Delta Mendota and California Aqueductwater. The supply water averaged 234mg/L in salinity, and the soil water,assuming a doubling or tripling in con-centration due to evapotranspiration,would be expected to reach nearly 700mg/L. However , measurements andmodel calculations demonstrated the soilwater to be 7,000 to 8,000 mg/L. This iswater that would penetrate deeper intothe profile and that would be captured bydrains to be discharged elsewhere or re-cycled for crop production. The IO-foldincrease in concentration is attributed todissolution of soil minerals, principallygypsum. Although a few crops could tol-erate such concentrations for selectedperiods, the long-term maintenance ofirrigated agriculture using such waters isdoubtful.

In summary, the major effects of sa-linity on soil properties are swelling ofsoil clays, dispersion of fine soil particles,crust formation, and decreases in water-transmission properties. The amount ofsodium adsorbed on the soil and theamount of sodium and salt in the irriga-tion water greatly influence the degree towhich salinity affects soil properties.

Dennis E. Ralston, J W Biggnr, and Donald R. Nielsenaw Professors, Department of Land, Air, and Water RP-ROUTCPS, Uniwrsity of California, Douis

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Case history: Salton BasinJewel1 L. Meyer Jan van Schilfgaarde

T h e Salton B a s i n e x t e n d s 2 0 0miles from San Gorgonio Pass inthe north through the Coachella,

Imperial, and Mexicali valleys to theGulf of California. The basin covers adrainage area of about 8,000 squaremiles and at its deepest point is 273feet below sea level - about the sameas Death Valley.

The desert climate is characterizedby long hot summers, short mild win-ters, and sporadic rainfall averagingonly about 3 inches per year. If watercan be supplied, the climate and alluvialsoil are ideal for many vegetable, fruit,and field crops.

Irrigation water delivery to the Impe-rial Valley began in June 1901. Withinthree years, over 150,000 acres werebeing planted to barley, grain sorghum,alfalfa, and cantaloupes, despite prob-lems with transportation and water de-livery, and severe living conditions forthe new settlers.

In March 1905, silt that had built up inthe Colorado River near the headgatessouth of Yuma, Arizona, diverted thefirst of several floods into the canalsystem. Flood water flowed through thecanals and the Alamo River into theSalton S e a , c u t t i n g a n e w , 60-footgorge, the New River. The Salton Sea,nearly dry in 1904, filled to a level of-195 feet; the sea covered 500 squaremiles and was 80 feet deep by early 1907,when the Southern Pacif ic Rai lwayCompany finally closed the breach.

The Imperial Irrigation District ,formed in 1911, had consolidated most ofthe mutual water districts under a singleentity by 1916 and enlarged its potentialboundaries to over r/z million acres. Withfederal assistance, Imperial Dam wasbuilt on the Colorado River and the All-American Canal was constructed. Waterdelivery to the Imperial Valley throughthese facilities started in 1943.

In contrast to the Imperial Valley,

The 8,000-square-mile Salton Basin, one of the most productive agricultural areas in the world, as seen by a Landsat camera.The Salton Sea serves as the drainage basin for saline irrigation waters from the Imperial, Coachella, and Mexicali valleys.

CALIFORNIA AGRICULTURE, OCTOBER 1984

Nearly dry in 1904, the Salton Sea was filled to a level of 195 feet below sea level byflooding of the Colorado River. It later dropped but has risen gradually in recent yearsto its current level of approximately -227 feet.

development in the Coachella Valleystarted slowly in about 1900 with use offresh water from artesian wells. When itwas recognized that irrigation by wellswould deplete groundwater and limit de-velopment, the Coachella Valley CountyWater District in 1934 contracted withthe U.S. Government to construct theCoachella Branch of the All-AmericanCanal to deliver Colorado River water tothe Valley. By the time the project wascompleted in 1948, 23,000 acres werebeing irrigated. The area irrigated hassince expanded to 60,000 acres andpumping of ground water has been great-ly reduced.

Coachella Valley soils are coarse gra-

c A. Beasley14 CALIFORNIA AGRICULTURE, OCTOBER 1984

nitic al luviums formed from recentoutwashes of intermittent streams of thesouthern Sierra. The Imperial Valley hasfine-textured lacustrine or basin soilsformed from the intermittent flooding ofthe Colorado River through the Alamoand New Rivers into the Salton sink.Although their soil conditions differ sig-nificantly, both valleys drain into thelandlocked Salton Sea, and both havesalinity problems where drainage is inad-equate.

In Coachella, adverse effects of highwater tables and resulting high soil salin-ity led to a drainage program beginningin 1950. By 1970, well over half of theland was subsurface-drained. Field stud-ies by the U.S. Salinity Laboratory andthe water district indicated that, before1963, irrigation water added more salt tothe land than was removed to the SaltonSea in drainage water. As the drainagesystem expanded, the salt balance shift-ed in the other direction in 1963. Therelatively coarse-textured soils simplifiedthe design and construction of the drain-age system, and the closed-conduit waterconveyance system helped minimize wa-ter spills.

