

involve either importation from out-of-basin sources,

desalination of all or part of the return flows or other

costly approaches (29).   Costs involved in desalting a

portion of the Coachella drainage waters were studied

recently by the Office of Saline Water and the Bureau of

Reclamation (30).  Cost estimates, based upon 2870 ppm

feedwater and 400 ppm product water, ranged from $220 to

$297 per acre foot, using electrodialysis and multistage ,

flash distillation respectively.

The Rio Grande Basin

     The Rio Grande Basin is divided into four geographical
segments for purposes of water-use discussions.  These are
the Upper Basin, Middle Basin, Lower Basin and the Pecos
River Subbasin.  The Rio Grande River begins in southwestern
Colorado on the east flank of the San Juan Mountain range
and flows approximately 1,900 miles  (3,057 kilometers) south
and east into the Gulf of Mexico at Brownsville, Texas.

Upper Rig Grande Basin

     The Upper Basin, located between the headwaters of the
river and Ft. Quitman, Texas, drains an area of about
32,000 square miles  (82,880 square kilometers).  Important
irrigated segments begin with San Luis Valley, located
adjacent to the headwaters of the river in south-central
Colorado.  The valley is a down-faulted, relatively flat,
high-altitude depression bounded by the Sangre de Cristo
Mountains on the east and by the San Juan Mountains on the
west.  Its northern part is a closed depression into which
surface drainage converges.  The valley contains very large
amounts of surface and subsurface water.  Estimated ground
water storage in the aquifer system underlying the valley is
placed at more than two billion acre-feet (2,466,980,000,000
cubic meters).  This water is contained in several porous


formations comprised primarily of extrusive rocks

represented by volcanic flows, tuffs, breccias and debris.

The thickness of this multiple aquifer may be as great as

30,000 feet (9,145 meters).  The uppermost aquifer is

unconfined, extensive and contains water at depths normally

less than twelve feet.  Recharge is chiefly from percolation

of applied irrigation water,  leakage from canals and

ditches, and precipitation.  Principal recharge to the deep

aquifer system is through infiltration from mountain streams

flowing across alluvial fans  edging the valley.

     Irrigation, dating to 1880, is vital to agriculture in

the  San Luis Valley inasmuch as the average annual rainfall

is only eight inches.  During the period 1880 to 1950 the

principal source of irrigation water was surface supplies

(31).  Excessive irrigation returns waterlogged a part of

the valley in the early part  of this century and a drainage

network was constructed between 1911 and 1921 in an attempt

to dewater the land but the problem created by the

excessively high water table  remains, at least in part, to

this day-

     Subirrigation is practiced in the San Luis Valley and

tends to aggravate the waterlogged condition.  This method

of applying water is common is some areas of the United

States and can be highly efficient if water levels are


carefully regulated.  Subirrigation requires a high water

table, water in continuous supply, and controlled drainage.

     The quality of the shallow ground water has

deteriorated as a result of mineral concentration caused by

comsumptive use and valley soils have been adversely

affected by significant alkali buildup.

     Irrigation is also practiced downstream from San Luis

Valley in the middle section of the Upper Rio Grande Basin

between the Colorado state line and San Marcial at the head

of Elephant Butte Reservoir.  Historically, irrigation was

practiced in this reach of the river during the Pueblo I and

Pueblo II eras, (700 to 1050 A. D.)  and it is estimated that

at the time of the arrival of the Spanish in the 16th

Century, 25,000 acres (10,120 hectares) were being

irrigated.  The first Spanish irrigation ditch was built in

1598 about 30 miles north of Santa Fe, New Mexico (32) .  A

recent study of water usage on the Upper Rio Grande (33)

placed the total irrigated land in the middle section at

approximately 150,000 acres (60,705 hectares).  Consumptive

ground water losses in the section are particularly high as

a result of phreatophyte usage.

     This reach of the river is served by several

conservancy and irrigation districts, some organized as


early as 1915, and numerous community ditch systems.

Agricultural production is confined chiefly to small

subsistence-type farms.  The main products are fruits,

garden vegetables, hay, forage crops and cotton.  Irrigation

return flow problems are beginning to receive attention in

this area and several significant investigations are in the

planning stage.

Middle Rio Grande Basin

     The Rincon and Mesilla Valleys lie along a 108 mile

reach of the Rio Grande River in the Middle Basin between

the Caballo Dam in New Mexico, and El Paso, Texas.  The

Rincon Valley contains about 15,000 irrigated acres (6070

hectares) and the Mesilla Valley about 70,000 irrigated

acres (28,330 hectares).  Salinity studies conducted over a

period of 20 years by Wilcox  (34), indicated an increase of

272 ppm, due almost entirely to the effect of salt loading

resulting from irrigation return flows in the Rio Grande

River between the Caballo Dam and El Paso.  Water quality

deterioration in the Rincon and Mesilla Valleys has been

accelerated by the increased consumptive use of ground water

for irrigation brought about by the drought of 1951 to 1957

when a critical surface water shortage existed.  More than

1700 water-supply wells were completed in the alluvial

aquifer during this period.  Today approximately 42 percent


of the water used in the Rincon and Mesilla valleys is

supplied by wells.  The average salinity of water taken from

a representative group of these wells indicates that the

ground water is considerably more saline than that in the

river  (35).  There is little doubt that the salinity of both

ground water and the river will continue to increase as a

result of use and reuse together with attendant

concentration through evapotranspiration.  The effects of

the deterioration of water quality will be increasingly

reflected in damage to valley soils.

     The overall efficiency of irrigation in the Rincon-

Mesilla Valley ranges between 40 and 50 percent.  Re-stated,

this means that as much as one-half the applied water is

lost by deep percolation.  The quality of the percolating

water is seriously degraded as it passes downward to the

water table.  Experimental research is currently underway to

reduce the amount of return flows through more efficient

application of water to the land.  The effects of trickle or

drip irrigation on water use efficiency in the area are also

under investigation (35).

     The quality of water in the Rio Grande River,

aggravated by irrigation returns, is of particular

importance to the cities of El Paso and Juarez.  Both are

growing rapidly and long-term projections indicate that


their municipal and industrial water needs may eventually

require the entire river flow.  Pumpage for municipal

purposes accounted for about 56 percent of the water used in

1960 and the ground water source which receives its recharge

from the river will continue to be relied upon to produce

the major part of future requirements.
     The Lower Rio Grande Basin includes the downstream

drainage area between Ft. Quitman, Texas and the Gulf of

Mexico.  The river marks the International Boundary between

the United States and Mexico throughout this reach and is

joined by several important tributaries originating in both

countries.  Among these are the Pecos and Devils Rivers in

the United States and the Rio Conchas, Rio Salado and the

Rio San Juan in Mexico.

     The principal irrigated area in the United States lies

in Hidalgo, Willacy, and Cameron counties in the Lower Rio

Grande Valley.  The gross value of Valley agricultural

products is about $100,000,000 per year.

     The fertile lands of the Lower Rio Grande Valley are

dependent upon water from the river for irrigation.

However, this source is supplemented during drought periods


from about 1500 irrigation wells capable of providing an

additional 2,200 acre-feet (2,713,680 cubic meters) daily.

