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FLOOD01329
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FLOOD01329
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Last modified
11/23/2009 12:58:19 PM
Creation date
10/4/2006 9:56:40 PM
Metadata
Fields
Template:
Floodplain Documents
County
Weld
Community
Pierce
Title
FIS - Pierce
Date
5/1/1979
Prepared For
Pierce
Prepared By
FEMA
Floodplain - Doc Type
Current FEMA Regulatory Floodplain Information
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<br />3.0 ENGINEERING METHODS <br /> <br />For flooding sour~es studied in detail in the community, standard hydrologic <br />and hydraulic study methods were used to determine the flood hazard data <br />required for this study. Floods having recurrence intervals of 10, 50, <br />100, and 500 years have been selected as having special significance for <br />flood plain management and for flood insurance premium rates. The analyses <br />reported here reflect current conditions in the watersheds of the flooding <br />sources. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for floods of the selected recurrence inter- <br />vals for each stream studied in detail in the community. <br /> <br />There are no streamflow gages on Spring Creek. A search of records <br />of existing gaged streams in Colorado indicated that there are no <br />basins of either similar size and physiographic characteristics or <br />with recorded rainfall distributions from which comparisons could be <br />made for a model of the basin hydrology. Therefore, synthetic <br />hydro graph analysis was used to develop storm discharges. <br /> <br />Rainfall ~ata and distributions used in the development of peak <br />disGharges for Spring Creek were obtained from the National Oceanic <br />and Atmospheric Administration Atlas for Colorado (Reference 5). <br />The U.S. Soil Conservation Service Method, as described in the <br />National Enqineerinq Handbook (Reference 6), was selected as the <br />method which would best represent the runoff characteristics of the <br />Spring Creek basin. Weighted average curve numbers were computed <br />using soil and land use maps for Weld County (References 7 and 8) . <br />The times of concentration were determined using stream hydraulics <br />of approximate cross sections taken from U.s. Geological Survey <br />topographic maps at a scale of 1:24,000, with a contour interval of <br />10 feet (Reference 9). Discharges were computed for the 10- and <br />100-year flood events and plotted on log-probability paper. The 50- <br />and 500-year discharges were obtained by straight-line extrapolation <br />of the 10- and 100-year values. <br /> <br />Peak discharge-drainage area relationships for the main channel of <br />Spring Creek and Spring Creek Overflow are shown in Table 1. <br /> <br />The discharges in Table 1 represent computations of split flow which <br />occurs at the intersection of Rowe Avenue and U.S. Highway 85, as <br />well as distribution of weir flow along the Union Pacific Railroad <br />tracks. <br /> <br />5 <br />
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