Runoff Curve Number Tables

The curve numbers in tables are for average runoff conditions and an initial abstraction ratio of 0.2.

Cover Type and Hydrologic Condition	Average Percent Impervious Area	A	B	C	D
*Fully developed urban areas (vegetation established)*
Open space (lawns, parks, golf courses, cemeteries, etc.)
Poor condition (grass cover < 50%)		68	79	86	89
Fair condition (grass cover 50% to 75%)		49	69	79	84
Good condition (grass cover > 75%)		39	61	74	80
Impervious areas:
Paved parking lots, roofs, driveways, etc. (excluding right-of-way)		98	98	98	98
Streets and roads:
Paved; curbs and storm drains (excluding right-of-way)		98	98	98	98
Paved; open ditches (including right-of-way)		83	89	92	93
Gravel (including right-of-way)		76	85	89	91
Dirt (including right-of-way)		72	82	87	89
Western desert urban areas:
Natural desert landscaping (pervious areas only)		63	77	85	88
Artificial desert landscaping (impervious weed barrier, desert shrub with 1- to 2-inch sand or gravel mulch and basin borders)		96	96	96	96
Urban districts:
Commercial and business	85	89	92	94	95
Industrial	72	81	88	91	93
Residential districts by average lot size:
1/8 acre or less (town houses)	65	77	85	90	92
1/4 acre	38	61	75	83	87
1/3 acre	30	57	72	81	86
1/2 acre	25	54	70	80	85
1 acre	20	51	68	79	84
2 acres	12	46	65	77	82
*Developing urban areas*
Newly graded areas (pervious areas only, no vegetation)		77	86	91	94

(Source: TR-55, SCS 1986)

Cover Type	Treatment	Hydrologic Condition	A	B	C	D
Cover Type	Treatment	Hydrologic Condition	A	B	C	D
Fallow	Bare soil		77	86	91	94
	Crop residue cover (CR)	Poor	76	85	90	93
		Good	74	83	88	90
Row Crops	Straight row (SR)	Poor	72	81	88	91
		Good	67	78	85	89
	SR + CR	Poor	71	Powered by Create your own unique website with customizable templates.