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" .- ,. m ..".. !... ... c.... !. . YAMPA RIVER BASIN I WATER RIGHT COl4PUTER ~10D In order to as sess the long-term yie"ld of the YaQpa Ri ver Reservoirs '"i'o. 1 and 2, it was necessary to deteraine. the hydrologic~onditions that would result from the operation of additional large-scale water projects in the Yampa Ri'"er basin. A hydrologic computer model was developed for the basin to enable the rapid calculation of reservoir storage and releases, and resul ting streamflows on a monthly or weekly basis. The program is capable of modeling any combination of projects listed on Table 1 for any give.n year or series of years. Each project is prioritized by water right seniority. If a senior project does. not fill to its decreed capacity, the most junior proj ect upstream is shut down until the senior right is satisfied. The' projects were also op~rated according to any stipulations that the tlater Court may have imposed on a particular decree. The program utilizes actual historic streamflow data for the particular year or years which are being modeled. The actual gaged data reflect historic streamflow conditions that result following existing diversions and water use within the basin. Thus, existing agricultural, municipal and industrial streamflow depletions and'consumptive,uses are inherent in the model. There are three primary types of data that must be input in to the program: mont"hly or. weekly streamf low data, the streamflow bypasses necessary below each project:.. to satisfy existing senior irrigation rights and to meet minimum streamflow requirements; and reservoir operation criteria. Each of these data needs are outlined in detail below. Bvd"roloqic Data. The model keeps track of virgin "and post- development streamflows at 26 accounting locations within the Yampa River basin. Discharge is calculated on a monthly basis from July through August as streamflows ~o not fluctuate rapidly during this period. During the April-June rUDoff period, discharge often changes rapidly and is therefore modeled on a weekly bas~s at most accounting points. The monthly and weekly streamflow data for the year or years to be modeled must be entered into the progrAQ for 14 locations. These sites are located at or near the diversion points of the simulated projects. The model calculates the discharge at twelve other' accounting points, which are generally located immediately below a given project. The streamflow accounting points including those for which data are required, are shown in Figur~ 1 . . The required hydrologic data were derived primarily from actual USGS stream gaging records in the Yampa Ri~er basin. The USGS has continuously monitored streamflow at or near eleven of the fourteen accounting points for which data must be entered. The streamflow data for the period of record for those locations and a statistical analysis of the data, were obtained frolll the USGS.