THE COLORADO RIVER and IMPERIAL VALLEY SOILS
I I ' ' '' ' ' '"' '
A CHRONICLE OF IMPERIAL VALLEY'S CONTINUING FIGHT AGAINST SALT FOREW ORD Elsewhere In the Untied States, soil conservation dlstricte - lormed as a result of referendum by landowners - are governed by an elected board ol directors. In Imperial Valley, Imperial lrriqatlon Dlatrict functions a.s the SoU Conservation District under a unique memorandum of aqreement with the U.S. Department of Aqr;culture. Soil conservotlon policy Ia ael by the District board which also aerves as a soli conservation board. Soil scl.ontlata. en91n..•r• and con&41rvatlonlsts provide technical assistance to farmers. Soil engineering lnforma1ton and survey da1a, prepared by either the liD or SCS, are freely interchanged. The Dlatrict provides clerical and office facllJUes lor SCS, as well as pub!Jc Information 01818tance.
Silt and Salt
Imperial Valley, the winter qreenhouse of the nation. has be&n oonqu.,rtng the pro!> !ems and obstacles tha1 have tendad to discourage Ita formers sin~ 1901. In 1900, thta was a bo11en deMrl. Wllh the construction ol a heading on the Colorado River, 60 mllos east ol the Valley, irrigation wa1er was brought lnto the thirsty d·-rt In 1901. This au~sful dlv"r slon ol water through o con ...... ~«-..l••·•t "' * or· VIIYOnc:e canol, many miles of which were In Mexico, was enJoyed (or the brief period of only four years before trouble developed. Looldnf eouth.. thl• oeriol •lew .atowa the beodworb of tl:•• AJI. A flood on the Colorado River washed out the control wor;ca Amenccm Cc:ma.L Tb• Colorado IU•tr ia ot left. Po:rt of the d..Utl.D9 and lor about two years, 1~7. the Colorado River flowed through bcu.W la a1 -.xtr•mt upper rigbt·hon4 com.r. SUt ftual\ed back ln.to th& Alamo and New Riv~ra mlo the lmpetlal Volley, forming the the riYtr from the botln• con bt •••n at upper left. (Genttf photo) Salton Sea. At qroot exp. nso. tho Southern Pacific Company llnolly closed By comparlaon, the Columbia River, which Is approxima tely the the qap on the Colorado River and now control worh were Installed. same lerlQth. has an annual flow ol 184 million ocr•feet. These were us~td to control lrrtqotlon walar anlerlnq the Vo lley until AuQm~tn tallon of the Colorado has been suqqesled as a means 1942 when the A II·Amerlcxm Canal was completed and Imperial ol fumiahinq lh
The aalt problem Is be.nq louqht vlqorou5ly and wtlh qreat It has boon esllma1ed that by the year 2020, aqricultural pro success. Yet, som,. d fflculttes conbnu.e to exist. duchon •n CaiJJornla will have to be doubled or tripled to take care of the estimated population. Colorado p.,.., Problema If the nver were auqmented with low wlinity water, the rlvllr's hiqh lovol of eallnlty would be reduced. Imperial lrriqoUon Althouqh 1111 a powerful end mpo. 1nq nver, the Colorado's flow Dlstnct atronqly supporta atudlee ol wcrya to auqment the Colorado Is small. Ita total lenqth Is about 1.400 mtles and II& watershed cove'" !57 million acrea ol land, yet the rtver produces only about 14 million acre-feet of wa ter per year. TypicolliUnt o.,.tatJon In lmperlol VolJ•y •howa inatallation oJ a bCJM lin•. Sub-turlace tiUng ln.a.a.. t tht tfllc:iency of drainage ayatem. remo•.. .oh dtpolita.
