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<br />~;TEP 10 (continur:.!!l <br /> <br />METHOD 1 - TABLE OF HYDRAULIC ROUGHNESS CONDITIONS <br /> <br />(Manning's n Valllle) <br /> <br />Estimate the portions of the channel and adjacent ov'~rbanks subject to flood <br />flows <br /> <br />Note the eonditions of the channdl and the overbanks with respect to <br />vegetation, soil, rocks, and anything that might affect roughness <br /> <br />If there is a substantial differenGe between the channel, the right overbank, <br />and the left overbank, plan on average roughness 'Values based on the <br />proportion of total flow in each portion of the total cross-section <br /> <br />Select the clescription which best repn~sents the conditions of the area you are <br />examining and note the roughness valllle in the Table of Roughness Conditions <br /> <br />If necessary, average the roughness values (If the various parts of the cross- <br />section to get an overall value <br /> <br />Description of Channel and Overbank Conditions n Value* <br /> <br />Heavily Vegetated ,070 <br /> <br />Rocky ,050 <br /> <br />Gravelly ,035 <br /> <br />Sandy or grassy <br />Concrete <br />1 hese are averag(: values, <br /> <br />,030 <br />,014 <br /> <br />,-.----- ---- <br />--,---------- <br /> <br />Note that the roughness values listed above are approximate, Roughness values can vary <br />according to depth of flow, water velocity, and the degree of maintenance performed among other <br />factors. These values are only intended to provide general guidance in the performance of an <br />approximate hydraulic ana lysis. <br />