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Last modified
1/26/2010 10:08:17 AM
Creation date
10/5/2006 4:07:55 AM
Metadata
Fields
Template:
Floodplain Documents
County
Larimer
Community
Fort Collins
Stream Name
Dry Creek
Basin
South Platte
Title
Dry Creek Hydrology Report Fort Collins FIS
Date
4/22/1977
Prepared For
Larimer County
Prepared By
Gingery Associates, Inc.
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br />I <br />I <br />I I <br />I <br />I <br />I I <br />I <br />I <br />I <br />I <br />II <br />! <br /> <br />I <br />I <br />I <br />I <br />II <br />I I <br />I <br /> <br />SCS soil maps and landuse maps for Larimer County. A 100-year <br />frequency point rainfall of 3.4 inches, as determined from the <br />NOAA Atlas, Volume III, Colorado, was used for a storm duration ~ <br />equal to the basin time of concentration of 3.8 hours. An ~~:~l <br />adjustment factor was used, where applicable, to determine <br />actual rainfall depths. The peak discharge at the reservoir is <br />7520 cfs and the hydrograph is plotted in the Appendix (Fig. 3). <br />A stage - storage curve and a stage - discharge curve for Douglas <br />Lake were developed from information on file at the State Engineer's <br />Office. The lake water surface elevation was assumed to be at <br />the spillway crest at the time of the storm. Douglas Lake storage <br />reduces the peak flow to 1750 cfs. The outflow hydrograph is <br />shown in the Appendix (Fig. 3). <br /> <br />Peak storage in Douglas Lake during the storm is 2050 acre feet <br />at an elevation 8 inches below the crest of the dam. W~ve action <br />:lik;',lyIroml;1igh winds during;the10,~...y'ear Sl$~b1ElVE;mt may <br />eaE?iJ.y cause the embankment 1:o'b'e"itvertopped: The analysis assumed <br />a constant crest elevation on the dam embankment. Irregularities <br />in the embankment may allow overtopping without wave action. <br />A visit to the dam site showed that the dam has considerable <br />seepage evidenced by constant discharge from a weep hole. <br />This seepage condition is also noted in a memo on file at the <br />State Engineer's Office. <br /> <br />The volume of storage in Douglas Lake does not consider the <br />effects of the three non-stream lakes upstream, particularly <br />Reservoir No. 15. Reservoir No. 15 has a large storage capacity, <br />however, it intercepts only about 6 square miles or 13 percent of the <br />basin above Douglas Lake. This upstream storage will reduce the <br />required storage in Douglas Lake to a minor extent. The SCS was <br />consulted regarding the curve number used for this basin. Curve <br />numbers developed by the SCS for the Box Elder Basin adjacent to <br /> <br />-3- <br />
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