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<br />/ <br />FJG. rJ <br />> <br />.. .... <br /> <br />1'110.3 <br />> <br />.... ... <br /> <br />The data in table 1 indicate the marked variation of Manning's <br /> <br />roughness, n, with depth in terms of hydraul ic radius. The relation of <br /> <br />Manning's roughness coefficient to the hydraul ic radius of the four <br /> <br />streams shown in figure 2 is typical of the relations of all of the <br /> <br />streams 1 isted in table 1. Roughness decreases markedly as depth of <br /> <br />flow increases. This change indicates the need for developing relations <br /> <br />between roughness and depth of flow. On three streams--Cottonwood <br /> <br />Creek, South Fork Rio Grande, and Trout Creek--flow was affected by bank <br /> <br />vegetation at the highest discharge. Dense willows created additional <br /> <br />turbulence and increased channel roughness markedly. The relation of <br /> <br />Manning's roughness coefficient to the hydraulic radius of these three <br /> <br />streams is shown in figure 3. This indicates that dense vegetation can <br /> <br />. have a marked effect on total flow resistance and should be accounted <br /> <br />for, as discussed earlier, by use of equation 5. <br /> <br />I <br /> <br />j1 <br />