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<br />0019GZ <br /> <br />Subbasin id numbers associated with County/HUC: <br />Unit 1(Archuleta/l4080101): 7, 14, 16, 19,20, 25, 28, 30, 31 (See Figure 3-6) <br />Unit 8 (Mineral/l4080101): 7 <br /> <br />Irrigated acreage above gage: (from GIS overlay) <br />Unit 1 (Archuletall4080101): 4,028 acres <br />Unit 8 (MineraIl14080101): 845 acres <br /> <br />Irrigated acreage in County/HUC: (Table 2-2) <br />Unit 1 (Archuleta/14080101): 17,626 acres <br />Unit 8 (MineraIl14080101): 845 acres <br /> <br />Share of County/HUC depletion used above gage: <br />Unit 1 (Archuleta/l4080101): 22.9 percent <br />Unit 8 (MineraI/14080101): 100 percent <br /> <br />Irrigated acreage above gage was divided by total irrigated acreage in County/HUC to determine <br />fraction of County/HUC depletions occurring above gage. Therefore, in natural flow calculations, <br />22.9 percent of the irrigation depletions in Unit 1 and 100 percent of the irrigation depletions in Unit <br />8 are added to the historic gaged streamflow at the San Juan River at pagosa Springs station. <br />Appendix E shows development of natural flow equations in detail for each of the 25 natural flow <br />stations . <br /> <br />Ground Water Storage <br />All return flows of newer projects were assumed to be ground water returns, which have not statted <br />returning to streams because ground water equalization has not yet occurred. Ground water storage <br />was computed for Dolores Project and NIIP lands. In addition, return flows were lagged using a unit <br />hydrograph in Spring Creek Basin (09355000) and McElmo Creek Basin (09372000) to obtain a better <br />water balance. This effectively emulates storage of return flows as ground water which return as <br />surface water at a later date. <br /> <br />Stock Pond Depletions <br /> <br />Stock pond consumptive use is assumed to be the evaporation from stock ponds developed to water <br />livestock. The total surface area of the stock ponds in the San Juan River Basin was taken from <br />Table 2, page 9 of the Livestock Water Use, 1975, published by U.S. Department of Agriculture, <br />Soil Conservation Service. Total surface areas are presented accurding to main tributary. The San <br />Juan River tributary stock pond surface area was disaggregated using livestock numbers as a <br />proponioning guide. The total surface area in each reponing area is treated as one unmeasured <br />reservoir. <br /> <br />An average free water surface (FWS) evaporation rate was taken from NOAA Technical Report NWS <br />33, Evaporation Atlas for the Contiguous 48 United States, June 1982, Map 3 of 4: Annual FWS <br />Evaporation. These values were used because of unavailability of pan evaporation data and to be <br />consistent with CSRCU&L. The location used in the 1981-85 repon was used to determine the FWS <br />evaporation and to assign the weather station for precipitation. The net evaporation was calculated as <br /> <br />DRAFT - SJRIP Hydrology Model Documentation <br />June 18, 1999 <br /> <br />23 <br />