V4 11 Stormwater Report Rev 3 1 26 2023

Chapter 2 Estimating Runoff, ‘Technical Release 5i Urban Hydrology for Small Watersheds Table 2-2a — Runoff curve numbers for urban areas / Curve numbers for — Cover description hydrologic. soil group Average percent Cover type and hydrologic condition impervious area ¥ A B c D Fully developed urban areas (vegetation established) Open space (lawns, parks, golf courses, cemeteries, ete.) Poor condition (grass cover < 50%) .. 79 86 89 Fair condition (grass cover 50% to 75%) 69 79 84 Good condition (grass cover > 75%) 61 74 380 Impervious areas: Paved parking lots, roofs, driveways, etc. (excluding right-of-way) 98 98 98 98 Streets and roads Paved; curbs and storm sewers (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 85 389 OL Dirt (including right-of-way) .. 72 82 87 39 Western desert urban areas: Natural desert landscaping (pervious areas only) -! 63 17 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 distric 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)... 77 85 90 92 WA acre .. 61 75 83 87 1 acre .. 57 72 81 86 1/2 acre .. 54 70 80 85 lacre .. 51 68 79 84 2 acres 46 65 7 82 Developing urban areas Newly graded areas (pervious areas only, no vegetation) . 7 86 91 94 Idle lands (CN's are determined using cover types similar to those in table 2-2c). 1 Average runoff condition, and I, + The average percent impervious area shown was used to develop the composite (N's. Other assumptions are as follows: impervious areas are directly connected to the drainage system, impervious areas have a CN of 98, and pervious areas are considered equivalent to open space in good hydrologic condition. CN's for other combinations of conditions may be computed using figure 2-3 or 2-4. 's shown are equivalent to those of pasture. Composite CN's may be computed for other combinations of open space cover type. ! Composite CN’s for natural desert landscaping should be computed using figures 2-3 or 2-4 based on the impervious area percentage (CN = 98) and the pervious area CN. The pervious area CN’s are assumed equivalent to desert shrub in poor hydrologic condition. 5 Composite CN's to use for the

based on the impervious area percentage (CN = 98) and the pervious area CN. The pervious area CN’s are assumed equivalent to desert shrub in poor hydrologic condition. 5 Composite CN's to use for the design of temporary measures during grading and construction should be computed using figuré based on the degree of development (impervious area percentage) and the CN's for the newly graded pervious areas. a or 24 (210-VETR- », Second Ed., June 1986)

Chapter 2 Estimating Runoff ‘Technical Release 55 Urban Hydrology for Small Watersheds Table 2-2b — Runoff curve numbers for cultivated agricultural lands Curve numbers for —— Cover description - hydrologic soil group ———— Hydrologic Cover type Treatment ¥ condition A B ce D “allow Bare soil = 7 86 91 94 Crop residue cover (CR) Poor 76 85 90 93 Good m4 83 88 90 Row crops Straight row (SR) Poor R 81 88 91 Good 67 78 85 89 SR+CR Poor 71 80 87 90 Good 64 B 82 85 Contoured (C) Poor 70 a) 84 88 Good 65 B 82 86 C+CR Poor 69 78 83 87 Good 64 74 81 85 Contoured & terraced (C&T) Poor 66 m4 80 82 Good 62 7 78 81 C&T+ CR Poor 65 B 79 81 Good 61 70 17 80 Small grain SR Poor 65 76 84 88 Good 63 75 83. 87 SR+CR Poor 64 B 83 86 Good 60 2 80 84 c Poor 63 74 82 85 Good 61 3B 81 Sd C+CR Poor 62 B 81 8d Good 60 2 80 83 C&T Poor 61 2 7 82 Good 59 70 78 81 C&T+ CR Poor 60 7 78 81 Good 58 69 17 80 Close-seeded SR Poor 66 7 85 389 or broadcast Good 58 2 81 85 legumes or c Poor 64 B 83 85 rotation Good 55 69 78 83 meadow C&T Poor 63 B 80 33 Good 51 67 76 80 ' Average runoff condition, and 1,=0.28 2 Crop residue cover applies only if residue is on al least 5% of the surface throughout the year. 2 Hydraulic condition is based on combination factors that affect infiltration and runoff, including (a) density and canopy of vegetative areas, (b) amount of year-round cover, (c) amount of grass or close-seeded legumes, (a) percent of residue cover on the land surface (good 2 20%), and (¢) degree of surface roughness. Poor: Factors impair infiltration and tend (o increase runoff. Good: Factors encourage average and better than average infiltration and tend to decrease runoff. 2-6 (210-VI-TR-55, Second Ea., June 1986)

