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<br />In order to develop simple mathematical relationships for the DUH, the SCS fit a <br />triangular unit hydroqraph to the DUH by matching the peah and the volumes on the rising <br />limb and recession limbs. For the triangular hydrograph. the volume of runoff Can be <br />computed as the area within the triangle which Can be expressed mathematically as <br />follows: <br /> <br />o <br /> <br />q p . (':p + tr) I 2 <br /> <br />(V-1) <br /> <br />where: <br /> <br />o = runoff volume <br />q = peak discharge <br />tp ~ time to peak <br />tr = recession time equal to time base of tlydrograph .. time to peak <br /> <br />with three-eights of the volume under the rising limb. tr = 1.67 fp and equation (V-1) <br />reduces to: <br /> <br />q p = .75' 0 I tp <br /> <br />(V-2) <br /> <br />When tp is hours and 0 is inches. equation (V-2) is multiplied by the dl'ainage area <br />(A) in square miles and the factor 64!53 to get 0 p in cfs <br /> <br />q p = (484' A' 0) I tp <br /> <br />(V-3) <br /> <br />2.0 Bureau of Reclamation Dimensionless Unit Hydrograpn <br /> <br />The Bureau has taken the dimensionless unit Ilydrograph and applied regionalized <br />parameters for the Great Plains, Rocky Mountain, and Colorado Plateau Areas. To <br />determine appropriate lag times and temporal distribution of runoff, the Bureau <br />reconstituted several hundred historic floods. From the flood reconstitutions, 162 flood <br />hydrographs considered representative of suliace runoff from rainfall events were selected <br />for analysis relative to regionalized trends in the laQ time relationships ant the time versus <br />variation of discharge relationships. <br /> <br />Lao Times- The Bureau developed regior.al relationst'lips to determine L9 from basin <br />characteristics. The relationships are shown in Figures 7-10 through 7-12. and the <br />supporting basin dala is on Tables 7.11 throu9h 71 <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />7-51 <br /> <br />a=wT <br />