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ground water leaving the Valley ground water basin was computed in the model as 102.7 kaf/yr. 5.3 Water Budget Balance -The Schroeder ground water budget for the San Luis Valley was forced to balance to represent a steady state condition. Summary of Previous Studies Emery in 1973 was the first to presents results of a water budget analysis for the San Luis Valley below an elevation of about 8,000 feet. In 1976, Huntley conducted a water budget investigation around the closed basin portion of the San Luis Valley. As part of Huntley's study, a water budget was also conducted for the San Juan Mountains to estimate ground water inflows from the San Juan Mountains. It was concluded that a significant amount of ground water was entering the closed basin from the San Jauns, in fact more than surface water inflows. This is a major water budget item that was missing in the previous Emery water budget. In 1987 HRS presented a water budget for the Alamosa Basin as part of its investigation of the San Luis Valley confined aquifer study. The Alamosa Basin is the San Luis Valley west and north of the San Luis Hills. Many of the HRS water budget parameters were estimated based on Emery's published data, and preliminary unpublished results by Hearne and Dewey. Hearne and Dewey, a year later, in 1988 published its water budget analysis of the Rio Grande basin above Embudo, New Mexico. The Alamosa Basin was one of several basins that a water budget was computed. The Hearne and Dewey study included a detailed water budget analysis of the San Juan Mountains to estimate the significant amount of ground water that enters the aquifers below the Alamosa Basin. The most recent water budget estimate in the basin was conducted by Schroeder in 1991. His investigation was limited to a water budget analysis around the ground water aquifers only, and did not report total inflows, outflows and consumptive uses in the valley. The following is a comparison summary of the five water budgets reviewed for each water budget item. Study Basins -The five water budget investigations do not share the same study areas (see Figure 1), which is the cause for some of the differences in water budget numbers reported in Table 1. Emery and Schroeder considered the entire San Luis Valley as the water budget study area. However, Schroeder's water budget is around the ground water basin underneath the valley reporting inflows to and from the ground water aquifers and does not readily provide total surface water inflows and total consumptive uses in the valley. Hearne and HRS Consultants share the same study boundaries of the Alamosa Basin (San Luis Valley west and north of the San Luis Hills). Huntley's study focused only on the Closed Basin. Study Periods -The five water budget investigations do not share the same study period, which also leads to differences reported in Table 1. The water budgets are reported on an average annual basis, however the period in which the average is calculated can result in a significant difference. For instance, Emery relies on a period of 1924-69, Hearne 1950-80, and Schroeder 1970-87. The average annual gaged out flows of the Rio Grande for these periods are; 330,000 af, 253,000 af, and 407,000 a£ Huntley and HRS Consultants have variable study periods, meaning various water budget components rely upon different periods of record that represent along-term average. Inflows -Inflows to the water budgets consists of up to four components; precipitation, surface water inflows, imports (diversions) and ground water inflows. Precipitation: In all the water budgets the precipitation contribution is generally consistent, with the long-term average of 7 to 8 inches over the study area. San Juan Surface Water: Surface water inflows from the San Juan Mountains were estimated using gaged stream flow records (actual and generated) by all investigators, except Hearne. Hearne rg_task8-1_2001-08.doc 13 of 19 Apri16, 2001