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<br />BED FORM <br /> <br />Plain bed <br /> <br />Ripples <br /> <br />Dunes <br /> <br />Transition <br /> <br />Plain bed <br /> <br />Standing waves <br />and antidunes <br /> <br />Water <br />surface) <br /> <br />.::.::.}..:.:.: <br />Bed <br /> <br />~~ <br /> <br />/.:.~::-> -;;:;c- <br />. . ..,.-,. <br /> <br />'.~'.:..:':,:'.:.:. <br /> <br />~ <br />~ <br /> <br /> <br />Resistance to flow <br />(Manning's roughness <br />coefficient) <br /> <br /> <br />Lower regime <br /> <br />Transition <br /> <br />Upper regime <br /> <br />STREAM POWER <br /> <br />Figure 2. --Fbrms of bed roughness in sand-bed channels. <br /> <br />Limerinos (1970) related n to hydraulic radius and particle size <br />based on samples from 11 stream channels having bed material ranging from <br />small gravel to medium-size boulders. Particles have three dimensions-- <br />length, width, and thickness--and are generally oriented so that length <br />and width are about parallel to the plane of the streambed. Limerinos <br />related n to minimum diameter (thickness) and to intermediate diameter <br />(width); his equation using intelTIediate diameter appears to be the most <br />useful because this dimension is most easily measured in the field and <br />estimated from photographs. <br /> <br />The equation for n using intermediate diameter, is <br /> <br />(0.0926)Rl/6 R <br />l.16 + 2.0 log(d) <br />84 <br /> <br />n = <br /> <br />(5) <br /> <br />where: R = hydraulic radius, in feet; <br />d84 = the particle diameter, in feet, that equals or exceeds <br />that of 84 percent of the particles (determined from a <br />sample of about 100 randomly distributed particles) . <br /> <br />Limerinos selected reaches having a minimum amount of roughness, other <br />than that caused by bed material, and reaches that correspond to the base <br />values given by Benson and Dalrymple (1967), shown in table l. <br /> <br />7 <br />