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although some of the gages were excluded because of insufficient data during the CDSS <br />study period, 1975-1991. For the YRBAS, gaps in the flow data were filled using regression <br />equations relating tributary area, average elevation and basin aspect. Some of the regressions <br />were used to predict annual flows which were then distributed into monthly estimates by <br />comparison to monthly patterns for recorded gages. For CDSS, regression equations were <br />also developed to fill data gaps, but were based on regressions similar to those recently <br />developed for the CWCB by Leonard Rice Consulting Water Engineers, Inc.. In the majority <br />of the cases, the regressions for YRBAS and the CDSS were both made against similar long <br />term gage records and are believed to be consistent with each other. We are not aware of <br />substantial differences in the resulting gage data used for inflows in the two models. <br />In the YRBAS, the majority of the existing uses in the basin (and the resulting stream <br />depletions) are implicitly modeled in the historical hydrology as reflected in the USGS gage <br />records. As such the effects of these water rights are left in the gage. In particular, existing <br />water rights that are senior to the 1954 priority of the Juniper Project are implicitly modeled, <br />with the following exceptions: 1) the senior agricultural water rights were given a demand <br />adjustment to reflect potential dry-year increases in diversion requirements (this adjustment <br />was made for 10 years out of the 53-year study period); 2) senior municipal and industrial <br />water rights were given a demand adjustment to reflect current levels of use over the course <br />of the entire study period (for example the city of Craig municipal demand needed to be <br />adjusted upward in earlier years of the study period in order to simulate current municipal <br />demands over the entire study period. Likewise, the effects of the industrial diversions at <br />Hayden and Craig Stations were adjusted to reflect use over the entire 53-year study period. <br />For simplification in the model, all of the existing senior demands were aggregated into only <br />26 demand nodes in the model. For example, all agricultural demands above Stagecoach <br />Reservoir were modeled as one aggregated demand. It is also noted that existing seniors on <br />small tributaries are assumed to included in the aggregation with water rights on the main <br />stem. This assumption may be warranted, provided that there are no shortages on the small <br />tributaries. <br />In the YRBAS, existing water rights that are junior to the 1954 Juniper decrees are explicitly <br />modeled, although they are aggregated into only six model nodes. In order to explicitly <br />model these existing juniors, it was necessary to back out the historical depletions <br />attributable to these rights from the historical gaged data. Historical depletions were provided <br />by the Division 6 engineer and are presumably based on estimates of historical irrigated <br />acreage and estimates of crop consumptive use. Diversions at each model node, whether <br />existing senior or junior, are estimated as a function of depletion and an assumed system <br />efficiency. By simulating diversions, it is also possible to estimate the quantity of return <br />flows. <br />Because of the planning nature of the YRBAS, the CRAM network model also includes <br />provisions for future demands in the basin. These are based on projections of future growth <br />in municipal demands, potential construction of new thermal electric power generating units <br />and some minimal level of increased agricultural uses. In the CDSS, the majority of the <br />active structures are explicitly modeled, specifically all structures which cumulatively <br />represent 75 percent of all absolute direct flow decrees in the basin. In the Yampa River <br />basin, this is equivalent to a representation of all structures that have decrees in excess of five <br />Yampa River Basin Information 5-2 <br />