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FLOOD06920
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FLOOD06920
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Last modified
1/25/2010 7:10:20 PM
Creation date
10/5/2006 2:36:06 AM
Metadata
Fields
Template:
Floodplain Documents
County
Boulder
Community
Jamestown
Stream Name
James Creek
Basin
South Platte
Title
Community File
Date
1/1/2001
Prepared For
CWCB
Prepared By
CWCB
Floodplain - Doc Type
Community File
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<br />. , <br /> <br />" <br /> <br />Table 1 <br />Lefthand Creek Basin <br />Stream.Gage Data' <br /> <br />Location <br /> <br />Approximate <br />Drainall:e Area <br />(sq. miles) <br /> <br />Gaging <br />Records <br /> <br />Lefthand Creek <br />Near Boulder <br />(2.5 mil~ above the <br />Foothills Highvay) <br /> <br />, <br /> <br />52 <br /> <br />Mayl929 <br />April 1947 <br />Oct. 1955 <br />Oct. 1976 <br /> <br />- Sept. 1931 <br />- Dec. 1953 <br />Sept. 1957 <br />- Present <br /> <br />James Creek <br />Mouth'" .. <br /> <br />18.7 <br /> <br />7 MaY.l.!!69 <br /> <br />* Spot discharge measurement. <br /> <br />,. <br /> <br />C. Hydro1oll:Y <br /> <br />The hydrologic analysis for James Creek consisted of determining the <br />magnitude of the 10-. 50-. 100-. and SOO-year floods. This was accomplished <br />by use of the Environmental Protection Agency's Storm Water Management Model <br />(SWMM). James Creek was a portion of a larger SWMM model for the Lefthand <br />Creek Basin which itself was a portion of a SWMM model to determine flood <br />flow frequencies in the St. Vrain Creek Basin. Rainfall values for the 10-, <br />50-. and 100-year; 1-, 3-. and 6-hour events were obtained from Precipitation <br />Frequency Atlas of the Western United States. Atlas 2. Volume III. Colorado, <br />published by the National Oceanic and Atmospheric Administration (NOAA) in 1973. <br />The SOC-year values were estimated by extrapolating the selected Atlas values <br />on semi-logarithmic paper. Adjustments for depth-area were based on the <br />depth-area relationship presented in the NOAA publication. <br /> <br />A discharge probability analysis was made at the U.S. Geological Survey <br />stream gage on Lefthand Creek listed as "near Boulder". -This gage was located <br />below the confluence of Sixmile Canyon with Lefthand Creek. The analytical <br />methods presented in Bulletin No. 17, published by the Water Resources Council <br />(WiRC) were used. Adjuetments for the length of record were made on logarith- <br />mic probability paper using Beard's table of expected probability adjustments <br />for various lengths of record. The results of this analysis were used as <br />a guide in the calibrati6n of the SWMM model. <br /> <br />Application of the 1-hour rainfall to the 19 square mile James Creek model <br />provided the discharges which were used in this etudy. A uniform infiltration <br />rate of 1 inch per hour was used for the entire Lefthan1 Creek basin. Deten- <br />tion storage of 0.5 inches was used for the 1-hour rainfall. <br /> <br />2 <br /> <br />
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