27
Hydrologic Soil Hydrologic Group
Land Use/Cover Condition A B C D
Herbaceous - grass, weeds & low- Poora/ - 80 87 93
growing brush; brush the minor Fair - 71 81 89
component Good - 62 74 85
Oak/aspen - oak brush, aspen, Poor - 66 74 79
mountain mahogany, bitter brush, Fair - 48 57 63
maple and other brush Good - 30 41 48
Pinyon/juniper - pinyon, juniper or Poor - 75 85 89
both; grass understory Fair - 58 73 80
Good - 41 61 71
Sagebrush with grass understory Poor - 67 80 85
Fair - 51 63 70
Good - 35 47 55
Desert scrub - saltbush, greasewood, Poor 63 77 85 88
creosotebrush, blackbrush, bursage, Fair 55 72 81 86
palo verde, mesquite and cactus Good 49 68 79 84
a/ Poor: < 30% ground cover (litter, grass and brush overstory); Fair: 30 to 70% ground cover; Good: >
70% ground cover.
Table B-4. Runoff Curve Numbers (Antecedent Moisture Condition II) for Arid and Semiarid
Rangelands (Soil Conservation Service, 1986).
Soil Hydrologic Group
Land Use A B C D
Open space (lawns, parks, golf
courses, cemeteries, etc.):
Poor condition (grass cover < 50%) 68 79 86 89
Fair condition (grass cover 50-75%) 49 69 79 84
Good condition (grass cover > 75%) 39 61 74 80
Impervious areas:
Paved parking lots, roofs,
driveways, etc.) 98 98 98 98
Streets and roads:
Paved with curbs & storm sewers 98 98 98 98
Paved with open ditches 83 89 92 93
Gravel 76 85 89 91
Dirt 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 1-2 in sand or gravel mulch
and basin borders) 96 96 96 96
Table B-5. Runoff Curve Numbers (Antecedent Moisture Condition II) for Urban Areas (Soil
Conservation Service, 1986).
% of Growing Season
Crop 0 10 20 30 40 50 60 70 80 90 100
