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<br />8 <br /> <br />Irrigation Systems and Managem~nt Problems <br /> <br />Federal Reclamation projects provide water tor 98,970 acres or 54 per- <br />cent of the irrigated cropland in the Lower Gunnison Unit. The Fruit- <br />growers Dam, Paonia Project, and Smith Fork Project are designed to <br />provide supplemental irrigation water supplies, while the Uncompahgre <br />Project is a full-service system. Total crop consumptive use on approxi- _ <br />mately 176,500 acres irrigated ea<.:h year is estimated at 271,500 acre-' <br />feet or about 1.5 acre-feet per acre. Farm del ivery is estimated to be <br />about 925,000 acre-feet (5,2 ac ft/ac), and total diversion is estimated <br />to be 1,320,000 acre-feet (7.5 ac ft/ac). <br /> <br />An analysis of the Gunnison River Basin prepared for 'he Water Conserva- <br />tion and Salvage Study (1973) estimated tne acres adequately treated and <br />needing treatment as follows: <br /> <br />Adequately Treated <br /> <br />Needing Tre~tm~nt <br /> <br />Treatment Item <br /> <br />Conveyance system <br /> <br />189,500 <br />68,000 <br /> <br />82,000 <br /> <br />Water supply <br /> <br />203,500 <br /> <br />Return system <br /> <br />66,000 <br />41,000 <br />148,400 <br /> <br />50,000 <br /> <br />On-farm systems <br /> <br />230,500 <br /> <br />Management <br /> <br />123,100 <br /> <br />Improvement Needs <br /> <br />Improved water management IS needed throughout the existing conveyance, <br />distribution, -application, and return systems. Improvement in the <br />irrigation efficiency and reduction in salt loading will require a total <br />system emphasis on diverting the amount of water needed for crop con- <br />sumptive requirements, soi 1 leaching, cultural practices and unavoidable <br />seepage and spillage losses or deep percolation. Because the source of <br />a large portion of the salt pickup is from the underlying Mancos shale <br />formation and alluvial aquifers, the overall emphasis will be placed on <br />reducing canal and lateral seepage losses, deep percolation, and in <br />maintaining positive control over return flows to el iminate erosion <br />from fields and drains. <br /> <br />Watershed Treatment Needs <br /> <br />Prel iminary evaluations indicate that the contribution of salt loading <br />in the erosion process is from local ized watershed areas with high erosion <br />rates from soils with high salt content. 003\;57 <br /> <br />The opportunity for greatest red~ction in stream sediment load lies in <br />treatment of high sediment yield areas. For the Lower Gunnison Unit, <br />