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I I I I I I I I I I I I I I I I I I I 002600 Plan of Study SUB- TASK 4c: Develoo Site-Soecific HvdrolOl!V As Needed 32 Purpose In order to carry out operations studies of alternative reservoir development projects, it will be necessary to estimate virgin or baseline inflows at those sites as well as inflows and river gains elsewhere in the basin. These estimates will be based on regional analyses prepared specifically for the Yampa River basin as part of this study. The results of this sub-task will be used to determine the inflow hydrology for evaluation of candidate sites in Task 5. Approach 1) The regional analyses will be based on records from current and past streamflow gages and on previous estimates of water yields at various points in the basin. The approach will utilize existing and reconstructed virgin flow records to derive physical water yield models (regression equations) which accept tributary area, average elevation, and aspect as .independent variables. These models may be dlsaggt'egated seasonally. The equations will permit derivation of monthly flows at ungaged sites in the basin from reconstructed virgin flow estimates at key sites and from the tributary area, elevation, and aspect of the ungaged site. 2) The veracity of the regional models will be tested by applying them to selected sub-basins for which virgin or nearly-virgin flows are recorded. A favorable comparison between predicted and recorded flows for these sub-basins will validate the approach. Output The product of this sub-task will consist of a number of data sets, equations and documentation which make up a regional hydrologic model of the Yampa River basin. For basins used for testing and calibration, inflow data sets will be provided.