Assessment of Surface Runoff for Tank Watershed in Tamil Nadu Using Hydrologic Modeling

Table 1

Runoff curve numbers.

Description of Land use	Hydrologic Soil Group
	A	B	C	D
Paved parking lots, roofs, driveways	98	98	98	98
Streets and Roads:
Paved with curbs and storm sewers	98	98	98	98
Gravel	76	85	89	91
Dirt	72	82	87	89
Cultivated (Agricultural Crop) Land:
Without conservation treatment (no terraces)	72	81	88	91
With conservation treatment (terraces, contours)	62	71	78	81
Pasture or Range Land:
Poor (<50% ground cover or heavily grazed)	68	79	86	89
Good (50–75% ground cover; not heavily grazed)	39	61	74	80
Meadow (grass, no grazing, mowed for hay)	30	58	71	78
Brush (good, >75 ground cover)	30	48	65	73
Woods and Forests:
Poor (small trees/brush destroyed by over-grazing or burning)	45	66	77	83
Fair (grazing but not burned; some brush)	36	60	73	79
Good (no grazing; brush covers ground)	30	55	70	77
Open Spaces (lawns, parks, golf courses, cemeteries, etc.):
Fair (grass covers 50–75% of area)	49	69	79	84
Good (grass covers >75% of area)	39	61	74	80
Commercial and Business Districts (85 impervious)	89	92	94	95
Industrial Districts (72 impervious)	81	88	91	93
Residential Areas:
1/8 Acre lots, about 65% impervious	77	85	90	92
1/4 Acre lots, about 38% impervious	61	75	83	87
1/2 Acre lots, about 25% impervious	54	70	80	85
1 Acre lots, about 20% impervious	51	68	79	84

Source: United States Department of Agriculture, Soil Conservation Service, 1986 [40]. Technical Release 55.