Poor quality of the return flow limits the use of drainage-

canal water but this source is also used as a supplemental

supply during periods of serious drought.  Drainage water

from the Texas side of the Rio Grande is not returned to the

river but is diverted to the Gulf of Mexico through the

Laguna Madre.

     The irrigated area is essentially deltaic, relatively

flat, low-lying, and slopes gently to the northeast from the

Rio Grande River toward the Gulf of Mexico.  There are few

natural channels for the removal of surface waters.  The

surface drainage problem is so severe that much of the

surface runoff from Hidalgo County must flow overland

through Willacy County to reach the Laguna Madre.

     Numerous underground drains have been installed but are

inadequate and have failed to keep pace with drainage needs.

The subsurface drainage problem is aggravated by over-

irrigation, excessive seepage from unlined irrigation

canals, undersized outlets, or even complete lack of

outlets, plus excessive water contributed by high intensity

storms and hurricanes (36).  Periodic hurricane-associated

floods may inundate the land for days or even weeks.

     This impairment of subsurface drainage is reflected in

surface drainage deficiencies.  Surface drainage ditches

lack depths sufficient to adequately lower the ground water

table.  Additionally, they are overloaded, suffer from

improper maintenance, structural deterioration, and lack

adequate outlets.  Numerous surface obstructions such as

roads, railroads, highways, canals, and drainways restrict

runoff and further aggravate the problem.  Frequent

waterlogging of a significant portion of the valley creates

serious problems involving ground water salinity and salt-

laden soils.

     The Comprehensive Study and Plan of Development, Lower

Rio Grande Basin, Texas (36)  states that the valley contains

690,000 acres (279,245 hectares)  of irrigable land having a

high water-table problem and, of this amount, 655,000 acres

(265,080 hectares)  have attendant salinity problems.  It is

estimated that crop yields are currently being reduced at

the rate of 10 to 15 percent by excessive salinity and in

some areas croplands may have to be removed from production

- a condition that will progressively worsen with time if

remedial steps are not taken.  The drain waters frequently

contain domestic sewage, untreated cannery and other food

processing wastes,  phosphates, pesticides, organic residues,

bacteria and silt.   At periods of low flow the chemical and

bacteriological  quality  of  the  irrigation  returns is very
     The Pec os River  is the  principal tributary of the Rio

Grande River in the United States.  Approximately 200,000

acres  (80,940 hectares) of agricultural  lands are being

irrigated in the Pecos River Basin in New Mexico.  Of this

amount, about 40,000  acres  (16,190 hectares) are being

irrigated using surface water; 125,000 acres  (50,590

hectares) using ground water and 35,000  acres (14,165

hectares) using combined  sources.  Principal crops in the

Basin are cotton and  alfalfa.  Secondary crops are grain

sorghum, barley and wheat.   The average  yearly consumptive

irrigation usage ranges from 0.85 to 1.8 acre- feet per acre

(2625 to 5550 cubic meters per hectare).

     It has been stated that "For its size, the Basin of the

Pecos River probably  presents a greater  aggregation of

problems associated with  land and water  use than any other

irrigated basin in the United States. ..." (37) .  Salinity

problems are particularly acute and irrigation return flows

add significantly to  the dissolved solids content of the

river, principally in the Middle and Lower sub-basins in New

Mexico and Texas.  Very heavy growths of phreatophytes and


other vegetation plus saline loads from salt springs and oil

field brines combine tc further deteriorate water quality.

Studies to date regarding Pecos Valley return flow problems

are rather generalized and sparsely documented.  However,

programs looking toward solutions to the problem of water

quality deterioration in the Pecos Valley are in the

planning stage.

Central^ Vail ey_Basj.nt_Calif2£nia

     The Central Valley Basin of California constitutes the

largest irrigated area in the United States and is not

without its share of water quality problems resulting from

irrigation return flows.  The valley is in the form of a

northwest trending, elongate bowl, bordered by mountains.

The lone outlet is a gap on the west in the San Francisco

Bay area through which the Sacramento and San Joaquin Rivers

discharge to the Pacific Ocean.  The Basin is roughly 500

miles (805 kilometers) long and 120 miles  (195 kilometers)

wide and constitutes more than one-third of the entire area

of the state.  It contains about 10,000,000 acres  (4,047,000

hectares)  of cropland of which approximately 6,000,000 acres

(2,428,200 hectares) are presently under irrigation.  The

Central Valley is roughly divided into three segments termed

the North or Sacramento Valley, the Middle or Delta area,

and the South or San Joaquin Valley.


Sacramento Galley

     The Sacramento Valley contains approximately 1,000,000

irrigated acres  (404,700 hectares).  Among important crops

produced is rice.  This cereal grain represents a major

commodity and its cultivation is carried out using modern

methods.  Aerial techniques are used to seed presprouted

rice and to apply pesticides and fertilizers.   (Figures 17

and 18JL  The quality of the applied water is very good.

Deterioration is largely caused by excessive nutrients

(nitrates and phosphates) and pesticides, with only nominal

problems associated with salinity.  During the early period

of development of irrigated agriculture in the Valley, water

was obtained from wells but in recent years surface supplies

have been rapidly replacing subsurface sources.  Development

of additional water resources has brought about increased

irrigation and attendant drainage problems associated with

high water tables created principally by excessive water

application.  It is estimated that approximately 50,000

acres  (20,235 hectares) are affected in this manner in the

Sacramento Valley (27).

Sacramento-San Joaquin Delta

     The Delta area, also known as the Delta Lowlands,

contains 738,000 acres,  (298,670 hectares)  of which more



                     '••>' aSH*
FIGURE 17.  seeding of presprouted  rice using air-
            craft.  Photo  courtesy  Soil Conservation
Service, U.S. Dept. of Agriculture.

FIGURE 18.  Application of pesticide by aerial
            crop spraying.  Photo courtesy Bureau
of Reclamation, U.S. Department of the Interior.
                            AWBERC LIBRARY U.S. EPA

than 500,000 acres (202,350 hectares) are in irrigated

agriculture.  The Delta is located at the confluence of the

Sacramento and San Joaquin Rivers and is one of the most

productive in California.

     The Delta is unique inasmuch as a significant amount of

its cultivated acreage lies below the level of the Delta

channels and the water must be siphoned over the channel

levees into deep drainage ditches where irrigation is

accomplished by capillary movement upward from the water

table into the plant root zone.  Salts accumulate in the

root zone and must either be removed or reduced to non-toxic

levels.  This is accomplished by periodic leaching, usually

during the winter months, and the saline return flows

discharged to the channel system.

