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<br />040'~ <br /> <br />SIMULATED EXISTING CONDITIONS <br /> <br />Existing hydrologic conditions in the study area were simulated to <br /> <br />provide a basis for computing changes resulting from the proposed <br /> <br />reservoir. Initial water level in the aquifer, bedrock altitude, aqui- <br /> <br />. <br /> <br />fer hydraulic conductivity, and land-surface altitude were input for <br /> <br />each grid point in the model,' Points on the aquifer boundaries, as well <br /> <br />as those points in the model corresponding to the South Platte River, <br /> <br />were assigned constant-head values. <br /> <br />Preliminary attempts to simulate existing conditions indicated that <br /> <br />water levels were close enough to land surface that evapotranspiration <br /> <br />should be considered, Based on reports available in the South Platte <br /> <br />River basin (Hurr and others, 1975) and other areas in Colorado (Emery, <br /> <br />1970), a function was defined that has a maximum of 5 ft (1.5 m) of <br /> <br />evapotranspiration per year when water levels are at land surface, and <br /> <br />decreases proportionately until there is no evapotranspiration 16 ft <br /> <br />(4.9 m) below land surface. In addition, the model indicated that water <br /> <br />levels were above land surface in the area of the mouth of Bijou Creek <br /> <br />(fig. 1). Therefore, a short length of Bijou Creek was modeled as a <br /> <br />constant-head boundary along with the South Platte River. The model was <br /> <br />then used to simulate existing hydrologic conditions in the South Platte <br /> <br />River valley near the proposed Narrows Reservoir. <br /> <br />/5 <br />