PROJ00170

• Contract/PO #: C153481
• 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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CHAPTER V: PLAN OF DEVELOPMENT

1.0 EXISTING CONDITIONS

Elkhead Lake Dam is an earth embankment with a structural height of 90 feet
and a crest length of 1140 feet at elevation 6375. It was constructed in 1974
for the CDOW. The current reservoir capacity at the maximum normal water
surface, el~vation 6365, is approximately 13,700 acre-feet. Figure V.l shows
the dam location, reservoir area, area capacity curve, and outlet and spillway
discharge curves.

The existing embankment has a crest ~idth of 20 feet and upstream and
downstream slopes of 3H to lV and 2.5H to lV, respectively. The embankment is
homogeneous in nature and consists of sandy clay (CL) and clayey to silty sand
(SC-Stl) obtained from the surrounjing hillsid~s. A 20-foot wide cut-off
trench to bedrock is provi ded through the sandy gravel foundati on. A 6-foot
wi de verti ca 1 Chimney drai n is incorporated into the dam to transmi t seepage
and control the position of the phreatic surface. This chimney drain is
conne:ted to horizontal gravel finger drains, 3-feet high by 12-feet wide,
which were installed to carry seepage from the chimney drain to the downstream
toe of the dam. Outer slope protection was provided by placing riprap on
graded beddi ng upstream and grass cover on the downstream face. The crest of
the dam is gravel surfaced.

The ma in outl et works conduit :onsi sts of a 36-i nch di ameter concrete pi pe
placed along the foundation near the base of the left abutment. Flow through
the outlet works is controlled by two pneumatically operated slide gates
located at the intake structure. The outlet conduit discharges directly into
the spillway chute through the right sidewall. The capacity of the outlet at
the maximum nonnal reservoir water surface, elevation 6365, is 165 cfs.

The Starr Di tch outl et consi sts of a lO-i nch di ameter iron pi pe, and is
controll ed by a mechani ca lly operated sl i de gate at the intake structure
ili111ediately to the left of the spillway crest. The pipe runs along the base

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