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<br />000375 <br /> <br />(Maddux et. aI. 1993a; U.S, Fish and Wildlife Service, 1993). Proposed critical razorback <br />habitat below Elkhead Reservoir includes the Yampa River below Cross MountainCanyon, the <br />Green River from its confluence with the Yampa River to the Colorado River, and the <br />CoIorado River down to Lake PowelL No razorback sucker have been observed in the <br />Elkhead Reservoir area or in Elkhead Creek below the reservoir, <br /> <br />Bony tail Chub (Gila elegans) <br /> <br />The Bonytail chub was listed as endangered in 1980 by the U.S. Fish and Wildlife <br />Service. Historically, Bony tail chub occurred throughout the Colorado River mainstem and its <br />major tributaries, including the Yampa River. There has not been a recorded capture of a <br />Bonytail chub in the Yampa River in recent years. A remnant population may exist in <br />Dinosaur Canyon as indicated by infrequent collection of individual fishes. The stated <br />recovery goal of the Recovery Program for this species is to ';prevent innnediate extinction. " <br /> <br />All of the proposed criticaI habitat reaches for the Bonytail chub are located downstream <br />of the Elkhead Project. These include the Yampa River beIow the boundary of Dinosaur <br />National Monument, the Green River from the confluence with the Yampa River to the <br />boundary of Dinosaur National Monument, the Green River from Summer's Amphitheater to <br />Fish Ford, the CoIorado River from Black Rocks to Imperial Canyon, and two additional <br />downstream reaches in the Colorado River in Utah and Arizona. <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 Iate <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 annuaI stream <br />discharge of the Yampa River near Maybell occurs in the months of May and June. Summer <br />precipitation augments this water supply in minimal amounts. TabIe 1 presents monthly stream <br />flows recorded at the Maybell gage from 1930 to 1982, On the average, peak flows at Maybell <br />typically occur during the fourth week of May. <br /> <br />EIkhead Creek is a small tributary to the Yampa River Iocated in Routt and Moffat <br />Counties. EIkhead Dam and Reservoir are Iocated on EIkhead Creek approximately four miIes <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 annuaI inflow to EIkhead Reservoir has been estimated at roughly 64,400 af. <br />Approximately 91 percent of the annual yield of EIkhead Creek occurs during the months of <br />April, May and June, On the average, peak flows in Elkhead Creek typicalIy occur during the <br />second week of May. <br /> <br />U.S. Fish and Wildlife Service - Section 7 Baseline Flows <br /> <br />In March, 1990, the U.S. Fish and Wildlife Service presented flow reconnnendations for <br />the Yampa River "necessary for aquatic resources recovery and maintenance." These flow <br />reconnnendations were based on the best available scientific and connnercial data on the habitat <br />needs of the endangered fish and on the "Section 7 Baseline" flows at DeerIodgePark <br />produced in the late 1980's by an application of the HYDROSS modeling methodoIogy to the <br /> <br />11 <br /> <br />'.- -"- :. <br />