Laserfiche WebLink
Dsm~ensionless Unit Hydro4raahs and Estimation of Laa <br />A variety of dimensionless unit hydrographs and S-graphs (a form of dimensionless unit <br />hydr~~graph) are available for use in flood hydrology studies. The U.S. Bureau of Reclamation <br />(USE~R) FloodHydro%gyManual (Cudworth, 1989) provides a few selected dimensionless unit <br />hydn~graphs and S-graphs. Those that are recommended for use in Colorado are provided by <br />Cudvvorth in Table 4-7 and Table 4-8 for the Great Plains (generally east of the Front Range); <br />Tabl~~ 4-9 and Table 4-10 for general storms in the Rocky Mountains; Table 4-11 and Table <br />4-12 for high intensity thunderstorms in the Rocky Mountains; Table 4-13 and Table 4-14 for <br />the (:olorado Plateau of western Colorado; and Table 4-17 and Table 4-18 for urban <br />watersheds. A more extensive compilation of S-graphs, some of which are applicable for use in <br />Colorado, is provided by Sabol (1987). For the USBR dimensionless unit hydrographs and <br />S-gr~3phs, the single parameter that defines the coordinates of the unit hydrograph is Lag. <br />Lac~:, The unit hydrograph Lag is estimated by: <br />033 <br />La 26 K~ LL~a 1 <br />g - n Sos ~ <br />Lag = lag time, in hours <br />L= distance of longest watercourse, in miles <br />L~ = distance from point of interest (basin or subbasin outlet) to a point <br />opposite the centroid of the drainage basin (or subbasin), in miles <br />S= overall slope of L measured from the point of interest to the drainage <br />basin divide, in feet per mile, and <br />K~ = a lumped parameter representing the resistance to overland flow from the <br />drainage basin incorporating a weighting of the various components of flow <br />resistance along the entire L flow path. <br />19 March 2007 14 <br />