FLOOD05215

• County: Douglas
• County: Arapahoe
• Community: Greenwood Village, Aurora
• Stream Name: Cherry Creek
• Basin: South Platte
• Title: Probable Maximum Precipitation Study for Cherry Creek Reservoir - Facts
• Date: 1/1/1997
• Prepared For: CWCB
• Prepared By: CWCB
• Floodplain - Doc Type: Project

Cherry Creek Resermir
Site-Specifie "robahle Maximum "recipitatiol1 Study
CWClI Fact Sheet

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lJ:tckground: the Flood Control Act of 1941 and 1944
authorized The Cherry Creek Lake project. Construction
was completed in 1950 and it operated as a dry dam until
a pennanent pool was established in 1958. An existing
spillway hydraulically connects the C~crry Creek basin
with the adjacent Toll Gate and Sand(geek hasins. The
Project controls 386 square miles of the 410 square mile
Cherry Creek Basin. The design storm for Cherry Creek
Reservoir was the May 30-31, 1935 storm and the dam is
designctl to pass this storm with a safety factor. The
emergency spillway could convey llood nows cast to
Tollgate Creek which is a Sand Creek tributary.

COLORADO
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NATURAL
RESOUU.cES

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Cherry Creek 1>;'"1 and Resen'oir Profile: Cherry
Creek Drainage basin is approximately 386 square miles. The average basin length is 57 miles and average
basin width is II milc.."S. The average annual rainfall is 16.6 inches, the maximum elevation is 7.580 feet msl.
The reservoir outlet invcrt is at 5,504 feet ms!. The major tributaries are East Cherry Creek, West Cherry
Creek, Antelope Creek, Willow Creek. and Happy
Canyon Creek. The years of recorded mayor floods are
1864, 1875, 1976,1878, 1885, 1912, 1933 (Castlewood
dam failure), 1935, 1945, 1946, 1965.

Chern Crel'k U;tlt1 Profile

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The Corps Study: The Army Corps of Engincers . ~ _ _.....:; /
(USACE) - Omaha District started a study that ,,;'~Al)~ n~Hood-
concluded iH ...ill:t .-\ Pr:ob:.lhl.' \f'l'''imull, P.recipitation evcnt and the resulting Probable Maximum Flood
event could potentially overtop the dam and put 100,000 people at risk and could cause $10.15 billion in
damages. The PMP study also concluded that the current project could safely control 75% of the PMF under
existing conditions with adequate freeboard. A 1993 Dam Safety Assurance Evaluation report produced
some alternatives th;lt illl..'lud~'''' that have been evaluated and further studied to includc: roller compacted
concrete hanlening of the dam, a I >-foot dam raise, 300-400 foot new spillway on Cherry Creek Dam with a
9-foot dam raisc, dry dam at Castlewood Dam Site with no dam raise, dry dam at West Cherry Creek with a
7.5 foot ~anl raise, and a dr~ da~l at Scott Road with a 12 foot dam raise.
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Colorado Sf:!te Genenll Assembly Resolution 99-023: In response to the controversial recommend(ui01'S
and public meetings rhe local gOl'ernmelUs worked wirh the Colorado General Assembly to create Resollllion
99-01.~Ex(erprsfrom the Senate Resollllion 99-013 ;[/ustrare the e\'ell/S that led to eW'CR inl'O/l'emelll:
"WIIEREAS, the u.s. Army Corps of Engineers Jws assllmed the Cherry Creek Dam '....illfailfollowing an
extraordinarily improbable chain of events, ...am! WIIEREAS. this error isfllrther compoum!e(! by the
erro"eolls assumptiOlJ rhat the topographic effects of the Palmer Dil'ide w;[/ i"crease the rainfall i"the

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