Stormwater Report 1

Chapter 2 Estimating Runoff Technical Release 55 Urban Hydrology for Small Watersheds Table 2-2c — Runoff curve numbers for other agricultural lands Y Curve numbers for Cover description hydrologic sof group Hydrologic Cover type condition A B c D Pasture, grassland, or range—continuous Poor 68 79 86 a9 forage for grazing. ¥ Fair 49 69 2) 84 Good 39 61 4 80 Meadow—continuous grass, protected from - 30 58 1 B grazing and generally mowed for hay. Brush—brush-weed-grass mixture with brush Poor 48 67 7 83 the major element. ¥ Fair 35 56 70 7 Good 304 48 65 73 Woods—grass combination (orchard Poor 57 vid 82 86 or tree farm). 9 Fair 43 65 76 82 Good 32 58 72 9 Woods. ¥ Poor 45 66 7 Fair 36 60 3 9 Good 302 55 7 7 Farmsteads—buildings, lanes, driveways, —_ 59 14 82 86 and surrounding lots. erage runoff coruition, and I, = 02S. A 2 Poor: <50%6) ground cover or heavily grazed with no mulch. Fair: 50 to 75% ground cover and not heavily grazed. Good: > 75% ground cover and lightly or only occasionally grazed. > Poor. <50% ground cover. Fair: 50 to 76% ground cover. Good: >75% ground cover. 4 Actual curve number is tess than 30; use CN = 90 for runoff computations. 5 CW's shown were computed for areas with 50% woods and 50% grass (pasture) cover. Other combinations of conditions may be computed from the CN’s for woods and pasture. © Poor: Forest litter, small trees, and brush are destroyed by heavy grazing or regular burning. Fair: Woods are grazed but not bumed, and same forest litter covers the soil. Good: Woods are protected from grazing, and litter and brush adequately cover the soll. (210-V1-TR-5S, Second Ed, June 1986) a7