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

I
I
I
,I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

-15-

Item 3 - The potential for breaching of the dam during overtopping was eva-
luated and an estimation of breach parameters was made.

Item 4 - Hydraulic routings of water from the dam during breach, along
with the base flood causing the breach, through significant downstream
areas were completed.

Item 5 - An Incremental Damage Assessment (IDA) was made to estimate the
impact of a dam breach on base flood conditions at significant locations
downstream of the dam. A determination of the level of flood routing
protection that needs to be provided by Sheriff Reservoir was made based
on the results of the IDA.

Item 6 - A meeting was held with the SEO to discuss the results of the
hydrology and incremental impact evaluations and confirm flood routing
requirements for the reservoir.

As subsequently discussed, the results of these evaluations confirmed the
findings of earlier studies by the COE and the SEO which indicated that the
existing spillway at Sheriff Reservoir does not provide an adequate level of
flood routing protection. Therefore, alternative feasibility level modifica-
tion concepts were identified and evaluated. Specifically, the following work
was completed:

Item 7 - A site visit and field explorations adjacent to the right side of
the existing spillway channel were completed in early October 1986.

Item 8 - Feasibility level layouts, sections, and details of four alter-
native modification schemes to provide the required level of flood
routing protection were developed.

Item 9 - Engineering cost estimates for the two preferred modification
schemes were made.

Item 10 - The most cost effective and technically preferred modification
option was selected for further feasibility evaluation and presentation
in th is report.

Important aspects of each of these items leading to the selection of the
preferred modification scheme as well as the plan of development for this
scheme are presented in the next two sections of this chapter.

IV.3 Hydrologic Evaluations

As shown in Figure 2, Sheriff Reservoir has a total tributary drainage
basin of approximately 12 square miles, including the Sand Creek subbasin
encompassing 4.50 square miles, the Trout Creek subbasin encompassing 7.44
square miles, and a reservoir surface area at maximum water level of 0.06
square mile. The terrain is characteristic of the Flatops Wilderness Area,
and consists of rugged mountains with dense forest cover, lush meadows, high
alpine tundra, and extensive talus slopes at the base of shear cliffs.
Important factors influencing basin hydrology are as follows: