The URL can be used to link to this page

Home My WebLink AboutSW3220302_Design Calculations_20220613 Table of Contents Narrative ……………………………………………………………………………………… 3 Storm Sewer Calcs for Ex. System to Remain……………………………………………… 4 Storm Sewer Calcs for Prop. System………………………………………………………… 16 Bmp Calculations…………………………………………………………………………………27 HydroCAD Report …………………………………………………………………… 28 Water Quality Calcs …………………………………………………………………… 114 Erosion Control Calculations……………………………………………………………………116 Skimmer Basin Calcs ………………………………………………………………… 117 Diversion Ditch Calcs ………………………………………………………………… 120 Outlet Protection Calc…………………………………………………………………123 Supporting Documents ………………………………………………………………………… 126 Drainage Area Maps…...……………………………………………………………………..… 141 Narrative Existing Conditions The existing site is partially developed on the eastern half with a gun store / gun range building and associated parking. The western end of the site is mostly wooded. Stormwater on the developed half of the site flows into an existing stormwater system that discharges off property. Stormwater on the undeveloped half of the site, flows to a old skimmer basin that still remains from the construction of the existing building. The site is composed of a mixture of mostly Hydrologic Group B soils. Proposed Conditions The undeveloped half of the site will be developed with a 12,000 SF manufacturing building that will have a large truck court in the rear. A 5,200 SF addition will be added to the existing building. Parking and drive aisles between the two buildings will be improved so that semi-trucks with trailers can navigate through the site. Erosion Control The main control measure for sediment runoff will be a skimmer basin which will contain the majority of the runoff. The existing stormwater system with stone inlet protection and silt sack inlet protection will be used to route runoff as well. Silt fence with rock outlets will be used to contain additional runoff. Additional measures will consist of construction entrances, inlet protections, and diversion ditches. Storm Water Detention, Water Quality Detention of the storm drainage is not required in this area but a 10-year storm must be conveyed non erosively. Detention has been provided for the 10-year storm to address drainage concerns since the existing outfall is on a neighboring property. The BMP was designed so that run off leaving the site through existing outfall would be less than run-off occurring in the sites current state. Detention will consist of a dry detention basin in the southwest portion of the site that ties into the existing stormwater system. Water quality will be provided via a surface sand filter and internal water storage below the system. EX. STORM DRAINAGE CALCULATIONS QFBL!GMPX!GSPNIZESPDBE!GPS!21ZS!TUPSN PROP. STORM DRAINAGE CALCULATIONS BMP CALCULATIONS Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 24-hr 1-Year Rainfall=2.81" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 10-Year Rainfall=3.50" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 25-Year Rainfall=4.15" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Type II 6-hr 50-Year Rainfall=4.68" Table of Contents Denver Defense Sand Filter Design BASIN A Input ge Area119,449.00SF2.74ACMax 10 Ac per SF Basin Draina Impervious Area to Basin72,929.00SF Filter Surface Elevation841.5 Reference NCDENR BMP Design Manual chpt 11 1. Simple Method for Runoff Volumetric runoff coefficient (Rv) Rv=0.05 + 0.9 * Ia Rv=Runoff coefficient \[storm runoff (in)/storm rainfall (in)\], unitless Ia= Impervious fraction \[impervious portion of drainage area (ac)/drainage area (ac.)