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Home My WebLink AboutSW6231002_Design Calculations_20240906 (3) 11 WithersRavenel Pond Design Our People.Your Success. Project Name: Serenity-Ph 8&9 Project#: 02190647 City/State: Harnett Co., NC Date: 9/4/24 SCM #9 - Stormwater Wet Pond Design Table 1:Surface Area to Drainage Area Ratio for Permanent Pool Sizing(Adapted from Driscoll, 1986) Piedmont and Mountain SA/DA Table(Adapted from Driscoll,1986) Permanent Pool Depth(feet) Impervious 3.0 4.0 5.0 6.0 7.0 8.0 10 0.51 0.43 0.37 0.30 0.27 0.25 20 0.84 0.69 0.61 0.51 0.44 0.40 30 1.17 0.94 0.84 0.72 0.61 0.56 40 1.51 1.24 1.09 0.91 0.78 0.71 50 1.79 1.51 1.31 1.13 0.95 0.87 60 2.09 1.77 1.49 1.31 1.12 1.03 70 2.51 2.09 1.80 1.56 1.34 1.17 80 2.92 2.41 2.07 1.82 1.62 1.40 90 3.25 2.64 2.31 2.04 1.84 1.59 100 3.55 2.79 2.52 2.34 2.04 1.75 Source:NCDEQ Stormwater Design Manual Minimum Design Criteria C-3 Wet Pond(4.18.2017) SCM #9 Drainage Area Information Total Drainage Area= 15.64 acres See Summary of Hydrology Inputs per Sub-Drianage Area Total Impervious Area= 8.13 acres Impervious Surface Area= 51.98 SCM #9 Normal Pool Information Minimum Required Permanent Pool Surface Area Provided Permanent Pool Surface Area Avg Depth= 3.00 ft Normal Pool Elevation = 362.5 SA/DA ratio= 1.85 From Table 1 Main Pool SA Provided = 14685 sq.ft. DA x SA -DA ratio 0.337 acres Minimum pond surface area (SA) = 100 SA= 12,600 sq.ft. 0.289 acres SCM #9 Water Quality Information 1-Inch Runoff Volume Calculation(Water Quality Volume) Provided Water Quality Volume Using"Simple Method" Runoff Volume Calculations Water Quality Pool Elev= 363.93 ft As described by Schueler(1987) Overflow Elev= 364.50 ft Rv = 0.05 +0.9 x I Where: Rv= Runoff coefficient(in./in.) Storage Volume Provided = 42,145 cu.ft. I = Percent impervious 0.968 acre-ft Rv= 0.52 in/in Total runoff volume from 1-inch precipitation: Runoff Volume(S) = Design Rainfall x Rv x Drainage Area S= 29,399 cu.ft. 0.675 acre-ft Page 1 of 6 1% WithersRavenel Pond Volume Our People.Your Success. Project Name: Serenity- Ph 8&9 Project#: 02190647 City/State: Harnett Co., NC Date: 9/4/24 SCM #9 Runoff Storage Volume Information Incremental Accumulated Pond Area Countour Contour Contour Contour Elevation Area Volume Volume (ft) (sf) (cf) (cf) 368.00 26,144 25,600 126,917 4-Top of Dam Storage 367.00 25,060 47,972 101,317 Volume 365.00 22,928 22,400 53,345 364.00 21,877 21,140 _ 30,945 363.00 20,411 9,805 9,805 Normal Pool 362.50 18,819 0 0 4-Normal Pool SCM #9 Pond Volume Information Incremental Accumulated Countour Contour Contour Contour Pond Area Elevation Area Volume Volum i (ft) MI (sf) a (cf) a i(cf) 362.50 14,685 6,968 52,378 4-Normal Pool 362.00 13,200 12,724 45,410 4-Bottom of Littoral Shelf Main Pool 361.00 12,254 11,793 32,686 360.00 11,338 10,888 20,893 359.00 10,445 10,004 10,004 4-Sediment Storage Volume 1511 nn 9,570 0 0 4-Pond Bottom 362.50 3,960 1,812 9,698 4-Normal Pool 