PROJ00259

• Contract/PO #: C153424
• Contractor Name: Colorado River Water Conservation District
• Water District: 0
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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natural one, formed by a ridge which is cut by the Dry Hollow
drainage. The USBR's 1980 estimate of the cost of Dry Hollow Dam and
Reservoir, including land, was $29,000,000, which is $1,240 per acre-
foot of storage.

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In the present study Dry Hollow Reservoir will receive water
only from the West Divide Creek system, either as return flow from
irrigated lands or water delivered directly when other reservoirs are
full. The reservoir need be only a few thousand acre-feet since the
irrigated area which could benefit is limited to the lower Multi-Trina
ditch, 1,800 acres. Potentially Dry Hollow Reservoir, which is rela-
tively efficient storage, could be used to store excess water when it
is available, thereby reducing the storage requirements on other
reservoirs.

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2.

Geologic and Geotechnical Analysis

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The proposed Dry Hollow Damsite is on Dry Hollow Creek near
the center of Section 3, Township 7 South, Range 92 West. The pro-
posed damsite was investigated by the U.S. Bureau of Reclamation in
1978 (Ref.27). The investigations included the drilling, sampling,
and hydrologic testing of five core holes along the axis of the dam
and an investigation of construction material in the reservoir area
(Ref. 27). A reconnaissance of the site was made on July 25, 1985.

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The geology of the Dry Hollow area is typical of that at the
southeast edge of the Piceance Creek Basin. The bedrock of the area
is the Wasatch Formation, which consists of interbedded lenses of
sandstone, conglomeratic sandstone, siltsone and claystone. According
to the studies of the U.S. Bureau of Reclamaiton, the contact between
the lower member of the Wasatch Formation, the Atwell Gulch member,
and the middle member, the Molina member, occurs about half way up the
abutments of the proposed dam. The bedrock is on the plunging nose of
the West Divide anticline and the beds dip downstream. Jointing is
conspicuous in the sandstone units. The principle set of joints is
parallel to the bedding. Typically there are joints at right angles
to the bedding and parallel or at right angles to the strike of the
beds.

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The bedrock in the area is covered by surficial deposits
except at the middle and upper parts of the dam abutments. The sur-
ficial deposits include colluvium and alluvium. Colluvium is derived
from the weathering of the bedrock and consists of angular boulders,
cobbles, and gravel composed of sandstone in a sandy and silty matrix.
Much of the reservoir area is floored with alluvium. The alluvium

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