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Erosion and Sediment Problems Critical erosion and sediment problems exist on the shale badlands or shale-derived alluvium entrenched by gul lies. Most of these critical areas are also associated with irrigation canal waste or field tailwater return systems. High sediment yields are generally associated with soils underlain at shallow depths by shales of the Mancos Formation. These areas generally contain soils with a sal ine substratum and through the erosion process are responsible for a large part of the salt pickup by irrigation return flows. The very high sediment yield suppl ies a sus- pended load of clay and silt particles, and a salt loading of calcium, sulphate, sodium and chlorides. Figure 2 is a general sediment yield map of the Lower Gunnison Basin Unit. Also, serious streambank erosion occurs on about 180 streambank miles and moderate erosion on about 170 streambank miles in the Lower Gunnison Basin Unit. This results in an estimated 408,000 tons of soil loss annually. The Uncompahgre Subbasin from above Montrose downstream to near Delta is the area of largest potential for improvement because of its very high sediment yield, large increases in salt loading and serious streambank erosion. This area is mostly within the USBRs Uncompahgre Project Improvement program scheduled for completion in FY 1977. Irrigation Systems and Management Problems Federal Reclamation projects provide water for 98,970 acres or 54 per- cent of the irrigated cropland in the Lower Gunnison Unit. The Fruit- growers Dam, Paonia Project. and Smith Fork Project are designed to provide supplemental irrigation water suppl ies. while the Uncompahgre Project is a full-service system. Total crop consumptive use on approxi- mately 176.500 acres irrigated each year is estimated at 271,500 acre- feet or about 1.5 acre-feet per acre. Farm del ivery is estimated to be about 925.000 acre-feet (5.2 ac ft/ac). and total diversion is estimated to be 1.320.000 acre-feet (7.5 ac ft/ac). An analysis of the Gunnison River Basin prepared for the Water Conserva- tion and Salvage Study (1973) estimated the acres adequately treated and needing treatment as follows: Treatment Item Adequately Treated Needing Treatment . Water supply Conveyance system Return system On-farm systems Management 189.500 68,000 66.000 41,000 148.400 82.000 203.500 50.000 230,500 123,100 6 003CB!