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<br />
<br />Study Area
<br />
<br />The Study Area covers about 1,100 square miles in Eagle County and is approximately 100
<br />miles west of Denver, as shown on Plate 1, The area includes the basin of the Eagle River to its
<br />confluence with the Colorado River near Dotsero, and the basin of the Piney River to its confluence
<br />with the Colorado River near State Bridge, as_shown on Plate 2,
<br />
<br />The drainage area of the Eagle River above its confluence with the Colorado River is
<br />approximately 950 square miles, The Piney River basin includes an area of about 123 square
<br />miles, For comparison, the drainage area of the Colorado River above State Bridge is
<br />approximately 2,670 square miles,
<br />
<br />Elevations in the Study Area range from under 7,000 feet, where the Eagle River meets the
<br />Colorado River, to over 13,000 feet in the high peak area of the Gore Range at its eastern edge_
<br />The most prominent topographic and scenic features are the high mountains of Vail Pass and the
<br />Gore Range in the eastern section of the area, This part is characterized by mountain ranges and
<br />alpine and subalpine vegetation, while the western lower region varies from desert-type to
<br />subalpine vegetation,
<br />
<br />Highway transportation in the east-west direction is provided by Interstate Highway 70,
<br />which is partially completed, and by U,S, Highway 6, The interstate route, especially with the recent
<br />completion of the Eisenhower Tunnel under the Continental Divide, provides convenient access
<br />to the Study Area from Denver.
<br />
<br />Study Objectives and Methodology
<br />
<br />In recognition of the complexity of a water resources project of this magnitude, the Denver
<br />Board of Water Commissioners determined the need for an independent comprehensive
<br />evaluation oi the Eagle and Piney River basins, This evaluation included definition of the geologic
<br />and topographic features, determination of the quantity of water that could be produced efficiently
<br />and responsibly by the Board from its appropriations, and assessment of the general
<br />environmental impacts that might be expected from such a program,
<br />
<br />The objective of this comprehensive evaluation was to identify and recommend an
<br />operational configuration that would provide the maximum reliable water supply, considering
<br />appropriately the economic and environmental factors_ To meet this objective, a study program,
<br />structured to have the flexibility to respond to the evolving results of the study activities, was
<br />developed in cooperation with the Department's staff, Assumptions used for basic guidance, such
<br />as those describing water use, were also developed jointly, Cooperation and coordination with the
<br />staff was on a close and continuing basis,
<br />
<br />The approach to estimating the streamflows available in the Study Area consisted of two
<br />l<ey phases, The first was to estimate the quantity of virgin, or undepleted, flows occurring in the
<br />two basins by applying historic streamflow data extended by using statistical procedures, The
<br />second was to estimate the water available to the Board's appropriations by superimposing
<br />present and certain potential future water demand on the undepleted flows, The results for both
<br />of these phases were achieved by the use of sophisticated analytical tools, computer technology
<br />and assistance from acknowledged experts in the fieids of water use and statistical hydrology,
<br />
<br />Because of the rugged and remote nature of the Study Area, the topographic features and
<br />structural geology were defined using airborne remote sensing techniques. Topographic maps and
<br />surficial geologic information appropriate for this level of study were developed efficiently and
<br />economically by this method, Limited subsurface geological investigations were conducted at
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