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concerning efficiencies for several of the larger ditch systems in Division 3. The revised <br />efficiency estimates were developed in consideration of more detailed information on canal <br />lengths, water loss rates, cropping and water application techniques. Table 3 presents revised <br />efficiencies for four of the larger irrigation systems. <br />Table 3 <br />Ditch Specific Irrigatio n Efficiencies <br />Conveyance Application Overall <br />Efficiency Efficiency Efficiency <br />Farmers Union Canal 71% 50% 31% <br />Prairie Ditch 65% 52% 34% <br />Rio Grande Canal 56% 61% 34% <br />San Luis Valley Canal 75% 63% 47% <br />The revised memo by the Consumptive Use Contractor also identified maximum application <br />efficiencies for all structures depending on water application technique. For lands using flood <br />irrigation techniques, a maximum application efficiency of 60 percent was recommended. A <br />maximum application efficiency of 85 percent was recommended for sprinkler irrigation. <br />Overall surface water efficiencies were estimated as follows: <br />eff• - conveyance eff• application eff <br />Where: SW conveyance eff. =User Input (maximum) <br />SW apprcafi°~ eff. = Crop Demand <br />Headgate Delivery <br />The Phase lc model and subsequent model development phases include surface water <br />efficiencies calculated using this method and represent average monthly efficiencies over the <br />1950-1997 study period. <br />Groundwater Use <br />The Consumptive Use Contractor identified that, in several areas, a combination of application <br />techniques was used to apply water from groundwater wells. As such, groundwater efficiencies <br />were determined using the following approach: <br />GW eff = <br />(GW Lands Flood Irrigated) * 0.60 + (GW Lands Sprinklered) * 0.85 <br />Total Ground Water Land Acreage <br />The Phase lc model and subsequent model development phases include groundwater <br />efficiencies calculated using this method and represent average monthly efficiencies over the <br />1950-1997 study period. <br />Summary <br />Development of the Phase la - lc Surface Water Model requires estimation of system water <br />use efficiencies. System efficiencies for modeled structures receiving surface water and <br />groundwater were estimated by the Consumptive Use Contractor and these estimates were used <br />in the Phase la and lb Surface Water Model. Subsequent refinements to these estimates based <br />C:Acdss\Task8-2.doc Efficiencies of Water Use September 8, 2000 -Page 3 of 4 <br />