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' <br />� <br />,� <br />' <br />I� <br />, <br />, <br />� <br />, <br />I !� <br />� <br />' <br />� <br />, <br />' <br />' <br />, <br />Il <br />' <br />Luis Valley Irrigation District and the San Luis Valley canals, the Prairie and Billings ditches. <br />A tabulation of diversions by these systems is included in Appendix E. The average diversions <br />for the time period 1950 through 1994 were 273,000 acre feet per year. The amount of natural <br />inflow from the mountains to the west was calculated by Phil Emery in his analysis of the <br />hydrology of the Valley to be approximately 23,000 acre feet per year. However, there is not <br />sufficient data currently available to document annual inflows from the mountains to the west. <br />To demonstrate and .understand the correlation between ground water levels and Rio Grande <br />diversions into the Closed Basin, a graph of the diversions versus change in aquifer storage was <br />prepared for the time period 1976 to 1989. The change in aquifer storage calculations aze <br />presented in Section 4.1. The graph is included as Figure 4-3. A point for each yeaz was plotted. <br />Each point represents the intersection of the total diversion, which is plotted on the horizontal <br />axis, and the change in unconfined aquifer storage, which is plotted on the vertical axis, for each <br />respective year. By using linear regression, a trend line was plotted through the points. The <br />data used to plot the graph is included in Appendix E. <br />A quick review of the graph in Figure 4 indicates that there is a direct relationship between <br />canal and ditch diversions into the Closed Basin and change in unconfined aquifer storage. <br />Further, the intersection of the trend line with the horizontal zero change line indicates that <br />diversions totaling approximately 270,000 acre feet per year results in a zero change in <br />unconfined aquifer storage assuming no material change in inflows from the surrounding <br />mountains. Since required diversions of f270,000 acre feet per year approximately equal actual <br />average diversions of 273,000 acre feet per year, it indicates that storage in the aquifer should <br />remain relative stable over the long term assuming no material change in inflows from the <br />surrounding mountains and no material increase in ground water withdrawals. The change in <br />unconfined aquifer storage chart in Figure 4-2 supports this conclusion showing maintenance of <br />storage over the long term, although there have been dramatic changes from year to year during <br />the study period. <br />Of this f273,000 acre feet of diversions and f23,000 acre feet of natural inflow to the Closed <br />4-3 <br />' <br />