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<br /> <br />Figure 5 summarizes the number of trees and their diameter; by using <br />this information and equation 11, vegd can be determined. <br /> <br />A value for flow depth must be determined for the flood plain, and <br />depth of flow is assumed to equal the hydraulic radius, R, for the flood <br />plain. An effective-drag coefficient is selected from figure 3. The <br />boundary roughness, no' is determined for the flood plain using <br />equation 9 and the n for the flood plain is computed using equation 7. <br /> <br />PIDTCGRAPHS OF FrroD PLAINS <br /> <br />The following series of photographs (figs. 6-20) represent densely <br />vegetated flood plains for which roughness coefficients have been <br />verified. The coefficients for these sites were determined as a part of <br />a study on computation of backwater and discharge at width constrictions <br />of heavily vegetated flood plains by Schneider and others (1976). By <br />using these photograf*1s for comparison with other field situations, n <br />values can be selected in the field. The photographs can then be used to <br />verify n values computed by other methods. <br /> <br />Information included with the photographs are site name and location; <br />n value determined for the area; base roughness, no; depth of flow on <br />flood plain; date of flood; and date picture was taken. <br /> <br />Several reports present photographs of channels for which roughness <br />coefficients are known and which would be helpful in determining roughness <br />values of other areas. Barnes (1967) presented photographs of natural, <br />stable channels having known n values ranging from 0.023 to 0.075; a few <br />flood plains were included in the report. <br /> <br />Ree and Crow (1977) conducted experiments to determine friction <br />factors for earthen channels planted with certain crops and grasses. The <br />values that were determined may be used to help estimate the roughness of <br />flood plains planted to the type of vegetation used in their experiments. <br />Photograf*1s and brief descriptions of the vegetation are given, and a <br />tabulation of the hydraulic elements are included. <br /> <br />Aldridge and Garrett (1973) presented photograf*1s of channels and <br />flood plains in Arizona having known roughness coefficients. Included <br />with the f*1otographs are channel geometry and a description of the <br />roughness factors involved in assigning an n value for the site. <br /> <br />Chow (1959) presented f*1otograf*1s of a number of typical channels, <br />, <br />accompanied by brief descriptions of the channel conditions and the <br />corresponding n value. <br /> <br />23 <br />