Stote ot CaiUomla- oUidGia of the Colorado JU ..r Boord ond Attorney General'• oUice Jook at a plotllc ·Uie-- loytnt mac.h1ne dwiog a recent lour of fmp•rlol Voii•Y· (Hoppo photo) River: however, becouao river cruomentaUon Ia not likely In the nearly two million tons of dluolvod salts from antorlno the rlvor r.tv.lr future, other methods must be utilized to reduce oallnJUes. each year. Over the years, the eahmty of Colorado River water delivered The qeoiOQlc background and the eventiul and colorful period to lmpenal Volley has be"n lncreaainq. By 1970, this amount hod of development ol Imperial Valley hove crttracted the mterest ol the risen to 1.27 tons per acre-foot (equivalent to about 930 porta per whole notion and hove offered a fertile Held for w rltora of all types, mllllonl. The Colorado River Boord of Colllomla has profe<;ted In both lito rory and acfenliftc. ua 1970 report ntttlo>d " Ne<>clfor Controlilnq Salm.ty of tho Colorado Perhaps th
f Plon11 9lve off wo tt r
Wohr t e01 oporotes
Salts remo•n beh1nd
4 Thore waa, lor instance. a story to the effect that the conllnuf>d th- loyera of soil. It con accumulate tn a layer of sandy soli In one deposits ol the larc;re volume of Colorado River sill on Its d81ta wem area and travel lhrouqh the sand to crop out some distance from so increastnq the woiqht on that sec;rment of the earth's crust that it where It entered. This couaee an artesian prouure which often gives would sink and permit the waters ol the c;rulf to rush In and sub the farmars and technicians some real concern befom it is dis· merc;re lmporlal Volley. covered. A hlc;rhly d1otortod story about the Valley has rocontly been In 1922 the Imperial ln1c;rt111on Dlslrtct stoned a system of drain· circulatenQlneers, soil sctenhsta and soli conRervotlonlsts, the farmers hove b ...n able to combat th problem aohsfoctortly. The Volley ts composepestta of waler transporteALTO f,J 51:'. A M E c 0 more as a lens or pocket. ORI\INAGE BASIN Salt, belnq the motn problem, has a way ol occumulotlnq In CAI,IfO,NIA ~ MtiCtCO
6 1 The woter fi'Qm moet the dlsaolvC>d salts. The ~rcentage of applied water that must pass stroama Jn the wnst"m through the root 7.one deponda on tho snit content of the wat&r and Un:tod Stat s contntna anita the ICllt toloranco of the crop. In Q•mernl, sensitive crops wi 1require of varyinQ lcir.ds and ooncen· about 25% mor& wolpr thnn the plant needs, and more tolerant lratlons. They oome from crops about I 0'}'•. soils whtch have been ex· posod to wat<>r flowing to Sal!nlly I ala con be mode to delermme lhe amounts of leach lower elevatiom:. Under no· woter noeded. In Qen ral. the ealfnlty love) at any depth In the aoll tural conditions !he concan· prol!le con be reducod ubout eo• • by tho appllcaUon of one foot trotlon of ealt variea with olleach wot r lor each loot of soli down to that depth. f'o:- leachlnq tb& amount of water flowing. to he f!octlve, a 11ood dra!nnqe ayatem must be provld<>d. Concentration was low when In 1940 the Imperial lrrtq:rllon D!stnct oslced the Soil Conser the flow '1108 h1qh and vtce vation Service to conduct reaearch on the draina11e and sol1m:y versa. prob!ema. from th13 work evolved the Donnan formula wh1c:h is boalc lor the tile d slqns being ronde today.
