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<br />1. SCS Dimensionless Unit Hydrograph- <br /> <br />PART V - SOIL CONSERVATIOf'-1 SEFIVICE (SCS) MEHtOD. <br /> <br />A dimensionless unit hydro9raph was developed by the Soil Conservation Service ,:SCS) <br />based on an analysis of measured runoff data. Dimensicnless unit hydrographs were <br />developed from unit hydrographs derived for a large number of watersheds. These <br />dimensionless unit graphs were then averaged to develop the SCS dimensionless unit <br />hydrograph (DUH). Characteristics of the DUH include, a curvilinear shape, a time base <br />equal to 5 times the time-to'peak, an inflection point on the recession limb at about 1.7 <br />times the time-to-peak, and approximately three-eights of the total volume prior to the time- <br />of-peak. The DUH can be dE>fined with the time and discllar(Je ratios in the following table: <br /> <br />Table }.1 0 <br /> <br />SCS DIMENSIONLESS UN!" <br />TIME (t I T p) <br />0 <br />.2 <br />,- <br />.0 <br />.7 <br />1.0 <br />1.3 <br />1.5 <br />2.0 <br />3.0 <br />4.0 <br />5.0 <br /> <br />r HYDFWGRAPH RATIOS <br /> <br />DI~~C~~!!GE ~CJ...I q p)__ <br />o <br /> <br />.10 <br /> <br />.47 <br /> <br />.82 <br />1.0 <br /> <br />.86 <br /> <br />.68 <br /> <br />.28 <br /> <br />.06 <br />.01 <br /> <br />o <br /> <br />where, the time ratio (t I T p) is the ratio of a selected time (t) to time from <br />beginning of rise to peak (T p) and the discharge ratio (q " q ,) is the ratio of discharge at <br />time t (q) to peak discharge (q p) <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />7-50 <br /> <br />CR4JT <br />