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<br />. <br /> <br />-. <br /> <br />8 <br /> <br />Areas of Il1IIilCt and Concern <br /> <br />The reach of currently k.nown occupied habitat that wi II receive the most impact <br />due to the upstream water withdrawals related to the proposed Muddy Creek <br />proj ect is the Ilainstem Colorado Ri ver between Pal i sade. Colorado (ri ver <br />lIile 185), and its confluence with the Gunnison River (river mile 170>' This <br />reach of the Colorado River is influenced by two large agricultural diversions <br />and one barrier dam. <br /> <br />The first of these water diversions is located inJRediately upstream from river <br />lIile 185. ~ as the Grand Valley Irrigation Company diversion, this <br />structure diverts up to about 640 cfs from the Colorado River during the growing <br />season (April to October) and smaller amounts during the winter for 1 ivestock <br />watering. . A radio-tagged adult Colorado sQuawfish swam over this low-head <br />structure ill 1986 (Kaeding pers. comm.>. The Service believes that adult <br />Colorado sQuawfish are able to successfully swim over this structure during all <br />but extremely lClf-flow stages. Until the 1980' s. crack.s and seepage areas in <br />the diversiOll _ provided some flow in the Colorado River below the structure, <br />even during extnsely low-flow conditions, but recent repairs have made it <br />virtually leak proof (Henderson 1985). <br /> <br />Another instreilll feature known locally as the Price Stub Dam is located about <br />3 miles upst~ from the Grand Valley Irrigation Company diversion (river <br />lIile 188.2). Built in the latter part of the 19th century for irrigation <br />purposes, tile.. is 8 feet high and spans the entire width of the river. It is <br />likely that this structure acts as an upstream barrier to fish migration during <br />a 11 f1 ow stages. <br /> <br />The final irrigation diversion on the upper Colorado River that currently <br />contributes to seasonal flow fluctuations in known occupied sQuawfish habitat is <br />the Grand River llater Users Diversion (otherwise known as Government Highline <br />Diversion), located about 8 miles upstream from Palisade, Colorado, (river mile <br />193.6) and ~ately above the confluence with Plateau Creek. This diversion <br />removes up to 1.6110 cfs from the Colorado River duri ng the growi ng season (Apri 1 <br />to October) anlIlOO cfs the remainder of the year. Approximately 625 cfs of the <br />diverted flOlf during the growing season and the 800 cfs diverted during the <br />remainder of tilt year are used to produce power and are returned to the Colorado <br />River near hlisade (river mile 185>' <br /> <br />The potential exists for the Colorado River to be nearly dewatered below the <br />Grand Valley Irrigation Company diversion by the combined effects of these major <br />diversions. llurillg times of low flow during the growing season, the diversions <br />are cooperatively operated to maximize the use of available water. Under this <br />cooperative ~1~JSEnt, water diverted by the Government Highline Diversion is <br />returned, or "dlecked back.," to the Colorado River upstream of the Grand Valley <br />Irrigation ~ diversion. The "checked back." water is subsequently diverted <br />fran the river it river mile 185 by the latter, more senior water right holder. <br />The contributi. of Plateau Creek and mi sce 11 aneous seepage/return flows help <br />