PROJ00202

• Contract/PO #: C153474
• Contractor Name: Oak Creek, Town of
• Water District: 0
• County: Rio Blanco
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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CHAPTER IV - PLAN OF DEVELOPMENT

IV.l Statement of the Problem

The National Dam Inspection Act of 1972 (Public Law 92-367) authorized
the U.S. Army Corps of Engineers (COE) to conduct inspections of non-federal
dams throughout the united States. As part of this effort, the COE contracted
with Charles T. Main Co. to complete a Phase I inspection and evaluation of
Sheriff Reservoir owned by the Town of Oak Creek. The Charles T. Main study
was completed in September 1980. As part of this study, the reservoir
spillway capacity was evaluated. Because the dam hazard classification is
II hi gh", the dam is requi red to pass the i nfl ow from a probab 1 e max i mum f1 ood
(PMF) resulting from a probable maximum precipitation (PMP) event. The
Charles T. Main study showed that the existing spillway could not safely pass
the PMF wi thout overtoppi ng the embankment dam, .wh i ch cou 1 d resu It in dam
failure and the release of water stored behind the dam. As a result of this
study, the COE put the dam and reservoir on a national list of unsafe dams.

In addition to supervising the efforts to inventory and evaluate dams
throughout the U.S., the COE, as part of the National Dam Safety Act, has
worked with all state governments to enact dam safety legislation and to
implement dam safety programs. Following creation of the national unsafe dams
list, the COE has continued efforts to get the states to have ~am owners
complete additional studies, designs, and construction of modifications to
eliminate dam safety deficiencies. The Colorado State Engineer's Office (SEO)
has requested the Town of Oak Creek to complete en9ineering studies and
designs of modifications to Sheriff Reservoir by December 31, 1986.
Correspondence pertaining to Sheriff Reservoir between the Town of Oak Creek
and the SEO concerning this problem is given in Appendix C.

In September 1986, a contract was established between the Town of Oak
Creek and Geotechnical Engineers Inc. (GEl) to complete engineering studies of
Sheriff Reservoir as well as feasibility level designs and cost estimates of
alternative modifications to the existing spillway and/or dam to remedy the
dam safety deficiencies. The information which follows is a summary of these
evaluations in order for the Colorado Water Conservation Board (CWCB) to con-
sider partial funding of the required construction work.

IV.2 Study Approach and Scope of Work

The engineering studies completed for Sheriff Reservoir included several
key work components as follows:

Item 1 - Hydrologic evaluations were completed to estimate the PMF event
for the Sheriff Reservoir catchment.

Item 2 - Hydraulic routings of the PMF and percentages of the PMF through
the reservoir and downstream of the reservoir past locations of struc-
tures and other significant property developments were completed.