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FLOOD04296
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Last modified
1/25/2010 6:45:51 PM
Creation date
10/5/2006 12:31:25 AM
Metadata
Fields
Template:
Floodplain Documents
County
Larimer
Community
Larimer County
Stream Name
Big Thompson River
Basin
South Platte
Title
Special Floodplain Information Report
Date
12/1/1986
Prepared For
CWCB / FIA / Larimer County
Prepared By
Gingery Associates, Inc.
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />characteristically have high peak discharges of short duration, <br />lasting only a few hours. As the flood flow passes through the <br />upper portions of the basin, little channel storage exists <br />to attenuate or reduce the flood discharge. As the flood moves <br />into the flatter areas below the canyon mouth, channel and <br />flood plain storage slow the flow velocities and reduce the <br />flood discharge and flood elevation. <br /> <br />and study findings. State-of-the-art hydrology study methods <br />were used in completing the hydrologic analysis. The study. <br />methods considered included: <br /> <br />The confined and hydraulically steep channel characteristic <br />of the Big Thompson River above the canyon mouth, will sustain <br />hazardous velocities throughout the canyon bottom for major <br />flood events. Properties not subject to flooding may be <br />subject to significant hazard and damage through the erosion <br />of the channel sides by the high flOOd velocities. <br /> <br />, <br />, <br />I <br />, <br />, <br />, <br />, <br />I <br />. <br />I <br />, <br />I <br />, <br />I <br />I <br />, <br /> <br />1. Log-Pearson Type III Frequency Distribution, <br />Water Resources Council Bulletin No. 17 <br />(Ref. 5) <br />2. "Manual for Estimating Flood Characteristics <br />of Natural-Flow Streams in Coloradow, Technical <br />Manual No.1, V. S. Geological Survey and Colorado <br />Water Conservation Boarq (Ref. 6) <br />3. Storm Water Management Model, Environmental <br />Protection Agency (Ref. 7) <br /> <br />Hydrologic AnalySis <br /> <br />The Log-Pearson Type III frequency distribution served as <br />the primary basis for estLmating the flood discharge-frequency. <br />The other two methods served as a means of checking the study <br />results. The Log-Pearson Type III method relies on the historic <br />stream flow records at various gages on the river. The stream <br />gages on the 8ig Thompson River considered in the study are <br />listed below: <br /> <br />A hydrologic study was completed to estimate the peak <br />discharges for the 10-, 50-, 100- and SOO-year recurrence interval <br />floods on the Big Thompson River and tributaries within the <br />study area. The results of this study serve as a basis for <br />determining the flood profiles for the various frequency floods <br />and ultimately, the basis for flood plain delineation, flood plain <br />insurance and flood plain management. <br /> <br />Period of Years of <br />Record Record Gaqe Name <br /> Big Thompson River, <br />1888-1976 49 at mouth of Canyon <br /> Big Thompson River, <br />1918-1955 38 below Powerhouse <br /> North Fork Big Thompson River, <br />1947-1976 30 " Drake <br /> Big Thompson River, <br />1947-1976 30 near Estes Park <br /> Big Thompson River, <br />1930-1976 '" ., Estes Park <br /> <br />The hydrology study was completed with the assistance and <br />cooperation of various federal, state and local agencies mentioned <br />earlier. <br /> <br />Two review meetings were held with the various agencies <br />mentioned previously tc discuss the hydrology study methods <br /> <br />-10- <br /> <br />-11- <br />
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