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is based on the consumptive use from 967 kaf/yr of agriculture use, 2 kaf/yr of livestock use, <br />5 kaf/yr of M/I use, and 5 kaf/yr of reservoir evaporation. The best estimate is believed to be <br />based on the total potential crop consumptive use, while the RGDSS estimate is based on the <br />actual crop consumptive use from precipitation and irrigation water (water supply limited). <br />The RGDSS estimate of potential consumptive use is 1,213 kaf/yr, which is closer to the best <br />estimate. <br />Surface Water Outflow -the RGDSS estimate is slightly lower than the best estimate. The <br />best estimate and the RGDSS estimate are based on different periods for the Rio Grande at <br />Lobatos stream flow gage <br />Ground Water Outflow -the RGDSS estimate is higher than the best estimate. The best <br />estimate is based on fives studies with values ranging from zero to over 100 kaf/yr. The <br />RGDSS estimate is based on a preliminary 1978 to 1987 average provided by the RGDSS <br />Ground Water Contractor. <br />The difference between the RGDSS and best estimate total change in storage term is due to the ground <br />water change in storage component. The best estimate is based on five studies in which four <br />investigators estimated no significant change in the ground water storage (steady state) and one <br />investigator, Hearne, reported a difference of 63,000 of/yr based on data. The RGDSS Ground Water <br />contractor estimates no significant change in ground water storage (steady state) over the long-term. A <br />best estimate for the change in surface water storage was not provided, as it was not addressed in the five <br />previous studies. <br />The purpose of computing the RGDSS Ground Water Area water budget analysis was to provide a more <br />detailed and documented assessment of inflows, outflows, and changes in storage than had been provided with <br />previous studies. Water budget items that have been improved over previous water budget investigations <br />include: <br />Consumptive uses caused by human activities: <br />- Crop consumptive use was estimated by using Blaney-Griddle calibrated crop <br />parameters and more detailed modeling of ditch system water supplies to determine the <br />water supply limited crop consumptive use. <br />- Municipal and industrial consumptive use was included specifically. With the <br />exception of Schroeder, the other water budgets excluded this term. <br />- Stock pond evaporation and livestock consumptive use was included specifically. This <br />term was ignored in previous water budgets. <br />Changes in ground water storage: <br />- More detailed ground water analyses was performed with improved inputs based on <br />detailed crop consumptive use analyses and consumptive use-based estimates of <br />ground water pumping. <br />ET of natural vegetation: <br />- Since this is the residual term in the water budget, improvements in the estimation of <br />other water budget items results in improved natural ET estimates. <br />Comments and Concerns <br />We believe the RGDSS Water Budget provides a better representation of the overall water balance in the San <br />Luis Valley than previous estimates. The RGDSS inflow, outflow and storage change terms are based on <br />more detailed analyses and modeling efforts. The following summarizes the comments and concerns <br />regarding the comparison of RGDSS results with previous results: <br />rg_task8-1_2001-08.doc 18 of 19 Apri16, 2001 <br />