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<br />Table 2.--Factors that effect roughness of the channel--Continued <br /> <br />Channel conditions <br /> <br />Example <br /> <br />n value <br />adjustmentY <br /> <br />Negligible <br /> <br />0.000-0.004 <br /> <br />A few scattered obstructions, which include debris <br />deposits, stumps, exposed roots, logs, piers, or <br />isolated boulders, that occupy less than 5 percent of <br />the cross-sectional area. <br /> <br />Minor <br /> <br />0.005-0.015 <br /> <br />f-' <br />o <br /> <br />Effect of <br />obstruction <br />(n3) <br /> <br />0.020-0.030 <br /> <br />Obstructions occupy less than 15 percent of the cross- <br />sectional area and the spacing between obstructions is <br />such that the sphere of influence around one obstruction <br />does not extend to the sphere of influence around <br />another obstruction. Smaller adjustments are used for <br />curved smooth-surfaced objects than are used for sharp- <br />edged angular objects. <br /> <br />Appreciable <br /> <br />Obstructions occupy from 15 to 50 percent of the cross- <br />sectional area or the space between obstructions is <br />small enough to cause the effects of several obstruc- <br />tions to be additive, thereby blocking an equivalent <br />part of a cross section. <br /> <br />Severe <br /> <br />0.040-0.050 <br /> <br />Obstructions occupy more than 50 percent of the cross- <br />sectional area or the space between obstructions is <br />small enough to cause turbulence across most of the <br />cross section. <br /> <br />Amount of <br />vegetation <br />(n4) <br /> <br />Small <br /> <br />0.002-0.010 <br /> <br />Dense growths of flexible turf grass, such as Bermuda, or <br />weeds growing where the average depth of flow is at <br />least two times the height of the vegetation; supple <br />tree seedlings such as willow, cottonwood, arrowweed, or <br />saltcedar growing where the average depth of flow is at <br />least three times the height of the vegetation. <br />