San^Jgaguin Valley

     The San Joaquin Valley contains over 7,000,000 acres

(2,832,900 hectares)  of irrigable land of which slightly

less than 4,000,000 (1,618,800 hectares)  are currently

developed.  Of this amount, 2,700,000 acres (1,092,690

hectares)  are located in the Tulare Lake Basin at the

southern end of the valley.  The importance of the San

Joaquin Valley as an agricultural province is readily

apparent when it is realized that the valley contains about


40 percent of the irrigable land of California.  Rapid

expansion of irrigation in the San Joaquin segment of the

Central Valley was stimulated by construction of the

California State Water Project, the Federal Delta - Mendota

Canal, and the San Luis Project,

     Salinity of irrigation returns is significant in the

valley.  Additionally, and of great importance, is the high

nitrate content, the source of which is inherent in the

soil.  The total solids content of irrigation water supplied

from the Sacramento River system ranges from 500 to 700

parts per million.  Severe degradation of quality resulting

from concentration through consumptive use and leaching of

natural salts, including nitrates and boron compounds from

the soils by deep percolation, has occurred and is

progressively worsening.  The salinity of some returns has

reached 20,000 ppm (27).  Deterioration of water quality is

often accompanied by high water tables in areas where

subsoil permeability is restricted and irrigation is

intensive.  Extensive damage to crops and soil has occurred

as a result of these factors.  Tile drains have been

emplaced beneath 34,000 acres  (13,760 hectares) in an

attempt to alleviate the problem.  It is estimated that the

amount of acreage actually benefited is much greater

inasmuch as the drainage network intercepts subsurface water

from adjacent and upslope areas  (38).  Plans call for


construction of a massive complex of tile drains beneath an

additional 300,000 acres (121,410 hectares)  of valley land. ,

     The effluent from the drainage system is either

returned to the San Joaquin River or recycled into the canal

delivery system.   The discharge of the returns into the

river poses a serious threat to the ecology of the San

Francisco Bay system.  The most troublesome pollutant is

nitrate.  Construction of the San Joaquin Master Drain, a

joint U.S. Bureau of Reclamation and California Department

of Water Resources project designed to collect, transport

and discharge the highly saline and nitrate-charged

agricultural waters from the valley to the Sacramento-San

Joaquin Delta will aggravate the ecological problem.

Evaluation of the effect of the discharge on the quality of

Delta and Bay waters has been undertaken by the Central

Pacific Basins Comprehensive Water Pollution Control Project

of the Federal Water Pollution Control Administration,

predecessor of the Environmental Protection Agency  (39).  An

additional study has been made by the California Regional

Water Quality Control Board (40) ..  Proposed methods of

denitrification of Master Drain waters include both

bacterial, and algal productioniand harvesting (algae

stripping) .  The study also considered desalination of the

wastewater to remove salts, including boron compounds.

     Summarizing, the vast San Joaquin Valley agricultural

province is beset by a complex set of return flow problems

including high concentrations of natural salts, toxic boron

compounds, excessive native  (plus applied)  nitrates, high

water tables and poor drainage conditions.

Yakima River_Basin^Washington

     The Yakima River Basin, located in south-central

Washington, contains about one-half million irrigated acres

and is one of the most intensively farmed in the United

States.  Five government-owned irrigation facilities plus

several privately-owned systems and districts serve the

Basin's water needs.

     Ample supplies of water in the Yakima Valley during the

early days of irrigation resulted in the application of

large quantities to the land.  Following a long history of

excessive irrigation, waterlogging of the soils occurred as

the ground water table rose and finally reached a point

where surface water accumulated in areas of inadequate

drainage.  Evaporation of the ponded water left a toxic

concentration of salts both on the surface and in the

shallow root zone and large amounts of land were severely


     Concentration of mineral salts^ in irrigation water

returning to the Yakima River system, particularly after

multiple diversions is caused principally by consumptive

use, leaching, and ion exchange.  Return flow quality is

also affected to a significant degree in the basin by

nutrient application, erosion, and crop removal.  A detailed

study of the return flow problem by the University of

Washington pointed to the excessive application of water as

the major source of deterioration of irrigation returns in

the Basin (4l).  It is estimated that 6*6 acre-feet per acre

(20,350 cubic meters per hectare) are diverted to the

surface and, of this amount, about 4.25 acre-feet per acre

(13,100 cubic meters per hectare) are actually applied to

the land.  The balance is lost in conveyance channels by

seepage, wastage of various forms, and evapotranspiration.

The study concluded, in part, that irrigation return flows,

both surface and subsurface, were the responsible factor in

influencing the overall water quality of the Yakima River.

It further concluded that excessive application of water was

instrumental in elevating the ground water table and

degrading ground water quality; that quality was lessened by

the addition of minerals and soluble nutrients to a degree

where the dissolved solids content increased approximately

five times that of the adjacent surface water; and, that

leaching and ion exchange were the mechanisms largely

responsible for the change in water composition.


     Crops irrigated with water affected by irrigation

returns in the valley were also heavily infested with

parasitic nematodes.  Unusally high sediment loads, together

with attendant adsorbed fertilizers and pesticides are

common in Basin return flows and are often of greater

importance than the effects of salinity on water quality

deterioration.  Excessive water application is responsible

for the high sediment loads.  A. study of the effects of

sedimentation in the Basin's Roza Irrigation District has

recently been undertaken  (42).  Investigators found that

sediment concentrations in return flows, even under the best

current irrigation system management, failed to meet the

water quality standards established by the Washington State

Department of Ecology, the standards-setting agency.

Returns often contained turbidity values in excess of 400

JTU  (Jackson Turbidity Units).  State standards require that

turbidity, even in Class "C" waters not exceed 10 JTU over

natural conditions.

Snak e_Ri yer_ Basin^Idahg

     Approximately 4,225,000 acres (1,722,000 hectares)  are

being irrigated in the Snake River Basin of southern Idaho.

The Bureau of Reclamation estimates that an additional

6,000,000 acres (2,428,200 hectares)  are potentially

irrigable.  Both surface and ground water in Idaho are of


high quality and suitable for irrigation purposes.  Ample

supplies are available and water allotments in the Snake

River Valley are particularly high.  They range from about

6.5 acre-feet per acre (20,500 cubic meters per hectare )to

nearly 13 acre-feet per acre (40,100 cubic meters per

hectare)  in areas where a range of between 2 and 3.5 acre

feet per acre (6,175 and 10,800 cubic meters per hectare)

would probably satisfy most requirements. Surface erosion

and deep percolation are problems created by these excessive

applications and, while not serious at this time, will no

doubt become so when the Basin's irrigable lands are fully

developed (27) .

     An evaluation of the effects of irrigation on water

quality in the Pacific Northwest has recently been completed

and provides a valuable insight into the problems of the

Snake and Yakima River basins (43).

Qther Ma1or Problem^Areas

     The Missouri River Basin and the Arkansas-White-Red

River Basin are in need of detailed study.  The upper

segment of the Missouri River Basin has several areas where

irrigation return flow problems exist but where significant

salinity increases in the stream system are not obvious

because of the diluting effect of ample water supplies.


     A study of diffuse or non-point irrigation returns

discharging into the North Platte River in Nebraska

immediately downstream from the Nebraska-Wyoming state line

indicated a 27 percent increase in the salinity of the river

during a period of low flow in 1964  (44).  The actual range

in total solids varied from 509 ppm at the state line to 647

ppm at Bridgeport, Nebraska, a distance of 60 river miles

(97 kilometers).  Even though the increase was nominal,

responsible authorities are concerned.  Water taken from the

North Platte River is used for irrigating many thousands of

acres in Nebraska and its deterioration could impose serious

detrimental effects on the economy of the state.

     Skogerboe and Law  (27) recount examples of serious

irrigation return flow quality problems existing in several

states.  Among these are high sodium concentrations in soils

near Riverton, Wyoming where the problem is so severe that

reclamation of once-irrigated lands is currently uneconomic

in many areas.  Problems are also beginning to develop in

both North and South Dakota in lands underlain by highly

saline formations of very low permeability.