362.00 3,298 2,887 7,886 4-Bottom of Littoral Shelf 361.00 2,494 2,179 4,999 Forebay 360.00 1,879 1,621 2,820 359.00 1,376 1,199 1,199 4-Sediment Storage Volume 358.00 1,030 0 0 4-Forebay Bottom Page 2 of 6 pp WithersRavenel Basin Sizing Our People.Your Success. Project Name: Serenity- Ph 8&9 Project#: 02190647 City/State: Harnett Co., NC Date: 9/4/24 SCM #9 Main Pool Average Depth Information Per NCDEQ"Stormwater Design Manual" Minimum Design Criteria: The average depth of a wet pond is to be calculated by one of these two options: OPTION 1: Average depth when the shelf is not submerged or the shelf is included in calculation Vperm_pool Davg = Aperm_pool Where: Davg= Average Depth (ft) Vperm_pooi = Volume of Permanent Pool (cf) Aperm_pooi = Area of Permanent Pool (sf) Vperm_pooi = 4- 2,374 cf (Total Volume- Sediment Storage Volume) Aperm_pool = 1- 4,685 sf Davg= 2.89 ft OPTION 2: Average depth when the shelf is being excluded from average depth calculation Vperm_pool — 0.5 X Dmax_over_shelf X Pperm_pool X Wsubmerged_shelf Da„g = "bot_shel f Where: Davg= Average Depth (ft) Vperm_pooi = Volume of Permanent Pool (cf) Dmax over shelf= Depth of water at the deep side of the shelf to permanent pool (ft) Pperm_pool = Perimeter of the main pool at the bottom of the shelf(ft) Wsubmerged_shelf= Width of the shelf at permanent pool (ft) Abot shelf= Area of Wet Pond at the Bottom of the Shelf(sf) Vperm_pooi = 4- 2,374 cf (Total Volume- Sediment Storage Volume) Dmax over shelf= 0.50 ft Pperm_pool = 520 ft Wsubmerged_shelf= 3.00 ft Abot shelf= 13,200 sf Davg= 3.18 ft Use Average Depth = 3.00 ft SCM #9 Forebay Sizing Information Per NCDEQ"Stormwater Design Manual" Minimum Design Criteria: The forebay volume shall be 15-20%of the main pool. Main Pool Volume = 42,374 cf (Total Volume - Sediment Storage Volume) Forebay Volume = 8,499 Forebay Volume=20%of Main Pool Page 3 of 6 4.111 WithersRavenel Drawdown Orifice Calculator Our People.Your Success. Project Name: Serenity- Ph 8&9 Project#: 02190647 City/State: Harnett Co., NC Date: 9/4/24 SCM #9 Water Quality Drawdown Information ORIFICE CALCULATOR Per NCDEQ"Stormwater Design Manual" Minimum Design Criteria: The design volume shall draw down to the permenant pool level in 2-5 days. Q = CdAV2gh 1"WATER QUALITY STORM VOLUME AT WATER QUALITY POOL ELEVATION Variables Constants WQ Volume: 0.675 acre-ft 29399 cf 0 g= 32.2 ft/s Head / Driving Head: 1.43 ft 0.48 ft Cd= 0.6 Draw down time: 50 hours 180360 sec Orifice Area = 0.049 sq.ft. 7.069 sq. in. Orifice Diameter= 3.00 in USE 3 INCH DIAMETER ORIFICE AT OVERFLOW ORIFICE ELEVATION Variables WQ Volume: 0.968 acre-ft 42145 cf Head / Driving Head: 2.00 ft 0.67 ft Draw down time: 61 hours 218520 sec Orifice Area = 0.049 sq.ft. 7.064 sq. in. Orifice Diameter= 3.00 in USE 3 INCH DIAMETER ORIFICE Page 4 of 6 WithersRavenel Anti-Flotation Our People.Your Success. Project Name: Serenity- Ph 8&9 Project#: 02190647 City/State: Harnett Co., NC