WSP02349

• File Number: 8449
• Description: Platte River Studies
• State: CO
• Basin: South Platte
• Date: 3/1/1993
• Author: City of Greeley
• Title: Peterson Reservoir Dam Hydrology and Hydraulics
• Water Supply Pro - Doc Type: Publication

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39.58). The right side of the dam (Sta 1+50 to Sta 2 +60) is set at elevation 9500 which will provide
approximately one foot of freeboard above the PMF.

Spillways
The service spillway and the stilling basin are designed to pass flows resulting from the 2 x lOO-year
storm. Also, flows caused by smaller storms will also pass through the service spillway. Flows are
contained in the spillway section by training walls on either side of the spillway section. The height of
the walls is based on anticipated flows down the face of the dam.

The PMF event will exceed the capacity of the service spillway and will overtop the dam crest from
station 0+00 to 0+ 75. The service spillway will also operate during the PMF event at a higher crest
depth. The left abutment of the dam is founded in rock which is close to the surface; therefore, little
overburden exists downstream of the crest. In overburden areas, there is a potential for erosion during
the PMF. This would only result in visual damage and would not jeopardize the integrity of the dam.
If scour would develop during the PMF, restoration may be required in the damaged area. The right side
of the dam is set at an elevation higher than the PMF to protect overburden areas below the dam. The
right training wall of the service spillway is set at an elevation higher than the PMF also to protect the
downstream area.

To date, no design criteria has been established for determination of flow characteristic of stepped
spillways. The Bureau of Reclamation has begun research into the development of such criteria. Several
laboratory model studies have been conducted to determine: the shape of the crest, the characteristics
of flow down the face based on step size, and the size requirements for the stilling basin. The following
references have been used for the design of the Peterson Dam Spillway.

1. Kathleen L. Houston, "Hydraulic Model Studies for the Upper Stillwater Dam Stepped
Spillway and Outlet Works," Bureau of Reclamation, REC-ERC-87-6, October 1987.

2. Kenneth Hansen and William Reinhardt, "Roller-Compacted Concrete Dams, pages 110 -
112, McGraw Hill, 1991.

3. Proceedings of the Conference sponsored by the ASCE, Roller-Compacted Concrete m,
K.H. Frizell, Hydraulics of Stepped Spillways for RCC Dams and Dam Rehabilitation.

The crest of the spillway is designed with an ogee configuration based on the shape of the lower nape
of the downstream jet. The unit discharge for the service spillway is 25.5 cfs/ft. The approach depth
of the spillway was set at 3.5 feet, and the maximum crest head is 3.7 feet. The spillway width is 75
feet. The face of the dam consists of one-foot, vertical steps from elevation 9490 to 9486. The top three
steps have longer horizontal benches which intercept the jet and begin the tumbling action down the face
of the dam. Two-foot steps are used from elevation 9486 to 9458 at the stilling basin floor elevation.