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Home My WebLink AboutSW3210403_Design Calculations_2021082444 64, 44 ;;jM&CIREED �� . 1, 233 Randolph 74 Solar I MC # 06836-0005 CALCULATIONS FOR: Stormwater and Erosion Control Measures DA TE. 03105121 REV. 06128121 `��1►iC oll/,�� SIE • 043862 8020 TOWER POINT DRIVE. CHARLOTTE, NORTH CAROLINA 28227 TEL 704.841.2688 FAX 704.841.2667 www.mckimcreed.com • • • • PROJECT NO.: 06836-0005 BY: cac �ii, M &CR DATE: 3/5/2021 T.M.: PMN 4� f REVISED: 6/28/2021 P.M.: PMN PROJECT SUMMARY INTRODUCTION: PROJECT SUMMARY The project is a proposed 2 MW solar farm to be constructed on approximately 17 acres of a +/- 35 acre parcel located north of Randolph Road and Southern Drive in Shelby, Cleveland County, NC. The proposed area of disturbance consists of (+/-) 17 acres of undeveloped wooded area and a couple dirt roads. The surrounding areas consist of wooded land, a solar farm, and commercial development. In addition to the installation of solar equipment, a gravel access road will be constructed with an entrance located off of Southern Drive to accommodate construction and maintenance operations. The access road and cable run to the point of interconnect will be located inside an access and utility easement on Walmart property. The proposed grades for the site will be very similar to the existing grades. There are streams located on the east and west side of the property, as well as some wetlands. There will be 1 stream impact for the access road crossing that is currently being permitted through the USA CE. No other jurisdictional features will be impacted. There is also a environmentally sensitive area near the access road that was avoided. The project is located in the Broad River basin. We were not able to locate any buffer requirements for the streams, however we did provide a conservative 30' buffer for protection. STORMWATER TREATMENT SUMMARY As the site is a solar farm, the site is considered low density and no constructed permanent stormwater measures are required. The site will comply with the design elements specified in Parts E-1 and E-6 of the Stormwater Design Manual. Although minimal grading will occur on the site, the entire project area is considered disturbed as a result of solar panel installation operations and equipment mobility. Due to the lack of site grading, the proposed drainage patterns will match the existing conditions. Most of the runoff will be directed to 2 sediment basins located on each side of the site through temporary drainage swa/es. The sediment basins will remain in place until final permanent stabilization. At that time, the basins with be removed and the area will be returned to pre -construction conditions. All pipe discharge points will have rip -rap aprons. Erosion Control for the access road and stream crossing will be accomplished with silt fence and silt fence outlet devices. The stream crossing will utilize super silt fence. • Randolph233 Solar �Mcla4 PROJECT NO.: 06836-0006 BY: cac DATE: 3/5/2021 T.M.: PMN REVISED: 8/24/2021 P.M.: PMN IMPERVIOUS CALCULATIONS SITE SF AC Property: 1026709 23.57 Easement Area: 131116 3.01 Total Site Area: 1157825 26.58 Impervious Area Access Road= 58276 W Transformer Pad= 120 ft2 Array Post Foundations (-670 posts at 6" x 6")= 167.5 ft2 Array Area with slopes >8% 120856 W Total Impervious= 179419.5 ft2 Total Pervious= 978406 ft2 Percent Impervious= 15.50% 233 Randolph 7• PROJECT NO.: 06836-0005 BY: CAC �MCICW&CREED DATE: 03105121 T.M.: PMN REVISED: NIA P.M.: PMN SKIMMER SEDIMENT BASIN CALCULATIONS SKIMMER SEDIMENT BASIN #1 DRAINAGE AREAS/REQUIRED STORAGE I DESIGN CRITERIA Total drainage area TDA 4.30 ac Pro osed sediment depth 2 ft Disturbed area DA 4.30 ac Bottom elevation of basin 827 ft (msl) Required sediment stora a 1800xDA 7740 cf Flow depth over emer. spillway 0.5 ft BASIN CONFIGURATION Bottom elevation 827 ft (msl) Sediment Storage elevation 829 ft (msl) Normal Pool 830 ft msl Spillway crest 830.5 ft (msl) Fop of Berm 832 ft msl ESTIMATED BASIN SIZE RECTANGULAR Length(ft) Width(ft) Bottom 84 40 To 104 60 BASIN EFFICIENCY Sediment storage provided: 10699 OKAY Sediment storage required: 7740 ft3 Surface area/Flow comparison: 6920 OKAY PLANNED BASIN SIZE REFER TO EROSION CONTROL PLAN Elev. Area (ft) Cumulative Volume CF 827 4605 0 827.5 4965 2393 828 5342 4969 828.5 5728 7737 829 6119 10699 829.5 6516 13857 830 6920 17216 