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<br />, <br /> <br />manmade structures that cause ponding, divert~ flow paths, .etc. <br /> <br />Table A-2includes a column listing an~.attenuat1on factor, f, <br /> <br />used to compute R. An f greater than 0.5 was selected for most of <br /> <br />the subareas because oi poor natural drainage systems and/or <br /> <br />manmade structures. therein. <br /> <br />5. Values of R were computed by multiplying respective T and f <br /> <br />values. <br /> <br />6, A routing constant for each subarea was computed by the equation, <br /> <br />R - 0.5t <br />lC ~ R + 0.5t <br /> <br />where K : routing copstant; <br /> <br />. R ~ attenuatio~ factor, in hours; <br /> <br />t : Unit time, hours, selected for unitgraph computation. <br /> <br />7. . An example of compu~ation of a I-hour unitgraph is shown in <br /> <br />attached Table A-3, a copy of the worksheet for subarea C-19. <br /> <br />Incremental equal flow ~ime areas progressing upstream from the <br /> <br />subarea outlet were obtained from the distance area curve, <br /> <br />accumulating hourly distances on the basis of average flow velocity <br /> <br />and reading aceumulative area from the curve. Instantaneous <br /> <br />discharges in cfs, Is' for each incremental area, were computed <br /> <br />equivalent to 1 inch of excess precipitation. The instantaneous <br /> <br />discharges were averaged as listed in the column I~. Discharges <br /> <br />13 <br /> <br />..._...#........,............ ...,...'"'....~ ......_......_w._, ____.__#............__ <br /> <br />~..n'~_~'_-......,.... <br /> <br />......,~. .Jf:...'~. <br /> <br />'S- <br /> <br />. <br />