     The areas cited are those for which there is documented

evidence regarding salinity imparted to water by irrigation

return flows.  There are additional areas where water

quality deterioration caused by irrigation practices are


important.  The problems involved are similar to those cited

and include increases in salinity of the receiving water;

elevation of the ground water table to critical levels;

damage to the soil,  surface and root zone; excessive erosion

and sedimentation; transfer of fertilizers and pesticides,

plus other water-degrading factors associated with irrigated



     The control of salinity and other pollution caused by

irrigation return flow cannot be easily achieved.   Control

methods include the application of current technology and

the development of new technology.  Current technology

includes known methods of increasing the efficiency of the

water development system, on-the-farm water management, and

elimination of surface discharges of irrigation waters.

These, combined with the application of irrigation

scheduling and increased water-use efficiency will minimize

pollution caused by irrigation returns.  These methods and

procedures must be coordinated with a careful reevaluation

of the institutional measures affecting irrigation.

Ea£S_Water Delivery System

     The water delivery system consists of conveyance

channels, beginning with major irrigation canals conveying

water from diversion points to the irrigation district or

farm system and terminating in the lateral distribution

network.   Estimates of seepage losses from canal systems

vary from 13 percent in the Uncompahgre, Colorado area, to

48 percent in the Carlsbad, New Mexico Project.  If 20

percent of all water diverted for irrigation in the United

States were lost by seepage (a conservative estimate), the


total would amount to 24,000,000 acre-feet (29,603,760,000

cubic meters)  per year based on current usage (27) .  This

amount of water could irrigate an additional 8,000,000 acres

(3,237,600 hectares)or could be available as a diluent to

improve the quality of existing water supplies.   Not only do

channel losses by seepage represent a potential  waste of a

valuable resource but percolating waters may leach

additional minerals from the soil and further deteriorate

the quality of the return flows.  The problem can be

alleviated or even eliminated by lining the canals and

ditches.  A. study of the effect of lining irrigation

conveyance channels on the reduction of ground water and

stream salinity was undertaken as part of the Grand Valley

Salinity Control Demonstration Project(45).  conclusions

drawn as a result of the study clearly indicated that

conveyance lining is a feasible Salinity control measure*

     Conveyance channel lining is incorporated into all new

projects initiated by governmental agencies and  is a proven,

effective deterrent to return flow water quality

deterioration.  Lining materials may be compacted earth,

hard-surface,  or membrane.  The hard-surface linings include

Portland cement, concrete, mortar, asphalt cement, and soil-

cement.   Such lining materials are used where structural

stability such as the prevention of canal bank failure or

velocity erosion in high-capacity delivery systems is


necessary.  The use of concrete head ditches results in

considerable saving of water, eliminates annual cleaning or

remaking earthen ditches and  enables more efficient control

of water flow and distribution.  Figures 19 and 20

illustrate the use of concrete in two methods of ditch

lining whereas the use of plastic lining in conveyance

channel construction is shown in Figure 21.   An operational

concrete-lined ditch is shown in Figure 22.

     A problem inherent to the open ditch is one of

evaporation losses from -the free water surface.

Substitution of closed conveyances such as steel, concrete

or plastic mainline or conduit is the logical alternative.

Pipelines, in addition to eliminating seepage and

evaporation losses ordinarily occupy less space and usually

provide better control over flow regulation.  Steel

irrigation pipe mainline is shown in Figure 23.  The early

stage of construction of a 30-inch steel pipe flume designed

to convey snow-melt runoff directly to a major irrigation

diversion is shown in Figure 24.

     Large earthen irrigation storage reservoirs are often

constructed to provide water for multiple users such as

FIGURE 19.     Earthen water conveyance ditch being
               lined by spraying or "shooting" with
concrete.  No reinforcement is used in this method.
Final County, Arizona.  Photo courtesy Soil
Conservation Service, U.S.  Dept. of Agriculture


FIGURE 20.     Pouring concrete ditch with size 12 wire
               mesh being placed in the concrete.
This ditch is 34 inches deep with 1 to 1 side slopes.
Pueblo county, Colorado.  Photo courtesy Soil Conser-
vation Service, U.S. Dept. of Agriculture.


     "  •  ^y^:::v-V

                                            •*.  ••
FIGURE 2],  The Delta B Canal, a large conveyance
            channel near Delta, Utah being lined
with plastic.  Two 32 foot plastic strips are being
used to line the canal.  Photo courtesy Soil Conser-
vation Service, U.S. Dept. of Agriculture.

FIGURE 22.     A modern concrete-lined irrigation
               canal.  Note control gates which can
be closed in order to regulate the flow of water
into the desired channel.  The crop is alfalfa.
Installation near Red Bluff, California.  Photo
Courtesy Soil Conservation Service, U.S. Dept.  of


    FIGURE 23.     Steel mainline (42 inch penstock)
                   capable of delivering 50 cubic feet
    per second of  irrigation water to 3000 acres of
    cropland.   Near Payette, Idaho.   Photo courtesy Soil
    Conservation Service, U.S*  Dept.  of Agriculture.

FIGURE 24.     Irrigation pipe being delivered by
               helicopter to site in mountainous
terrain.  This 30 inch flume will deliver snow-
melt runoff water directly to an open diversion
ditch.  Near Gypsum, Colorado.  Photo courtesy
Soil Conservation Service, U.S.  Dept.  of Agriculture.

irrigation or conservation districts.  Storage reservoirs

are also useful in areas where the sources of water are

limited.  For example, a low-productivity well or wells can

supply water continuously to the reservoir while the latter

is used intermittently to irrigate.   These structures may be

a source of seepage and subsequent impairment of ground

water quality if improperly constructed.   Leakage can be

eliminated by sealing the reservoir walls and floor with

impervious materials.   Figure 25 illustrates the

application of "gunnite" (grout)  to excavation walls.

Figure 26 illustrates the placement of polyethylene lining

in an irrigation reservoir.   Excellent treatments of the

subject of ditch lining and reservoir sealing have been

issued by the U.S.  Department of Agriculture and the U.S.

Bureau of Reclamation (46, 47, 48) .
     Many delivery systems in use today contain no provision

to meter or otherwise regulate the amount of water provided

to the irrigator.  Correct measurement not only increases

water application efficiency, but is a sound water manage-

ment practice.   A higher degree of water-use efficiency can

be attained when the amount of water passing principal

points in a delivery system is known.

FIGURE 25.     Earthen irrigation storage reservoir
               being lined with grout or "gunflite
reinforced with wire mesh.  Sealing the walls and floor
of the structure virtually eliminates seepage.
San Diego County, California.  Photo courtesy Soil
Conservation Service, U.S. Dept. of Agriculture.


FIGURE 26.  Polyethylene lining being placed in large
            irrigation reservoir to render the
water-holding facility impervious to leakage.
Riverside County , California.  Photo courtesy Soil
Conservation Service, U.S. Dept. of Agriculture.

Farm Water Management System
     The judicious management of water applied to irrigated

crops on the farm represents the most practicable method of

controlling water pollution imparted by irrigation return


     Controlled application such as irrigation scheduling

will reduce excessive seepage losses and eliminate surface

runoff while maintaining correct available moisture capacity

in the plant root zone.

