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<br /> <br />c. Runoff characteristics. <br /> <br />Perennial main stream(s). <br /> <br />. . Major floods caused by rain or combined rain and snowmelt. <br /> <br />Hydrograph recessions usually indicate surface runoff <br /> <br />plus minor interflow, <br /> <br />The upper limiting curve for t~e set of data used to define Curve A <br /> <br />has a C value of 2.50 and has been designated A+ on Plate 9. <br /> <br />A basin factor, <br /> <br />LL <br />ea <br />-, <br />./T' <br /> <br />was computed for each subarea for which a <br /> <br />unitgraph was obtained by the dimensionless graph-lag time method. <br /> <br />For those subareas which have two or more long watercourses such as <br /> <br />MU-8, St. Vrain above Lyons, a weighted basin factor was computed. <br /> <br />Lag times were read from the lag curves shown on Plate 9, main text. <br /> <br />Table A-I, attached, lists the subarea~, basin factor, lag curve used, <br /> <br />lag time, and respective dimensionless graph selected for use. <br /> <br />Clark unitgraphs. The Clark method of developing unitgraphs has been <br /> <br />used in some Region LM IDF studies; for example, those for Pueblo <br /> <br />damsite and AlcovQ, Pathfinder, and Seminoe Dams. The Clark' method <br /> <br />is based.on the concept that a @treamflow hydrograph may be considered <br /> <br />as a combination of two componet1ts.: (1) translation, .a flood wave <br /> <br />translated in time without modification in shape; and (2) attenuation, <br /> <br />hydrograph flattening and elongation due to temporary channel <br /> <br />10 <br /> <br />. "~-' '.", ',. ~_~.t' <br /> <br />-' <br /> <br />, ...... <br /> <br />. <br />