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Last modified
1/25/2010 7:10:20 PM
Creation date
10/5/2006 2:35:53 AM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Community
State of Colorado
Basin
Statewide
Title
The NWS Simplified Dam Break-Flood Forecasting Model
Date
5/16/1986
Prepared By
FEMA
Floodplain - Doc Type
Historic FEMA Regulatory Floodplain Information
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<br /> <br /> <br />l <br /> <br />h <br />r <br /> <br />Figure 1 (a) and (b) <br /> <br />Once the K and m parameters have been computed for the dam face cross <br />section, the flow (Q ) that produces the depth (h ) (shown above) must be <br />v v <br />evaluated and compared with Qbmax to determine whether the maximum depth is <br />above or below hv' The flow Qv is evaluated using the Manning equation, i.e., <br /> <br />Qv <br /> <br />1.49 <br />=- <br /> <br />81/2 <br /> <br />((m +\)5/3) <br /> <br />h (m + 5/3) <br />v <br /> <br />(7) <br /> <br />n <br /> <br />where: n <br /> <br />Manning roughness coefficient <br /> <br />Note: <br /> <br />8 = Channel bottom slope immediately downstream of dam <br /> <br /> <br />K & m = Channel fitting coefficients <br /> <br />The Manning roughness coefficient may be estimated to be 0.04 for a <br /> <br /> <br />cross-section located in an area of pastureland, .07 for a <br /> <br />moderately wooded area and 0.10-0.15 for a heavily wooded area (use <br /> <br /> <br />the higher value to account for effects caused by significant <br /> <br />amounts of debris in the downstream valley). <br /> <br />If Qv is found to be greater than <br />h ,and h is determined using the <br />max max <br /> <br />Qb ,then hv must be greater than <br />max <br />relation: <br /> <br />h = <br />max <br /> <br />t/b <br />eb:aj <br /> <br />(8) <br /> <br />.. <br /> <br />where <br /> <br />1.49 <br />a=- <br />n <br /> <br />81/2 <br /> <br />K <br />(m + 1)5/3 <br /> <br />(9) <br /> <br />b = m + 5/3 <br /> <br />(10) <br /> <br />1-6 <br />
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