     Irrigation scheduling is defined as the process of

applying an optimum amount of water to any particular crop

when it is needed.  In many irrigated areas the farm

operator is inclined to irrigate when his field is dry

rather than attempt to maintain an optimum moisture level in

the soil.  Over-application of water on a discontinuous

basis frequently occurs and may result in possible damage to

the crop, unnecessary runoff, and excessive deep

percolation.   Optimum irrigation scheduling is currently

being practiced in a number of areas in the western states

and may ultimately be adopted as the accepted method of

irrigation on a nation-wide scale.  Demonstration projects

using scheduling techniques are becoming more numerous and


computerized programs involving water application to

irrigated farms are being developed.

     The Bureau of Reclamation is conducting a pilot

irrigation-management study in southern Idaho to develop a

useful computerized-management program that can be employed

by both irrigation districts and individual irrigators (49,

50).   The program1s goal is the development of a system

which will schedule both the application of irrigation water

to the farm and delivery of water through the system.   The

program was the outgrowth of a study which indicated that

regional farmers were obtaining less than 45 percent

effective use of applied water.  The low efficiency resulted

from excessive  application and inexact timing.  The soil

moisture reservoir was not being fully utilized.  Experts

estimated that proper scheduling of irrigation, plus

improved on-the-farm water management, could increase

efficiency to 55 or 60 percent.  The program was implemented

in 1969 with eight farmers initially participating on a non-

assessment basis and has since expanded to 76 users,

irrigating approximately 14,000 acres (5,665 hectares) of

the 76,000 irrigable acres (30,755 hectares) in the project

area.  Scheduling techniques involving the field-computer

approach have also been developed by the Salt River

Project's Agriculture section, Arizona (51, 52).  Project

personnel work closely with the individual irrigator in an


effort to achieve optimum use of water for a particular crop

growing in a typed soil.  Field services rendered include

fertilizer application recommendations along with the

evaluation of current in-use irrigation system efficiencies.

The concept of scientifically-determined irrigation

scheduling is rapidily expanding and several commercial

irrigation management services capable of providing the

irrigator with computerized analyses and trained

agriculturists are available to the prospective client.

     On-the-farm water management practices, less

sophisticated than computerized scheduling, can be applied

by the irrigator to effect substantial decreases in return

flow volumes.  These include the  prevention of overflow in

head ditches and laterals; improved distribution of water

over the field, elimination of "lows" or depressions in the

graded field to prevent ponding of water; contoured terraces

constructed to prevent runoff; and prudent choice of

irrigation method.  These factors, along with others

somewhat less important, constitute good conservation-

irrigation practices.

     Modern equipment and methods to accurately control

distribution of water applied to the land are available to

the present-day irrigator.  Substantial reductions in the

amount of applied water can be achieved after leveling or


releveling the land and maintaining the improved
configuration.  Reductions as great as 40 to 50 percent in
water use may occur following leveling and the installation
of simple (Parshall flume) water measuring devices.  Over-
irrigation results in excessive water losses due to
abnormally high seepage and evaporation, causes soil
waterlogging in low spots, and creates potential drainage
problems.  Planned water use reduces labor costs.  The well-
managed system also requires less attention.  Farm ditches
kept clean and free of weeds,  grasses and debris will
prevent clogging, overflowing, and attendant water  wastage
and erosion.
Water Application Methods

     There are three basic methods of applying water to an
irrigated tract.   These are surface, sprinkler, and
subsurface.  Choice of method is principally a function of
land slope, soil  type, water quality, plant acceptance and
soil erodability.

Surface Methods

     In the surface method, water is applied directly to the
ground at ground  level and flows by gravity  over the


surface of the field.  The amount of land slope is important

in the surface irrigation system inasmuch as the

distribution of water over the field is totally dependent

upon natural flow.  The surface must be relatively flat and

any slope present must be very gentle. Irrigation of close-

growing crops is accomplished by flooding the entire field,

which is surrounded by a dike, levee, or border to confine

the water.  in the irrigation of row crops, the water is

directed down the furrows between the rows through siphon

tubes from an adjacent water  supply ditch.  Surface

application by the level border or furrow method is adapted

to soils that have relatively low infiltration rates.  Care

must be taken to avoid too rapid application which could

result in abnormal waste, excessive leaching, waterlogging,

erosion,and accumulation of tailwater.  Absolute control

over these factors probably cannot be achieved.  Control of

tailwater, however, can be accomplished by recirculating or

reusing the excess water applied on the farm.  The reuse

system also allows the irrigator a reasonable degree of

application latitude and enables the use of minimulm |

allowable stream flows in each furrow.  Minimal furrow

stream flow in turn, normally results in decreased furrow

erosion, higher irrigation efficiencies and larger crop


Trickle and Drip Methods

     A variation of the surface method is the relatively new

trickle or drip irrigation system.   In the trickle method,

water is applied very slowly to the soil surface  adjacent

to the base of the plant through a  series of tiny holes or

valves in irrigation pipe laterals.  Water from these point

sources moves through the soil by the action of gravity and

capillarity.   Evaporation losses are greatly reduced and

water released is confined to a relatively small segment of

soil adjacent to the plant root zone.  This method offers

considerable promise in future control of  return flows and

is capable of achieving very high irrigation efficiencies

under many conditions (53, 54).

     Drip irrigation is versatile and can be applied to

field crops, orchards, vineyards, or pasture.  A problem

inherent to the method is the accumulation of salts at the

periphery of the wetted portion of the moisture profile,

where evaporation leaves a deposit of solids.  Periodic

leaching may be required to carry these salts below the root

zone.  Other problems are mechanical and involve a lack of

uniform water application caused by manufacturing

imperfections in water emitters, emitter clogging, and

emission rate fluctuations resulting from friction-induced

pressure drops in the conveyance lines.  These have been the


object of recent investigations  (55).  Problems and

potentials of both trickle and drip systems have recently

been summarized  (56) .

Sprinkler Methods

     Sprinkler irrigation imitates rainfall — nature's

ordinary  method of applying moisture to the land.

Sprinkler methods can be applied to soils having high intake

rates, on steep and irregular slopes, and on soils that are

rough or too thin to level because of danger of exposure of

subsoil.  Irrigation of sloping, irregular land must be

almost entirely limited to sprinkler methods inasmuch as

homogeneous distribution of water can only be accomplished

by sprinkling — provided water is applied slowly enough to

prevent erosion.  Automatic controls are adaptable to

sprinkler methods so that systems can be  designed with a

high degree of operational flexibility.  Fertilizers,

including liquid animal wastes, cannery waste lagoon

effluents, and pesticides can be readily applied through

sprinkler systems.  Drawbacks to the use of sprinkler

methods exist.  If the crop grown is subject to fungi

development or other diseases  aggravated by high-moisture

conditions, the method may have severe limitations.  Also,

highly saline water may leave toxic, and often lethal,

deposits on the foliage if applied during periods of high


ambient temperatures.  High winds may distort spray patterns
and reduce the efficiency of sprinkler application.
Excessive amounts of silt, along with sand and trash in the
water supply may cause nozzle plugging and excessive erosion
of moving parts.  This foreign material must be removed from
the water prior to its introduction into the system.
     Subsurface irrigation or subirrigation, as originally
defined, reguired that the ground water table be close to
the plant root zone or that an impervious layer of rock or
soil be present to confine the applied water to a position
immediately below the root zone.  In the subsurface method,
water is supplied to the ground water mass  through canals
and laterals or by a system of subsurface  pipelines in
quantities which carefully regulate the height of the water
table below the root zone.  Capillarity th|ein conveys the
water to the roots of the plant.  The system possesses a
dual capability and is, in reality, a combination irrigation
and drainage network capable of both supplying water and
disposing of excess water if well-managed and properly

     An interesting adaptation of water table management  in
subirrigation is cited in recent investigations of the use


of subsurface drains to maintain the water table at proper

depth to supply the needs of growing crops (57).

