Laserfiche WebLink
<br />Table 4.-~tline and example of procedures for determining n values <br />for a hypothetical channel and flood plain--Continued <br /> <br />SECTION 3--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 />2 <br /> <br />Subdivision of cross <br />section <br /> <br />There is overbank flood-plain flow <br />on both sides of the channel. <br />Subsection 1 is flood-plain flow <br />through trees, subsection 2 is <br />channel flow, and subsection 3 is <br />flood-plain flow through a cotton <br />field. Assign a base nb to each <br />subsection. <br /> <br />Channel Roughness (steps 3-13) Subsection 2 <br /> <br />3 <br /> <br />(a) 'IYpe of channel <br /> <br />(b) Conditions during <br />flow event <br /> <br />(c) Comparable streams <br /> <br />A stable channel made up of firm <br />soil. <br /> <br />Assume channel conditions are <br />representative of those that <br />existed during the peak flow. <br /> <br />See photographs of similar <br />channels in Barnes (1967, p. <br />16-17). Channel made up of same <br />type of material. Barnes used n <br />of 0.026 for the channel. <br /> <br />4 Roughness factors <br /> <br />Trees along the bank should be <br />considered as obstruction (n3) <br />for the channel. <br /> <br />5 Divide into segments <br /> <br />Not necessary. <br /> <br />6 'IYpe of material and grain <br />size <br /> <br />Firm soil (clay). <br /> <br />7 Base nb <br /> <br />Table 1 gives a base nb value <br />for firm soil of 0.020 to 0.030. <br />Use 0.025. <br /> <br />8 Adjustment factors for <br />segments <br /> <br />None. <br /> <br />9 Base for ...:ighting n <br /> <br />10 Weighting factors and <br />weighted n <br /> <br />Not applicable. <br />Not applicable. <br /> <br />56 <br />