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Home My WebLink AboutSW6230803_Stormwater Report_20230816 Stormwater Narrative & Calculations Dove Subdivision - North Spence Mill Road Fuquay-Varina, 27526 Harnett County, North Carolina July 6, 2023 Prepared for: mattamyHomEs Mattamy Homes, LLC 11000 Regency Parkway Suite 110 Cary, NC 27518 Prepared By: 4,fr* MCKEM&CREED 1730 Varsity Drive, Suite 500 Raleigh, North Carolina 27606 okiiiiirrr,0 Phone: (919) 233.8091 �.\` \\ CARD��''%, Fax: (919) 233.8031 ;��O;�DEESS/0 l�!�9'�; 9 :---! �•� SEAL 044644 M&C Project No. 04739-0014 ,�,.FN ��:<�� PROJECT DESCRIPTION This project involves the construction of a 20 single family lots in Harnett County, North Carolina with associated roadway, utility and storm drainage infrastructure. There will be two public roads installed. One road will connect to Spence Mill Road (Mourning Dove Lane) and will stub to the main subdivision road (Hope Passage Court). Both roads have a 50' right-of-way with roadside drainage ditches. The proposed post development impervious area is approximately 3.07 acres. The built-upon area is 8.57% of the total acreage. SITE DESCRIPTION The existing site is approximately 35.82 acres and is vacant. The site was previously used for agriculture and will be designed in two separate construction documents for the north side and the south side, divided by Spence Mill Road. The site lies within the Cape Fear River basin and a high quality watershed. This site will be developed as a low density subdivision and will utilize vegetated conveyance measures with less than 12% impervious in accordance with the high quality watershed regulations. This site contains wetlands and two existing ponds, which will remain undisturbed. The project site is located in Other Areas Zone "X", areas determined to be outside of the 500-year flood area per FEMA FIRM Panel 3720065400J with an effective date of 10/3/2006. The topography of the site suggests that the majority of the site drains to the northern property line. There is an existing high point along Spence Mill Road to the southwest and a saddle to the northeast. STORMWATER CONTROL STRUCTURES In accordance with regulations for a project located within a high quality watershed, this project will not require a stormwater control measure as it maintains less than 12% impervious and will utilize vegetated conveyance methods. Stormwater will be routed via vegetated road side swales and RCP culverts to two (2) discharge swales. STORMWATER CALCULATIONS To properly size and design the culverts installed with this project, Hydraflow Express in AutoCAD Civil 3D was utilized. The stormwater flow in each pipe that was modeled was determined by the rational method. To determine the intensity, the National Oceanic and Atmospheric Administration (NOAA) precipitation data for the project location was obtained. A copy of the precipitation data table is included in this report. The 10 year, 5-minute storm event was input to the rational method equation to calculate the amount of stormwater entering each pipe. The ultimate drainage area for each culvert (Pipe 1 and Pipe 2) was delineated; along with the composite c-value taking into account the final impervious acreage. Upon determining and entering these variables to the rational equation - the 10-year stormwater flow to each pipe was obtained. To model the stormwater flow in each culvert Hydraflow Express requires a minimum and maximum amount of stormwater entering the pipe. This range is provided in the calculations report for each culvert and is