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Home My WebLink AboutSW3240101_Design Calculations_20240517 CES$ Storm wa ter Calculations For Huntley Brothers Home Office 12400 Old Camden Road Midland, NC 28107 CONCORD PROJECT NO. 210123.000 Owner: Client: Huntley Brothers Client Representative: Ed Huntley 8217 Fairview Road Charlotte, NC 28227 P.980.237.3291 ed@huntleybrothers.com Preparer's Name: James G. Eaves Ill, PE CESI NCBELS Corporate License Number C-0263 PO Box 268 Concord, NC 28026 \\\\\\��,,,ui ��i M.704.791.3160 \\\ 1N ,�, RO .,. jayeaves@cesicgs.com ��: ;``%,,/ rtilV - 7837 I _I �4CINE�- ��\' ///i,/'„ki, C.� EP�\\\\\ - Narrative and Summary of Results - Impervious Area Summary - Pre-Development Calculations - Pre Development Nodal Diagram - Pre-Development Drainage Areas WET POND DETAILS TOP OF POND 684.5 BOTTOM OF MAIN POOL 675.5 BOTTOM OF FOREBAY 675.5 - Hydraflow Results - Riprap Calculations - Appendix SUMMARY OF RESULTS PRE-DEVELOPMENT DRAINAGE AREA SUMMARY DRAINAGE AREA AREA (ACRES) TC CN Pre DA-A 13.190 18.20 62.2 Total 13.190 POST DEVELOPMENT DRAINAGE AREA SUMMARY DRAINAGE AREA AREA (ACRES) TC CN Post DA-Wet Pond 16.896 10.00 59.2 Post DA- Bypass 8.520 10.00 60.0 Total 25.416 PRE-DEVELOPMENT RUNOFF RESULTS DRAINAGE AREA 1 YR/24 HR 10 YR/24 HR 100 YR/24 HR Pre DA 2.343 18.96 45.4 POI 4.358 30.04 68.09 POST-DEVELOPMENT RUNOFF RESULTS DRAINAGE AREA 1 YR/24 HR 10 YR/24 HR 100 YR/24 HR Post DA-Wet PoNd 16.18 36.68 60.33 Post DA- Bypass 2.02 15.71 36.91 Wet Pond 1 0.29 8.73 42.49 POI 2.14 18.12 75.65 POST DEVELOPMENT PEAK-STAGE RESULTS 1 YR/24 HR 10 YR/24 HR 100 YR/24 HR WP1 (T.O.B. = 685.00) 682.06 683.07 683.79 SOIL AREA SUMMARY Pre-development Post-Development Hydrologic Soil Group C 12,139 sq. ft 12,139 sq. ft Hydrologic Soil Group B 562,417 sq. ft 683,514 sq. ft pret—Development Drainage Area FREEBOARD 100 YEAR 24 HOUR ELEVATION 682.06 2.44 10 YEAR 24 HOUR ELEVATION 683.07 1.43 1 YEAR 24 HOUR ELEVATION 683.79 0.71 WATER QUALITY/PONDING ELEVATION 684.50 0.00 OUTLET STRUCTURE DETAILS RIM ELEVATION 684.50 SLOT WEIR ELEVATION (D) 0.00 SLOT WEIR WIDTH (D) 0.00 OUTLET STRUCTURE SIZE 4.00' X 4.00' STRUCTURE FOOTING DETAILS (K) FOOTING LENGTH 6.00 FOOTING WIDTH 6.00 FOOTING DEPTH 6.00 WET POND DETAILS TOP OF POND 684.50 BOTTOM OF MAIN POOL 679.50 BOTTOM OF FOREBAY 675.50 3. Impervious Area Summary Pre-Development Total Existing On-Site inpervious area 0 SQ FT Post-Development Total on-site impervious area 208,226 SQ FT On-site area required to be treated by SCM 208,226 SQ FT1 Total area treated by SCM 208,226 SQ FT Equal to the post-development impervious area minus the Pre-devlopment Impervious Impervious area not being treated by SCM is located at entrance to site. Driveway sheet flows North towards Zane Road therefore, not being treated by Sand Filter Pre-Development Drainage Area Pre Development Nodal Diagram PRE DA POI Pre-Development Drainage Area Land use Condition Hydrologic Area(SF) Area(Acres) Cn Weighted Cn Soil Group Woods good B 436,471 10.020 60 45.6 Open Space good B 138,085 3.170 69 16.6 Impervious N/A B - - 98 0.0 574,556 