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<br />6,1,3 Rainfall-Runoff Modellina, For situations where historic streamflow data are inadequate or <br />nonexistent, a rainfall-runoff model is commonly used for flood-runoff estimates, Generally, a rainfall- <br />runoff model must be used if it is intended to evaluatE' the effects of either landuse changes or <br />structural modrrication in the watershed. Rainfall,runoff models are generally divided into two classes: <br />sin91e event and continuous streamflow modellin9. Sin9le,event modellin9 Involves simulatin9 the <br />runoff response of the hydrol09ic system to precipitation for a sin91e unique storm event. Continuous <br />streamflow modellin9 involves continuously accountin9 for sustained periods of precipitation over a <br />basin wrth special emphasis on adjustin9 the soil moisture, evaportranspiration, and subsurface flows <br />during periods of no precipitation. The primary interest in flood hydrology is the flood hydrograph, so <br />consequently, single-event modelling is usually the procedure used for analysis, <br /> <br />Sin9le-event modellin9 usually follows the steps listed below, <br /> <br />(1) Determination of subbasin average precip'tation <br /> <br />(2) Determination of precipitation excess from infiltration losses <br /> <br />(3) Transformation ot precipitation excess into a runoff hydr09raph <br /> <br />(4) Routing of stream flows <br /> <br />(5) Reservoir routing <br /> <br />(6) Combination of hydrographs <br /> <br />(7) Facility design <br /> <br />6,1,3,1 Types of Rainfall-Runotf Models <br /> <br />1, Lumped Parameter Model- This type of model transforms rainfall into runoff at only one particular <br />spatial location, Flow rates and water levels are computed separately, <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />6,2 <br /> <br />DRAF[' <br />