The much finer soils in the ImperialValley made drainage systems more diffi-cult abd more expensive to construct.The open-ditch conveyance system, withessentially no storage except in the ca-nals themselves, made it difficult toavoid some spillage. Leakage from canalsadded to a water table problem. Forexample, a study by the Imperial Irriga-tion District and U.S. Salinity Laborato-

A sophisticated irrigation and drainagesystem maintains the salt balance in theImperial Valley. Growers have spentmillions of dollars to line irrigation canalsand reduce water losses.

ry estimated that 150,000 acre-feet peryear were lost during 1900-48 by seepagefrom the Coachella Canal before comple-tion of the Coachella Branch of the All-American Canal through the easternedge of the Imperial Valley.

As waterlogging and salinity problemsincreased, open ditch drain constructionbegan in about 1921, supplemented withattempts at subsurface drainage. In the194Os, federal agencies, the University ofCalifornia, and local interests cooperatedin an extensive drainage program. By1981, over 27,800 miles of drain tile(tube) had been installed under 427,500acres of Imperial Valley land - equiv-alent to drains spaced 125 feet apart.

Drainage removes that amount of wa-ter that must be passed through the croproot zone to satisfy the leaching require-ment. If, for example, a field receives 2feet of water and the leaching require-ment is 10 percent, 0.2 foot of water mustpass through the root zone and be re-m o v e d . L e a c h i n g m a y t a k e p l a c ethroughout the cropping season as partof normal irrigation, but if not enough isapplied or if the soil takes in water tooslowly to keep up with crop demand,additional leaching is needed off-season.Between 1946 and 1950, an area of 9,000to 20,000 acres in the Imperial Valleywas leached by cont,inuous ponding.Now, because of better drainage and man-agement, the area ponded is negligible.

Average salt balance calculations de-termined from input-output studies, asin the Coachella Valley, may be mislead-ing: some fields may be “salting out”while others are adequately leached; also,salts of geologic origin or those storedunderground long before irrigation start-ed may affect the salt-output figureswhile there is still excessive accumula-tion in the root zone. Extensive calcula-tions made in the Imperial Valley duringthe 1970s by Rhoades and Kaddah, ofthe U.S. Department of Agriculture Agri-cultural Research Service, showed thatonly one-third of the salt discharged tothe Salton Sea came from the root zone.The rest came from the groundwater.

Present situationThe Imperial Valley has 460,000 irrigat-ed acres, 130,000 of which are double-cropped. The Imperial Irrigation Districtreceives 2.8 million acre-feet of water peryear in the All-American Canal and de-livers 2.6 million acre-feet of this to farmheadgates, for an average applicationdepth of 5.6 feet. This water contains, onaverage, between 850 and 900 mg/L ofsalt.

About a million acre-feet are dis-charged to the Salton Sea, with an aver-age salt content of about 3,000 mg/L.Evaporation has concentrated the salin-

The rising water level in the Salton Sea has flooded adjacent farmland and recreationalproperty and has jeopardized the Sea’s role as a collecting basin for saline drain water.Evaporation of the land-locked Sea. shown here at.the entrance of the Alamo River, hasmade it more salty than the ocean.

Below: Salt added to Imperial Valley soil Max Clover

by irrigation is leached out by continuousor intermittent ponding. “Berms” holdwater in fields.

ity in the sea to nearly 40,000 mg/L,slightly more than that of sea water.However, since the drought years of the193Os, evaporation has not been suffi-cient to prevent a slow, somewhat irregu-lar rise in the Salton Sea’s water level(see graph). Storms have also causeddramatic increases: in September 1976,the water level rose 0.8 foot after a singlestorm; in August 1977, 0.5 foot. In thespring of 1981 and 1982, the level wasabove -227 feet. This rise has causedflooding of farmland as well as recrea-tional property near the water.

A question being considered is wheth-er it is technically and economically fea-sible to reduce the amount of waterdrained into the Salton Sea without ad-versely affecting agricultural production.With the present crop mix and produc-tion, water use by crops presumablywould remain essentially the same, and areduction in drainage flow would be ac-companied by reduced diversions at Im-perial Dam.

Recent studies (1984) by researchersCA. Beasley

CALIFORNIA AGRICULTURE, OCTOBER 1984 15

Oster, Meyer, Hermamier, and Kaddah,at the University of California and theU.S. Department of Agriculture Agricul-tural Research Service, have providedsome data on the partitioning of water.In the Imperial Valley, 12 percent of thewater diverted becomes deep percolation(leaching water), and runoff (tail water)accounts for 16 percent. In the CoachellaValley, the leaching fraction is somewhathigher, and there is hardly any tail water.Quantitative information from thesestudies supports the belief that, techni-cally, a reduction in drainage flow isfeasible.

