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Section 4 <br />Agricultural Conservation Measures <br />When evaluating agricultural water conservation improvements, it is inlportant to <br />distulguish between practices that lead to improved application efficiency, as <br />opposed to reduced consumptive use. Water use efficiency is defuled as the ratio of <br />water applied coinpared to water consunled by crop (i.e., ET.) Increasing efficiency is <br />likely to reduce losses from deep percolation ~1d rwloff (thereby altering historic <br />return flow patterns), but it may or nlay not materially affect tlle anlount of water <br />consunled by t11e plant. Muc11 of the water lost to these inefficiencies will return to the <br />river or groundwater system for use by downstream diverters. For this reason, tlle <br />~~~ ~~~~~~~~~ ~~~~~~ ~~ ~ law and customs in Colorado are clear that water <br />In Ce~tain Situati0ns, imprOVed conserved due to water conservation practices that result <br />irrigati0n Systems SuCh as u1 inlproved efficiency is not available to fl1e original <br />sprinklers and drip systems may ~ppropriator for additional irrigation or other expanded <br />result in improved application uses. <br />uniformity over the entire field. <br />COnsequently, areas that Exanlples of ineasures that increase efficiency ulclude: <br />previously were under-irrigated <br />and where crop yields suffered ^ Ditch lining <br />now receive adequate water to ^ Pressurized pipe <br />meet full crop ET. The net result ^ Conversion of flood irrigation to gated pipe, sprinklers, <br />may be increased crop or drip <br />COnsumptive use on a whole ^ Land leveling to increase irrigation uniforn~ity <br />field basis and greater water ^ Furrow diking and contour farnung <br />use. ^ Peduced tillage systems <br /> ^ Irrigation scheduling and nlonitoring <br />^ Tail water recovery <br />^ Polyacrylanude (PAM) use in ditches and furrows <br />T11e efficiency of various irrigation systenls <br />vary. Flood irrigation normally ranges <br />from 30 to 50 percent efficiency. This <br />means that 30 to 50 percent of the water <br />diverted at fl1e farm headgate is <br />consunlptively used, while the renlainder <br />is returned to flze environnlent via tail <br />water runoff, deep percolation, and <br />evaporation. Estimated efficiencies and <br />costs for various irrigation nlethods are <br />sunlmarized in Table 4-1. <br /> <br />DRAFT 4-1 <br />