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<br />" <br />Neithel' has the Distl'ict diverted~ ~or dO~B it intend to divert water through <br />the 1\J.l-1\:merican Canal solely Tor deV'elop~ng power at. hydl'oeleatr1c plant.s in <br />lin;perial Valley. The only water going tm;-~ these plants is that reCl.uil'ed. <br />to meet il'rigation and domestic demands w:\,thin the District. Pilot Knob <br />power plant Will discharge water back to Colora.do River and is therefo1'e in <br />a. different category from the othel' plants on the Canal, which are in Imperial <br />Valley propel' and within the drainag13 ares. of Salton Sea. <br /> <br />II ~ DRAINAGE IN ~IAL VALLEY <br /> <br />Necessity 1'01' Drainage <br /> <br />~e dl'ainage problem: in Imperial'Valley is linkedclollely with <br />problems of Salton Sea and water quality.] As in otlileI' inigation pl'ojects~ <br />the necessity of adeCl.ua.te drainage was not fUlly appreciated during early <br />development of lin;perial Valley. As a conseCl.usnce, pl'oductivit;r of thousands <br />of acres was seriously affected by high water table and incl'eased soil <br />salinity. Some lands went out of produc~ion. <br /> <br />Object 01' Drainage <br /> <br />Most western wat.ers,. conta.in sa],ts Which, without proper ilI'a:tnage, <br />affect the productivity of land and. evenllually make it unfit for agdeultural <br />use. "The lllain objects at drainage are to lllaintain the groundwate1' level at <br />a proper depth below<.land surface and to . remove salts fl'om, and prevent their <br />concentration in, the root ~one. '!he prOblem: in Imperial Valley is most. <br />difficult. "The soUtar great depths is. Colol'll.do River silt, highly stratified, <br />in disconnect.ed pockJts aJ1d lenses, and ranging from: sand to colloidal clay. <br />'!here. are no gravel and sand waterbearin~strata. Neither is there iI. "general" <br />underground water table as found under mpst irrigationpro.lects. In most 01' <br />the Valley, the water table is "perched"] on relatively :lJllpervious strata. <br />Because of these conditions, pumping for' dra:tnage is not possible. <br /> <br />Construction of Drainage System <br /> <br />The Districtts drainage system:,jCODllll,enced in the early 20t:s, now <br />consists of 1360 miles 01' open drains, ir depths of 12 01' 14 feet for the lllain <br />drains and 7 Ol' 8 feet for lateral drains. Most 01' the lllaindrains discharge <br />into 1\J.lli!I10 River or N'ew River, w:hic1l. sewe as ou.tlets to Salton Sea; a f.ew . <br />discharge directly into the Sea. It wa~ early discovel'ed that complete <br />solution d.epends on dra:tnage 01' individ$.l farms. CODllll,encing in 1928, some <br />3600 miles of tile farm drains have beeI!. laid. The l:l.nes f;l.l'e spaced mostly <br />200 feet aRart and 5 or 6 feet below the surface. Average cost 01' draining <br />a farm is l\I50 to $60 an acre, exclusive :01' engineering, which is furnished <br />Without Clost to the landowner by the Di$tl'ict or the Boil Conservation .Service. <br />Results indicate that effective drain:ag$ ClU). be pel'llllUlent1;r provided on the <br />tightest soils of lin;pel'ia1 Valley. <br /> <br />Salt Balance <br /> <br />One measure 01' the effectivenells of dra:tnage is the amount of salt <br />r.emoved from: the project. Continued production reCl.uires removal 01' at least <br />as much salt as is brought in with the irl'igation water. The District has <br />l'ecords of the tonnage 01' salt coming i:nto the Valley through the 1\J.l-1\:mel'ican <br /> <br />~28~ <br />