9900 19TH AVE SE 2018-01-02 MF Import

SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1962) Runoff curve numbers for selected agricultural, suburban and urban landuse for Type I rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC SOIL GROUP LAND USE DESCRIPTION A B C D Cultivated land(t): winter condition 86 91 94 95 Mountain open areas: low growing brush and grasslands 74 82 89 92 Meadow or pasture: 65 78 'tt5 89 Wood or forest lard: undisturbed or older second growth 42 64 U 81 Wood or forest land: youn5 second growth or brush 55 72 1811 86 Orchard: with cover crop 81 88 94 Open spaces, lawns, parks. golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 80 ® 90 fair.condition: grass cover on 50% to 75% of the area 77 85 93 92 Gravel roads and parking lots 76 85 e9 91 Dirt roads and parking lots 72 82 87 88 Impervious surfaces. pavement• roofs. etc. 98 98 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 Single Family Residential (2) Dwelling Una/Gross Acre % Impervious (3) 1.0 DU/GA 15 Separate curve number 1.5 DU/GA 20 shall be selected 2.0 DU/GA 25 for pervious and 2.5 DU/GA 30 impervious portion 3.o DU/GA 34 of the she or basin 3.5 DU/GA 38 .- 4.0 DU/GA 42 ,S , 4.5 DU/GA 46 5.0 DU/GA 48 5.5 DU/GA 50 6.0 DU/GA 52 6.5 DU/GA 54 7.0 DU/GA 56 Planned unit developments. % impervious Condominiums, apartments, must be computed commerdial business and industrial areas. (i) For a more detailed description of agricultural land use curve numbers refer to Nauonai Engineering Handbook, Section 4, Hydrology, Chapter 9. August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. ( (3) The remaining pervious areas Pawn) are considered to be in good condition for these curve number l