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environmental impact analysis of proposals of the Central Utah Project attempt to <br />evaluate adverse impacts to major tributaries of the Duchesne River. <br />The present condition of the Duchesne River is the result of changing climate, <br />changing land use, and the history of direct diversions of streamflow. Because <br />streamflow has been exported from the headwaters of the Duchesne to the Utah Lake <br />drainage basin since 1915, there is potential that the present condition of the Duchesne <br />River has changed greatly from its "natural" condition. The natural condition has not <br />likely existed since the nineteenth century. Without an appreciation for the changes that <br />have already occurred in the basin, analysis of future impacts and the appropriateness of <br />mitigation measures can not be understood within their proper context. <br />Qur~ose <br />The purpose of this report is to describe the physical changes that have occurred <br />in the Duchesne River between Myton and Ouray since 1875. This report compares <br />channel planform and width measurements made in the Uinta Basin in the late nineteenth <br />century with similar measurements made in 1995,. and evaluates the timing of these <br />changes based on detailed analysis of channel changes at detailed study sites. <br />DESCRIPTION OF THE STUDY AREA <br />The study area is the Duchesne River valley between Myton and Ouray, a distance <br />u~ <br />of about 70 km (Fig. 1). The study area is located within the Uinta Basin, a broad <br />structural depression located between the Uinta Mountains and the Tavaputs Plateau. The <br />headwater valleys of the mainstem of the Duchesne River and each of its south-flowing <br />tributaries are entrenched into the uplifted Uinta Mountains or into the surrounding <br />7 <br />