13.190 62.2 tc Calculation L up down slope n pipe size(in) area(sf) perimeter (ft) Sheet Flow 100 706.87 706.39 0.48% 0.15 Grass:Short Praire Shallow Concentrated 426 706.39 674.71 7.44% Un-Paved CALCULATED TC= 18.20 MIN SEE HYDRAFLOW TR-55 TC CALCULATION SHEET TC USED IN CALCULATION= 18.20 MIN MINIMUM TC OF 10 MINUTES WET POND DETAILS TOP OF POND 0.011 BOTTOM OF MAIN POOL 0.05 BOTTOM OF FOREBAY 0.06 Grass:Dense Grass 0.24 Grass:Bermuda Grass 0.41 Range:Natural 0.13 Woods:Light Underbrush 0.4 Woods:Dense Underbrush 0.8 Roughness Coefficients(Manning's N)for Channel Flow Excavated Channels:Short Grass 0.027 Post-Development Drainage Area Post Development Nodal Diagram Post DA- Post DA-WP BYPASS SF1 POI Post-Development Drainage Area-Wet Pond Land use Condition Hydrologic Area(SF) Area(Acres) Cn Weighted Cn Soil Group Open Space good B 526,731 12.092 61 43.7 Impervious(Asphalt/Concrete) N/A B 25,825 0.593 98 2.0 Impervious(Gravel) N/A B 173,232 3.977 85 12.2 Impervious(Building) N/A B 10,186 0.234 98 1.4 735,974 16.896 59.2 TC USED IN CALCULATION= 10.00 MIN MINIMUM TC OF 10 MINUTES WET POND DETAILS TOP OF POND 685 BOTTOM OF MAIN POOL 679.5 BOTTOM OF FOREBAY 675.5 Wet Detention Pond Design Calculations Area(sq.ft.) Area(acres) Attenuation Requirements Total Drainage Area 735,974 16.896 1-year,24-hour storm Pervious Area 527,748 12.115 10-year,24-hour storm Impervious Area 208,226 4.780 Emergency Spillway Requirement 100 year,24-hour storm,6"freeboard Simple Method for Runoff Volume Rv=0.05+0.9*IA 0.30 Rv=Runoff Coefficient(unitless) IA=Impervious fraction 0.28 DV=3630*RD*Rv*A 18,684 DV=Design Volume(cu ft) RD=Design Storm Depth(in) 1.0 A=Drainage Area(ac) 16.896 Average Depth Double Interpolation from SA/DA Table DA,=Vpp/App 3.06 3.00 3.06 4.00 0.90 3.25 3.21 2.64 Vpp=Volume of permanent pool(Main Body only) 27,976 0.28 1.42 App=Area of permanent pool(Main Body only) 9,150 1.00 3.55 3.51 2.79 Main Pool Volume(SA/DA Method) Total DA 735,974 SA/DA 1.42 Surface Area Required(DA*((SA/DA)/100)) 10,428 Surface Area Provided(Main Body only) 9,150 Table 1:Piedmont and Mountain SA/DA Table(Adapted from Driscoll,1986) 3.00 4.00 5.00 6.00 7.00 8.00 0.10 0.51 0.43 0.37 0.30 0.27 0.25 0.20 0.84 0.69 0.61 0.51 0.44 0.40 0.30 1.17 0.94 0.84 0.72 0.61 0.56 0.40 1.51 1.24 1.09 0.91 0.78 0.71 0.50 1.79 1.51 1.31 1.13 0.95 0.87 0.60 2.09 1.77 1.49 1.31 1.12 1.03 0.70 2.51 2.09 1.80 1.56 1.34 1.17 0.80 2.92 2.41 2.07 1.82 1.62 1.40 0.90 3.25 2.64 2.31 2.04 1.84 1.59 1.00 3.55 2.79 2.52 2.34 2.04 1.75 Forebay 1 Main Bay Forebay 2 Incremental Cumulative Incremental Cumulative Incremental Cumulative Elevation Area Depth Volume Volume Elevation Area Depth Volume Volume Elevation Area Depth Volume Volume 675.50 13 675.50 4,998 0 0 675.50 12 676.50 356 1.00 184 - 676.50 5,968 1.00 5,483 5,463 676.50 356 1.00 184 - 677.50 772 1.00 564 748 677.50 6,930 1.00 6,449 _ 11,932 677.50 740 1.00 548 732 678.50 1,259 1.00 1,016 1,764 678.50 8,004 1.00 7,467 19,399 678.50 1,225 1.00 983 1,715 679.50 1,819 1.00 1,539 3,303 679.50 9,150 1.00 8,577 27,976 679.50 1,781 1.00 1,503 3,218 Temporary Pool