     A new concept in subsurface irrigation, and one that

shows exceptional promise in the field of return flow

quality control, does not require the presence of a shallow

ground water table.  Water is applied underground to the

root zone through tiny holes or valves in small diameter

pipes buried in the row at the level of the root zone.

Application rates can be carefully regulated to irrigate at

frequent intervals with small amounts of water.  Evaporation

is reduced and salinity concentrations minimized.  The

application of water directly to the root of the plant has

reportedly resulted.in comparable crop yields using one

half, or less, of that needed in "conventional" irrigation

methods.  This method then, may literally  double the

potential acreage that can be irrigated by a given quantity

of water in those areas where its use is feasible.  The

method needs further testing over several agricultural

cycles before its range of application can be established.

A significant drawback is the system's capital cost which

ranges from $345 to $850 per acre ($850 to $2100 per

hectare), depending on pipe spacing.  The principal

application of subsurface irrigation techniques of this type

will be in the cultivation of high-value crops in areas

where water is expensive  (56).


Minimum Tillage

     Suppression of evaporation and transpiration of

moisture from the soil reduces irrigation water demand and

subsequently lessens the likelihood of excessive return

flows.  A cultural practice, known to agronomists for many

years but not widely applied in irrigated agriculture is the

no-tillage or minimum-tillage technique.  The system

requires that mulch left by a prior planting be retained on

the soil surface.  Significant reductions in runoff, soil

erosion and nutrient loss, caused by destructive action of

rainfall, can be achieved by preserving this protective

ground cover.  Rises in crop yields are the result of

increased water infiltration and decreased evaporation.

Minimum tillage techniques do have disadvantages.  Weeds

must be controlled by application of herbicides  prior to

planting.  Plantings in areas infested by bermudagrass or

johnsongrass are ineffective inasmuch as herbicides fail to

control these grasses.  Pests such as cutworms, armyworms,

wireworms and slugs tend to be protected by the mulch.  It

may be difficult to control volunteer  crop plants and,

unless reasonable use of herbicides can effect control,

reversion to tillage or cultivation will be necessary.  The

possible application of the technique to irrigated farming

was discussed during a recent no-tillage symposium  (58).


£g£g—Water^Removal System

     The removal of applied water is an important aspect of

the irrigation water management system.  Both surface and

subsurface returns must be considered.

     Cultural practices designed to conserve water applied

to the field and thereby reduce surface returns are well

known and basically simple.  Surface  runoff is likely to

occur if application of water to the land is unavoidably

excessive as it might be in areas having very tight soils.

Such soils have very low intake rates and require large

amount of water for leaching.

     Runoff can be minimized by deep-plowing.  This creates

a rough surface and facilitates soil moisture uptake and

retention.  Infiltration into deep-plowed soils may be

increased by a factor of eight-to-fifteen times that of

lightly-plowed soils.  Contour planting and contour tilling

can reduce soil loss caused by runoff, particularly on

slopes of low-to-moderate grade, by as much as 50 percent.

Contour strip cropping, a method of alternating strips of

grass,  which is close-growing, with strips of grain or

other row crops can likewise be very effective in

suppressing field erosion in addition to reducing runoff.

The grass strip acts as a partial barrier to runoff,


decreases its velocity, and acts as a filter, trapping a

significant quantity of sediment while allowing the water to

pass.  Formed structures such as terraces and berms are

commonly used to reduce concentrated runoff or intercept

moderate-to-high velocity flows.

     Surface runoff control lessens the degree of sediment

transport and decreases the likelihood of important losses

of nutrients and pesticides adsorbed on sediment particles.

Filtration of water through a few feet of soil ordinarily

eliminates nearly all adsorbable pesticides and nutrients

but may have little effect on soluble minerals or highly

soluble nutrients.  The irrigator should remain continuously

aware of the fact that a significant increase in water

retention will tend to increase the subsurface  component of

irrigation return flow and increase the risk of stream and

ground water pollution.

     Excess water applied to the field can be collected in a

reuse reservoir or tail ditch and recycled through the

irrigation distribution system.  In this manner, nutrients,

pesticides, organic debris, dissolved solids, bacteria and

plant parasites can be confined to the field.  If not

reused, tailwater may enter the surface or subsurface drains

and provide contaminant loads similar to that of surface

runoff, its non-consumptive counterpart.  The difference in


composition between anplied water and irrigation runoff
water in small watersheds has been the subject of recent
studies by the U.S. Department of Agriculture (59).

     Reuse of runoff water is a desirable conservation
practice and can significantly reduce the ultimate cost of
water, particularly to the irrigator who has found it
necessary to develon a water well system at considerable
capital expenditure.  Reuse systems are not uncommon and
need not be complex.  The components usally consist of a
collection pit, screen, pump, and automated controls (Figure
27).  The system, including the possibility for use as an
animal waste disposal facility in conjunction with farm
livestock programs, has been described by the Nebraska
Agricultural Experiment Station in cooperation with the
Agricultural Research Service (60) .  Recycling excess
irrigation water offers an excellent method of return flow

     Subsurface drainage systems are often necessary to
prevent waterlogging of the soil and are used to control
buildup of salinity at or near the ground surface.  Shallow
water tables impede achievement of salt balance by
increasing leaching requirements.  Tile drainage networks

                           - i —,-

FIGURE 27.  On-farm irrigation tailwater return
            pit.  Intercepted water is recycled by
pumping through a plastic pipeline to a con-
crete-lined ditch for reuse.  Near Pecos, Texas.
Photo courtesy Soil Conservation Service, U.S.
Dept. of Agriculture.

are extensively used to convey water from the soil and to

depress the ground water table to a point where it will not

endanger crops.  The tile drain and collection system offers

a point source for treatment and control of pollutants.  The

problem of pollution by water emanating from tile drains has

been addressed by the Federal Water Pollution Control

Administration and others (39, 61) .
       Methods of Return Flow Control
     The methods and procedures cited as  pollution controls

are those currently available to the irrigator and can be

catergorized as state-of-the-art measures.  They are

technically feasible, practicable, economically viable,

socially acceptable, and without adverse legal constraint.

Their implementation would require few additional structural

facilities or institutional changes on the part of the


     Feasiblity investigations that may provide additional

measures of control of pollution created by irrigation

return flow include several important studies now underway.

Among these are measures designed to conserve water by

minimizing evapotranspiration.  The rate and amount of this

loss is a function of numerous factors including solar

radiation, temperature, relative humidity, wind velocity -


available soil moisture, type of crop, stage of crop

growth, length of growing season, degree of tillage, and

surface mulch conditions.  Any practicable method to reduce

evapotranspiration is desirable and will increase irrigation

efficiency.   Reduction of evapotranspiration losses can be

accomplished through judicious project  planning (62).  It

has been shown that evapotranspiration  can be diminished by

using artificial barriers.  These inhibit the downward

movement of  water and thereby curtail losses by deep

percolation.  Soil water evaporation losses to the

atmosphere may also be reduced by these barriers (63, 6H,

65).  The most successful of these methods employ asphalt

emplaced by tractor at depths of approximately two feet.