Steps have been taken in recent yearsto initiate water savings and assess theeconomic consequences of such prac-tices. The federal government finishedlining the Coachella Canal in 1981. TheImperial Irrigation District has acceler-ated its canal lining activities, and it hasconstructed four off-site reservoirs toprovide temporary storage, with plans toconstruct two more. The District alsohas established more flexible rules forwater orders: instead of receiving a fixed

The UC Mobile Lab monitors water use tohelp Imperial Valley growers improveirrigation efficiency.

24-hour delivery, an irrigator now canrequest a reduction in delivery as late asnoon of each day and limited changes upto 3:00 p.m. during the final delivery day.Research workers from the AgriculturalResearch Service are investigating thesubstitution of drainage water (with3,000 mg/L salt) for part of the irrigation

water and are assessing the potential for“dead level” surface irrigation to elimi-nate tail water.

The University of California operatesa “Mobile Lab” with instruments andequipment, working from the ImperialCounty Cooperative Extension office inEl Centro, to monitor water use andsuggest ways to improve irrigation effec-tiveness. Trained personnel take the labinto the fields of cooperating farmers,where they measure tail water. They alsocheck soil moisture status with neutronprobes and recommend irrigation sched-uling programs. Measurements in 1983showed that tail water was noticeablyreduced from that observed in earlieryears. This reduction was attributed togreater awareness of the problems associ-ated with excessive water use, togetherwith increased off-canal storage andmore flexible delivery policies by theirrigation district.

Jewel1 L. Meyer is Irrigation and Sods Specialist, Cooperatiue Extension. Unil,ersityofColifnrnin, Riverside, andJan uon Schilfggoarde is Director, Cl S Salinity Laboratory,Riverside

Case history:San Joaquin ValleyLouis A. Beck

M ost of the San Joaquin Valleyhas been farmed in one fash-ion or another for more than a

hundred years The Valley trough wasgenerally dry-farmed until deep-wellturbine pumps were developed in the1930s and 1940s and irrigation becamecommon. Even though much of the landwas in production, it was not irrigatedevery year: there was some pattern ofrotation, such as dry-farming for oneyear, irrigation for two, and fallow forone. Now, almost 5 million acres ofagricultural land on the Valley floor areirrigated.

The Valley, about 250 mile? long and50 miles wide, consists of two drainagebasins: the northerly San Joaquin Ba-sin, which drains to the San JoaquinRiver and then to the Sacramento-SanJoaquin River Delta and San FranciscoBay; and the southerly Tulare Basin,which normally has no outlet.

Salinity problems in the San JoaquinValley have adversely affected almost600,000 acres of agricultural land now

16 CALIFORNIA AGRICULTURE, OCTOBER 1984

in production. Perched saline ground-water within 5 feet of the soil surfacecauses a loss of 10 percent or more inannual crop production.

This perched water can be con-trolled by the installation of tile drains- a system of perforated pipes 6 to 8feet belowground that keep the waterlevel below the root zone. The drainsconduct the water to a corner of thefield, where it is discharged to a dispos-al system.

The perched water in the Val leytrough is saline, ranging from 3,000 to25,000 mg/L of total dissolved solids. Inother areas where the perched water isnot saline, it can be used for irrigationor discharged to watercourses. Salinewater must be disposed of so that itdoes not affect surface or ground-water. It is the lack of safe disposalsys t ems , a r ea s , o r m e t h o d s t h a tcauses the drainage problem in thetrough of the San Joaquin Valley. Theproblem area is expected to exceed 1million acres within the next 50 years.

Development of the problemThe drainage problem became serious inthe Valley when a full water supply wasassured. In the northern area (essentiallywithin the San Joaquin Basin), problemsbegan about a decade after the Delta-Mendota Canal was built and started todeliver water in about 1950. During the1960s tile drain systems were installedto allow farmers to continue normal pro-duction. Most of the water from thesesystems is discharged to the San JoaquinRiver. Because of the relatively smallvolume and the dilution in the river,discharge of drainage water causes onlyslight degradation of the quality of theriver and minor changes in agriculturalpractices.

A water supply to the Tulare Basinwas guaranteed when the CaliforniaAqueduct started delivering water to theSan Luis service area of the federal Cen-tral Valley Project and to the State Wa-ter Project service area in 1968. Drainageproblems began by the end of the 1970s.Now several agencies are starting to im-plement local interim solutions to solvetheir drainage disposal problems; draintile will not help, since there is no river todischarge to or any other system to carrythe drainage waters away.

SolutionIt was proposed during the 1960s thatthe state and federal governments to-gether construct drainage disposal facili-ties that would serve the entire Valley