Woter Goea, Salt Stays Us nq this formula. the d algner must know the permeability, 1 I& dopth, drowd Jwn. barrier loco• on and drainage coolbclent The lncrecr.se In the ovvr-all conc.nlratlon Is due to the evapora beloro tile spacing can he computed. Spacmqs in the Valley range tion ICM!Ses from the storage reservoirs, such as lake Mead, and the from 50 feet m the silty clny soils to 400 feet in the sandy so1!s. return of drotnaqe water from Irrigation proJects. As the woter evaporates, the ealta remcrln. Thl• l1•ld re ..mbl•• a wom corpet du• to 1ah accu.mulatlon.. f'uture tncrtW'Iftea In d With excess •olt occumulr.tllon already In the soli and additional cnnounts orrlvlnq dally In "fro•h" Irrigation wator, tho problems must he eolvtld In one of two wuyo: , lth11r lind additional sources of pure wah r. or I ncr• oae the t>UI<"ioncy of th11 drainage system to transport qrooter amounts of dlaaolved salts. The system for malnlalnmg the soh balance In Imperial Volley cons'"Is of two m tin out! •II t rnnchca the New and Alamo Rivers Into which mply th I 400 miles of open ditch drolns. dug and molnt 1lned Ly thf hnp.>111t lrrlyot on D air ~·t. Theso opon drama s rve 11 ou 11 1 for lh 11 e rir 1 no•N ayat rna ol th tnd•vldunl l The 10 I r m v th n d flCJ ds on a proec>ss coiled leachmq and ts a mplishoxl by k plnq th anita moving down through the so I hy applymg m r wo r han h p u s. Th.. X WOI r f. a lhr uoh th root Z!>ll oorrymQ away 10 • NET ACRES CONCRETE LINING TILE INSTALLED IRRIGATED 1929 to 1970 MJieoge Tilt Acteag• 1944 to 1970 1954 to 1970 Year ln•tolled Tlltd 1929 to 1943 53b08 2.~.120 Ytor Acree Ytor Mdtl ] 944 ooo-o OOfHOO OooOoO oto .. 0-ooooO...... o GO.OO 1,880 1945 ...... 55.00 3.240 1944 384.256 1954 _ ...... 50 1946 133.25 5,480 1945 •• 3'13.699 1955 1.65 1947 325.00 17,920 19~6 405,646 1956 ...... 4.91 I 1948 393.80 17.220 1947 412.083 1957 7.53 .I 1949 455.62 21670 1(148 420.821 19S8 6.72 1 9~0 458.00 22,610 1919 ~ 28,925 1959 11.63 .,. 195 I 603. 10 22.665 19: 0 429.()45 1960 8.22 1952 709.54 23,345 1951 ...• 434,648 1961 ...... _ ...... 13.47 1953 512.19 16.000 19'i2 ...... 444,853 1962 .... 19.10 19'i4 491.12 14.960 1953 • 445,061 1963 33.20 1955 6.92 1~. ICO 19)4 4 ,391 1964 :>3.04 1956 519.36 13,290 474,557 1965 54.53 1 9~5 1957 560.97 12.200 19o6 482.374 1966 68.99 1958 490.88 10,690 1957 ...... 494,234 1967 60.64 1959 546.54 9,550 1958 496.922 1968 52.70 19CO '194.0.~ ]< 713 19 9 440293 1969 56.38 1961 857.51 17,921 1960 434,379 1970 ..... 39.35 1962 611.01 11,485 1961 .•.. . . 435,664 TOTAL ...... 492.56 I ' 1963 766.02 10,129 1962 .. 429.557 1964 993.97 12,707 . 43~.181 1963 ••·•···· • 1965 734.52 7,958 19G4 .... 431 708 1966 527.38 6,634 1965 • 432,612 1967 634.00 6.~ 1 9 1966 ..... 437,529 1968 754.33 6046 1967 ·····- ...... 445.428 1969 808.64 6010 1968 . 441.155 1970 1,03C.61 8 ?.30 19G9 ..... • ...... 41 1.300 1970 437,336 TOTALS I ,89 .41 362 2 12 13 Moet ttle linea me Installed nt elx-foot averaoe depth because "IIC'IItno" bncause the electrical conductivity ie usually qreater than elun"'" by tht1 Sot! Conanrvotlon ~rvlce and the r.aults of actual lour mllltmhoa per cubic em and sodlum-porccntaqe Is less than 15. lnstallotlona have shown that this dnpth wtll ade>quotely serve the Ordinarily the pH ia lesa than 8.2. great maJority of sotll In tho District. Occasionally, soils have stratiltcalions that require tile elqht to 12 feet deep. Saline eolia are often recoqnlm by the white crust on the surface. Salinity may oceu.r tn soils havinq distinctly developed The District maintains lie opon dro!n syst~m to provide a gravity profiles or In strallfred profiles as found In Imperial Valley. The outlet lor a!x-loot Ule depth. Tho Dlatr.ct installs. operates and mom· chemical charactorlstics of aoila classod as 80hne are mainly dotor lalTUI a eump pump tor a!Jc.foot depth Ulo at thoao localtoTUI whel9 mtn In Jmponal Valley the SCllt balance can be mainioinod by The table on paqo 16 Is a summary of the salt balance report adequate lectchmQ. Our colc SALT BALANCE BY CONSTITUENTS Excluclino Water and Salt from Mexico TONS OF CO N STITUE N TS Total Oi1c.har9• Total Total TotaJ 1170 A.F'. • • Co Mg Na+lt: Hco. so, Cl Cation• Anion.