WSP07009

• File Number: 8221.106.J
• Description: Eagle-Piney
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1974
• Title: Eagle-Piney/Eagle-Colorado Water Study--Summary Report
• Water Supply Pro - Doc Type: Report/Study

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Study Area

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The Study Area covers about 1.100 square miles in Eagle County and is approximately 100
miles west of Denver, as shown on Plate 1. The area includes the basin of the Eagle River to its
confluence with the Colorado River near Dotsero. and the basin of the Piney River to its confl~ence
with the Colorado River near State Bridge, as shown on Plate 2.

The drainage area of the Eagle River above its confluence with the Colorado River is
approximately 950 square miles. The Piney River basin includes an area of about 123 square
miles. For comparison, the drainage area of the Colorado River above State Bridge is
approximately 2,670 square miles.

Elevations in the Study Area range from under 7.000 feet, where the Eagle River meets the
Colorado River, to over 13.000 feet in the high peak area of the Gore Range at its eastern edge.
The most prominent topographic and scenic features are the high mountains of Vail Pass and the
Gore Range in the eastern section of the area. This part is characterized by mountain ranges and
alpine and subalpine vegetation. while the western lower region varies from desert.type to
subalpine vegetation.

Highway transportation in the east-west direction is provided by Interstate Highway 70,
which is partially completed. and by U.S. Highway 6. The interstate route. especially with the recent
completion of the Eisenhower Tunnel under the Continental Divide, provides convenient access
to the Study Area from Denver.

Study Objectives and Methodology

In recognition of the complexity of a water resources project of this magnitude. the Denver
Board of Water Commissioners determined the need for an independent comprehensive
evaluation of the Eagle and Piney River basins. This evaluation included definition of the geologic
and topographic features. determination of the quantity of water that could be produced efficiently
and responsibly by the Board from its appropriations, and assessment of the general
environmental impacts that might be expected from such a program.

The objective of this comprehensive evaluation was to identify and recommend an
operational configuration that would provide the maximum reliable water supply. considering
appropriately the economic and environmental factors. To meet this objective. a study program.
structured to have the flexibility to respond to the evolving results of the study activities, was
developed in cooperation with the Department's staff. Assumptions used for basic guidance, such
as those describing water use, were also developed jointly. Cooperation and coordination with the
staff was on a close and continuing basis.

The approach to estimating the streamflows available in the Study Area consisted of two
key phases. The first was to estimate the quantity of virgin, or undepleted. flows occurring in the
two basins by applying historic streamflow data extended by using statistical procedures. The
second was to estimate the water available to the Board's appropriations by superimposing
present and certain potential future water demand on the undepleted flows. The results for both
of these phases were achieved by the use of sophisticated analytical tools, computer technology
and assistance from acknowledged experts in the fields of water use and statistical hydrology.

Because of the rugged and remote nature of the Study Area, the topographic features and
structural geology were defined using airborne remote sensing techniques. Topographic maps and
surficial geologic information appropriate for this level of study were developed efficiently and
economically by this method. Limited subsurface geological investigations were conducted at

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