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<br />,-- <br /> <br />METHODS EXAMINED <br /> <br />Veap-ta~ion Densitv <br /> <br />The ~--"'.t~!i..,9t 'ikY~jlt..&ted.floo<i"?1Ua is a .....ce~ many <br />variables. Included are the flow viOl I'l~, the distribution and size of the <br />veqeeA&a.. on the flood plain, the cross-section~ the ~Pt4 of flow on <br />the flood plain, and the ~'of the flood-plain boundary. <br /> <br />petryk and Bosmajian (1975) developed a procedure to determine roughness <br />coefficients for densely vegetated flood plains by analysis of the vegetation <br />density. This analysis uses a simple flow model. The velocity is assumed to <br />be small enough to limit plant bending. This means the projected area of the <br />plant in the direction of flow is independent of velocity. The analysis <br />requires that maximum flow depth be less than the maximum height of the <br />vegetation. <br /> <br />The equations were derived for steady, uniform flow, but the results may <br />be applied to gradually varied flow. Considering a channel reach as a <br />control volume between two cross sections (fig. 1) and using the momentum <br />equation, the sum of the forces in the x-direction are equal to zero, or <br /> <br />EFx = 0 <br /> <br />(3) <br /> <br /> <br />(j) 01 O2 <br /> 03 <br /> C2l <br /> I <br /> J J <br /> I I <br />I I <br />I I <br />I I <br />I I <br />I I <br />I J <br />J I <br />J I <br />J I <br />I I <br />(j) lAL -X <br /> Tw @ <br /> L1ALS Bed slope. S <br /> <br />Figure l.--Flow resistance model. <br /> <br />3 <br />