Incremental Cumulative Elevation Area Depth Volume Volume 679.50 13,386 - - - 680.50 15,000 1.00 14,193 14,193 681.50 16,686 1.00 15,843 30,036 682.50 18,444 1.00 17,565 47,601 683.50 20,274 1.00 19,359 66,960 684.50 22,176 1.00 21,225 88,185 24,678 12,338.78 Permanent Pool Volume: 34,497 32,903 16,451.70 Forebay Volume: 6,520 Forebay Percentage 18.9% Wet Pond CESI Land Development Services JOB NO.: 210123.000 BY: MAC P.O.Box 268 DATE: 5/9/2024 P.M: JGE Concord,NC 28026 REVISED: FLOATATION CALCULATIONS Calculations Given Data Standard Footing Assumptions Density of Concrete 150 Ibs/ft^3 1. Footing base to be 1 ft.wider than structure Density of Water 62.4 Ibs/ft^3 on all sides. Safety Factor(S.F.) 2 Equations used: Outlet Structure Weight, W(s)= (w+2t)^2*h-w^2*(h-t)x D(c) where, w= outlet box inside dimension,ft. Displaced Water Weight, W(w)= (w+2t)^2 x D(w)x h t= structure wall thickness,ft. h= height of structure,ft. Required Base Weight, W(b)= (W(w)x S.F.)-W(s) D(c)= density of concrete,lbs/ft^3 WET POND DETAILS D(w)= density of water,lbs/ft^3 TOP OF POND tired Footing Volume,V(f)= W(b)/Dc-Dw S.F.= safety factor BOTTOM OF MAIN PC 674 BOTTOM OF FOREB/ 675 Elevation at bottom of structure= 675.50 Elevation at top of structure= 685.50 Height of structure,h= 10.00 ft. Outlet Structure Weight, W(s)= 14700 lbs Structure wall thickness,t= 6 in. Displaced Water Weight, W(w)= 15600 lbs Average outlet box inside dimension, w= 4 ft. Req'd Base Weight, W(b)= 16500 lbs Footing Size Required Footing Volume, V(fr)= 188 cf Standard Footing Length,L= 6.00 ft. Provided Footing Volume, V(fp)= 216 cf Standard Footing Width, W= 6.00 ft. Footing Check okay Minimum Footing Depth,D= 1.00 ft. Footing Size to be used: Length= 6.00 ft. Width= 6.00 ft. Depth= 6.00 ft. Post-Development Drainage Area-Bypass Land use Condition Hydrologic Area(SF) Area(Acres) Cn Weighted Cn Soil Group _ _ Woods good B 371,131 8.520 60 60.0 371,131 8.520 60.0 TC USED IN CALCULATION= 10.00 MIN MINIMUM TC OF 10 MINUTES Hydraflow Results 1 Hydrograph Summary Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SCS Runoff 2.343 2 728 14,268 PRE DA 3 SCS Runoff 16.18 2 720 41,961 POST DA-WET POND 4 SCS Runoff 2.017 2 724 9,504 POST DA-BYPASS 6 Reservoir 0.285 2 1148 38,986 3 682.06 32,705 WET POND ROUTING 8 Combine 2.343 2 728 14,268 1, PRE DA 9 Combine 2.138 2 724 48,491 4,6, POST DA-ROUTED 210123.000 Stormwater Calculations.gpw Return Period: 1 Year Wednesday, 05/ 15/2024 2 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Wednesday,05/15/2024 Hyd. No. 1 PRE DA Hydrograph type = SCS Runoff Peak discharge = 2.343 cfs Storm frequency = 1 yrs Time to peak = 728 min Time interval = 2 min Hyd. volume = 14,268 cuft Drainage area = 13.190 ac Curve number = 60* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 18.20 min Total precip. = 2.90 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 *Composite(Area/CN)=[(10.022 x 60)+(3.167 x 61)]/13.190 PRE DA Q (cfs) Hyd. No. 1 -- 1 Year Q (cfs) 3.00 - 3.00 2.00 - 2.00 1.00 1.00 0.00 '- 0.