Date: 9/4/24 SCM #9 Anti-Flotation Calculations Density Values Unit Weight of Water 62.4 lbs/cf Unit Weight of Concrete 142 lbs/cf Riser/Barrel Details Riser Inside Height(Hr) 16.75 ft Riser Wall Thickness (Dro) 6 in Riser Inside Wall Dimension (Dri) 5.00 ft Floor Thickness (FI) 6 in Exposed Barrel Length (Lb) 0.00 ft Barrel Inside Diameter(Dbi) 42 in Barrel Outside Diameter(Dbo) 4.25 ft Total Overflow Weir/Orifice Area (if present) 6.25 SF ID of Drawdown Pipe(if present) 4 in ID of Drain Pipe(if present) 4 in Is there a Concrete Pipe Collar Present? Yes Volume Calculations Water Offset by Riser/Barrel 621.00 CF Concrete in Riser(no openings) 202.25 CF Concrete Removed for Overflows 3.13 CF Concrete Removed for Pipe Penetrations 4.94 CF Concrete Collar Volume 11.25 CF Total Concrete Volume 205.44 CF Weight Calculations Weight of Offset Water 38,750 lbs Total Weigth of Concrete 29,172 lbs Factor of Safety 1.2 Minimum Weight of Ballast Concrete 17,328 lbs Minimum Volume of Ballast Concrete Required = 4.75 CY Page 5 of 6 ;• VV thersRavenel Riprap Dissipator Project Name: Serenity-Ph 8&9 Project#: 02190647 City/State: Harnett Co.,NC Date: 9/4/24 SCM #9 - Design of Riprap Outlet Protection Per NYDOT Dissipator Method for Use in Defined Channels Step 1: Compute flow velocity at culvert outlet. Velocity(Vo) = 8.4 ft/s OR Based on Q10= Step 2: Determine D. For circular pipe culverts, Do= Pipe Diameter For pipe archs,archs, box culverts,and paved channel outlets, Do=,/A. Where A.=cross-sectional area of flow at outlet For multiple openings, Do= 1.25 x Do of single culvert Culvert Type= Circular Pipe Pipe Diameter(ft)= 3.50 Single or Mulitple Openings= Single D.= 3.5 ft Step 3: Determine zone for apron material per Figure 8.06C. Note: For apron slopes >_ 10%, use next higher zone. Determine apron size per Figure 8.06d 25 _ . LENGTH OF APRON --- C "C PPOTEC" TO PREVENT SCOUR ' APRON MATERIAL OULVEPT HOLE USE L2 ALWAYS j L2 E' --- -- 1 Li zo `,I --- ------ 1 STONE FILLING(FINE) CL A 3X D. 44D, �— — ti_ - 2 STONE FILLING UGIHTI CL.B 3 X D. 6 x D. Z---- _ - ---- -- ------ -- -- --- 3 STONE FILLING(MEDIUM)CL 1 4 X D. 8 x D 15 ___ ._.- d , �� " -- �1 _7.i.-__.. , _______ 4 STONE FILLING(HEAVY) CL.1 4 X D. 8 x D. } -i - ---t 5 STONE FILLING(HEAVY) CL.2 5 X D. 10 x D, U '--'- _ _ - . . __ _ _._;� 6 STONE FILLING(HEAVY) CL.2 6 X D. 104D. • LU -- 7 SPECIAL STUDY REQUIRED(ENERGY DISSIPATORS.STILLING > - -- ----- _ BASIN OR LARGER SIZE STONE). . `N'---' -• Fipure 8.06d 2F- '- -3 .Q Wkh=?nme:pipeis;s ,I 5 • ''I NCDOT Rip Rap Material Classiciation � i n Class Dmin D50 Dmax��s- Class'A' 2 4 6 0 I w Vr xrc I I -1- 0• 5 10' 15• 20• 5 Class'B' 5 8 12 DIAMETER(Ft.) —Class Class'1' 5 10 17 Figure 8.06c _ Class'2' 9 14 23 Riprap Dissipator Sizing Information Per NCDOT 2018 Standard Specifications,Section 1042 Zone= 3 Min Apron Length= 28.00 ft Min Apron Width= 10.50 ft Min Apron Depth= 2.13 ft Min Riprap Size= NCDOT Class'1' Page 6 of 6