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The Following types of synthetic unit hydrographs are recommended for estimating inflo~N design floods in Colorado: • Dimensionless unit hydrographs such as those in the U.S. Bureau of Reclamation (USBR) Flood Hydro%gy Manual (Cudworth, 1989) • S graphs such as those in the USBR Flood Hydro%gy Manua/(Cudworth, 1989). • Clark unit hydrograph Tho~~e unit hydrographs can be applied to watersheds (or modeling subbasins) that range in size from a fraction of a square mile to several hundred square miles. For i:he purposes of unit hydrograph selection in these guidelines, watersheds in Colorado are classified as: • Rocky Mountain - The central highlands of Colorado. Watersheds and modeling sub-basins for which the Rocky Mountain unit hydrographs are to be used are those in which the watercourses are well defined in high elevations with steep topography. Overbank flow is often precluded by deeply incised watercourse banks. Two Rocky Mountain unit hydrographs are recommended; Tables 4-9 or 4-10 of Cudworth (1989) for low-intensity general storms, and Tables 4-11 or 4-12 of Cudworth (1989) for high-intensity thunderstorms. • Great Plains - The plains of the Front Range and inter mountain valleys such as North Park, Middle Park, South Park, San Luis Valley and other isolated valleys. Watersheds and modeling sub-basins for which the Great Plains unit hydrograph is to be used are those in which the upper reach watercourses are swales, and the well defined drainage networks are limited to the lower parts of the basins. Overbank flow conditions have shallow flow and high flow resistance. The recommended Great Plains unit hydrographs are provided in Tables 4-7 or 4-8 of Cudworth (1989). • Colorado Plateau - The high plateau region of western Colorado. Watersheds and modeling sub-basins for which the Colorado Plateau unit hydrograph is to be used are arid regions of western Colorado with sparse vegetation, fairly well defined drainage networks, and terrain varying from rolling to very rugged in the more mountainous areas. The recommended Colorado Plateau unit hydrographs are provided in Tables 4-13 and 4-14 of Cudworth (1989). • Agricultural Fields • Urban 19 March 2007 6