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 1 Time (min) 3 Hydrograph Summary Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SCS Runoff 18.96 2 726 65,109 PRE DA 3 SCS Runoff 36.68 2 720 96,511 POST DA-WET POND 4 SCS Runoff 15.71 2 722 43,371 POST DA-BYPASS 6 Reservoir 8.732 2 734 93,319 3 683.07 49,713 WET POND ROUTING 8 Combine 18.96 2 726 65,109 1, PRE DA 9 Combine 18.12 2 724 136,690 4,6, POST DA-ROUTED 210123.000 Stormwater Calculations.gpw Return Period: 10 Year Wednesday, 05/ 15/2024 4 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Wednesday,05/15/2024 Hyd. No. 1 PRE DA Hydrograph type = SCS Runoff Peak discharge = 18.96 cfs Storm frequency = 10 yrs Time to peak = 726 min Time interval = 2 min Hyd. volume = 65,109 cuft Drainage area = 13.190 ac Curve number = 60* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 18.20 min Total precip. = 5.10 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 *Composite(Area/CN)=[(10.022 x 60)+(3.167 x 61)]/13.190 PRE DA Q (cfs) Hyd. No. 1 -- 10 Year Q (cfs) 21.00 21.00 18.00 18.00 15.00 15.00 12.00 12.00 9.00 9.00 6.00 6.00 3.00 3.00 0.00 0.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 1 Time (min) 5 Hydrograph Summary Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SCS Runoff 45.40 2 726 145,383 PRE DA 3 SCS Runoff 60.33 2 720 162,532 POST DA-WET POND 4 SCS Runoff 36.91 2 722 96,844 POST DA-BYPASS 6 Reservoir 42.49 2 726 159,248 3 683.79 62,821 WET POND ROUTING 8 Combine 45.40 2 726 145,383 1, PRE DA 9 Combine 75.65 2 722 256,092 4,6, POST DA-ROUTED 210123.000 Stormwater Calculations.gpw Return Period: 100 Year Wednesday, 05/ 15/2024 6 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Wednesday,05/15/2024 Hyd. No. 1 PRE DA Hydrograph type = SCS Runoff Peak discharge = 45.40 cfs Storm frequency = 100 yrs Time to peak = 726 min Time interval = 2 min Hyd. volume = 145,383 cuft Drainage area = 13.190 ac Curve number = 60* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 18.20 min Total precip. = 7.60 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 *Composite(Area/CN)=[(10.022 x 60)+(3.167 x 61)]/13.190 PRE DA Q (cfs) Hyd. No. 1 -- 100 Year Q (cfs) 50.00 50.00 40.00 i 40.00 30.00 30.00 I 20.00 20.00 10.00 10.00 0.00 - - 0.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 1 Time (min) 7 Hydraflow Rainfall Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Wednesday,05/15/2024 Return Intensity-Duration-Frequency Equation Coefficients(FHA) Period (Yrs) B D E (N/A) 1 62.1764 12.7000 0.8901 2 69.8703 13.1000 0.8658 3 0.0000 0.0000 0.0000 5 79.2597 14.6000 0.8369 10 88.2351 15.5000 0.8279 25 102.6072 16.5000 0.8217 50 114.8193 17.2000 0.8199 100 127.1596 17.8000 0.8186 File name:Concord IDF Curve.IDF Intensity= B/(Tc+ D)^E Return Intensity Values(in/hr) Period (Yrs) 5 min 10 15 20 25 30 35 40 45 50 55 60 1 4.82 3.86 3.23 2.79 2.46 2.20 1.99 1.82 1.68 1.56 1.46 1.37 2 5.69 4.61 3.89 3.38 2.99 2.69 2.44 2.24 2.07 1.93 1.81 1.70 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5 6.57 5.43 4.65 4.08 3.65 3.30 3.02 2.79 2.59 2.42 2.27 2.15 10 7.24 6.04 5.21 4.59 4.12 3.74 3.43 3.17 2.95 2.77 2.60 2.46 25 8.25 6.95 6.03 5.34 4.80 4.38 4.02 3.73 3.48 3.26 3.07 2.91 50 9.04 7.65 6.66 5.92 5.34 4.87 4.49 4.16 3.88 3.65 3.44 3.25 100 9.83 8.36 7.30 6.50 5.87 5.36 4.94 4.59 4.29 4.03 3.80 3.60 Tc=time in minutes.Values may exceed 60. 