based on the 10-year flow in each pipe. Pipe 1, at the intersection of Mourning Dove Lane and Hope Passage Court, was sized to be an 18" RCP culvert. Pipe 2, located along Hope Passage Court, was sized to be a 24" RCP culvert. The stormwater conveyed by the culverts and roadside ditches will be discharged utilizing stormwater swales. The rational method was used to determine the ultimate stormwater flow in each swale based on the 10-year storm event. A calculation taking the total flow, length, slope, and depth of water within the swale into account was used to determine the liner material of each swale. The values used in the calculation is included in this report. Swale 1 , the discharge point for Pipe 2 located along Hope Passage Court, was determined to require a liner material of straw with net. Swale 2, located at the northwestern cul-de-sac along Hope Passage Court, was also determined to require a liner material of straw with net. STORMWATER SUPPORTING CALCULATIONS/DOCUMENTS • PIPE 1 DESIGN CALCULATIONS • PIPE 2 DESIGN CALCULATIONS • NOAA PRECIPITATION DATA • SWALE CALCULATIONS Culvert Report Hydraflow Express Extension for Autodesk®Civil 3D®by Autodesk, Inc. Thursday,Jul 6 2023 Pipe 1 - Mourning Dove Lane and Hope Passage Court Intersection Invert Elev Dn (ft) = 351.64 Calculations Pipe Length (ft) = 70.53 Qmin (cfs) = 6.00 Slope (%) = 1.42 Qmax (cfs) = 8.00 Invert Elev Up (ft) = 352.64 Tailwater Elev (ft) = Normal Rise (in) = 18.0 Shape = Circular Highlighted Span (in) = 18.0 Qtotal (cfs) = 6.00 No. Barrels = 1 Qpipe (cfs) = 6.00 n-Value = 0.013 Qovertop (cfs) = 0.00 Culvert Type = Circular Concrete Veloc Dn (ft/s) = 6.93 Culvert Entrance = Groove end projecting (C) Veloc Up (ft/s) = 5.12 Coeff. K,M,c,Y,k = 0.0045, 2, 0.0317, 0.69, 0.2 HGL Dn (ft) = 352.38 HGL Up (ft) = 353.59 Embankment Hw Elev (ft) = 354.03 Top Elevation (ft) = 356.61 Hw/D (ft) = 0.93 Top Width (ft) = 22.34 Flow Regime = Inlet Control Crest Width (ft) = 0.00 Elev(0) Pipe 1-Mourning Dove Lane and Hope Passage Court Intersection Hw Depth(a) 357.00 I I 4.36 356.OD 3.36 jdiiii 355.00 �- � 2.36 353.00 - - 0.36 - r Ilr 352.33 -~ -0.64 351.D0 -1.64 350.00 1 -2.64 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Circular Culvert HGL Embank Reach(a) Culvert Report Hydraflow Express Extension for Autodesk®Civil 3D®by Autodesk, Inc. Thursday,Jul 6 2023 Pipe 2 - Hope Passage Court Invert Elev Dn (ft) = 345.95 Calculations Pipe Length (ft) = 57.98 Qmin (cfs) = 15.50 Slope (%) = 0.91 Qmax (cfs) = 18.50 Invert Elev Up (ft) = 346.48 Tailwater Elev (ft) = Normal Rise (in) = 24.0 Shape = Circular Highlighted Span (in) = 24.0 Qtotal (cfs) = 15.50 No. Barrels = 1 Qpipe (cfs) = 15.50 n-Value = 0.013 Qovertop (cfs) = 0.00 Culvert Type = Circular Concrete Veloc Dn (ft/s) = 7.43 Culvert Entrance = Groove end projecting (C) Veloc Up (ft/s) = 6.51 Coeff. K,M,c,Y,k = 0.0045, 2, 0.0317, 0.69, 0.2 HGL Dn (ft) = 347.21 HGL Up (ft) = 347.90 Embankment Hw Elev (ft) = 348.66 Top Elevation (ft) = 350.04 Hw/D (ft) = 1.09 Top Width (ft) = 20.00 Flow Regime = Inlet Control Crest Width (ft) = 0.00 Elev tej Culvert B-Crossing Low Point Hw Depth(tt) 351.00 4.52 350.00 - 3.52 349.00 .11. „.. ,. .,jil __._ _ __ 2.52 348.00 1.52 347.00 0.52 346.00- -0.48 345.D0 -1.48 344.00 -2.48 0 5 10 15 20 25 30 35 40 45 50 55 50 80 Circular Culvert HGL Embank Reach I 7/6/23,6:01 PM Precipitation Frequency Data Server NOAA Atlas 14,Volume 2,Version 3 .,eo % Location name: Fuquay Varina,North Carolina, r,,,,-, „ .I xp USA* none IL3Latitude:35.5272°,Longitude: -78.8224° I.Foss' Elevation:360 ft** V 