The work is  in the experimental and demonstration stage.

Implementation costs range from $200 to $250 per acre.

     Consumption of water by phreatophytes (those plants

that habitually obtain their water supply from the zone of

saturation either directly from or through the capillary

fringe) is quite large in arid and semiarid regions.  The

control and   partial elimination of these water users would

release appreciable volumes of water for beneficial uses.

However, the destruction of phreatophytes such as saltcedar,

willow, cottonwood and mesquite would have to be undertaken

on a limited orderly and carefully planned basis inasmuch as

many forms of animal life such as birds,  fowl, game animals


and useful predators depend on the sanctuary of dense

phreatophytic environments for survival.

     Of all water uses  (and losses) involved in the field of

agriculture, the use of water by a growing plant is the most

wasteful and involves efficiencies of only one to two

percent.  It is apparent that if plant efficiency could be

increased by only a few percent, millions of acre-feet of

water could be conserved.  An interesting technology in

evapotranspiration control is aimed at reducing the fluid

loss from the growing plant per se.  The concept is not new

and has been used by nurserymen to combat desiccation of

damaged trees and shrubs whose preservation was considered

essential.  A family of non-toxic chemicals designed to

accomplish transpiration control more efficiently than at

present is currently being developed.  These compounds,

called antitranspirants, fall into three catergories and

include chemical leaf sealants, materials that increase leaf

reflectivity and thus reduce plant heat load and, finally,

chemicals which tend to reduce the size of the stomata or

plant pore.


     Research and demonstration projects needed in the fielc

of irrigated agriculture should emphasize  those aspects

with the greatest near-term impact upon water quality

control.  These fall into two major catergories and are, 1)

technical, including management of the soil-plant-water

system and, 2)  institutional-legal, involving possible

innovation, revision and reformation of irrigation district

structure, reevaluation of Western water law and its

conflict with water quality standards, and other institu-

tional constraints.  Both recognize that excessive water use

is the greatest cause of water quality degradation

associated with irrigation.


A blend of research and demonstration is neeeded to- develop

methods of increasing efficiency in irrigation practices.

This concept involves sound design and subsequent operation

of an irrigation project which will maintain crop yields and

at the same time reduce water requirements, volume of

irrigation returns, and amount of salt transported to

surface or subsurface waters.  Elements of the project must

also be economically feasible.

     Increased efficiency can be accomplished in several

ways.  Included is judicious management of the  water-soil-

plant system conducted, under conditions where climate, water

salinity and soil type are the major variables.  Such

methods use proven irrigation techniques to increase the

efficiency of the water delivery system, the on-farm

application system and the water removal system.

     Methods of water application can greatly influence

irrigation efficiency.  Significant increases using

subirrigation, drip-trickle and bubbler methods  can be

attained but will create a need for additional research

inasmuch as the environment to which the irrigated crop will

be exposed is radically changed.  Soil-water in drip-trickle

methods remains uniformly and continuously high.  Organism

populations in the surface soil may change and give rise to

new and differing plant  diseases.  The possibility of

adverse pathogenic effects also exist.  Poor management of

the drip-trickle system could be damaging and create

hitherto unknown problems.  Nutrient utilization will also

be affected by a continuously moist environment.  Salinity-

nutrient interactions under these conditions are known to

occur but little is known of the mechanism or its effects on

plant response.  Plant stress interactions between relative

humidity and salinity, and between ozone (polluted  air) and

salinity are recognized.  Adverse effects of air pollution


can occasionally be overcome by salt stress and may be
useful in maintaining ornamentals in a healthy state by
artificial salination of the soil where air pollution is a

     Control of water application to establish a uniformly
moist environment might be achieved through the use of
sensors  to monitor soil salinity at given depths.  Soil
salinity is a function of the amount of transitory drainage
water.  A salinity sensor grid might represent a major
component of future irrigation systems.  The foregoing con-
cepts represent only a few of many possibilities designed to
increase irrigation efficiency through advanced technology
(66) .  The concept of irrigation return flow water quality
improvement through application of more efficient methods is
in harmony with the Environmental Protection Agency's
position that remedial measures should be applied at the
pollution source rather than by treatment of the effluent.

     Research within the framework of the National
Irrigation Return Flow Research and Development Program
prepared for the Office of Research and Monitoring,
Environmental Protection Agency contains a summary of
worthwhile needs (16).  A major thrust of the program is
directed toward the development and demonstration of
improved crop, plant,  nutrient and pesticide management


methods, — all based upon interaction between soil,

hydrology, salt and nutrient movement, fate of pesticides,

and other factors.  The development and demonstration  of

new and improved water delivery systems, application

methods, drainage systems and tailwater reuse systems must

necessarily be an integral part of the same program.

Additional research needs and potential solutions for con-

trolling quantity and quality of irrigation return flow are

summarized in a prior Environmental Protection Agency

publication  (27) .


     A demonstration or research program need not

necessarily be limited to technologically-oriented projects

but can include institutional approaches.  These, like the

technological approach, employ the concept of improved water

management practices.  Projects could include the

restriction of irrigation development in areas of

potentially high salinity; consolidation of irrigation

companies and water supply districts into single management

units; and encouragement of local acceptance of control

measures through educational programs on  the local,

regional and State levels.

     Other projects might include evaluations of the

operational and proposed programs of Federal, State and

local agencies to determine what future courses of action

will be required to achieve reduction in pollution created

by irrigation return flows.  An important facet of such

evaluation would include regulatory powers and authorities

needed regarding land and water management and the

possibility of integrating  these into a return flow control


     The control of diffuse returns is complicated by the

difficulty of quantification, including determination of

their measurement of pollutional effects.  Additional com-

plications are the basic conflicts between Western water law

and water quality standards.   The legal rule that water must

be used to maintain the continued right to its use

aggravates the problem.

     Institutional constraints have been responsible for1

numerous salinity problems in many irrigated areas in the

United States.  Among these constraints are legal,

political,  cultural and economic.  The legal constraint

involves water rights.  A water right is the legal right to

the use of water and grants the right to divert and excerise
physical control over the water.  The right determines who

can take the water, the amount to be taken, and the time of


taking.  The right is established as to priority of use and

affords legal protection to the user.  An irrigator having

an adequate water  right has little economic incentive to

institute  efficient water management practices.  As a

result, excessive irrigation often occurs.  Rights cannot be

bartered, bought, sold or leased, but must revert to the

original grantor if not used.  The "property right in water"

concept created through  the prior appropriation doctrine

thus is a major deterrent to the implementation of water

management technology.  The element of water quality  is not

considered.  The path to the resolution of the water

management problem in the West could be cleared to a large

degree by changes, or reinterpretation, of the doctrine.

Perhaps strict enforcement of the law may, in many

instances, be all that is required to implement control.

