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<br />wooded-flood plain. A boundary roughness, "0, is determined from <br />equation 9 and the n value is determined using equation 7. Steps 14 <br />through 23 in "Procedures for Assigning n Values" are used in the <br />computation of n for this subsection. <br /> <br />Subsection 2 of this cross section has channel flow. The channel is <br />composed of firm soil, and no subdivision of the channel is necessary. <br />Steps 1 through 13 are used in the computation of n for this subsection. <br /> <br />Subsection 3 is also flOOd-plain flow. The flood plain is a field <br />planted in ,cotton. There is no need to subdivide the subsection, and the <br />depth of flow is equal to the height of the vegetation. Steps 14 through <br />23 are used in the computation of the n for this subsection, and equation <br />6 is used to determine the n value for the flood plain. <br /> <br />Sl1-1MARY <br /> <br />In this design guide, procedures are presented for assigning <br />reliable n values to channels and flood plains. The roughness <br />coefficient applies to a reach of a channel and should be representative <br />of that entire reach. It may be necessary to divide a channel and flood <br />plain into subsections and to assign n values to each subsection. <br /> <br />In the case of channel roughness, a procedure is presented that <br />involves a series of decisions based on the interaction of <br />roughness-causing factors. A base value is assigned to the channel and <br />adjustments are made for certain roughness-causing factors. <br /> <br />A similar procedure is used to assign n values to flood plains. A <br />base value is determined for the flood plain related to certain roughness <br />factors; then an option, based on the measurement of vegetation density <br />of the flood plain, is used to determine the total roughness of <br />flood-plain subsections. 'Ihe vegetation density of the flood plain is <br />determined from f*1ysical measurements of the vegetation in a <br />representative sample area of a flood-plain subsection. <br /> <br />Photograf*1s of flood plains for which n values are known are <br />presented to aid in the determination of roughness coefficients. The <br />f*1otograf*1s can be used for ccmparison with field situations to help <br />verify selected n values. <br /> <br />Step-by-step procedures are presented to determine the roughness <br />coefficients for channels and flood plains, and examples showing how to <br />use the procedures are included. <br /> <br />60 <br />