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<br /> <br />FACT SHEET <br />Cherry Creek Reservoir <br />Site-Specific Probable Maximum Precipitation Study <br />Colorado Water Conservation Board <br /> <br />COLUI{lI.I)U <br /> <br />I~] <br /> <br />Background: The Flood Control Act of 1941 and 1944 <br />authorized The Cherry Creek Lake project. Construction of <br />the flood control reservoir was completed in 1950 and it <br />operated as a dry dam until a permanent pool was <br />established in 1958. The average basin length is 57 miles <br />and average basin width is 11 miles. The average annual <br />rainfall is 16.6 inches and the maximum watershed <br />elevation is 7,580 feet msl. The major tributaries are East <br />Cherry Creek, West Cherry Creek, Antelope Creek, Willow <br />Creek, and Happy Canyon Creek. The years of recorded <br />major floods in cherry Creek were: 1864, 1875, 1976,1878, <br />1885, 1912, 1933 (Castlewood dam failure), 1935, 1945, <br />1946, 1965. The Project controls 386 square miles of the <br />410 square mile Cherry Creek Basin. The design storm for Cherry <br />Creek Reservoir was the May 30-31, 1935 storm and the dam is <br />designed to pass this storm with a safety factor. The emergency <br />spillway will convey flood flows east to Tollgate Creek that tributary to <br />Sand Creek. <br /> <br />I:IJJ~RI ~'''l\.1 dl <br />NATUIZ.AL <br />lUSOURCES <br /> <br /> <br />Cherry Creek Dam Profile <br />Feature Elevation Capacity <br /> (feet mean sea level) (Acre feet) <br />Base of Dam/ reservoir outlet 5504 ---- <br />Top of Conservation Pool 5550 13,220 <br />Spillwav Crest 5608.7 ----- <br />Top of Corps ownership 5624 110,310 <br />Top of Dam 5644.5 142,230 <br />Projected top ofPMF Pool 5646.5 ------ <br /> <br />..., <br /> <br /> <br /> Cherry Creek PMP and Storm Study History <br />PMP & Storm Studies Storm Total Rainfall Runoff (Inches) Peak Discharge (CFS) PMP Volume <br /> Length (inches) (Acre-feet) <br /> (hours) <br />1935 Storm Event 9 11.5 8.1 187,000 166,700 <br />HMR44 96 23.9 9.7 376,000 207,00 <br />HMR55A 96 29.22 16.25 635,000 359,000 <br />Site Specific PMP (Corps) 72 24.7 12.75 524,700 262,500 <br /> <br />The U.S. Army Corps of Engineers Study: The Corps <br />of Engineers - Omaha District contracted with the National <br />Weather Service so conduct a PMP study for Cherry Creek <br />Reservoir mplete a study for the Probable Maximum <br />Precipitation (PMP) event and a the NWS concluded that the <br />resulting Probable Maximum Flood (PMF) event that could <br />potentially overtop the dam. Corps findings put 100,000 <br />people at risk and the potential for $10-15 billion in flood <br />damages if the dam failed. The draft Corps Dam Safety study <br />also concluded that the current Cherry Creek Lake Project <br />could safely control 75% of the PMF under existing <br />conditions with adequate freeboard. A 1993 Dam Safety <br />Assurance Evaluation Report produced some altematives that <br />have been evaluated and further considered to include: roller <br />compacted concrete hardening of the dam, a 15 foot dam <br /> <br />1 <br /> <br />Top the Dam <br />elevation 5644.5 <br /> <br />Elev. 5608.7 <br /> <br />USACE/NWS Reservoir Profile <br />1995 PMP Study <br /> <br />Top of USACE PMF Pool Elevation 5647.5 <br /> <br /> <br />Top of Conservation Pool <br />Elev. 5550 <br /> <br />Elev. 5504 <br />