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estimated for non-irrigated lands using the original or a modified version of the relationship developed <br />by Emery relating consumptive use to depth to water. Huntley, modified Emery's original relationship <br />such that the maximum consumptive use was 37.3 in/yr, versus 60 inches per year. Hearne and HRS <br />Consultants used a maximum Et of 54in/yr. <br />Surface Water Ou flow: Surface water outflows were derived fairly consistently using gaged outflows <br />of the Rio Grande near Lobatos. However given different study the average annual outflows ranged <br />from 253,000 of to 407,000 of as discussed above in the study period summary. Also, note that <br />Schroeder's surface water outflow is that component of ground water that discharges directly to Rio <br />Grande or is spring water (e.g. it is not the total surface outflow from the San Luis Valley). <br />Ground water Ou flow: Ground water outflows from all the investigators, except Huntley, are also <br />fairly consistent and on the order of 50 to 100 kaf/yr. <br />Change in Ground Water Storage -All investigators estimated no significant change in the ground water <br />storage except, Hearne. Hearne reported a decrease in storage of 63,000 of/yr. This was based on the 1950- <br />1969 total change in storage estimated from the analog simulation model by Emery and others (1975), and <br />changes in the hydraulic head reported by Crouch (1983). <br />Water Balance -Emery, Huntley, and Schroeder balance their water budgets where inflows equal outflows <br />and there is no change in storage. HRS Consultants and Hearne leave the water budgets unbalanced with <br />inflows exceeding outflows 450,000 of/yr, and 350,000 of/yr, respectively. The investigators report the <br />imbalance is likely the result of errors in estimating the two largest unknowns, San Juan ground water <br />inflows, and consumptive use from evapotranspiration. <br />Conclusions <br />Based on our review of the five previous water budgets, the following is our best estimate of the order of <br />magnitude that is reasonable for each of the water budget items for a water budget around the San Luis <br />Valley study area. The exception is San Juan ground water inflows and non-beneficial evapotranspiration in <br />which data is lacking to arrive at a conclusion, so a range is provided. These ranges, based on previous <br />efforts, are believed to be appropriate to compare to the RGDSS water budget components. <br />Inflows <br />• Precipitation 1,220 kaf/yr <br />In all the water budgets, the precipitation contribution is generally consistent <br />with the long-term average of 7 to 8 inches over the study area. We believe <br />Emery's estimate is representative of the long-term average yield for the San <br />Luis Valley. <br />• San Juan Surface Inflows 1,200 kaf/yr <br />Averaging the estimated San Juan surface water inflows to San Luis Valley by <br />Emery (1,260 kaf/yr), and Hearne and Dewey (1,137kaf/yr), equals about 1,200 <br />kaf/yr. The difference between the two author's yields is attributed to different <br />study periods and methods. <br />San Juan Ground water Inflows <br />130 - 890 kaf/yr <br />This water budget item is one of the most difficult to estimate given the range of <br />reported values by previous authors who have attempted to estimate this water <br />budget item. The range is from 124.7 kaf/yr by Schroeder to approximately 890 <br />kaf/yr by Hearne and Dewey. Since the HRS and the Hearne and Dewey water <br />rg_task8-1_2001-08.doc 15 of 19 Apri16, 2001 <br />