• Tone lnflu nt 2,754 898 400,7bC 132~90 556.997 bl 773 1.3.~2 862 32.G33 I 090,253 , '47, ;a 3,33'l,J21 Effluont 1.020.503 288.198 142.127 793.791 169.729 I J.l9 4101 1,09882(1 1,22•1,116 2.417,9)5 3.642.071 &.! once Uonsl 112.568 +9.537 +236.994 192 045 203 4CI <16.193 + 133 963 + 170.687 +304 sso % G •Plus 11qn denot•• qa n 1n aa.l rc-IDOTW ~ • D harq• I u 1•1 ha ~-eon ct >J.&ted by aub'roctun wote- tnOow f·om Mexico M&nua agn denorea lou ln eaJ:t removal t: h<" mrtc- .-~ outlet d hutt;o Ton• ol C'C<;;.atituent$ hove been odicsted by ubtractlnQ 1 na ot -on tit enr tnllow from ~•1uc:o lrom t~eo to&,::~l ton.s cl con It n 1 ow n AI o and f,•w fbvet at outlel corop~ted prior to a~:huahnQ or~• ror woJtrr nllow lrom Mo:lll eo 14 There was conslderoble baH exchange 1r1 addition to a SALT BALANCE REPORT - 1970 Excluding Water and Salt from Mexico Summary Influent Summory Adju•ted Effluent Adjuoted Yoarly Summary 1958-lt70 Total Monthly Ton.t Total Monthly Tona Tont oJ Salt Ton• of Ptr Cent Oltcharo• of Dlecharv• of Brought into Salt Lou or Month Ac.·l't. Salt Ac. 1'1. Salt Ytar the Art et Rtmo•t d Gain January 171.0<;3 220.754 76.953 304398 1958 . .. 2.723,153 3,341,376 22.70'JI. 16 17 Industry of the world. The qutdonce and concern of the Imperial The Bureau of Reclamation's Colorado River Bnsln salinity lrri9allon Oislrlct. wtth the osststance of the Soli Conservation _·ontrol pruqram will provide for "stru 11on and operoUon of Service, and In cooperation with other branches of the USDA, hove proJects and tne tmpiementauon of other measures that would pre helped him raach o hiqh plateau of success. von! millions of Ions ol dtssolved salts from reaching the river. This proqrom will take many years to complete, but beneflls will accrue Jmpo>rlo! lrrlq::r.ton Dlatnct mt nda to assure the ccnllnuaUon of to lmpenal Vallt1y farmers aa each element of the proqram Ia com· thla suce~~uful aQrlculturnl operation by worklnq with the Colorado pleted and placed Into opcrohon. River Boord on o federal salinity control proqrom that will reault In prevenbnq dts'!Oived salts from en• •lrq th"' Colorado River. Poatbt)":.-s for auQmanlmQ th• river wtlh low·sallnlty water lndude (ol tncrea.,nQ preopltallon tn the mountomous heodwolor Summinq Up oreas of the Colorado (weother modillcotionl: (b) desaltinq ocean wa:er and lmporiinq it to the Colorado River: (c) desalting the Qec; The 1.40Q.mtl•~lonq Colorado Rlv"r Is thfl lifellnfl of Imperio! th.•rmo: aluam resourws undorlyinq lmpertn! Valley; (d) lncreoslnQ Valley, Ita water makes It possible to lrrlqote more than 500,000 runoff from the Colorado River's watershed by veqatallve manoQ& acres In 1ddillon to servlnQ some 78,000 o n•s In the Coachella ment (replaclnq woody shrubs with qrassea); and (e) lmportlnq Otviston ..wd 67,000 OCf91 In the Yuma Pro!oct m California and naturally""'<:CUrrir>Q water from bostna with a plentiful surplus. Anzona. In addition, there Is the posslbihty of reducmq the rtver's water But whJie the river is powerful and losclnotinq in Its beauty, it losses lhrouqh channelization of the river and removal of phrealo comes only o compomttve:y small amount of water. This has phytes. Because of the llrrui In 1968. the liD pr-ntod •esttmony bof<'>r .. th Subcommittee Up to Ooly Up to Not More Than ...... 