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<br />"'" <br />,.... <br />C\l <br />..... <br /> <br />ONFARM PROGRAM FOR SALINITY CONTROL <br />GRAND VALLEY SALINIlY STUDY <br /> <br />, <br />'d <br /> <br />c...) <br /> <br />Irrigation System Improvements - Five types of improvements have' been iden- <br /> <br />tified as needed for existing enfarm irrigation systems. First, ditch <br /> <br />lining or pipelines will reduce seepage from enfarm distribution and field <br /> <br />head ditches. One standard design for ditch lining will be applicable for' <br /> <br />all locations. In cases where a preference for pipe was expressed, the pipe <br /> <br />sizes considered ranged frem 4 inches te 36 inches in diameter. Pipe sizes <br /> <br />are displayed by size greups in Table 23. Necessary components of the ditch <br /> <br />lining program will be the installation of water measuring devices and <br /> <br />inflow and outflow control structures. The measuring devices will include <br /> <br />small wiers or critical depth flumes at key locations on each farm so that <br /> <br />water delivery to each field can be carefully controlled. Outflow control <br /> <br />structures will be needed to dissipate kinetic energy in the flowing water <br /> <br />and prevent erosion. <br /> <br />Second, land leveling is needed on half of the irrigated land in the valley. <br /> <br />Land leveling serves two major purposes; it adapts the field to the use of <br /> <br />lined ditches or gated pipes, and it allows a more uniform application of <br /> <br />water across the field during irrigation. Ditch lining and land leveling <br /> <br />are mutually complementing practices. <br /> <br />Third, subsurface drains in place of existing open drains are recommended <br /> <br />where improved salinity control can be enhanced through larger field sizes <br /> <br />and more effective irrigation systems. <br /> <br />Although there are 1,600 acres of <br /> <br />land where cultivation and crop yields are impaired by an existing high <br /> <br />watertable, the plan dees not include additional drainage measures for the <br /> <br />purpose of increasing crop yields. As canal and lateral seepage is reduced <br /> <br />by lining and as field irrigation efficiency is improved, the watertable <br /> <br />57 <br /> <br />Revised November 1979 <br />