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<br />Table 4. --outline and example of procedures for determining n values <br />for a hypothetical channel and flood plain--COntinued <br /> <br />Flood-Plain Roughness (steps 14-23)--Continued <br />Subsection 1 (made up of trees) --COntinued <br /> <br />Step <br /> <br />Item to be determined or <br />operation to be performed <br /> <br />Factors on which decisions are <br />based and the results <br /> <br />19 <br /> <br />Mjustment factors <br /> <br />Irregularity is minor, a few rises <br />and dips across the flood plain. <br />nl = 0.005 (table 2). Obstruc- <br />tions are negligible, consisting <br />of scattered debris, exposed roots, <br />and downed trees. n3 = 0.004 <br />(table 3). <br /> <br />20 <br /> <br />no <br /> <br />no = (nb + nl + n2 + n3 + n4')m <br />no = (0.020+0.005+0+0.004+0)1.0 <br />no = 0.029 <br /> <br />Vegd = 0.0115 <br />Is an average value from three <br />sampling areas. <br /> <br />21 Vegetation density of <br />representative sample area <br /> <br />22 n for the flood-plain <br />subsection <br /> <br />R = 2.9 ft <br />C* = 11.0 <br />Vegd = 0.0115 <br /> <br />n = <br /> <br />n 1 + (Veg ) (C ) (1.49)2( 1~R4/3 <br />o d * n 2g <br />o <br /> <br />n = 0.029 1 + (.0115) (11.0)(~O~~)2(6~.4)(2.9)4/3 <br />n = 0.137 <br /> <br />23 Compare with other flood <br />plains <br /> <br />Photographs of similar flood plains <br />found in this report (fig. 14). <br /> <br />Flood-Plain Roughness (steps 14-23) <br />Subsection 3 (cotton field) <br /> <br />14 (a) '!ype 0 f flood plain Flood plain is a cotton field in <br /> full growth. <br /> (b) Conditions during Conditions are similar to flood <br /> flow event event. <br /> (c) Comparable flood None. <br /> plains <br /> <br />58 <br />