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l3, 10 <br />' • Selectionof modifyingn for obstructions such as debris deposits, stumps, <br />exposed roots, fallen logs: <br />Relative effect of <br />obstructions <br />Negligible <br />Minor <br />Appreciable <br />Severe <br />Modif iv ne n <br />0. 000 <br />0. O l5 <br />0.030 <br />0.060 <br />5. Selection of the modifying n for the effect of vegetation: <br />Decree of effect of <br />vegetation Modifying n <br />Low retardance 0. 005 to 0. 010 <br />Medium retardance 0. Ol0 to 0.025 <br />High retardance 0. 025 to 0, 050 <br />Very High retardance 0.050 to 0. L00 <br />6. Selection of the modifying n forthe effect of meandering. Add the basic <br />n and modifying n values estimated in I through 5; designate this subtotal <br />as ns. Compute the modifying n as follows: <br />~~ <br />Decree of meandering Modifying n <br />Minor 0..000 <br />Appreciable 0., l5 x ns <br />Severe 0. 30 x ns <br />The effect of meandering should be considered only in channels; i, e. , <br />this effect should be disregarded in estimating an n value for the flood <br />plain part of a cross section. <br />7. Add the values determined in lthrough6 to obtainthe n valuefora chan- <br />nel or a part of a cross section. <br />I~ <br />