PROJ00515

• Contract/PO #: FS0019X
• Contractor Name: Turkey Creek Snowball Creek Project CWRPDA 1985
• Contract Type: Loan
• Water District: 0
• County: Archuleta
• Loan Projects - Doc Type: Feasibility Study

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economical spillway design was determined to be a service spillway combined
with an emergency spillway. The service spillway was sized to pass 270 cfs
with 5-feet or head over the intake. The emergency spillway is capable of
passing the remaining 1292 cfs of the maximum thunderstorm with 4.2 feet of
head over the emergency crest. The emergency spillway will commence
operation when depth over the service spillway crest reaches 3 feet and the
service spillway discharge reaches 200 cfs.

The service spillway consists of a concrete morning glory intake
structure. It will be located near the right abutment and connected to a
48-inch reinforced concrete pipe (RCP). The 48-inch pipe follows the
downstream toe of the dam to an energy impact basin located in the
streambed of Snowball Creek. The impact bas~n is designed to dissipate the
energy and reduce the velocity of the flow in the RCP pipe before flowing
into Snowball Creek. A bypass from the outlet works to allow water from
the reservoir to be released into Snowball Creek is connected to the
48-inch RCP just upstream of the energy impact basin. The proposed service
spillway is shown on Sheet 7 in Appendix B.

The emergency spillway consists of a 50-foot wide, grass-lined channel
with 3:1 side slopes that empty into a side drainage. Two concrete cutoff

structures would be installed perpendicular to the spillway channel to
control erosion in the event of a large storm. The emergency spillway's
main purpose is to ensure that flood flows in excess of the 100-Year storm
are removed far enough away from the dam, to protect the main embankment
and dam features. In the event of a PMF or maximum thunderstorm flood, the
channel would probably sustain significant damage from erosion, but the
main dam embankment would not be affected.

The above design assumes that the State Engineer would classify the
dam as a high hazard structure and would require a spillway capable of
passing either the PMF or the maximum thunderstorm. In order to convince
the State Engineer that a smaller spillway would be acceptable, proof would
have to be submitted that loss of life would not occur if the dam failed

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