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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IV.

GEOLOGIC AND MAPPING

The Study Area is characterized by the rugged mountain peaks and deep glaciated valleys
of the Gore Range on the east and the more gently sloping sedimentary rock to the west. The
formation of the mountain ranges, and the subsequent effects of erosion and deposition by
glaciers and other natural elements that occurred countless years ago, played an important role
in the planning of this water resources project.

The geologic and mapping programs were undertaken to define the land features in the
Study Area that will affect the cost and operation of the four configurations. The program was
accomplished in two stages. The first stage defined the topography and geology of the storage
and conveyance system associated with the Eagle-Piney configuration, and was initiated in the
summer of 1971. A second, supplementary geologic and mapping program was undertaken in
the summer of 1972 to develop data and information for other operational configurations which
were identified durin.g the first year's work as possessing distinct merits.

The results of the geologic program showed that an impoundment site contemplated for
the Eagle-Piney configuration near Camp Hale on the Eagle River was unsuitable because of a deep
pervious foundation. Consequently, for the purposes of this study, the site was eliminated from
further consideration. Otherwise, the geologic and mapping programs indicated that the geology
of the area should not involve excessive costs in the construction of the structural elements of
the four configurations. However, the programs identified potential construction problems,
especially in the shear and other difficult zones through which the conveyance tunnels must pass.
Since it is expected that these zones represent a fairly small percentage of the total length
traversed by the tunnels, the overall increase in construction costs due to these areas of
unfavorable rock conditions should be slight.

The location and alignment of the structures and the determination of suggested
construction procedures to help minimize costs were based on the information gained from the
geologic and mapping programs. For example, where the geology suggests the presence of softer
sedimentary rocks, significant economies may be realized during project implementation by the
use of tunnel boring machines.

The dam type selected was also guided by the geology at the dam site and the availability
of material to economically construct the facility. Therefore, the cost estimates of the four
configurations were based largely on the geology and topography of the area and application of
construction practices that can be effectively and economically utilized.

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