Chapter 2 Estimating Runoff chnical Release 5: Urban Hydrology for Small Watersheds, Table 2-2c — Runoff curve numbers for other agricultural lands -———--~ Cover description Curve numbers for hydrologic soil group — Hydrologic Cover type condition A B c D Pasture, grassland, or range—continuous Poor 68 79 86 89 forage for grazing, ¥ Fair 49 69 79 84 Good 39 61 4 80 Meadow—continuous grass, protected from _ 30 58 a 78 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 30" 48 65 B Woods—grass combination (orchard Poor 57 3 82 86 or tree farm). Fair 3 65 76 82 Good 32 58 2B 79 Woods. Poor 45 66 7 83 Fair 36 60 B 79 Good 304 55 70 7 Farmsteads—buildings, lanes, driveways, — 74 82 86 and smrounding lots. ! Average runoff condition, and I, = 0.28. Poor: <50%) ground cover or heavily grazed with no mulch. Fair: 50 to 75% ground cover and not heavily grazed. Good: >7 <50% ground cover. 50 to 75% ground cover. Good: >75% ground cover. 1 Actual curve number is less than 30; use C ° CN's shown were computed for areas with 50% wo from the CN’s for woods and pasture. % Poor: Forest litter, small trees, and brush are destroyed by heavy grazing or regular bumning. oods ani 4 ground cover and lightly or only occasionally grazed. 0) for runoff computations, 50% grass (pasture) cover. Other combinations of conditions may be computed Fair: Woods are grazed but not burned, and some forest lilter covers the soil. Good: Woods are protected from grav (210-VET) ng, and litter and brush adequately cover the soil. 5, Second Ed., Jume 1986)

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)

STORM SEWER COMPUTATIONS Project: Daughters of Israel RATIONAL METHOD - (Q=CIA) Date: 01/26/23 25 YR. STORM By: JAF PIPE SEGMENT Pipe Travel Time(min) Pipe/Box Length (FT.) Capacity (FULL) (cfs) Velocity (Design) (fps) I-Rainfall Int. (in./hr) Qp-Peak Runoff (cfs) Pipe/Box Size (IN.) AxC-Incremental

Pipe/Box Size (IN.) AxC-Incremental Cumulative (cfs) Qp-Peak Runoff C-Runoff Coef. A-Incremental Tc (MIN.) Slope (%) FROM TO Type "B" #6-4 Type "B" #6-3 0.64 0.75 0.48 6.0 5.60 2.69 2.69 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #6-3 Type "B" #6-2 0.34 0.75 0.26 6.0 5.60 1.43 4.12 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #6-2 Type "B" #6-1 5.37 0.75 4.03 6.0 5.60 22.55 26.67 2.0% 24" HDPE 34.75 11.06 0.00 Type "B" #7-2 Type "B" #7-1 0.18 0.99 0.18 6.0 5.60 1.00 1.00 1.0% 15" HDPE 7.65 6.24 0.00 Type "B" #7-1 Type "E" #6-1 0.03 0.99 0.03 6.0 5.60 0.17 1.16

0.00 Type "B" #7-1 Type "E" #6-1 0.03 0.99 0.03 6.0 5.60 0.17 1.16 1.0% 15" HDPE 7.65 6.24 0.00 Type "E" #6-1 Basin #2 0.15 0.99 0.15 6.0 5.60 0.83 28.67 2.0% 24" HDPE 34.75 11.06 0.00 2'x2' #10-3 Type "E" #10-2 0.07 0.99 0.07 6.0 5.60 0.39 0.39 1.0% 12" PVC 4.22 5.38 0.00 Phase 1 Roof Leaders Type "E" #10-2 1.03 0.99 1.02 6.0 5.60 5.71 5.71 1.0% 10" PVC 7.8* 4.76 0.00 Type "E" #10-2 Subsurface Basin #1A 0 0.99 0.00 6.0 5.60 0.00 6.10 1.0% 15" HDPE 7.65 6.24 0.00 Subsurface Basin #1A MH #5-6 5.88 3.5% 24" HDPE 45.97 14.63 0.00 Basin #2 MH #5-6 21.66 2.0% 24" HDPE 34.75 11.06 0.00 MH #5-6 Type "B" #5-5 27.54 3.5% 24" HDPE

