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<br />. <br /> <br />-24- <br /> <br /> <br />. <br /> <br />An important part of the hydraulic analysis is the <br />selection of roughness coefficients "n's" for each <br />cross section, based on the existing conditions <br />along the stream and floodplain. These "n's," which <br />represent the roughness or resistance to water flow <br />as created by vegetation and rocks, are essential <br />for appropriately describing the flow. Past flood <br />data, if available, is used to verify the adopted <br />roughness coefficients, taking into consideration <br />any alteration in the channel subsequent to the <br />floods. If there are stream gaging stations within <br />the study reach, the computed water surface profiles <br />are checked against the rating curves (see Glossary) <br />for those stations to assist in the n-value <br />verification. . <br /> <br />. <br />