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Home My WebLink AboutSW6231002_Design Calculations_20240906 (2) 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 #6 - 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 #6 Drainage Area Information Total Drainage Area= 11.82 acres See Summary of Hydrology Inputs per Sub-Drianage Area Total Impervious Area= 6.23 acres Impervious Surface Area= 52.71 SCM #6 Normal Pool Information Minimum Required Permanent Pool Surface Area Provided Permanent Pool Surface Area Avg Depth= 3.50 ft Normal Pool Elevation = 332.5 SA/DA ratio= 1.73 From Table 1 Main Pool SA Provided = 8931 sq.ft. DA x SA -DA ratio 0.205 acres Minimum pond surface area (SA) = 100 SA= 8,886 sq.ft. 0.204 acres SCM #6 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= 334.09 ft As described by Schueler(1987) Overflow Elev= 335.00 ft Rv = 0.05 +0.9 x I Where: Rv= Runoff coefficient(in./in.) Storage Volume Provided = 35,894 cu.ft. I = Percent impervious 0.824 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= 22,499 cu.ft. 0.517 acre-ft Page 1 of 6 a 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 #6 Runoff Storage Volume Information Incremental Accumulated Pond Area Countour Contour Contour Contour Elevation Area Volume Volume (ft) (sf) (cf) (cf) 340.00 23,989 23,144 135,648 FTop of Dam Storage 339.00 22,309 41,385 112,504 337.00 19,117 35,225 71,119 Volume 335.00 16,150 29,514 35,894 333.00 13,407 6,379 6,379 Normal Pool 332.50 12,121 0 0 <-Normal Pool SCM #6 Pond Volume Information Incremental Accumulated Pond Area Countour Contour Contour Contour Elevation Area Volume Volume (ft) (sf) (cf) (cf) 332.50 8,931 4,203 35,732 #-Normal Pool 332.00 7,890 7,557 31,529 FBottom of Littoral Shelf Main Pool 331.00 7,228 6,907 23,973 330.00 6,590 11,960 17,066 328.00 5,390 5,106 5,106 <-Sediment Storage Volume 327.00 4,828 0 0 FPond Bottom 332.50 2,954 1,299 6,651 FNormal Pool 332.00 2,257 2,036 5,353 ‹-Bottom of Littoral Shelf 331.00 1,823 1,614 3,316 Forebay 330.00 1,414 1,110 1,702 329.00 832 592 592 FSediment Storage Volume 328.00 381 0 0 ‹-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 #6 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 = 30,626 cf (Total Volume- Sediment Storage Volume) Aperm_pool = 8,931 sf Davg= 3.43 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 = 30,626 cf (Total Volume- Sediment Storage Volume) Dmax over shelf= 0.50 ft Pperm_pool = 420 ft Wsubmerged_shelf = 3.00 ft Abot shelf= 7,890 sf Davg= 3.84 ft Use Average Depth = 3.50 ft SCM #6 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 = 30,626 cf (Total Volume - Sediment Storage Volume) Forebay Volume = 6,059 Forebay Volume=19.8%of Main Pool Page 3 of 6 1. WithersRavenel Drawdown Orifice Calculator Our People.Your Success. 'roject Name: Serenity- Ph 8&9 Project#: 02190647 City/State: Harnett Co., NC Date: 9/4/24 SCM #6 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 = CdA✓2gh 1"WATER QUALITY STORM VOLUME AT WATER QUALITY POOL ELEVATION Variables Constants WQ Volume: 0.517 acre-ft 22499 cf g= 32.2 ft/s Head / Driving Head: 1.59 ft 0.53 ft Cd= 0.6 Draw down time: 52 hours 188280 sec Orifice Area = 0.034 sq.ft. 4.905 sq. in. Orifice Diameter= 2.50 in USE 2.5 INCH DIAMETER ORIFICE AT OVERFLOW ORIFICE ELEVATION Variables WQ Volume: 0.824 acre-ft 35894 cf Head / Driving Head: 2.50 ft 0.83 ft Draw down time: 67 hours 240480 sec Orifice Area = 0.034 sq.ft. 4.890 sq. in. Orifice Diameter= 2.50 in USE 2.5 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 #6 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) 10.50 ft Riser Wall Thickness (Dro) 6 in Riser Inside Wall Dimension (Dri) 4.00 ft Floor Thickness (FI) 6 in Exposed Barrel Length (Lb) 0.00 ft Barrel Inside Diameter(Dbi) 24 in Barrel Outside Diameter(Dbo) 2.50 ft Total Overflow Weir/Orifice Area (if present) 2.25 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 275.00 CF Concrete in Riser(no openings) 107.00 CF Concrete Removed for Overflows 1.13 CF Concrete Removed for Pipe Penetrations 1.70 CF Concrete Collar Volume 8.50 CF Total Concrete Volume 112.68 CF Weight Calculations Weight of Offset Water 17,160 lbs Total Weigth of Concrete 16,000 lbs Factor of Safety 1.2 Minimum Weight of Ballast Concrete 4,592 lbs Minimum Volume of Ballast Concrete Required = 1.25 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 #6 - Design of Riprap Outlet Protection Per NYDOT Dissipator Method for Use in Defined Channels Step 1: Compute flow velocity at culvert outlet. Velocity(Vo) = 5.9 ft/s OR Based on Q10= Step 2: Determine Do For circular pipe culverts, Do= Pipe Diameter For pipe archs,archs, box culverts,and paved channel outlets, Do=,/A. Where Ao=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)= 2.00 Single or Mulitple Openings= Single Do= 2 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 — I w -C PROTECT TO PREVENT SCOUR t — i APRON MATERIAL OJLVEPT HOLE USE L2 ALWAYS z — u +- . 20 : ' `_. '. 1 STONE FILLING(FINE) CL A 3 X Da 4 x(7). .x 2 STONE FILLING(LIGHT) CL.B 3 X Da 6 x D. _ - �— -- ) --- 3 STONE FILLING(MEDIUM)CL 1 4 X Da 8 x D. d 15 �l ._.--- -- Tom_ _---- 4 STONE FILLING(HEAVY) CL.1 4 X Da 8 x 0• t. — - - =t� -------— 5 STONE FILLING(HEAVY) Cl..2 5 X Da 10)(D. � 6 STONE FILLING(HEAVY) CL.2 6 X Da 10 x D ` 7 SPECIAL STUDY REQUIRED(ENERGY DISSIPATORS.STILLING _.- _ - _ BASIN OR LARGER SIZE STONE). -- - - —T- Figure 8.06d ' 2)----\= 3)f 1 •.�. .1•`i' R kh=?tune:pipe is;xm I s \ T ` ___ ;' NCDOT Rip Rap Material Classiciation =- �; L. — Class Dmin D50 Dmax o —`� � -+ Class'A' 2 4 6 i w•v"."` __Class'B' 5 8 12 a10' 15' 20' 25' DIAMETER(Ft.) 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= 2 Min Apron Length= 12.00 ft Min Apron Width= 6.00 ft Min Apron Depth= 1.50 ft Min Riprap Size= NCDOT Class'B' Page 6 of 6