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<br />00110.0 <br /> <br />. <br /> <br />. <br /> <br />Road Relocation <br /> <br />Existing roads in the drainageway, across the new emergency spillway crest, over the <br />crest of the existing Elkhead Dam and several locations around the reservoir perimeter would <br />be relocated. Road relocation activities would not adversely affect habitat used by any of the <br />endangered species addressed previously. <br /> <br />HYDROLOGY <br /> <br />Yampa River and Elkhead Creek Hydrology <br /> <br />Natural flows of the Yampa River are highly seasonal, typically reaching a peak in late <br />spring and declining. considerably by late summer to minimum levels in late fall or winter. <br />Most of the yield of the Yampa River Basin is produced primarily by melting snowpacks in the <br />higher elevations. Approximately 64 percent of the 1.135 maf of average annual stream . <br />discharge of the Yampa River near Mayben occurs in the months of May and June. Summer <br />precipitation augments this water supply in minimal amounts. Table 1 shows monthly <br />volumetric stream flows recorded at the Maybell gage from 1930 to 1989. Figure 4 shows a <br />typical annual hydrograph for the Yampa River at Maybel1. Peak flows at Maybell typically <br />occur during the fourth week of May. <br /> <br />Elkhead Creek is a sman tributary to the Yampa River located in Routt and Moffat <br />Counties. Elkhead Dam and Reservoir are located on Elkhead Creek approximately four miles . <br />above the confluence with the Yampa River. Flows in Elkhead Creek follow a seasonal pattern <br />similar to the Yampa River and are greatly influenced by spring and summer snow melt. The <br />average annual inflow to Elkhead Reservoir has been estimated at approximately 64,400 af. <br />Approximately 91 percent of the annual yield of Elkhead Creek occurs during the months of <br />April, May and June. Peak flows in Elkhead Creek typically occur during the second week of <br />May. <br /> <br />USFWS - HYDROSS Model <br /> <br />In 1986, the U.S. Fish and Wildlife Service applied the HYDROSS methodology to the <br />Yampa and Green River basins to assist in assessing the cumulative impacts on streamflows of <br />water diversions for irrigation, power, municipal, and recreational purposes. HYDROSS is a <br />system of computer programs originally developed by the Bureau of Reclamation for <br />conducting monthly water supply studies in the Missouri River basin. . <br /> <br />The Service's HYDROSS application to the Yampa and Green Rivers was aimed <br />primarily at identifying the impacts associated with the Stagecoach Reservoir Project near <br />Steamboat Springs. Four separate scenarios were modeled using HYDROSS: 1) historical <br />conditions; 2) present level of development; 3) a baseline condition that included a future level <br />of development with al1 proposed projects likely to be developed, and 4) a baseline plus the <br />proposed Stagecoach Project which defined a "Section 7 baseline" condition including the <br />Stagecoach project. The fourth HYDROSS scenario was used in defining .Interim Flow <br />Recommendations at Deerlodge Park. The corresponding modeled flows at the Maybell gage <br />are referred to herein as the "Section 7 Baseline flows." <br /> <br />13 <br /> <br />;, <br /> <br />-,ji;..,A <br />