'source:ESRI ,(.91 **source:USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M.Bonnin,D.Martin,B.Lin,T.Parzybok,M.Yekta,and D.Riley NOAA,National Weather Service,Silver Spring,Maryland PF tabular I PF graphical I Maps & aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hour)1 Average recurrence interval(years) Duration 1 2 5 10 25 50 100 200 500 1000 5-min 5.06 5.93 6.84 7.60 8.42 9.05 9.61 10.1 10.7 11.2 (4.62-5.56) (5.42-6.50) (6.25-7.50) (6.92-8.33) (7.64-9.23) (8.18-9.89)_ (8.65-10.5) (9.06-11.1) (9.50-11.7) 1 (9.86-12.3) 10-min 4.04 4.74 5.48 6.07 6.71 7.20 7.64 8.02 8.48 8.84 (3.69-4.43) (4.33-5.21) (5.01-6.01) (5.54-6.66) (6.10-7.35) (6.52-7.87)_ (6.87-8.35) (7.18-8.78) (7.52-9.28) (7.77-9.68) 15-min 3.37 3.98 4.62 5.12 5.67 6.08 6.44 6.75 7.12 7.40 (3.08-3.70) (3.63-4.36) (4.22-5.07) (4.67-5.61) (5.15-6.21) (5.50-6.65) (5.79-7.03) (6.04-7.38)_ (6.31-7.78) (6.50-8.10) 30-min 2.31 2.74 3.28 3.71 4.20 4.58 4.93 5.25 5.66 5.99 (2.11-2.53) (2.51-3.01) (3.00-3.60) (3.38-4.07) (3.81-4.60) (4.14-5.01) (4.43-5.39) (4.70-5.75) (5.02-6.19) (5.26-6.56) 60-min 1.44 1.72 2.10 2.42 2.80 3.10 3.39 3.68 4.06 4.37 (1.32-1.58) (1.57-1.89) (1.92-2.31) (2.20-2.65) (2.54-3.06) (2.81-3.39) (3.05-3.71) (3.30-4.03) (3.60-4.44) (3.84-4.79) 2-hr 0.846 1.02 1.26 1.46 1.72 1.94 2.15 2.36 2.65 2.90 (0.767-0.938) (0.925-1.13) (1.14-1.40) (1.32-1.62) (1.55-1.90) (1.73-2.14) (1.91-2.37) (2.09-2.61) (2.32-2.93)_ (2.51-3.20) 3-hr 0.597 0.718 0.893 1.04 1.24 1.41 1.58 1.76 2.01 2.22 (0.542-0.663) (0.654-0.797) (0.810-0.990) (0.946-1.16) (1.12-1.37) (1.26-1.56)_ (1.40-1.75) (1.55-1.94) (1.75-2.22) (1.91-2.46) 6-hr 0.357 0.430 0.535 0.626 0.749 0.853 0.960 1.07 1.23 1.37 (0.326-0.394) (0.392-0.474) (0.487-0.589) (0.569-0.690) (0.675-0.823) (0.765-0.936) (0.853-1.05) (0.944-1.18) (1.07-1.35) (1.17-1.50) 12-hr 0.209 0.251 0.314 0.370 0.446 I 0.511 0.579 0.652 0.755 0.845 (0.190-0.231) (0.229-0.278) (0.286-0.348) (0.335-0.409) (0.400-0.490) (0.456-0.561) (0.511-0.634) (0.569-0.714) (0.648-0.827) (0.715-0.925) 24-hr 0.123 0.148 0.188 0.219 0.261 0.296 0.331 0.368 0.419 0.459 (0.113-0.133) (0.137-0.161) (0.173-0.203) (0.202-0.236) (0.240-0.283) (0.271-0.320) (0.303-0.358) (0.335-0.398)1 (0.379-0.453) (0.414-0.498) 2-day 0.071 0.086 0.107 0.125 0.148 0.167 0.187 0.207 0.235 0.257 (0.066-0.077) (0.079-0.092) (0.099-0.116) (0.115-0.135) (0.136-0.160) (0.153-0.181) (0.171-0.202) (0.188-0.224) (0.213-0.254) (0.232-0.279) 3-day 0.050 0.060 0.075 0.087 0.103 0.116 0.130 0.144 0.163 0.178 (0.046-0.054) (0.056-0.065) (0.070-0.081) (0.080-0.094) (0.095-0.111) (0.107-0.125) (0.119-0.140) (0.131-0.155) (0.148-0.176) (0.161-0.192) 4-day 0.039 0.047 0.059 0.068 0.081 0.091 0.101 0.112 0.126 0.138 (0.037-0.042) (0.044-0.051) (0.055-0.063) (0.063-0.073) (0.075-0.087) (0.084-0.097) (0.093-0.109) (0.102-0.120) (0.115-0.136) (0.125-0.149) 7-day 0.026 0.031 0.038 0.044 0.051 I 0.058 0.064 0.070 I 0.079 0.086 (0.024-0.028) (0.029-0.033) (0.035-0.041) (0.041-0.047) (0.048-0.055) (0.053-0.062) (0.059-0.069)1(0.065-0.076) (0.072-0.085) (0.079-0.093) 10-day 0.021 0.025 0.030 0.034 0.039 0.044 0.048 0.053 0.059 0.063 (0.019-0.022) (0.023-0.026) (0.028-0.032) (0.032-0.036)(0.037-0.042)1(0.041-0.047) (0.045-0.051) (0.049-0.056)1 (0.054-0.063) (0.058-0.068) 20-day 0.014 0.016 0.019 0.022 0.025 0.028 0.030 0.033 0.037 0.039 (0.013-0.015) (0.015-0.017) (0.018-0.021) (0.020-0.023) (0.023-0.027) (0.026-0.030) (0.028-0.032) (0.030-0.035) (0.034-0.039) (0.036-0.042) 30-day 0.011 0.013 0.016 0.017 0.020 I 0.022 0.023 0.025 1 0.028 0.029 (0.011-0.012) (0.012-0.014) (0.015-0.017) (0.016-0.019) (0.018-0.021)1(0.020-0.023) (0.022-0.025) (0.023-0.027) (0.025-0.030) (0.027-0.032) 45-day 0.009 0.011 0.013 0.014 0.016 0.017 0.019 0.020 0.022 0.023 (0.009-0.010) (0.011-0.012) (0.012-0.014) (0.013-0.015) (0.015-0.017) (0.016-0.018) (0.017-0.020) (0.019-0.021) (0.020-0.023) (0.021-0.024) 60-day 0.008 0.010 0.011 0.013 0.014 0.015 0.016 0.017 0.018 0.019 (0.008-0.009) (0.009-0.011) (0.011-0.012) (0.012-0.013) (0.013-0.015) (0.014-0.016) (0.015-0.017) (0.016-0.018) (0.017-0.019) (0.018-0.021) 1 Precipitation frequency(PF)estimates in this table are based on frequency analysis of partial duration series(PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90%confidence interval.The probability that precipitation frequency estimates(for a given duration and average recurrence interval)will be greater than the upper bound(or less than the lower bound)is 5%.Estimates at upper bounds are not checked against probable maximum precipitation(PMP)estimates and may be higher than currently valid PMP values. Please refer to NOAAAtlas 14 document for more information. Back to Top PF graphical https://hdsc.nws.noaa.gov/pfds/pfds_printpage.html?lat=35.5272&Ion=-78.8224&data=intensity&units=english&series=pds 1/4 7/6/23,6:01 PM Precipitation Frequency Data Server PDS-based intensity-duration-frequency (IDF) curves Latitude: 35.5272°, Longitude: -78.8224° 101 Average recurrence interval (years) -c .Z' 10° - \\7\ — \ 5 c c \\ — 10 — zs co — 50 y ` ro 10-1 - \ --.__ — 100 .a — 200 V ,_ �\ — 500 ` — 1000 10-2 - r I I I I I I I I I I I I 1 I I I E E E E E N OS u5 N 4 v vv 7 77 v 77 i N n 4 N .�-� m $ Duration Ni - N m v V) 101 _ - - L C Duration .Z' 10° • c — 5-min — 2-day II — 10-min — 3-day c 15-nin — 4-day 0 10-1 — 30-min — 7-day a — 60-min — 10-day i — 2fir — 20-day ` — 3-hr — 30-day — 6fir — 45-day 10-2 — 12-hr — 60-day I I I I I I I — 24fir 1 2 5 10 25 50 100 200 500 1000 Average recurrence interval (years) NOAA Atlas 14,Volume 2,Version 3 Created(GMT):Thu Jul 6 22:01:06 2023 Back to Top Maps & aerials Small scale terrain https://hdsc.nws.noaa.gov/pfds/pfds_printpage.html?lat=35.5272&Ion=-78.8224&data=intensity&units=english&series=pds 2/4 7/6/23,6:01 PM Precipitation Frequency Data Server Ar. 'i 03 --_ .-. . - - -_ , .•'' ipt c _ , * a x „)..: , , ,, a t 3km ltir 21mi Lar a scale terrain n;ton-S al em 0 • • Durham Rock Mown Greens b*ro Raleigh • RTH C AROL INA —!— 'Green vill 'Charlotte Fayetteville• �' Jac ille 100km ic_A 60mi Wilmingon (v;/ „ • Ba Large scale map ,,.....\a instonS lem Greensboro o Durham Rocky Mount 0 Raleigh North ' Greenville Carolina UM arlotte F etteville Jac le 0 100km 60mi Wilmington Large scale aerial https://hdsc.nws.noaa.gov/pfds/pfds_printpage.html?lat=35.5272&Ion=-78.8224&data=intensity&units=english&series=pds 3/4 7/6/23,6:01 PM Precipitation Frequency Data Server Winston-Salem Greensboro Durham. Rocky Mount • Raleigh • Greenville North • Carolina Charlotte Fayetteville • JacM le 100km 60mi k 'thlmiriton Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service National Water Center 1325 East West Highway Silver Spring,MD 20910 Questions?:HDSC.Questions@noaa.gov Disclaimer https://hdsc.nws.noaa.gov/pfds/pfds_printpage.html?lat=35.5272&Ion=-78.8224&data=intensity&units=english&series=pds 4/4 YARD SWALES Swale# Total Total Begin End Tc Slope C Intensity Qio Depth Shear Liner Area (ac) Length Elevation Elevation Elevation Dove North SWALE 1 5.80 220.7 346.0 343.0 2.9 2.62 0.013 0.6 7.69 26.76 1.20 1.00 Straw w/Net SWALE 2 0.79 162.9 352.2 348.0 4.1 1.62 0.025 0.6 7.69 3.63 0.40 0.64 Straw w/Net