Yampa River Basin Water Resources Planning Model Final Report

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• Three aggregated reservoirs were added to represent 33,822 of of decreed storage not ' explicitly modeled in the Phase II model. This storage composes all decreed storage rights not explicitly modeled under Phase II. • Three aggregated stock ponds were added to represent 15,958 of of stock pond storage not explicitly modeled in the Phase II model. These stock ponds represent all stock pond use as identified in Task Memo 2.09 -12, "Consumptive Use Model Non - Irrigation Consumptive ' Use and Losses in the Yampa River Basin. ". • Three aggregated municipal and industrial (M &I) nodes were added to represent 8,163 of of ' consumptive use not explicitly modeled in Phase H. This use represents all consumptive use exclusive of irrigation diversions, transmountain diversions, and evaporation from reservoirs and ponds, as identified in Task Memo 2.09 -12, "Consumptive Use Model Non - Irrigation Consumptive Use and Losses in the Yampa River Basin. ". • Consumptive use on the Green River within Colorado was added to the model as one aggregated node. This improvement assures that the model represents all use in Colorado above the Green River at the State Line. • Miscellaneous refinements to the Phase II model. 1.3 Model Extent The Yampa River originates at the Continental Divide and terminates near Colorado's western border, where it flows into the Green River. A fundamental objective in developing the Phase IIIa water resources planning models is to represent all the State's consumptive use of Colorado River basin water. To fulfill this objective, the in -state portion of the Green River basin was included in the Yampa -model as a single aggregated diversion node representing approximately 1900 acres of irrigated land. The acreage was determined from the State's 1993 GIS database. The Green River hydrology was estimated to equal Colorado's contribution to the Green River and does not include inflow from Wyoming. Portions of the Little Snake River basin, a major subbasin of the Yampa River, lie in Wyoming. Diversions on the Little Snake River in Wyoming were represented with four aggregated nodes. One node represents diversions to the City of Cheyenne for municipal supply, and the other three represent demands associated with approximately 14,000 acres of irrigated land in Wyoming. The most upstream of the four nodes was designated a baseflow node, where the flow contribution from Wyoming enters the modeled system. This approach assured that the model reasonably simulated physical water supply to the Little Snake River users in Colorado, and that consumptive use, in turn, could be accurately estimated by the model. Executive Summary _ 1 -2