2~C• on lrrlQatlon and Reclamahon of the Hou~" of R >presentallves MiUimhoo Mllllmhoo Millhaho• Commtnee on Interior and Insular Aflairs lndicahnq that <;t further Barley Rye F'teld Beans deterioration of water comtnq into the liD system will mean lhal a Beets Wheal Ladlno Clover considerobly qreator quanhty of wato~r will be needed by the D!slrtct Cotton Sorqhum Radishes to do the same Job II Is do•ng now tn washing salts and other Bermuda Grass F'lox Celery Impurities out of Valley soils. Dotes Alfalfa Green Beane Hlqhest soltnily level of th" riv~o~r durlnQ the year · nda t•, oe<:ur Asporoqus Tomato.. Oranq.. a In winter durlnq I he Qerml nation period of the plants, the time when U>ttuce Grap fruit plant seed 5 more susceptible to salt damaQ~. Carrots lemons Gropes Various ways to remedy the altuabon have been suqqosted. Cantaloupes There is one maJor proqram thai would remove salts from the river's •Etectrlcol conducUvity of acturohon ex.tracl of the toll Th• •lectrical wot<>r which con be lmpl >mnnttod now, and several lonq-ranqe conductivity Ia the reciproc:ol of the e1eetrieoJ reslsllvity The raals~ poo.atb.:lh••• that wc.uid dilute the rivur'a ao.· load by addtnQ water II•UY 11 !he re•1at u\re 1n ohma ot o conduC1or wh1ch I• I <-:1\ lon9 and hO$ a crouHCtlonol or.a ol I c:m1 Henc:., e1Ktnco1 condueh•ltY lt or low salinity to the river. expre.. ed In rec:~pr~X<~ I ohtna per eenumeter, or mhot per nntunete• 18 19 SALT BALANCE DATA Colorado Rl ver Water Enlerlnq hnperlal Valley 1944 lo 1970 To.. OJ.tchcrr9• Below Total To111 Total To1>.1 C:oln ( +) Plants give off Drop No. I Solt Jmport•d Salt Exported or water In Acrt·F••t • T.D.I. P.P.M. rio A.A.C. ucl. Mexico•• Lou (-) 1944 2.44~.002 0.96 706 2.342.420 2.102,938 -239.482 1945 2.515,586 1.01 742 2.544,585 2.332,480 -212.105 1946 2,697.450 1.00 735 2,701,835 2,288,977 -412,858 1947 2.633,390 1.02 750 2.685.445 2.321,893 -363,552 1948 2.699.314 0.98 720 2,655,204 2.542.314 -112.890 1949 2.761,992 0.93 684 2.~64.129 2,709.346 + 145.217 1950 2.938.666 0.94 691 2,749.108 2,855,378 + 106.270 1951 3,066,618 1.00 735 3,056,565 3,139,970 + 83.405 1952 3.203.411 0.95 698 3.043.417 3,364.335 +320.918 1953 3,3:>3.244 0.98 720 3,273.515 3.684.315 +410.900 1954 3,095.783 1.01 742 3,132.052 3.648,649 +516.597 1955 2,927,165 1.17 860 3.419.238 3,577,562 + 158,324 f~ 1956 2,906.746 1.27 933 3.682.548 3,713,208 + 30,660 1957 2.781.792 1.22 897 3399,439 3.603,489 -'-204.050 Salts remain $ 9 , 9 \I ,\ 1958 2,730.876 1.00 735 2,723.153 3,341.376 +618,223 1 behind - "" )959 2,840,173 1.00 735 2.852.019 3,401,652 +549.633 Jlf,l 1.06 779 3,162 485 3.558,534 + 396,049 9 1960 2,983.860 Y 1-w ' 1961 2.957,200 1.13 831 3 330,087 3.572.808 +242,721 9 I I I 9 1%2 2 9~1266 1.15 845 3.399.464 3.806.946 +407,482 I 1963 2.991.429 1.13 831 3,378.583 4,050.087 + 671.504 9 1964 2,770.474 1.19 875 3.284,284 3,635. 121 +350.837 Water and salts 9 t 1~1 b f: 1965 2.6?.4 363 1.30 955 3,406,457 3,819.255 + 412 798 move upward --~~V!(IIT' ~:Lli:':P'__.;-.:::---""-~-9 __..., ___ 1966 2.817,912 1.30 955 3.650447 4 148.874 + 498,427 from a W 1!. -- 1967 2,719.Bul 1.22 897 3.306.261 4,1J9.477 +833.216 ~ 1968 2.806,124 1.21 889 3,408.548 4,012.009 + 603,461 water table '$¥ - ~ 1969 2.675.833 1.27 933 3.396.105 3,754 477 +358,372 1970 2.7>4.898 1.27 933 3.488.023 3.780.732 -292.709 •The diver on a1 trop J f.i'~t"lurir 1 any w Jlnt d•hvcred 10 MftiiC'O ••1'11• toM of • rtl fi"J)Otlud 10 tlu eolu111n rmhtlt J '[wpelt" ••elude <'QI'IItlhu· Ilona by M• :rl 21 20 IMPERIAL DAM- WATER DIVERSION DESlLTING In the drolnaqo boatn between Park<•r and lmpertal [).