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<br />Table 3.--Factors that affect roughness of flood plains <br />[Modified from Aldridge and Garrett, 1973, table 2] <br /> <br />Flood plain conditions <br /> <br />n value <br />adjustment <br /> <br />Example <br /> <br />Smooth <br /> <br />0.000 <br /> <br />Degree of irregularity <br />(nl) Minor <br /> <br />I-' <br />..,. <br /> <br />0.001-0.005 <br /> <br />Compares to the smoothest, flattest flood plain <br />attainable in a given bed material. <br /> <br />Is a flood plain with minor irregularity in shape. <br />A few rises and dips or sloughs may be visible <br />on the flood plain. <br /> <br />Moderate <br /> <br />0.006-0.010 <br /> <br />Has more rises and dips. Sloughs and hummocks may <br />occur. <br /> <br />Severe <br /> <br />0.011-0.020 <br /> <br />The flood plain is very irregular in shape. Many <br />rises and dips or sloughs are visible. Irregu- <br />lar ground surfaces in pastureland and furrows <br />perpendicular to the flow are also included. <br /> <br />Variation of flood- <br />plain cross section <br />(n2) <br /> <br />0.0 <br /> <br />Not applicable. <br /> <br />Effect of obstructions <br />(n3) <br /> <br />Negligible <br /> <br />0.000-0.004 <br /> <br />A few scattered obstructions, which include debris <br />deposits, stumps, exposed roots, logs, or isolated <br />boulders, occupy less than 5 percent of the cross- <br />sectional area. <br /> <br />Minor <br /> <br />0.005-0.019 <br /> <br />Obstructions occupy less than 15 percent of the <br />cross-sectional area. <br /> <br />Obstructions occupy from 15 to 50 percent of the <br />cross-sectional area. <br /> <br />Appreciable 0.020-0.030 <br />