WSP00978 - Laserfiche WebLink

Home Browse Search

',. ., ~ N w co . i I ;-, I ; .f!j '",.n' ,'I. "".,<.,-~ The program for the opt:imal on-farm salinity control program depencls on the desired level of control which was selected prior to implementation. Depe\'lding on the chosen level of salinity cOlltrol for an area, heacl ditch lining woulcl be the first measure to be implementecl until approximately 42 percent of salt is to be removed, st which tiimecutbeck furrow irrigetion (semi~automated) woulcl start to replace the ~eaclclitchlinings to remove up to 67 percent. If control above the 67 percent level is llesirecl, then construc- t:l.on of gated pipe tailwater reuse systems or other similar automatecl systems are initiated to remove up to 80 peroent of the attainable aalt before sicle~ roll sprinklars become cost-effect:Lve. Drip irrigation, if applicable, is the last alternative to be implementecl. This edditive approach is illustrated by FiguTe 19 which sho"Ws the nonlinearity of the cumulative on-farm cost- effectiveness function. The annual costs can be computed using Equation 8 and establishing the on-farm A and B values for ;eaohirrigated erea. Throughout this: analyeis it was assumecl that inigatior\ scheduling anc\a higher level of management would be imposecl on theon-farm irrigat:ion programs. This arrey of on-farm altecrnatives is. not intended to be all inclusive, . but rather to :l:ndicatethe types of, systems which should be imp1ementeclto achieve a c1es:l.recl level of contToL The Soil Conservation Service or other implementing agency should approach this strategy in terms of establishing poliCies or priotides for c1istdbudngcost-sharing monies for on-farm improvements. For example, a gTadueted ecale of cost:-shaTing percentages could be formulatecl "With the highest level of goveTnment contribution being evailable for the most efficient on-farmim~rovements. Collection, Treatment and Disposal qf ReturllFlOws.-7 . ". ..' .. ... '. . In many cases where salt pickup is apart1cularlY' severeprOb'lem,sub- . surface return flo"Ws from irrigated lancls may be so.brackish that no further use of the water. is p.ossible. . Such flows significantly degracle the quality of a river,stream, or grouncl"Water reeource.l\.n alternadveto expenditures . aime.c1 at reducing the volume of these flows by improving irrigation effiCiency is to collect the subsurface return flows before they enter reoeiving waters, The ,collected flows can then be directed to. a deselination plant that removes most: of the salts ancl returns the "Water to the stream or directly toa dis7 posal area. Major disposal eltecrnativesinc:ludedeep well injection anc\ evaporation ponlls. Various desalination methoclsare discussecl indetail'by Walker (1978). . The costa of collection, desalination, injection wells, anclevaporation p")ldsa,,e describedfor,planningc1~urpq$esby the United States Department of '-, 'ehe"""Interior (1'972').' '. A mathematical' description o'f' the~:'same infoo.natiotL is .givenby Walker. (1978). . In gllneral, the costa ,of the collection, desalina- ..... .tion,.;and. brined:tsposal. for salinity..con'trol exceeds the costs required to . achieve the same level of salt reduction by, improving irrigation efficiencies. HowoWer, by comparison, lining large conveyance systems or implementing highly automated irrigation systems iecostlier. The c1esalination alternative is relatively free of the institutional complications involvecl in improving an entire irrigated area, but is an intensive user of snergy. ','" .", ."~. -;.- . 62 ,.