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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PROJECT SUMMARY

Elkhead lake Dam was constructed in 1974 by the Colorado Division of Wildlife
{CDOW}. It consists of an earth embankment 90 feet high with a crest length
of 1140 feet at elevation 6375 and a concrete-lined service spillway with a
capacity to discharge about 17,000 cubic feet per second. The dam is located
on Elkhead Creek, a tributary to the Yampa River, about ten miles northeast of
the City of Craig in Section 16, Township 7, Range 89W, 6th P.M., i~offat
County, Colorado. The dam is situated in Water Division 6, Water District
44. The current reservoir capacity at the normal water surface elevation 6365
is approximately 13,700 acre-feet. CDOW maintains 5,390 acre-feet of storage
for recreational purposes, and the remaining 8,310 acre-feet are committed to
the Colorado-Ute Electric Association as a back-up cooling water supply for
their nearby power generating facilities.

During the Phase I inspection of the National Dam Safety Program, sponsored by
the Corps of Engineers in 1979, it was found that the spillway did not have
the capacity to safely pass the probable maximum flood {PMF} without
overtopping the embankment. Safely handling the PMF is required by the
Colorado State Engineer's Office (SEO) for dams with a high hazard rating such
as Elkhead lake. In 1984, The CDOVl performed a hydrologic analysis of the
Elkhead Lake draina3e basin in accordance with the SEO guidelines. The inflow
design flood approved by SEO was 37,387 cubic feet per second, which exceeded
the primary spillway capacity by over 20,000 cubic feet per second.

I n April of 1985, the CDm. contracted wi th i~orri son-Knudsen Engi neers, I nc.
(I1KE) to explore the feasibility of constructing a lining of roller compacted
conc rete (RCC) over the c rest and downstream face of El khead lake Dam to act
as an auxiliary spillway that would satisfy the overtopping requirements of
the SEO . Although the RCC 1 i ner di d not prove to be an economi ca 1 sol uti on,
an alternative design utilizing an auxiliary spillway channel through the left
abutment was determined to be feasible. This design was finalized and the
construction drawings, specifications, final design report, and cost estimate
were submitted to the SEa for approval in April of 1986.

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