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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The bottoms of the creek valleys are covered wi th alluvium
and the divides between creek by alluvial terrace deposits. The allu-
vium in the creek valleys consists of blocks and gravel of sandstone,
"obbles and gravels of basalt, and sand, silt and clay. Most of the
material has been derived from the erosion of the "olluvial slopes and
the terrace deposits. The terra"e deposits occur on the divide bet-
ween East and Middle Mamm Creeks and between Middle and West Mamm
Creeks. Hunter Mesa, northwest of West Mamm Creek, is "overed by a
terrace deposit. The terra"e deposits consist of cobble and gravel of
basalt, and other hard igneous and metamorphic rocks, in a sand and
silt matrix. On top of the terrace deposit on Hunter Mesa is a fine-
grained silt, probably of Aeolian origin. (See Figure IV-6)

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Materials for "onstru"tion of earthfill or rollercrete dams
is probably available locally. The "olluvium and alluvium could be
processed for fill or rollercrete. Aggregate for concrete and sand
for concrete and filler material could be processed from the terrace
deposits. There are no local sources of hard rock for a rockfill dam.
Large boulders' of hard rock could probably be processed from the
terra"e deposits for riprap.

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Geologic and geotechnical investigations will be required for
preliminary design and feasibility studies. Topographi" and geologic
maps should be made of the damsites and reservoirs. Holes drilled for
core and for testing other permeability of the formations, should be
drilled along he dam alignments. Materials investigations, ,ffiich
would include mapping sampling and testing, should be conducted to
define the quantities and engineering properties of materials
available for construction of the dam and appurtenant stru"ture.

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3. Dam Layouts

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Three dam and reservoir layouts were completed for ea"h of
the two sites on Mamm Creek. The largest, at 9,000 acre-feet, was at
the Upper Mamm Creek site. The intermediate and smallest sized dams
at this site are 6,000 and 3,000 acrewfeet. The largest reservoir
considered at the Lower Mamm Creek site was 3,500 ac-ft. The other
two layouts studied at the Lower Mamm Creek site are 2,300 and 1,160
acre-feet. Quantities and "osts were then "alculated for each of the
three layouts at each site for both earth embankment and roller com-
pacted "oncrete (RCC) type dams.

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4. Flood Hydrology and Spillway Layouts

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Spillway design floods were developed, and reservoir routing
was completed according to the methods described in Section IV, A, 4,

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IV-23

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