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<br />Table 4.--Qutline and example of procedures for determining n values <br />for a hypothetical channel and flood plain <br /> <br />[Modified from Aldridge and Garrett, 1973, table 6] <br /> <br />SECTION 1 <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 />1 <br /> <br />Extent of reach <br /> <br />The reach extends one section width <br />above section 1 to midway between <br />sections 1 and 2. ~signated as <br />reach A (fig. 23). <br /> <br />2 <br /> <br />Subdivision of cross <br />section <br /> <br />Only channel flow, no overbank <br />flood-plain flow. Assign a base <br />nb to entire channel. <br /> <br />Channel Roughness (steps 3-13) <br /> <br />3 <br /> <br />(a) 1ype of channel <br /> <br />A stable channel made up of firm <br />soil. <br /> <br />(b) Conditions during <br />flow event <br /> <br />Assume channel conditions are <br />representative of those that <br />existed during the peak flow. <br /> <br />(c) Comparable streams <br /> <br />None. <br /> <br />4 Roughness factors <br /> <br />Add adjustments for grass and <br />trees in channel and for channel <br />alinernent. <br /> <br />5 Divide into segments <br /> <br />Not necessary. <br /> <br />6 1ype of channel <br /> <br />Firm soil. <br /> <br />7 Base nb <br /> <br />Table 1 gives a nb value for <br />firm soil of 0.020-0.032. Use <br />0.025. <br /> <br />8 Adjustment factors <br />for segments <br /> <br />None. <br /> <br />9 Basis for weighting n <br /> <br />N:Jt applicable. <br /> <br />10 weighting factors and <br />weighted n <br /> <br />N:Jt applicable. <br /> <br />52 <br />