1903 HOLLOW DALE PL 2018-01-02 MF Import

■ oUNTY, WASHINGTON, SURFACE WA'I'Eft DESIGN MANUAL I SCSWESTERNIVASIIINGTON RUNOFF CURVE NUMBERS SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type to rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC GROUP LAND USE DESCRIPTION A B D Cultivated land(1): winter condition 66 91 94 95 Mountain open areas: low growing brush and grasslands 74 82 69 92 Meadow or pasture: 65 78 85 69 V ood or forest lard: undisturbed or older second growth 42 64 76 81 Wood or forest land: young second growth or brush 55 72 81 86 Orchard: with cover crop 81 88 92 94 Open spe_es, lawns, parks, golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 60 86 90 lair condition: grass cover on 50 % to 75 % of the area 77 85 90 92 Gravel roads and parking lots 76 65 69 91 Dirt roads and parking lots 72 82 87 69 Impervious surfaces, pavement, roofs, etc. 98 98 98 ?8 I Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100 I Single Family Residential (2) .Dwelling Unit/Gross Acre % Impervious (3) 1.o 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 3.0 DU/GA 34 of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 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 compulcd commercial business and industrial areas. (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Section 4, Hydrology. Chapter 9, August 1972. (2) Assumes root and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. 3.5.2.3 11/92