27.54 3.5% 24" HDPE 45.97 14.63 0.00 Type "B" #5-5A Type "B" #5-5 0.04 0.99 0.04 6.0 5.60 0.22 0.22 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #5-5 Type "B" #5-4 0.05 0.99 0.05 6.0 5.60 0.28 28.04 3.5% 24" HDPE 45.97 14.63 0.00 Type "B" #5-4A Type "B" #5-4 0.3 0.99 0.30 6.0 5.60 1.66 1.66 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #5-4 Type "B" #5-2 0.03 0.99 0.03 6.0 5.60 0.17 29.87 3.5% 24" HDPE 45.97 14.63 0.00 Type "B" #5-2A Type "B" #5-2 0.37 0.99 0.37 6.0 5.60 2.05 2.05 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #5-2 Type "B" #5-1 0.06 0.99 0.06 6.0 5.60 0.33 32.25 3.5% 24" HDPE 45.97 14.63 0.00

Type "B" #5-1 MH #8-1 0.14 0.99 0.14 6.0 5.60 0.78 33.03 3.5% 24" HDPE 45.97 14.63 0.00 Phase 2/3 Roof Leaders Subsurface Basin #1B 1.75 0.99 1.73 6.0 5.60 9.70 9.70 1.0% 10" PVC 10.40** 4.76 0.00 Subsurface Basin #1B MH #8-1 9.26 5.0% 15" HDPE 17.12 13.95 0.00 Type "B" #4-7 Type "B" #4-6 0.21 0.99 0.21 6.0 5.60 1.16 1.16 1.2% 15" HDPE 8.39 6.83 0.00 Type "B" #4-6 Type "B" #4-5 1.35 0.75 1.01 6.0 5.60 5.67 6.83 1.2% 15" HDPE 8.39 6.83 0.00 Type "B" #4-5 Type "B" #4-4 0.91 0.75 0.68 6.0 5.60 3.82 10.66 1.2% 18" HDPE 12.50 7.07 0.00 Type "B" #4-4 Type "B" #4-3 0.75 0.75 0.56 6.0 5.60 3.15 13.81 1.2% 24" HDPE 26.92 8.57 0.00 Type "B" #4-3 Type "B" #4-2 0.26 0.99 0.26 6.0 5.60 1.44 15.25 1.2% 24" HDPE 26.92 8.57 0.00 Type "B" #4-2 MH#4-1 0.47 0.75 0.35 6.0 5.60 1.97 17.22 1.2% 24" HDPE 26.92 8.57 0.00 Type "B" #4-1A MH#4-1 0.6 0.75 0.45 6.0 5.60 2.52 2.52 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #3-2 Type "B" #3-1 0.59 0.75 0.44 6.0 5.60 2.48 2.48 1.0% 15" HDPE 7.65 6.24 0.00 Type "B" #3-1 MH#4-1 0.11 0.99 0.11 6.0 5.60 0.61 3.09 1.0% 15" HDPE 7.65 6.24 0.00 MH #4-1 Basin #3 22.83 1.2% 24" HDPE 26.92 8.57 0.00 2'x2' #11-3 2'x2' #11-2 0.08 0.99 0.08 6.0 5.60 0.44 0.44 2.0% 12" PVC 5.97 7.60 0.00 2'x2' #11-2 2'x2' #11-1 0.13 0.99 0.13 6.0 5.60 0.72 1.16 2.0% 12" PVC 5.97 7.60 0.00 2'x2' #11-1 Basin #3 0.13 0.99 0.13 6.0 5.60 0.72 1.88 3.0% 12" PVC 7.31 9.31 0.00 Basin #3 Type "B" #1-7 9.56 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #1-7A Type "B" #1-7 0.24 0.75 0.18 6.0 5.60 1.01 1.01 2.0% 15" HDPE 10.83 8.82 0.00 Type "B" #1-7 Type "B" #1-6 0.11 0.99 0.11 6.0 5.60