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

consists of sand, silt and clay with local boulders and lenses of gra-
vel composed of basalt and sandstone. (See Figure IV-3)

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The report by the Bureau of Reclamation indicates that there
is adequate fill material available for an earthfill dam. Aggregate
and sand for concrete and filler material will probably have to be
obtained from gravel pits along the Colorado River to the north.
These pits may also be the only source for riprap. No hard formation
is locally present for a rockfill dam or for riprap.

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The geotechnical studies by the U.S. Bureau of Reclamation
are adequate for preliminary design. Additional hydrogeologic studies
will be required to define the leakage through the bedrock ridges that
will form the abutments, and to des:lgn the cutoff trench and/or grout
curtain to reduce leakage under the dam. The Bureau reports that
there is adequate borrow material in the reservoir area for the
construction of the dam. The quantities and the engineering proper~
ties of these material need to be confirmed for final design.

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3. Dam Layouts

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Six dam layouts (See Figure IV-3) were done for the Dry
Hollow site, three embankment dams and three RCC dams. The geometry
of the Dry Hollow dam site lends itself to relatively large dams. The
range of reservoir sizes studied was 6,200 acre-feet to 19,000
acre~feet. The area-capacity curve shows that roughly the first forty
feet of dam height produces 11 ttle storage. Only after the dam is
quite high does the efficiency of the site begin to be realized.

4. Spillway Layouts

The drainage area above the Dry Hollow Dam site is very small
(3.7 mi2) relative to the other darns. Consequently the spillway is
also relatively small.

The spillway inflows design. flood and design flows are shown

below:

IV~13

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