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<br />Table 4.--Qutline and example of procedures for determining n values <br />for a hypothetical channel and flood plain--Continued <br /> <br />Channel Roughness (steps 3-13) Subsection 2--Dontinued <br /> <br />Step <br /> <br />Item to be determined or <br />operation to be performed <br /> <br />11 <br /> <br />Factors on which decisions are <br />based and the results <br /> <br />Add adjustments for entire <br />channel <br /> <br />Obstructions (n3)--negligible-- <br />scattered trees and tree roots <br />along edge of channel banks. <br />n3 = 0.003 <br />Meander is minor, m = 1.00 <br />n = (nb + nl + n2 + n3 + n4)m <br />n = (0.025 + 0 + 0 + 0.003 + 0)1.00 <br />n = 0.028. <br /> <br />12 <br /> <br />Compare with other streams <br /> <br />Similar to channel in f*1otographs <br />in Barnes (1967, p. 16-17). The h <br />value reported was 0.026. <br /> <br />13 <br /> <br />Check flow regime <br /> <br />l'bt applicable. <br /> <br />Flood-Plain Roughness (steps 14-23) <br />Subsection 1 (made up of trees) <br /> <br />14 <br /> <br />(a) 'IYPe of flood plain <br /> <br />(b) Conditions during <br />flow event <br /> <br />(c) Comparable flood <br />plains <br /> <br />A slightly irregular flood plain <br />covered with hardwood trees. Jik) <br />undergrowth. <br /> <br />Assume present conditions are <br />representative of those that <br />existed during the peak flow. <br /> <br />Flood plain is similar to one <br />shown in fig. 14 of this report. <br /> <br />15 M=thod to be used in <br />assigning n <br /> <br />Use the ''vegetation density" <br />method. Need to determine a value <br />for boundary roughness. <br /> <br />16 Subdivision of flood plain <br /> <br />The flood plain is uniform <br />throughout. <br /> <br />17 Roughness factors <br /> <br />Trees are major roughness factor, <br />surface irregularity and some <br />obstructions are on flood plain. <br /> <br />18 <br /> <br />Base nb <br /> <br />Table 1 gives a base nb value <br />for firm soil of 0.020-0.030. Use <br />0.020. <br /> <br />57 <br />