200114.000 Pitts School Flex Park Final Engineering\2-Engineering\2-Calculations\4-Erosion Control\Concord PCP.pcp Rainfall Precipitation Table (in) Storm Distribution 1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr SCS 24-hour 2.90 3.50 0.00 4.40 5.10 6.00 6.80 7.60 SCS 6-Hr 2.06 2.48 0.00 3.09 3.57 4.21 4.72 5.23 Huff-1st 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff-2nd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff-3rd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff-4th 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff-Indy 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Custom 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Riprap DESIGN OF RIPRAP OUTLET PROTECTION User Input Data Calculated Value Reference Data Designed By: MAC Date: 5/15/2024 Checked By: JGE Company: CESI Project Name: Huntley Brothers Project No.: 210123.000 Site Location (City/Town) Midland, NC Culvert Id. FES-100 Step 1. Determine the tailwater depth from channel chaiac tei i.tics below the pipe outlet for the design capacity of the pipe. If the tailwater depth is less than half the outlet pipe diameter. it is classified inuiirmtun tailwater condition. If it is greater than half the pipe diameter. it is classified niaxuntun condition. Pipes that outlet onto wide fiat areas with no defined channel are assumed to have a minimum tailwater condition unless reliable flood stage elevations show otherwise Outlet pipe diameter, Do (in.) 24 Tailwater depth (in.) 0 Minimum/Maximum tailwater? Min TW (Fig. 8.06a) Discharge (cfs) 12.90 See 10 year Stormwater Calculation results Step 2. Based on the tailwater conditions determined in step 1. enter Figure 8.06a or Figure 8.06b.and determine d,o riprap size and minimum apron length (L). The d,, size is the median stone size in a well-graded riprap apron. Step 3. Determine apron width at the pipe outlet, the apron shape. and the apron width at the outlet end from the same figure used in Step 2. Minimum TW Maximum TW Figure 8.06a Figure 8.06b Riprap d50, (ft.) 0.45 Minimum apron length, La (ft.) 13 Apron width at pipe outlet (ft.) 6 6 Apron shape Trapezoidal Apron width at outlet end (ft.) 15 2 Step 4. Determine the maxinnun stone diameter dm.a■ I.5 x d5D Minimum TW Maximum TW Max Stone Diameter, dmax (ft.) 0.675 0 Step 5. Determine the apron thickness Apron thickness = 1.5 x d,,,,, Use class b riprap Minimum TW Maximum TW Apron Thickness(ft.) 1.0125 0 RIP RAP CLASS MINIMUM MIDRANGE MAXIMUM A 2 IN (0.17 FT) 4 IN (0.33 FT) 6 IN (0.5 FT) B 5 IN (0.42 FT) 8 IN (0.67 FT) 12 IN (1 FT) 1 5 IN (0.42 FT) 10 IN (0.83 FT) 17 IN (1.42 FT) 2 9 IN (0.75 FT) 14 IN (1.17 FT) 23 IN (1.92 FT) Step 6. Fit the riprap apron to the site by making it level for the minimum length. La. from Figure 8 06a or Figure 8.06b. Extend the apron farther downstream and along channel banks until stability is assured Keep the apron as straight as possible and align