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<br />r.>.r, ~J \.i '" <br />U:"P "V ,JD <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />the annual diversion required to meet the full consumptive use requirement <br /> <br />is approximately 4,100 acre-feet, based on a crop consumptive use requirement <br /> <br /> <br />of Z.2 acre-feet per acre and a maximum inigation efficiency of 50 percent. <br /> <br /> <br />For this study, irrigation efficiency is the percentage of water diverted from <br /> <br /> <br />the stream that is consumed by evapotranspiration and evaporation during the <br /> <br /> <br />irrigation process. For inigated areas above the 7000 foot elevation, the annual <br /> <br /> <br />diversion required for to meet the full consumptive use requirement would be <br /> <br /> <br />about 27,900 acre-feet, based on a consumptive use requirement of 1.7 acre-feet <br /> <br /> <br />per acre and a 50 percent inigation efficiency. Total annual diversions required <br /> <br /> <br />to meet the full crop consumptive use requirement would be 3Z,OOO acre-feet. <br /> <br />The Water Commissioner for Water Districts Z9 and 77 has indicated <br /> <br /> <br />that generally there is a good supply of wafer, especially along the larger river <br /> <br /> <br />segments and at higher elevations. Occasionally, some late season shortages <br /> <br /> <br />occur on the smaller tributaries, but do not affect the overall river depletions <br /> <br /> <br />appreciably. In-igated areas in the San Juan river basin upstream from the <br /> <br /> <br />confluence of the Navajo River generally receive a full inigation water supply, <br /> <br /> <br />resulting in an average stream depletion of about 16,000 acre-feet. <br /> <br />Because much of the inigated land in the basin is located adjacent to <br /> <br /> <br />the San Juan River or its tributaries, groundwater return flows resulting from <br /> <br /> <br />inigation were estimated to occur generally within a one month period. There- <br /> <br /> <br />fore, the monthly stream depletion associated with inigation is approximately <br /> <br /> <br />equal to the monthly potential consumptive use of inigation water for the 9,050 <br /> <br /> <br />acre irrigation area. <br /> <br />Evaporation from the 118 acre surface of Echo Canyon Reservoir, a <br /> <br /> <br />Game, Fish and Parks Commission recreation reservoir, has averaged about <br /> <br /> <br />340 acre-feet per year since 1969 when it was first filled. The reservoir storage <br /> <br /> <br />does not fluctuate appreciably, and therefore river depletions due to the storage <br /> <br /> <br />and release of water are negligible. Evaporation from the 15 acre surface of <br /> <br /> <br />the Pagosa Springs wastewater disposal ponds have averaged about 40 acre-feet <br /> <br />-22- <br /> <br />;i>",,,, <br />