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<br />..;........ <br /> <br />" <br /> <br />.~ <br />tV <br />W <br />J-6 <br /> <br />" ; <br /> <br />t~ <br /> <br />of this report, SCS values will be used sine.. it is anticipated that they will <br />be c10ing most of the lateral llnd head c1itc;,ll l.ip.ings. <br /> <br />The costs of converting a small c1itch or lat:eral to a pipeline conveyance <br />involves two cost estim..tes. The c1erivations of the cost-effectiveness func- <br />tions lire the ssme as given abov... Irrigation pipeline materials range from <br />plastic to concrete to metal. In adclition to 'the costs of. th.. pipe., installa- <br />tion costs aT" generally ..stimat'..d at $3. 50/m ito $4.00 1m depending upon the <br />pipeaize ancl local excavating condit:l:ons. Th.. Soil Cona..rvation Servic... in <br />the Grand Vall..y is pres..ntly estilllSting. 'pipelineco..te, materials plus <br />inotallat:ion at $0.55 peT inch of c1iam..ter per foot ($.O.72/cm diamet:er/met..r) <br />ine1ucling flow m..asuTement:, trash SCTeens and inlet stTuctures. <br /> <br />As a general rule, Slip-form concr..teand low h..ad (50 feet-head) PVC <br />pipelines hav.. about th.. same salinity control cost-effectivenes.s.. . However, <br />the use of low-h..ad PVCP:l:p.. is geneTally not, r..commended. Th..us.. of other <br />,m"terials in these ,small cspacity systems result in much highe" costs .and are, <br />. there~ore, no.t generally cos.t-effective in comp..r:t..on. The costs of commonly <br />avail"ble pipeline m'lterials ar.. stlIIlIIlarizecl in Appenclix C. <br /> <br />. On-Farm Improvements-- . <br />The mo..t significant improvements to recluce ,water div..rsions and. cOt\trol <br />waterlogging anclsalinity problems potentially come from improv..d on~farm <br />water management. This is particularly tTue for areas cont:aining larg.. quan- <br />tities. of naturally occurring nUs in.the soil profile.' Poor irr;!.gation <br />pract;\.ces on the farm are th.. primary cause of exce..sive "Water c1iversions, as <br />well 'Is. the primary source ofirrigationret~tnflO"WqualityprOblem". <br /> <br />A common misconception concerning salinity control is tllat improving <br />.irrigation efficiencies and r..c1ucing canal and lateral seepage would decrease; <br />the volume of percolating water, but may not.decrease the total ll1Ilountof salt <br />leach..c1. This would be true only if salt concentrating effects. were the only <br />phenomenon pl:esent and if th.. leaching water h..c1en infinite cap..oity to <br />dissolve salts. However, in most ..rid ..reas such a.. the Colorado River <br />Basin, salt pickup_ rather then concentrating. sffe!;ta is.. the c1ominantsource of <br />salinity. <br /> <br />The exact chemical phenomenon involved with water moving through the soil <br />. .p,rofiJ.e is v..rycomplex ancl diff:tcu1:t. to accurately predict: or mod.el. How" <br />ever, the basic processe.. are as the dilute irrigatecl water moves through <br />the soil profil.. it tends to dissClJ.ve .salts "Wh:l.ch.are illher.ent in the soil, <br />"'.whi'le'the salts.'whic.h'w..re coneentratecl' by crop use'"tend'..to pr..cipitate:.out o.f <br />. ".soluUoninto the soil. Thu..,..!l..irrigation effiei..ncie" "re increasecl, the <br />. .,.......diasolvecl solids .concentration in 'the' so.n also"'increase 'and .the1:'eis. .. <br />graclual shift from c1issolution of salts to conditions favoring th..i"p"ecipi- <br />tation. Therefore, an increaae in irrigation efficiency will always recluce <br />th.. smount of salt in the subsurface return 'flows (van Schilfgaarde ancl <br />Oster, 1977). <br /> <br />'-'. <br /> <br />""'.-' <br /> <br />,.J, <br /> <br />""., <br /> <br />The amount of s..lte which "Will b.. recluced by improvemente in water manage- <br />ment is ve"y often nonlinear ancl difficult to acc....s. Fortunately, in the <br />UCRB the chemical properties of the saline soils ancl parent materials tend to <br /> <br />54 <br /> <br />-~ :;--', ~ '. , <br />