Yampa River Basin Water Resources Planning Model Final Report

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� I i 4.2.3 Historical Diversion File - yampaT.ddh The historical diversion data file summarized in the rightmost column of Table 4.2.1a contains diversion estimates for each of the structures modeled in the basin. Monthly historical diversions were used to estimate baseflows at the stream gage locations and designated baseflow locations. ' In addition, historical diversions were used for calibration. The following assumptions were made concerning the explicitly modeled historical diversions: A monthly historical demand time series for the entire study period, i.e. water years 1975 -1991, was developed for each diversion structure. • Missing monthly values were filled with averages if the structure existed during the study period or zero if it had not been constructed. All data filling was accomplished through the demandts utility, which used diversion records from the Colorado River Decision Support System ( CRDSS) database and formatted the time series for input into StateMod. The program reads the direct diversion station file (yampaT.dds) and accesses the CRDSS database for the appropriate diversion time series. For aggregated irrigation structures, the CRDSS CU model was executed for all the individual structures represented by the aggregations. The irrigation water requirements for the individual structures within an aggregation were summed by demandts, to produce an irrigation water requirement for each aggregated structure. Demandts also divided this requirement for each aggregation by basinwide average system efficiency to produce an estimate of the historical diversions attributable to the structure. � t For aggregated municipal and industrial structures, historical diversions were set to the depletions estimated for these structures, and efficiencies were set to 100 percent, as described in Section 4.2.1 Because of the Stillwater Ditch delivers water to both the Yampa and Colorado river basins, two historical time series were developed for this structure, one to represent inbasin deliveries and the other to represent transmountain deliveries. These time series were developed outside the CRDSS database for inclusion in the yampaT.ddh input file. The methodology employed to create the two time series is described in Appendix B, Section 2.1. Because Wyoming diversion structures are not included in the CRDSS database, time series for their historical depletions were also developed outside the database. The depletion amounts used to model Wyoming diversions are discussed in Appendix B, Section 2.2. Phase IIIa enhancements that impacted the historical diversion file included addition of twenty -seven ' aggregated irrigation nodes, one explicitly modeled transmountain diversion, and three aggregated municipal and industrial nodes; and replacement of one node representing Wyoming irrigation r depletions with three nodes representing the same use as diversions. Appendix D.9 describes how these changes were made. 4.2.4 Direct Diversion Demand File - yampaTH.ddm Three direct diversion demand files were developed: p computed (yampaTC.ddm), baseline (yampaTB.ddm), and historical (yampaTH.ddm). The historical direct diversion demand file is Diversions 4 -9