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<br />28 <br /> <br />. <br /> <br />the range of Manning's roughness coefficients specified for each bed form, <br /> <br />that higher roughness coefficients should be used for flood studies and lower <br /> <br />. <br /> <br />roughness coefficients should be used for sediment transport analysis. Because <br /> <br />of the relatively wide variation in Manning's coefficient considering all <br /> <br />possible flow conditions and the full range of sand sizes, recommentled values <br /> <br />. <br /> <br />for design are given in Table 2-2. <br /> <br />2.4.3 Regime of Flow in Alluvial Channels <br /> <br />The flow in sand-bed channels is divided into two flow regimes with a <br /> <br />. <br /> <br />transition zone between. Each of these two flow regimes are characterized <br /> <br />by similarities in the shape of the bed configurations, mode of sediment <br /> <br />transport, process of energy dissipation, and phase relation between the <br /> <br />. <br /> <br />bed and water surfaces. The two regimes and their associated bed configu- <br /> <br />rations are: <br /> <br />A. Lower flow regimes <br /> <br />. <br /> <br />1. Ripples <br />2. Dunes <br /> <br />B. Transition zone: bed configurations range from dunes to plane beds <br />or to antidunes. <br /> <br />. <br /> <br />C. Upper flow regimes <br /> <br />1. Plane bed with sediment movement <br />2. Antidunes <br /> <br />. <br /> <br />a. standing waves <br />b. breaking antidunes <br /> <br />3. Chutes and pools <br /> <br />. <br /> <br />In Table 2-3, variations of different variables with flow regimes and <br /> <br />bed forms are given for two sand sizes. A relationship (Figure 2-8) was <br /> <br />developed by Simons and R;chardson (l966) that relates stream power (, V), <br />o <br /> <br />. <br /> <br />median fall diameter of bed mater;al, and form roughness. If the depth, <br /> <br />. <br />