it with the flow of the receiving stream Make any necessary alignment bends near the pipe outlet so that the entrance into the receiving stream is straight. Some locations may require lining of the entire channel cross section to assure stability. It may be necessary to increase the size of riprap where protection of the channel side slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are excessive, a plunge pool should be considered, see page 8.06.8_ 30 Outlet W • Do + La 90 i pipe diameter (Do) `..r La — •I•1 80 if iidigiii 11 Ater lc 0.5Do : _1P :.. , La=13 40 • f ........ .......... . . _ ,!r _ ... 1 %, :. ., ' l r.. * ofrA . . .. „...- .....*---e'*-- t t i-t t t Aif AgilsAV- 1 o .>;;;;...—t.---"--- ,, . — - • - .,,1)- AiKiliFfirt ' ._ o ..-.. . _..�.- _. .1 ........... ♦.... A 0 9:41 000,Alp2 IV idedieVAP. s. .4002/r. . :)'-.: -: .7. T. 0111110gOillir hilt,' 10 is:i II:';i v = 15 : ��'r d50=0.45 -~v. Coro '- - _.- 'r 1 ID v=s _„,,..r +w"-- 1 0 3 5 20 50 100 200 500 1000 12.90 cfs Discharge(tt3/sec) Curves may not be extrapolated. Figure 8.06a Design of outlet protection protection from a round pipe flowing full,minimum tadwater condition(T.c 0.5 diameter) Re.-.12 93 8.06.3 DESIGN OF RIPRAP OUTLET PROTECTION User Input Data Calculated Value Reference Data Designed By: MAC Date: 5/15/2024 Checked By: JGE Company: CESI Project Name: Huntley Brothers Project No.: 210123.000 Site Location (City/Town) Midland, NC Culvert Id. FES-99 Step 1. Determne the tailwater depth from channel chaiac tei i.tics below the pipe outlet for the design capacity of the pipe. If the tailwater depth is less than half the outlet pipe diameter. it is classified zninimtun tailwater condition. If it is greater than half the pipe diameter. it is classified niaxuntun condition. Pipes that outlet onto wide fiat areas with no defined channel are assumed to have a nuinnium tailwater condition unless reliable flood stage elevations show otherwise Outlet pipe diameter, Do (in.) 24 Tailwater depth (in.) 0 Minimum/Maximum tailwater? Min TW (Fig. 8.06a) Discharge (cfs) 26.56 See 10 year Culvert Calculation results Step 2. Based on the tailwater conditions determined in step 1. enter Figure 8.06a or Figure 8.06b.and determine d,0 riprap size and minimum apron length (L). The d,, size is the median stone size in a well-graded riprap apron. Step 3. Determine apron width at the pipe outlet, the apron shape. and the apron width at the outlet end from the same figure used in Step 2. Minimum TW Maximum TW Figure 8.06a Figure 8.06b Riprap d50, (ft.) 0.5 Minimum apron length, La (ft.) 16 Apron width at pipe outlet (ft.) 6 6 Apron shape Trapezoidal Apron width at outlet end (ft.) 18 2 Step 4. Determine the maxinnun stone diameter dm.a■ I.5 x d5D Minimum TW Maximum TW Max Stone Diameter, dmax (ft.) 0.75 0 Step 5. Determine the apron thickness Apron thickness = 1.5 x d,,,,, Use class B riprap Minimum TW Maximum TW Apron Thickness(ft.) 1.125 0 RIP RAP CLASS MINIMUM MIDRANGE MAXIMUM A 2 IN (0.17 FT) 4 IN (0.33 FT) 6 IN (0.5 FT) B 5 IN (0.42 FT) 8 IN (0.67 FT) 12 IN (1 FT) 1 5 IN (0.42 FT) 10 IN (0.83 FT) 17 