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• Table 4.2-1 CN Values Type of Area ~ SEDCAD+ Classification CN Vatue Undisturbed portions of the ~ Arid and Semiarid Rangelands, Oak, fair 57 watershed ;cover Cut slopes, Soil Guard An estimated value, between a 88 classification of a Fully Developed Urban Impervious Area of Din and Gravel Street and Roads Fill slopes, bare (worst case), Developing Urban Area (No Vegetation) 91 and vegetated areas subject to disturbance by traffic Hardstand areas and roads, Fully Developed Urban Area, Impervious 87 bare soil Areas, Streets and roads, Dirt Gravel hardstands and roads Fully Developed Urban Areas, 89 Impervious Areas, Streets and roads, ~ Gravel, Hydrologic Soil Group C 4.3 Hydrograph Response Shape and Lengths of Overland . Flow 4.3.1 Hydrograph Response Shape Hydrograph response shapes reflect the rapidity with which water runs off a watershed, rated in SEDCAD+ as fast, medium, or slow. A slow response shape would correspond to a forested area or an area with a lot of obstructions, while a fast response shape would correspond to an unvegetated or poorly protected area. These ratings are for overland flow. Once overland flow is surpassed, a fast rating is assigned. 4.3.2 Lengths of Overland Flow Lengths of overland flow (sheet and rill drainage) are direct input parameters in SEDCAD-+~ for sedimentology analyses, and have an indirect influences on other parameters, such as LUC. Overland flows eventually collect into more concentrated flows [perhaps grass waterways (swales or depressions), and on into upland gullies, streams, and rivers]. 4.3.3 Hydrograph Response Shape and Length of Overland Flow Parameters Hydrograph response shapes and maximum permissible lengths of overland flow for the varying types of ground cover and slopes considered in this analysis are presented in the following table. • (Lone Pine Gulch sAEs Demonstration, 12 October 95, Page 7 of 13)