For example, there are direct statutory restrictions to the

excerise of a water right as in Colorado Revised Statute

Section 148-7-8 providing "during the season it shall not be

lawful for any person to run through his irrigation ditch a

greater quantity of water than is absolutely necessary for

irrigating his land and for domestic and stock purposes; it

being the intent and meaning of this section to prevent the

wasting and useless discharge and running away of water"-

Further limiting this water right, the Colorado court held

in 1893 that no one is entitled to a priority of more water

than he has actually appropriated nor for more than he

actually needs (67) .

     A particularly troublesome institutional deterrent to

control of return flow salinity exists in the Lower Rio

Grande Valley.  Irrigation is controlled and administered by

34 separate irrigation districts and four drainage districts

plus water and other metropolitan districts.  Each district

has its own  power and authority over the use, development,

protection and administration of water within its

jurisdiction.  Each district designed and built its

distribution and drainage facilities to serve only the area

within its boundaries.  Little attention was paid to the

overall effect on Valley irrigation.  These and other

factors pertinent to the institutional problem of the Valley

are presented in several important studies prepared by Texas

ASM University (68, 69, 70).  Conflicts created by these

numerous and overlapping authorities account for a

significant part of the Valley salinity and drainage

dilemma.  Cultural institutions in the Valley involve the

continued use of time-honored concepts, customs and

traditions that are no longer applicable in many instances

and should be discontinued.  These involve water application

and use practices, labor use and crop preference.

     A recent Environmental Protection Agency in-house study

of salinity created by irrigation return flows concluded, in

part, that the solution of the problem can only be

accomplished through a basin-wide control program.  The

study also concluded that, "Improved water management

practices, particularly the use of water at optimum

efficiencies on the  farm, is the most feasible approach to

controlling excessive salt loads from irrigation return

flows to many of our western river systems.  Present

technology would permit the implementation of several

salinity control measures that are not now widely employed

...."r and "Legal and institutional means must be  found to

control water salvaged through improved water management in

order to finally achieve a solution to basin-wide salinity


     Present levels of government concern and effort can be

expected to produce major achievements relating  to

permanent and definitive solutions to the problem of control

of salinity and other pollutants.

                     GLOSSARY OF TERMS
  -^sS-Wat6.?. ~ water diverted for irrigation but returned to
the source without having been applied to the land.
	   - water discharged into the atmosphere as
vapor and no longer available for use by the discharging system.

Evapotranspiration - water lost as vapor from the combined
process of evaporation from the soil and transpiration from
vegetation.  Evapotranspiration represents an important
consumptive use of water.
              ion - the application of water to furrows
 (narrow trenches dug by farm equipment)  to irrigate crops
planted in, or between, the furrows.

Leaching^reguirement - the amount of water that must pass
through the root zone to maintain a prescribed salt level.
Expressed as a percentage of the total water applied to the

Qsmgtic_ action - the diffusion of water through a
semipermeable membrane (example - soil moisture extracted by
plant root hairs).

Perched_ground_water_body - a ground water mass located within
the zone of aeration, and seprated from the main underlying
ground water body by a zone of unsaturated rock.

Permeability - the capacity of a material  (soil) to transmit
fluid (air and water) .

£°.£2.§i±Y. ~ tne ratio of the aggregate volume of interstices,
voids, pores or other openings of a soil sample to the total
 (bulk) volume.  Usually expressed as a percentage.

Prior appropriation^doctrine — a basic doctrine that all
waters in a State, whether above or below the ground, are the
property of the people.  A vested right to the use of the
water  is acquired by appropriation and the application of the
water to beneficial use.   The individual first in time is
first in right and beneficial use is the basis, the measure,
and the limit of the right.

Salt_loadin2 - the addition of dissolved solids to water
from both natural and man-made sources.  Not to be confused
with salt concentrating which increases salinity by stream
flow depletion and concentration of the salt burden in a lesser

volume of water.  Salt loads may originate in surface runoff,
diffuse ground water discharges, mineral springs, municipal
and industrial waste, and irrigation.
            !!ts - a group of low-nutrient organic materials
such as compost, peat, and sewage sludge that may be
incorporated into the soil or used as mulches.  Amendments
have a dual effect of improving the condition of the soil
while providing some plant nutrient.

Tajlwater - water which is the excess remaining after
an irrigation.

Trickle_ irrigation - water applied very slowly to the
surface of the soil through tiny holes or valves in plastic

Wat er^ infiltration - the downward flow of water from the
soil surface into the soil.  Infiltration implies flow into
the soil as contrasted to percolation  which denotes flow
through the soil.

                      REFERENCES CITED
1.   Committee on Pollution,  National Academy of Sciences
          - National Research Council, "Waste Management and
          Control".,  Publication 1400.   A Report to the
          Federal Council for Science and Technology, p.
          141.  Washington,  D. C., 1966.

2.   "Planning for an Irrigation System".  American
          Association for Vocational Instructional Materials
          in Cooperation with the Soil Conservation Service,
          United States Department of Agriculture, pp. 17-
          21, Engineering Center, Athens, Georgia, June,

3.   Law, James P. and Witherow, Jack L., "Irrigation
          Residues", Journal   of Soil and Water Conservation,
          Vol. 26, No. 2, pp. 54-56.  March-April, 1971.

4.   Characteristics and Pollution Problems of Irrigation
          Return Flow.   Utah  State University Foundation.
          Robert S. Kerr Research Center, Federal Water
          Pollution Control  Administration, United States
          Department of  the  Interior, Ada, Oklahoma, May

5.   Bishop, A. Alvin, "Conflicts in Water Management",
          Forty-second Honor  Lecture, Winter 1971.  The
          Faculty Association, Utah State University, Logan

6.   Public Health Service Drinking Water Standards,
          1962.  Public Health Service Publication No. 956,
          U.S. Department of  Health, Education, and Welfare,
          Washington, D. C.

7.   Water Quality Criteria.   Report of the National
          Technical Advisory Committee to the Secretary of
          the Interior.  Federal Water Pollution Control
          Administration.  Washington, D. C., April 1968.

8.   Hely, Allen G., Lower Colorado River Water Supply -
          its Magnitude and  Distribution.  United States
          Geological Survey Professional Paper.  486-D,

9-   Irelan, Burdge, Salinity of Surface Water in the
          Lower Colorado River-Salton Sea Area.  United
          States Geological Survey Professional Paper.
          486-E, pp. E-31 and E-32, 1971.

10.  Diagnosis and Improvement of Saline and Alkali
          Soils, United States Salinity Laboratory Staff,
          Agriculture Handbook No. 60.  United States
          Department of Agriculture, Washington, D. C.
          August, 1969.

11.  Carter, R.F., Presentation  of Imperial Irrigation
          District, Environmental Protection Agency
          Conference.  Las Vegas, Nevada, Feburuary 15, 1972.

12.  Need for Controlling Salinity of the Colorado
          River.  Colorado River Board of California.  The
          Resources Agency.  State of California, August,

13.  The Mineral Quality Problem in the Colorado River
          Basin, Appendix A., "Physical and Economic
          Impacts", U.S. Environmental Protection Agency
          Regions VIII  and IX, 1971.

14.  Quality of Water, Colorado River Basin, Progress
          Report No 5.  United States Department of the
          Interior, Washington, D. C., January 1971.

15.  Upper Colorado Region.  Comprehensive Framework
          Study.  Appendix XV.  Water Quality Pollution
          Control and Health Factors.  Workgroup of the
          Upper Colorado Region State-Federal Interagency
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