IN (1.42 FT) 2 9 IN (0.75 FT) 14 IN (1.17 FT) 23 IN (1.92 FT) Step 6. Fit the riprap apron to the site by making it level for the minimum length. La. from Figure 8 06a or Figure 8.06b. Extend the apron farther downstream and along channel banks until stability is assured Keep the apron as straight as possible and align it with the flow of the receiving stream Make any necessary alignment bends near the pipe outlet so that the entrance into the receiving stream is straight. Some locations may require lining of the entire channel cross section to assure stability. It may be necessary to increase the size of riprap where protection of the channel side slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are excessive, a plunge pool should be considered, see page 8.06.8_ 30 Outlet W • Do + La 90 i pipe diameter (Do) I. r`� La —•1 f10 - if ialigiii lwater c 0.5D0 : ; / .r P60 4 .[likm N. �n��Jtn 50 I .: i : 1 '•\ f I 40 Iti / b 4 4.. f t hilt11 . hi,(.-,.. �� 30 .Y s e. ' 111111111,.I...,'' : ,,N5Arilleff 15 ....1117.111.1:,: , "P' 4,4 AS;4•4r. 1 . . . I . t ArtmtrAiT --4' *:- - —I . .01"Z: -1.4 40' '4 ,,, ,.;7,.'il.4 3 :4 I I 1 1'llari7F 194 1: r ri 4 b li:..1 1-.4 2 C::LN 41 2:- ' .1- •Ai A .tl :_ nr n v .2 . .. _ v = to /3��i.�/ _ v _ 5 I 0 3 5 10 20 50 100 200 500 1000 Discharge(tt3/sec) 26.56 cfs 1 Curves may not be extrapolated. Figure 8.06a Design of outlet protection protection from a round pipe flowing full,minimum tadwater condition(T,•c 0.5 diameter) Re.-.1293 8.06.3 TRAPEZOID RIPRAP APRON FES-100 FES-99 RIP RAP CLASS B B WIDTH AT PIPE OUTLET (FT.) 6.00 6.00 WIDTH AT APRON OUTLET (FT.) 15.00 18.00 LENGTH OF APRON (FT.) 13.00 16.00 MINIMUM DEPTH OF APRON (FT.) 1.01 1.13 Appendix Table 4: HSGs for North Carolina Soil Types * Urban areas runoff curve numbers fro SCS method (SCS 1986) Cover Description Curve Number by HSG A B J C D Fully developed urban areas Open Space (lawns, parks,golf courses, etc.) Poor Condition (<50%Grass Cover) 68 79 86 89 Fair Condition (50%to 75%Grass Cover) 49 69 79 84 Good Condition (>75%Grass Cover) 39 61 74 80 Impervious areas: Paved parking lots, roofs, driveways, etc.) 98 98 98 98 Streets and roads: Paved; curbs and storm sewers 98 98 98 I 98 _ Paved; open ditches 83 89 98 98 Gravel 76 85 89 91 Dirt 72 82 85 88 Developing Urban Areas _ Newly graded areas 77 86 91 94 Pasture (<50%ground cover or heavily grazed) 68 79 86 89 _ Pasture (50%to 75%ground cover or not heavily grazed) 49 69 79 84 Pasture (>75%ground cover or lightly) 39 61 74 80 Meadow-continuous grass, protected from grazing and generally mowed for hay 30 58 71 78 Brush (<50%ground cover) 48 67 77 83 Brush (50%to 75% ground cover) 35 56 70 77 Brush (>75%ground cover) 30 48 65 73 Woods (forest liter, small trees, and brush destroyed by heavy 45 66 77 83 grazing or regular burning Woods (Woods are grazed but not burned, and some forrest 36 60 73 79 litter covers the soil) Woods (Woods are protected from grazing, and litter and brush 30 55 70 77 adequately cover the soil) *Table taken from NCDECI Sormwater Design Manual Part B: Calculations Guidance, revised 3/5/2017