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Storage-Indication + Translation Method <br />• The basic storage-indication method accounts for only the storage effects of a reach. Other <br />techniques must be used to account for the kinematic effects of long reaches. HydmCAD provides <br />the option of adding a time lag or translation to the normal storage-indication routing. <br />Time Translation <br />The "Stor-Ind+Trans' routing method first performs astorage-indication routing, and then translates <br />the resultng hydmgraph by the travel time. A close examination of the resulting hydrograph will <br />reveal that the peak dischazge no longer corresponds to a point on the inflow curve, but is <br />translated (delayed) by the prescribed amount. <br />L <br />Tc = --- <br />.6 <br />8 <br />I (S+1) <br />where L = <br />• .5 <br />1900 Y <br />1000 <br />and S = ------ - 10 <br />CN <br />where: <br />Tc=Time of Concentration [hours] <br />L=Lag time [hours] <br />I=Hydraulic length of the watershed [feet] <br />Y=Average land slope [percent] <br />S=Potential maximum retention [inches] <br />CN=Weighted Curve Number <br />Note the use of the average land slope, and not the slope of the hydraulic path. Although some <br />caze is required to determine this value, the Curve Number method has the advantage of using a <br />small number of fairly objective pazameters. This provides more consistent results than some other <br />approaches. <br />.~ <br />Whirlwind Mine June 07 D-31 <br />