9606 19TH AVE SE PREMIER STORAGE 2025-07-29

/ CITY OF EVERETT STORMWATER MANAGEMENT MANUAL Table 5.6 Runoff Curve Numbers Runoff Curve Numbers for Selected Agricultural, Suburban, and Urban Areas (DOE 2005 Stormwater Management Manual for Western Washington) CNs for hydrologic soil group Cover type and hydrologic condition. A B CD Curve Numbers for Pre-Development Conditions Pasture,grassland,or range-continuous forage for grazing: Fair condition(ground cover 50%to 75%and not heavily grazed). 49 69 ,�7.9 84 Good condition(ground cover>75%and lightly or only occasionally grazed) 39 61 Cr" .. 80 Woods: Fair(Woods are grazed but not burned,and some forest litter covers the soil). 36 60 73 79 Good(Woods arc protected from grazing,and litter and brush adequately cover the soil). 30 55 70 77 Curve Numbers for Post-Development Conditions cemeteries,Open space(lawns,parks,golf courses, landscaping,etc.) Fair condition(grass cover on 50%-75%of the area). 77 85 90 92 Good condition(grass cover on>75%of the area) 68 80 90 Impervious areas: Open water bodies:lakes,wetlands,ponds etc. 100 100 it$ 100 Paved parking lots,roofs:,driveways,etc. (excluding right-of-way) 98 98 Cal 98 Permeable Pavement Landscaped area 77 85 90 92 50%landscaped area/50%impervious 87 91 94 96 100%impervious area 98 98 98 98 Paved 98 98 98 98 Gravel(including right-of-way) 76 85 89 91 Dirt(including right-of-way) 72 82 87 89 Pasture,grassland,or range-continuous forage for grate: Poor condition(ground cover<50%or heavily grazed with no mulch). 68 79 86 89 Fair condition(ground cover 50%to 75%and not heavily grazed). 49 69 79 84 Good condition(ground cover>75%and lightly or only occasionally grazed) 39 61 74 80 Woods: Poor(Forest litter,small frees,and brush are destroyed by heavy grazing or regular burning). 45 66 77 83 Fair(Woods are grazed but not burned,and some forest litter covers the soil). 36 60 73 79 Good(Woods are protected from grazing,and litter and brush adequately cover the soil). 30 55 70 77 Single family residential: Should only be used for Average Percent Dwelling Unit/Gross Acre subdivisions>50 acres impervious area;4 1.0 DU/GA I5 Separate curve number 1.5 DU/GA 20 shall be selected for 2.0 DU/GA 25 pervious&impervious 2.5 DU/GA 30 portions of the site or 3.0 DU/GA 34 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 7.5 DU/GA 58 PUD's,condos,apartments,commercial %impervious Separate curve numbers shall businesses,industrial areas& must be be selected impervious and &subdivisions<50 acres computed impervious portions of the site For a more detailed and complete description of land use curve numbers refer to chapter two(2)of the Soil Conservation Service's Technical Release No.55,(210-VI-TR-55,Second Ed.,June 1986). Volume 1—Minimum Technical Requirements 5-6