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Last modified
11/23/2009 12:58:12 PM
Creation date
10/4/2006 10:14:09 PM
Metadata
Fields
Template:
Floodplain Documents
County
Larimer
Community
Larimer County
Stream Name
Big Thompson River
Title
Evaluation of the Flood Hydrology in the Colorado Front Range Using Streamflow Records and Paleoflood Data for the Big Thompson River Basin
Date
5/1/1986
Prepared For
USGS
Prepared By
USGS
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />Precipitation data <br /> <br />Rainfall that produced the 1976 Big Thompson River flash flood in <br /> <br /> <br />Larimer County was reported to have occurred at an elevation of 8,300 feet <br /> <br /> <br />(2,530 meters) (Miller et al., 1984). This general statement, however, <br /> <br /> <br />needs clarification. The higher elevations where intense precipitation was <br /> <br /> <br />reported were associated with isolated mountain peaks above the general <br /> <br /> <br />topographic elevation of 7,500 feet (2,300 meters), The maximum flood <br /> <br /> <br />runoff occurred below 7,500 feet (2,300 meters) (McCain et al., 1979). <br /> <br /> <br />Miller et al. (1978) evaluated reconstructed flood peaks based on rainfall- <br /> <br /> <br />runoff analyses to estimate the storm precipitation in areas where <br /> <br /> <br />precipitation data were lacking. These investigators found it difficult or <br /> <br /> <br />impossible to reconcile slope-area indirect peak discharges with rainfall <br /> <br />measurements. Reconstructed peaks based on rainfall-runoff analyses <br /> <br />generally were 25 to 50 percent lower than slope-area measurements for the <br /> <br />higher-gradient streams, However, Miller et al. (1978) chose to accept that <br /> <br /> <br />the indirect peak discharges (McCain et al., 1979) were correct and to <br /> <br /> <br />increase the rainfall (intensities and volumes) accordingly for the storm. <br /> <br /> <br />This same practice was done for the 1964 Montana Storm (Boner and Stermitz, <br /> <br />1967). Jarrett (1986) has reported that peak discharges calculated using <br />the slope-area method for higher gradient streams (slopes greater than <br /> <br />0,01) consistently are overestimated, typically, by 75 to 100 percent, <br /> <br />/1 <br />
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