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<br />001146 <br /> <br />9 <br /> <br />Most of the water yield within the Yampa River basin is produced by melting snowpatks in the <br />higher elevations. Summer precipitation augments this water supply in minimal amounts. Natural flows <br />of the Yampa River are highly seasonal, typically reaching a peak in late spring and declining <br />considerably by late summer to minimum levels in late fall or winter. Approximately 64 percent of the <br />annual stream discharge of the Yampa River near Maybell occurs in the months of May and June. Water <br />yield varies throughout the basin, reflecting spatial climatological variation. Annual" precipitation ranges <br />from more than 40 inches in the high alpine zones to negligible amounts in the arid western portion of <br />the basin. <br /> <br />Water storage projects have been developed on the mainstem of the Yampa River and several of <br />its major tributaries and are shown on Figure 4-1, Mainstem impoundments include Yamcolo Reservoir, <br />Stagecoach Reservoir and Lake Catamount. Yamcolo and Stagecoach Reservoirs are contracted for <br />agricultural and municipal uses and for cooling purposes for power generation at the Hayden and Craig <br />stations, Lake Catamount is a private recreational facility. <br /> <br />Storage projects have been developed on several tributaries to the Yampa River. Those of <br />significant size include Steamboat Lake and Elkhead Reservoir. Steamboat Lake is located on Willow <br />Creek, a small tributary to the Elk River, and is used as a popular recreation area. Elkhead Reservoir is <br />located on Elkhead Creek and is contracted for storage of water for the Craig power station and a <br />Colorado Division of Wildlife recreational pool. <br /> <br />Previous studies In the basin have identified potential reservoir sites on several other tributaries <br />to the Yampa River. Although may of these sites exhibit excellent morphologic characteristics, the <br />natural hydrology often can suPPOrt only very small reservoirs. <br /> <br />Data Development Approach <br /> <br />In order to carry out operations studies .of alternative reservoir devClopment projects. it was <br />necessary to estimate inflows at those sites as well as inflows and river gains elsewhere in the Yampa <br />River Basin. Hydrologic information developed in this task was used directly as input data in the Yampa <br />River Basin Model. In addition, the results of this effort were use~ in a first-cut fatal flaw analysis of <br />alternative reservoir sites based on average annual stream inflow. <br /> <br />A regional hydrologic analysis was conducted based on records from current and past <br />streamflow gages and on previous estimates of water yields at various points in the basin. This approach <br />utilized existing and reconstructed virgin flow records to derive physical water yield models (regression <br />equations) which accepted tributary area, average elevation, and aspect as independent variables. <br />Stream flows predicted using annual flow models were disaggregated into monthly flows using average <br />distribution patterns over the gaged periods. <br /> <br />Veracity of regional regression models was tested by applying them to selected sub-basins for <br />which a substantial period of record of virgin or nearly.virgin flows were recorded, Favorable <br />comparisons between predicted and recorded flows for these sub-basins validated this approach. <br />Produced in this task were a number of data sets, equations and documentation which make up a <br />regional hydrologic model of the Yampa River basin. <br /> <br />'-~'-' 'j <br />