2019-03-06_REVISION - C1981019 (2)

Home Browse Search

TABLE 1— SCS CURVE NUMBERS COVER COVER TYPE HYDROLOGIC CONDITION PERCENT VEG. COVER HYD. CURVE SOIL NUMBER GROUP Mountain Shrub Good 85 C 61 Undisturbed Oak -Aspen Good to Fair 50-85 C 57 Sagebrush Good 50 C 47 Sagebrush Fair 50 C 63 Topsoil Stripped Roads Bare N/A B 85 Disturbed Spoil Piles & Active Bare N/A B 74 Pits, Reclaimed Topsoil & Seeded2 Bare N/A B 80 1 to 2 Year Growth3 Fair to Good 25-45 B 74 (Excluding 3+ Year Growth4 Fair to Good 70+ B 62 Prospect Basin) Prospect Basin Reclaimed Topsoil & Seeded Bare N/A B 83 1 to 2 Year Growth Fair to Good 25-45 B 77 3+ Year Growth Fair to Good 70+ B 74 Sources: Table 8, attached, derived from National Engineering Handbook (NEH-4) (USDA -SCS, 1985) - Undisturbed lands are assumed HSG C, based on SCS county mapping units; except for Prospect drainage disturbed lands are HSG B based on measured infiltration rates reported in Striffler and Rhodes, 1981 in conjunction with Part 630 NEH, Chapter 7, Hydrologic Soil Groups. For Prospect Drainage, all CNs, disturbed and undisturbed, are generally assume HSG C. Notes: 1) This CN applies only to tributary portions of active pit area, which are significantly roughened and contain numerous large equipment induced local depressions. Active pit areas where all runoff is captured within the pit are not included in modeled runoff calculations. CNs for tributary active pit and spoil pile areas are considered as "Cultivated land, without conservation treatment' with HSG B, in Table 7 2) CN based on an average of "Fallow, with Crop Residue, Poor Condition", Table 8, with 50% HSG A and 50% HSG B 3) CN based on an average of "Pasture or Range, Fair Condition", Table 7, with 50% HSG A and 50% HSG B 4) CN based on an average of "Pasture or Range, Good Condition", Table 7, with 50% HSG A and 50% HSG B, conservatively revised upward. Exhibit 7 Page 4 Revision Date: 3/6/19 Revision No.: TR -131