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In acldition to L, L.~ and S, Table 6 lists the percent impervious area (RTIMP) for each urban <br />watershed. Previous research (Sabol, 1993) indicates that K~ is independent of percent <br />impervious area as well as each of the other variables listed in that table. Due to the <br />variability of K~ for urban watersheds and lack of a means to estimate K~ for urban <br />watersheds, the use of the USBR urban dimensionless unit hydrograph is not recommended. <br />The ~~lark unit hydrograph is recommended for urban watersheds and subbasins. At best, <br />only general conclusions, as listed below, can be reached from the urban K~ data: <br />A. For large, homogeneous urban areas, the use of K~ = 0.015 is reasonable. <br />B. K~ for urban areas should not exceed 0.02 unless adequately documented. <br />C. K~ may be as low as 0.01 for small, highly urbanized drainage areas. <br />Suenmary Of Unit Hvdro4raah Selection And Recoenmended K~ Values <br />The recommended unit hydrograph and K~ values to be used with selected dimensionless <br />unit liydrographs are presented in Table 7. It is noted and cautioned that these are typical <br />K~ values based on regional classifications. Every watershed varies according to vegetation, <br />landform and other factors which dictate the actual value of K~,. Therefore, site specific <br />data, watershed observations and experienced hydrologic judgment must be applied in <br />selecting K~ for use with dimensionless unit hydrographs. The values in Table 7 are <br />presE~nted as reasonable values for review and as quali~r assurance guidelines. <br />19 Mar~:h 2007 23 <br />