WSP10308

• File Number: 8449
• Description: Platte River Studies
• State: CO
• Basin: South Platte
• Date: 3/23/1993
• Author: Smith Geotechnical
• Title: Design Report Peterson Lake Dam
• Water Supply Pro - Doc Type: Publication

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PETERSON LAKE DAM

I. PROJECT DESCRIPTION

A. General.

Peterson Lake Is located In Larimer County, Colorado Township 7 North, Range 76
West. The reservoir Is located on a small unnamed creek which Is a tributary to
the Cache La poudre River.

The dam that Impounds Peterson Lake Is an earthflll dam that was constructed In
the early 1920's. The dam Is 67 feet In height, has a crest length of 176 feet,
and Impounds 1,262 acre-feet at the normal water surface elevation. The
reservoir has a pipe service spllIway through the dam embankment and a 360
foot emergency spillway Is lacated at the south-east corner of the reservoir.

A more complete descrlptlon of the existing dam and splllways can be found In
the Feasibility Study for Rehabilitation of Peterson Lake Dam and Reservoir by
Morrison-Knudsen Engineers. Inc.

B. Proposed Rehabilitation,

The City of Greeley has contracted with The Engineering Company (TEC) of Fort
Colllns, Colorado to design the rehabllltation of the Peterson Lake Dam. TEC
has contracted with SMITH GEOTECHNICAL of Fort ColIlne, Colorado to prOVide the
geotechnical and structural design of the dam,

Based on the Information In the Feaslblllty Study and on further engineering
studies conducted by TEC and SMITH GEOTECHNICAL, It has been decided by the
City If Greeley to replace the existing dam with a Roller Compacted Concrete
(ReC) Dam. This dam will be located approximately 76 feet upstream of the
existing dam and the existing dam wlll be removed. The existing emergency
spillway wllI be raised and wllI not be utilized as a spillway. The splllway wllI
be Incorporated with the RCC dam as an overfiow section.

The RCC dam is 260 feet In length and has a structural height of 69 feet. The
dam crest elevation varies due to incorporating the splllway into the dam as an
overflow section. The dllm section has a minimum crest width of Ii feet and has
a downstream slope of 0.66 horizontal to 1.0 vertical. In the maximum section
the slope flattens to 1 11 to 1 V below elevation 9466.0 feet. This was done to
Increase the stability and also this portion of the dam will be buried and does
not need to have a formed face. The I H to I V slape will allow construction
without forming the face.

C. Dam Foundation.

The dam will be situated on Precambrian metamorphic and igneous bedrock. Dark
gray gneiss, schist, granite, and white pegmatite of the Idllho Springs Formation
outcrop at the ieft (west) abutment and were detected In borings conducted by
M-K as described in the Feaslblllty Study, The same type of foundation
materiais are expected to exist at the proposed dam site as were found at the

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Peterson Lake Dam Design Report