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Last modified
1/25/2010 7:14:43 PM
Creation date
10/5/2006 3:41:09 AM
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Floodplain Documents
County
Statewide
Community
State of Colorado
Basin
Statewide
Title
Determination of Urban Watershed Response Time
Date
12/1/1974
Prepared By
E.F. Shulz and O.G. Lopez
Floodplain - Doc Type
Flood Mitigation/Flood Warning/Watershed Restoration
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<br />Table 3 <br /> <br />Espey Channelization Factor <br /> <br />01 Classification <br /> <br />0.6 Extensive channel improvement and storm sewer system, <br />closed conduit channel system. <br /> <br />0.8 Some channel improvement and stann sewers; mainly <br />cleaning and enlargement of existing channel. <br /> <br />1.0 Natural channel conditions. <br /> <br />Table 4 <br /> <br />Espey Seasonal Channelization Factor <br /> <br />02 Classification <br /> <br />0.0 No channel vegetation, <br /> <br /> <br />0.1 Light channel vegetation. <br /> <br /> <br />0.2 Moderate channel vegetation, <br /> <br />0.3 Heavy channel vegetation. <br /> <br />o 01 + 02 <br /> <br />where K is the urbanization factor, <br /> I is the percent of impervious I..atershed, <br /> L is the equivalent length, <br /> e <br /> L is the length of the longest channel, <br /> n is the Manning friction factor, <br /> s is the weighted slope of the longest <br /> channel. <br /> <br />\C <br /> <br />( L )0,6 <br />1.2 - <br />IS <br /> <br />(natural main channels but sewered <br />secondary drainage), <br /> <br />Both Carter (1961) and Snyder (1958) found that water- <br />shed response time (lag or time of concentration) <br />could be correlated with a length-slope parameter. <br />Carter (1961) found that some of the effects of urban- <br />ization could be quantified through the coefficient in <br />the relationship between lag time and the length-slope <br />parameter. These equations were derived for several <br />streams in the Washington area: <br /> <br />TLC = 0,53 (.l.)0.6 (completely sewered, complete <br />IS urbanization). <br /> <br />Carter based his analysis on flood peak discharge hav- <br />ing a return period of 2.33 years. The evolution of <br />the watershed to a completely sewered watershed re- <br />sulted in 1.8 increase in the peak discharge over a <br />pristine watershed. Similar relationships were re- <br />ported by Espey et al. (1965) for the watersheds near <br />Houston. The coefficients for the Houston watersheds <br />are not given here because the units and the definition <br />of lag time appears to differ from Carter. <br /> <br />\C <br /> <br />( L )0.6 <br />3.1 - <br />IS <br /> <br />(pristine conditions), <br /> <br />In the analysis of the Louisville data, Eagleson <br />(1962) used the more conventional expression of the <br />watershed parameter: <br /> <br />8 <br />
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