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Precipitation inflow (1,085 kaf/yr) to the Alamosa basin was taken from the Hearne and <br />Dewey study. <br />3.2.2 Consumptive Uses -Evapotranspiration (Et) of irrigated crops for the entire Rio Grande <br />Basin was reported by Agro Engineering to be 1,035 kaf/yr. HRS adjusted the reported <br />values to be consistent with the Alamosa Basin study area and came up with a value of 975 <br />kaf/yr. <br />Agro Engineering (1987) reported an Et value for phreatophytes and rangeland of 1,211 <br />kaf/yr for the entire9 Rio Grande Basin. However, they qualified that estimate with a <br />warning that there may be significant error in the consumptive use estimates and acreage for <br />phreatophyte or high water table areas. As a result, HRS in its 1989 update of the water <br />balance chose to go with the Hearne and Dewey non-beneficial Et estimate of 1,448 kaf/yr. <br />Agro Engineering reported that municipal use in the Valley was on the order of 11,200 of <br />per year, compared to an estimated agricultural demand of 2,000,000 of/yr. The <br />consumptive use associated with municipal demand was not considered in the water budget. <br />3.2.3 Change in Storage -HRS did not estimate a change in the transient ground water storage. <br />3.2.4 Outflows -Outflows from the Alamosa Basin consist of surface water and ground water. <br />Surface water outflows (332 kaf/yr) were taken from Emery (1973). Ground water outflows <br />were estimated by HRS to be 64 kaf/yr from the unconfined and shallow confined aquifers, <br />and 7 kaf/yr from the deep confined aquifers. The HRS report references calculations done <br />by Coons and Kelly in 1984 where they estimated the probable maximum ground water flow <br />across the state line to be about 89 kaf/yr. <br />3.3 Water Budget Balance -The updated HRS water budget does not balance with 453 kaf/yr more <br />inflows than combined outflows and consumptive uses. They conclude this disparity may result <br />from several sources including; 1) mountain area sub-basin yields may be too high, 2) Et may be <br />significantly higher from high water table areas, and 3) there may be an increase in the transient <br />ground water storage in the valley. <br />4.0 Hearne and Dewey, 1988 <br />4.1 Water Budget Area and Study Period -The study area includes the Rio Grande drainage basin above <br />Embudo, New Mexico, and the Closed Basin in Colorado. The study area was divided into five <br />physiographic subdivisions, one of which is called the Alamosa Basin. The Alamosa Basin is the <br />San Luis Valley Floor area west and north of the San Luis Hills. A detailed water budget was also <br />conducted for another physiographic subdivision called the San Juan Mountains. The San Juan <br />mountain water budget was conducted to determine inflows to the Alamosa Basin. The water <br />budgets were conducted by averaging flows over the study period of 1950 through 1980. <br />4.2 Approach and Assumptions -The approach in this study was a detailed water budget investigation of <br />the San Juan Mountains to determine inflows to the Alamosa Basin. The inflows from the Sangre de <br />Cristo Mountains were estimated using a regression analysis of available streamflows. <br />Evapotranspiration was computed for irrigated lands, and non-irrigated land. Et was estimated using <br />the relationship of Et Vs depth to ground water developed by Emery (1971). Change in the transient <br />ground water storage for the study period was estimated from results of previous investigations. <br />Ground water outflow from the basin was calculated as the residual component of the water balance. <br />rg_task8-1_2001-08.doc 9 of 19 Apri16, 2001 <br />