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Last modified
11/23/2009 10:40:01 AM
Creation date
10/4/2006 9:58:59 PM
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Floodplain Documents
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Statewide
Title
Guide for Selecting Roughness Coefficient n Values for Stream Channels
Date
12/1/1963
Prepared By
USDA Soil Conservation Service
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br /> <br />txJ <br />, <br />b <br /> <br />Table B,lEXamples of effect of vegetation on n. (Sheet 1 of 3) <br /> <br />Example <br />No. <br /> <br />Names and Descriptions of Channels. Names, Plates and Tables <br />Refer to USDA Technical Bulletin No, 129, November 1929 <br /> <br />Range in <br />mean <br />velocity <br /> <br />Range in <br />hydraulic <br />radius <br /> <br />Average <br />value <br />n <br /> <br />Modifying <br />value <br /> <br />1. <br /> <br />Fountain Head dredged channel near Champaign, Illinois; <br />Plate 31-B and C, Table 9. Average cross section of <br />channel resembles a parabola. At bankfull stage depth <br />about 8 ft., top width about 30 feet, <br /> <br />2.09 to <br />2,59 <br /> <br />1. 73 to <br />2.42 <br /> <br />a. <br /> <br />Dormant season. <br />tion on bottom, <br /> <br />Dry weeds on side slopes, no vegeta- <br />Retarding effect of vegetation negligible. <br /> <br />0.031 <br /> <br />b. Growing season, otherwise vegetation same as above. <br />Heavy growth of weeds and grass in full foliage on side slopes. <br /> <br />0,037 <br /> <br />0.006 <br /> <br />2. <br /> <br />Cummins Lake dredged channel near Gould, Arkansas; Plate 18-B <br />and C, Table 7. Average cross section of. channel resembles a <br />parabola. At bankfull stage depth about 13 ft., top width <br />about 75 feet, <br /> <br />0.53 to <br />1.82 <br /> <br />2.41 to <br />6,23 <br /> <br />a. Side slopes moderately irregular from erosion and slough- <br />ing; estimated n for channel without vegetation 0.035. <br /> <br />b. Dormant season. Willows about one year old and 6 to 10 <br />feet high continuous along side slopes except for about <br />the upper third of sides. No growth in a strip about 20 <br />feet wide along bottom, No foliage. <br /> <br />0.056 <br /> <br />0.021 <br /> <br />c. Growing season, 'otherwise vegetation same as above. Willows <br />and some weeds in full foli"ge, No vegetation along bottom. <br /> <br />0.072 <br /> <br />0.037 <br />
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