V4 11 Stormwater Report Rev 3 1 26 2023

Chapter 2 Estimating Runoff Technical Release 55 Urban Hydrology for Small Watersheds, able 2-2d — Runoff curve numbers for arid and semiarid rangelands 1/ Curve numbers for — hydrologic soil group ———-— — Cover description Hydrologic Cover type condition ¥ AY B @ D Herbaceous—mixture of grass, weeds, and Poor 80 87 93 low-growing brush, with brush the Fair 7 81 89 minor element. Good 62 ™ 85 Oak-aspen—mountain brush mixture of oak brush, Poor 66 74 79 aspen, mountain mahogany, bitter brush, maple, Fair 48 57 63 and other brush. Good 30 4 48 Pinyon-juniper—pinyon, juniper, or both; Poor ® 85 a) grass understory. Fair 58 B 80 Good 4 61 7 Sagebrush with grass understory. Poor 67 80 85 Fair 51 63 70 Good 35 a7 55 Desert shrub—major plants include saltbush, Poor 63 7 85 88 greasewood, creosotebush, blackbrush, bursage, Fair 55 2 81 86 palo verde, mesquite, and cactus. Good 49 68 79 84 | Average runoff condition, and I,, = 0.28. For range in humid regions, use table 2: 2 Poor: <30% ground cover (litter, grass, and brush overstory), Fair: 30 to 70% ground cover. Good: > 70% ground cover. 3 Curve numbers for group A have been developed only for desert shrub. c. 2-8 (210-VETR- Second Ed., Jume 1986)