-,ms. are the motor sources of ausponded matter to be ramoved by doslltlnq boatns. Imperial Dam, a Vital linlc between the Colorado River and the All-American Conal, hoe a Primary function of dlverhnq water Into Tod lmpenal !moatlon D!stricl Is responstble for the operation and CONCRETE LINING maintenance of the All-American Canal headworks portion of lmpenal Dam. which Includes troshtaek. roller qatea. and the The District continue$ to waqe a viqorous campaiqn lor more dealltlnq boalna. The Bureau of Reclamation Is responsible lor the concrete llninq of l Cnnol mmnr, nono· due to silt aCf'Umulatlon was a constant In D<>comb{lr 19?0 th11 flQ\nos were chonqtld. Now the land· problem to the District. formers were continuously forced to relevel own••r pays 30 per c·•nt wtth a llmit of $3 per llnool fool per land· their land. Du..,nq 1901-38, more than 100,000 acre-loot of silt owner. and the District ?0 per cent. flowed throuqh the canal system onto the ftelda. Botween 1923 and A total of 39.35 miles of these laterals was concrete hned tn 1930, the District spent on avvraq~> of more than thte<· quarters of a million dollars annually lor alit control. 1970 lor the Dlslrict's operation and maintenance, bnnqlnq the total since tho boQmrunq of the proqrom (1954·?0) to 492.56 mllll'l. The All·Amerlcon Canal, located enbrvly within the United States, replaced the Alamo Canal as a delivery canal lor Imperial Valley. Startmq with the complebon of Hoovar Dam. the amount of sediment arrlvinq at Imperial Dam has been qraduolly reduced as addiUono! re.... rvOtrs hove be..n CNated behind Davis and Porker Dome. Chartnel deqrudotton and bonlc eroelon, alonq wtth ram runoff 22 23 IMPERIAL DAM ENGINEERING DATA HISTORIC DATA- Con!roct for construction of Imperial Dam and All-Amerlcan Canal dealltln9 works was awarded in December 1935. Con tract work startod in January 1936 and was completed In July 1938. OVER-All LENGTH: 3.475 feet tneludlnq 490-foot d•ke at Arizona end. OVERn.OW WEIR SECTION: length- 1.197.5 feet. Hoiqht -from base to crest at 181.0 foet elevation- 31 feet. OPERATING BRIDGES OVER NON.OVERf'LOW SEC'J'lON: Elevation 197.0 feet. Freeboard above cr~>St of maximum calculated flood- 6 feet. MAXIMUM CALCULATED FLOOD OVER WEIR: !Ofeet. TYPE CONSTRUCI'ION: R&tnforc.Pd concrete slab and buttreaa type, MAXIMUM DIVERSION CAPACITIES: AI!-Amertcan Canal- 15.155 aecond·leet. Gila Canal - 2.200 second-feet. LOCATION: Clo••·up of acrapera In d ..llllng baaJn which movt 11lt to c:enter of Approximately 20 mlles north110st of Yuma. Arizona. on the mounting pedeatalt. Sctap•r• rotat• one• •ete.h 13 .mlnut•.. Photo Colorado River. Can be ren~hed by county road from •howa betaln emptied ot water for repoil or mahUenonce work eueb a.a Winterhaven, Ca!Jfomla. mou control. DESILTING: All-American Canal - Three desUtinQ basins are locaiod Immediately below Imperial Dam. Each basin has a dealqned flow capaclly of 4,000 cul:>1c feet per second. Swlft-llowinq water keeps the eedlment in sus pension between tne Intake Qates and the doellunq basins. VelOCity is reduc"d as wat~>r llowe into the baaine, pnrmitUnq solids to be deposited. Silt Ia continuously sluiced back lo the nver lhrouqh underqround papoa. Clear water, skimmed off the top of the basins, Oows into the All·Amerioan Canal. Gila Canal- One deslltinq basin removes eediment prior lo entry of the wator Into the Gila Canal. Sttdiment Is returned to the river. when necaa~~eny. by openhtQ •luiceway qotee located on the lower ond of the desllttnq baatn. 24 £otT&..O ,_NO PV.Lt.HI"O . ... COMMUN ITY AND $PI!CIA l. SU VtC« • IMPERIAL IRRIGATION DISTRICT BULLETIN NO. 372 • SECOND PRINTING - - ...,, a.CIIIfa.&C.W