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1.0 EXECUTIVE SUMMARY The White River Water Resources Planning Model (White Model) was developed jointly by the Colorado Water Conservation Board and the Division of Water Resources as part of the Colorado River Decision Support System (CROSS). The objective was to develop a monthly water allocation and accounting model which includes 100 percent of the basin's consumptive use and would be capable of making comparative analyses for the assessment of historic and future water management policies. 1.1 Background The White River basin lies just north of the Colorado River basin in northwestern Colorado. The White River drains all or parts of Rio Blanco and Garfield counties and supplies an annual flow of approximately 595,100 acre-feet to the Green River. The White River basin contains a minimal amount of complexity and an abundant supply of water. Only two reservoirs (Taylor Draw and Big Beaver) are greater than 1,500 ac-ft. Piceance Creek is the primary stretch of river subject to administrative regulation. On the mainstem of the White River, the reach between Miller Creek and Flag Creek contains several relatively large, senior diverters which historically have placed a call on the White River once, in 1977. 1.2 Approach The White River Basin Model was developed using StateMod, the State of Colorado's Stream Simulation Model, and is operated on a monthly time step from water years 1975 to 1991. It was developed in two steps as follows: 1. Phase II, completed in October 1996, explicitly modeled approximately 18,700 acres of irrigated land, 88 key diversions, 2 reservoirs and 6 instream flow reaches. Key structures were identified using the following approach: • A list of diversion structures, based on the structure's net absolute decreed amount, 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, or they were abandoned. 2. Phase IIIa enhanced the previous model to account for 100 percent of the basin's consumptive use. This was accomplished using the following procedure: Execurive Summary 1-1