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water inflows from the San Juan and Sangre de Cristo mountain ranges were not estimated. <br />Surface water inflows to the Valley were estimated on an average annual basis using long- <br />term gaged stream flow records, adjusted short-term streamflow records and by applying an <br />altitude-runoff relationship to ungaged basins. The altitude-runoff relationship was <br />reportedly developed from gaged basin data using a procedure developed by Moore (1968). <br />According to Moore, the procedure is primarily for use in preliminary or reconnaissance <br />evaluations. The mathematical relationship developed nor the statistical strength of the <br />relationship was provided in the report. The approach for determining the amount of <br />precipitation falling on the basin was not discussed. <br />1.2.2 Consumptive Uses -Evapotranspiration (Et) is reported at 2,420 kaf/yr, with 1,000 kaf/yr <br />being consumed by non-beneficial vegetation. The approach and assumptions for this <br />determination are not discussed by Emery. Et is estimated to take place where depth to <br />water is less than 12 feet. <br />1.2.3 Change in Storage -Emery reports for the unconfined aquifer, "No long-term fluctuation in <br />the water table has been detected". A similar comment was also made for the unconfined <br />aquifer, "No widespread, long-term, head decline has occurred in the confined aquifer". As <br />a result, Emery did not include changes in ground water storage as part of the water budget. <br />1.2.4 Outflows -Outflows are reported to average 330 kaf/yr as surface water and 50 kaf/yr as <br />ground water. The approach and assumptions for this determination is not discussed by <br />Emery. However, the 1924-1969 average of USGS stream gage records for Rio Grande near <br />Lobatos, CO is 330,000 of (rounded). <br />1.3 Water Budget Balance -Emery presents a balanced water budget, in other words inflows equal Et <br />plus outflows. The residual variable was not described in the text but is estimated to be Et, since <br />surface water inflows and outflows were either measured or computed. Ground water inflows and <br />change in ground water storage were both estimated to be zero. Ground water outflows are small in <br />comparison to Et, but could also have been part of the water balance residual. <br />2.0 Huntley, 1976 <br />2.1 Water Budget Area and Study Period -Huntley conducted an average annual water budget for the <br />northern San Luis Valley (Closed Basin). The Closed Basin (Figure 1) is bordered by the San Juan <br />mountain range on the west and north where it meets the Sangre de Cristo mountain range, which <br />also is the eastern border of the valley. The border on the south is roughly defined by the ground <br />water divide of the unconfined aquifer just north of the Rio Grande. No specific study period was <br />used; instead, the water budget relies on varying historic periods, depending on availability of data <br />that represent long-term average conditions. <br />2.2 Approach and Assumptions -One of Huntley's purposes for the study was to quantify the ground <br />water recharge to the aquifers of the Closed Basin, which was absent in the previous Emery <br />investigation. Huntley conducted separate water budgets on the San Juan and Sangre de Cristo <br />Mountains that are tributary to the Closed Basin to estimate ground water recharge from these <br />adjacent mountain ranges. Other recharge sources included rainfall, surface inflows, and return <br />flows from imported irrigation diversions from the Rio Grande. Huntley estimates no long-term <br />change in ground water storage as did Emery, and estimates no surface or ground water outflows <br />from the Closed Basin. <br />rg_task8-1_2001-08.doc 6 of 19 Apri16, 2001 <br />