Laserfiche WebLink
for grains to 2.4 ft/yr for alfalfa. Non-irrigated pasture was estimated to consume 1.7 of/yr, <br />the same as non-irrigated lands with a depth to water table of 4 to 6 feet. Total crop <br />consumptive use was estimated at 1,376 kaf/yr. <br />Non-irrigated land Et was estimated to be met by ground water and natural precipitation. <br />Ground water consumption was estimated using the graph developed by Emery (1971) <br />relating ground water depth to evapotranspiration rates. The maximum rate is 4.5 ft/yr for <br />water courses and riparian areas, and no consumption of ground water occurs when depth to <br />water exceeds 12 feet. Consumption of the average annual precipitation was estimated to <br />also be dependent on depth to ground water with no consumption for water course and <br />riparian areas to full consumption (.64 ft/yr) for areas where the depth to ground water <br />exceeds 12 feet. Total non-irrigated land consumptive use was estimated at 1,448 kaf/yr. <br />4.2.3 Change in Storage -Hearne and Dewey estimated an average annual loss in ground water <br />storage of 63,000 of/yr. This was based on two time periods; 1950 -1969 and 1970 to 1980. <br />The 1950-1969 total change in storage was estimated from the analog simulation modeled by <br />Emery and others (1975) to be 730,000 af. The 1970 to 1980 change in storage was <br />estimated by Hearne and Dewey to be 1,200,000 of based on changes in the hydraulic head <br />reported by Crouch (1983). Thus, from 1950 to 1980 the total volume in ground water <br />storage was estimated to decrease by 1,930,000 of or 63,000 of/yr. <br />4.2.4 Outflows -Outflows from the Alamosa Basin consist of surface water and ground water. <br />Surface water outflow (253 kaf/yr) is based on the average streamflow in the Rio Grande <br />near Lobatos, Colorado for the study period 1950-80. Ground water outflow was the <br />residual variable in the water budget computed as 345,000 of/yr. However, Hearne and <br />Dewey felt this was not accurate since the value was small in comparison to other estimated <br />flows in the water budget and chose to leave the water budget unbalanced. <br />4.3 Water Budget Balance -The Hearne and Dewey Alamosa Basin water budget does not balance with <br />345 kaf/yr more inflows than combined outflows and consumptive uses. They conclude errors in <br />estimating Et and subsurface recharge could account for the imbalance. <br />5.0 DeWayne Schroeder, 1991 <br />5.1 Water Budget Area and Study Period -The study area (Figure 1) includes the San Luis Valley as <br />studied by Emery (1973). However, the water budget is around the ground water aquifer beneath the <br />San Luis Valley, rather than the entire basin as evaluated by Emery (1973). A study period of 1970- <br />1987 was used. <br />5.2 Approach and Assumptions -The approach in this study was to develop a detailed ground water <br />model of the aquifer (confined and unconfined) under the San Luis Valley. We are unaware of any <br />formal documentation of the study. The water budget values in Table 1 were obtained from trial <br />exhibit 208 -Steady State Ground Water Budget (Run M24), Case No. 86-CW-46. Information <br />regarding the water budget components has been obtained from Schroeder's AWDI testimony <br />question and answer script, and the transcripts of DeWayne Schroeder's testimony in Case No. 86- <br />CW-46. <br />5.2.1 Inflows -The San Luis Valley ground water budget inflows consist of surface water rim <br />inflows from the San Juan mountains and Sangre de Cristo mountains, ground water return <br />flows from surface water irrigation diversions, ground water inflows from the San Juan <br />mountains, ground water return flows from flowing irrigation wells (flowing and pumped), <br />rg_task8-1_2001-08.doc 11 of 19 Apri16, 2001 <br />