Yampa River Basin Water Resources Planning Model Final Report

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• Simulates a wide variety of operating agreements and exchanges between one or more structures through user - supplied input data • For a given structure, simulates one or more return flow patterns returning to one or more stream nodes to represent the impact of surface and ground water returns on the stream system Simulates transbasin imports and diversions from a basin • Uses an efficient, direct solution algorithm which recognizes the impact of a diversion's return flows during the current time step without having to iterate • Estimates a base or natural streamflow from gaged or estimated streamflow, diversion, and reservoir data • Performs extensive input data checking • Provides extensive output reporting capabilities • Operates on both a PC and a workstation • Is available to the public and maintained by the State of Colorado The Yampa Model is operated on a monthly time step from water years 1975 to 1991. It was developed in two steps as follows: Phase II, completed in July, 1996, modeled 246 key diversion structures, 9 reservoirs, and 73 instream flow rights. Key structures were identified using the following approach: • A list of diversion structures, based on the structure's net absolute decreed amounts, was compiled and ranked form largest to smallest. • The list was shortened by including those structures that represent 75 percent of the basin's net absolute decreed amounts. • Meetings were held with division and district engineers in the basin and the preliminary list of structures was refined to include structures that were considered important by the district engineers. Also, some structures were removed from the model because they historically ' diverted significantly less than the decree amount, they were abandoned or removed, or they had infrequent diversion records. Phase IIIa enhanced the model to account for 100 percent of the basin's consumptive use. This enhancement featured the following changes from the Phase II model: • Twenty -seven aggregated irrigation structures were added to represent 449 structures supplying 24,960 acres of irrigated land. These lands compose all land in the 1993 survey which were not explicitly modeled in the Phase II version of the model. 1 1 • Three aggregated reservoirs were added to represent 33,822 of of decreed storage not explicitly modeled in the Phase H model. This storage composes all decreed storage rights not explicitly modeled under Phase H. • 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 Model Development 3 -2