\], unitless Pre Dev. Imp Area0S.F.=0.00ACPre Ia = 0.0% Post Dev. Imp. Area72,929S.F.=1.67ACPost Ia = 61.1%(using s.f. #'s) Drainage Area119,449S.F.=2.74AC Rv = 0.599 (Wqv) 2. Compute Volume Controlled 2 WQv = 1.0*Rv*A/1 WQv = water quality protection volume (ac-ft) Rv = volumetric runoff coefficient A = total drainage area (acres) WQV = cu. Ft. 5,967.4 WQV = cu. Ft.20% WQV for forebay895 adj 4475.5 3. Determine SA of SF + Sed Chamber h= WQV/A+A maxfilteradjsandsed WQVA+A adjSF 0.54475.53448,951.07 14475.53444,475.53 1.54475.53442,983.69 24475.53442,237.77 2.54475.53441,790.21 34475.53441,491.84 3.54475.53441,278.72 44475.53441,118.88 4.54475.5344994.56 54475.5344895.11 5.54475.5344813.73 64475.5344745.92 4. Compute Sand Filter Area to Treat Water Quality Volume Min Surface Area of Sand Filter Bed (WQv*df)/(k*(hf+df)*tf) Af = Where Af = surface area of filter bed (sq ft)sq ft df = filter bed depth (ft)1.5ftMIN 1.5 FT (ft/day)=3.5ft/day = 1.75 in/hr k = coefficient of permeability of filter media hf = average height of water above filter bed (ft)1ft gn filter bed drain time (days)2daysNC BMP MAN tf = desi A = 511.5s.f. F Develop Stage Storage for Sand Filter Media At elevation of 5 feet above filter bed Qo=6265.75cf/day=0.073cfs At elevation of 4 feet above filter bed Qo=5370.64cf/day=0.062cfs At elevation of 3 feet above filter bed Qo=4475.53cf/day=0.052cfs At elevation of 2 feet above filter bed Qo=3580.43cf/day=0.041cfs At elevation of 1 feet above filter bed Qo=2685.32cf/day=0.031cfs At elevation of 0 feet above filter bed Qo=1790.21cf/day=0.021cfs 4. Size Undrains Compute minimum drawdown discharge Water quality volume = 4,475.5cu. ft. WQv/ (48 hours*3,600 sec/hour) = Drawdown = 0.026cfsNC BMP MAN Compute perforation capacity 4 rows of perforations / ft Number of cleanouts in pipe=6(1 per 50 ft , at each end of sytem and bends) total length of underdrain pipe87ft Number of perforations =1296holes 50 percent of perforations = 648holes (2gh)^0.5 Capacity of one hole = CA =0.0083cfs Total Capacity=5.35cfs y Compute underdrain pipe capacit For 6-inch PVC underdrain pipe at 0.005 ft/ft slope: Diameter of Pipe = 6inches Area of pipe =28.27sq. in.0.1964sq. ft. Slope of pipe =0.005ft/ft mannings n = 0.013 Capacity of pipe = (1.49/n)(A)(A/P)^0.67(S)^0.5 =0.40cfs Fifty percent assuming clogging =0.20cfs *Underdrain capacity okay because Underdrain calc capacity is greater than sand filter infiltration Qo 5. Size Concrete Anti-flotation Block: EROSION CONTROL CALCULATIONS User Input Data Intermediate Calc Final Calc REF: N.C. EROSION AND SEDIMENT CONTROL PLANNING AND DESIGN MANUAL 1. SKIMMER BASIN NUMBER 1 2. DETERMINE RUNOFF FOR 10-YEAR STORM DRAIN. AREA (AC.)2.34ACRES(total from site and offsite) )2.03ACRES(phase 1) DIST. AREA (AC. C0.4BARE SOILS TIME OF CONC.5.00MINUTES(USE 5 MINS TO CONSIDER POST) INTENSITY (10 YR.)7.09IN./HR. Q = CIA6.6C.F.S. 3. DETERMINE STORAGE CAPACITY REQUIRED: 1800 CF/AC x DIST. AREA = STORAGE VOLUME 3 ft STORAGE VOLUME =3,654.00 3 ft@ 2' Depth Storage Volume Provided5,679.00 4. SIZE BASIN: 2 ft Surface Area(sf) = Q10 x 325 SF 2,157 REQD Avg Depth=2ft 2 ft@ 2' Depth Surface Area Provided3,538 5. SPILLWAY: FROM NC EROSION AND SEDIMENT CONTROL PLANNING AND DESIGN MANUAL, TABLE 6.60A L=Q/C * H 3/2 Q6.6 C*H 3/23.00 L=2 Use 10' Min. User Input Data Intermediate Calc Final Calc Minimum Sizing (Design) Basin Volume3654Skimmer Size2 Days to Drain2Orifice Radius0.7 Orifice Diamater1.4 Max Sizing (At Spillway) Basin Volume11759Skimmer Size2.0 ys to Drain5Orifice Radius0.8 Da Orifice Diamater1.6 Source: SUPPORTING DOCUMENTS DRAINAGE AREA MAPS