830.5 7329 20779 831 7745 24547 831.5 8167 28525 832 8595 32716 SPILLWAY DESIGN DESIGN FLOW Q=CIA SPILLWAY DESIGN Bare soil coefficient'C' = 0.6 Spillway design: (L=Q/(C*h^1.5)); C= 2.8 Area 'A' = 4.30 ac h= 0.50 10 yr. storm rainfall intensity, '1' = 7.44 in/hr Spillway length @ flow depth 20 ft Computed flow from site, 'Q' = 19.20 cfs SURFACE AREA/FLOW COMPARISON Formula: A=325*Q 1 7.44 10 year storm A: Minimum Surface Area (acres) measured at the crest of the principal spillway Q desi n : 19 CFS A(Required): 6238 sf of surface area at norm pool elev Q: Peak inflow rate of 10 year storm in cfs A(Provided) 6920 OKAY uetermining the sKimmer Size sKimmer sizing criteria (tors aay araw aown) NCDENR optimal dewatering time is 3 days Skimmer Size 3 Max. Flow Capacity Orifice Factor Volume to be dewatered over 3 days: 17216.25 ft (in.) Skimmer Size: 2.5 in 1.5 5184 2880 2 9849 3369 Orifice Diameter 2.5 18702 3810 Max Drawdown Volume for Skimmer: 18702 ft3 3 29322 4146 Orifice Factor: 3810 4 60327 4803 Formulas: 5 98496 4926 Area = Volume/Orifice Factor 4.52 in 6 155520 5442 r = Area/7r 1.20 in 8 293934 5961 Orifice Diameter= 2.4 in 233 Randolph 7• PROJECT NO.: 06836-0005 BY: CAC �MCICW&CREED DATE: 03105121 T.M.: PMN REVISED: NIA P.M.: PMN SKIMMER SEDIMENT BASIN CALCULATIONS SKIMMER SEDIMENT BASIN #2 DRAINAGE AREAS/REQUIRED STORAGE I DESIGN CRITERIA Total drainage area TDA 5.95 ac Pro osed sediment depth 2 ft Disturbed area DA 5.95 ac Bottom elevation of basin 814 ft msl Required sediment stora a 1800xDA 10710 cf Flow depth over emer. spillway 0.5 ft BASIN CONFIGURATION Bottom elevation 814 ft (msl) Sediment Storage elevation 816 ft (msl) Normal Pool 817 ft msl Spillway crest 817.5 ft (msl) Fop of Berm 819 ft msl ESTIMATED BASIN SIZE RECTANGULAR Length(ft) Width(ft) Bottom 100 48 To 120 68 BASIN EFFICIENCY Sediment storage provided: 14072 OKAY Sediment storage required: 10710 ft3 Surface area/Flow comparison: 8638 OKAY PLANNED BASIN SIZE REFER TO EROSION CONTROL PLAN Elev. Area (ft) Cumulative Volume CF 814 6272 0 814.5 6644 3229 815 7030 6648 815.5 7423 10261 816 7821 14072 816.5 8226 18084 817 8638 22300 817.5 9055 26723 818 9479 31356 818.5 9909 36203 819 10346 41267 SPILLWAY DESIGN DESIGN FLOW Q=CIA SPILLWAY DESIGN Bare soil coefficient'C' = 0.6 Spillway design: (L=Q/(C*h^1.5)); C= 2.8 Area 'A' = 5.95 ac h= 0.50 10 yr. storm rainfall intensity, '1' = 7.44 in/hr Spillway length @ flow depth 27 ft Computed flow from site, 'Q' = 26.56 cfs SURFACE AREA/FLOW COMPARISON Formula: A=325*Q 1 7.44 10 year storm A: Minimum Surface Area (acres) measured at the crest of the principal spillway Q desi n : 27 CFS A Re uired : 8632 sf of surface area at norm pool elev Q: Peak inflow rate of 10 year storm in cfs A Provided 8638 OKAY uetermining the 5Kimmer Size 5Kimmer Sizing criteria (tors aay draw down) NCDENR optimal dewatering time is 3 days Skimmer Size 3 Max. Flow Capacity Orifice Factor Volume to be dewatered over 3 days: 22299.5 ft (in.) Skimmer Size: 3 in 1.5 5184 2880 2 9849 3369 Orifice Diameter 2.5 18702 3810 Max Drawdown Volume for Skimmer: 29322 ft3 3 29322 4146 Orifice Factor: 4146 4 60327 4803 Formulas: 5 98496 4926 Area = Volume/Orifice Factor 5.38 in 6 155520 5442 r = Area/7r 1.31 in 8 293934 5961 Orifice Diameter= 2.6 in 233 Randolph 74 Solar I i111:1:1i ipp Ti• �`o-i �'I �+2I�1� �I�Ir�JI�� del III •.. ..r•.,�d�f�L�,l.. 0R S IR . ,• M :d "q MMI! 0ACIUM&C?EED PROJECT NO.: 06836-0005 BY: CAC DATE: 03/05/21 T.M.: PMN REVISED: NIA P.M.: PMN 10 YEAR STORM PIPE CALCULATIONS DRAINAGEMIN . SLOPE DIA. PIPE MANNING COVER AREA RUNOFF I FLOW CAPACITY STARTPIPE O. FT FT/FT IN TYPE n FT ACRES C IN/HR CFS CFS FPS] ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- ------ -------- 4-"*'�NTg0 M&CREED TRAPEZOIDAL CHANNEL COMPUTATION SHEET PROJECT: 233 Randolph 74 Solar I LOCATION: Shelby, NC Z f6 C N p U j w .-. t •� co .... "" w J t CL w -a E O 00 t F C in wX 'a fn Z R da .�+ co R U - li O LL •w LL t �w w0 0 LL t. C "' �U w w 0� p .�-� �,� Q N ^ i� y cn U O N �, � n0 E Z J w w C co t U R Q Q L Of j j j T TD #1A 0.38 0.60 7.44 341.0 2.00 0.00 8.00 2 0.025 123.29 1.70 0.40 5.28 0.078 1.95 18 Synthetic Mat ✓ TD #1 B 2.82 0.60 7.44 438.0 2.00 0.00 1200. 3 0.033 52.17 12.59 1.17 3.05 0.010 0.73 3 Straw with Net ✓ TD#2 0.13 0.60 7.44 446.5 2.00 0.00 8.00 2 0.033 33.44 0.58 0.44 1.52 0.010 0.27 3 Straw with Net ✓ TD #3 2.18 0.60 7.44 662.0 2.00 2.00 10.00 2 0.025 199.23 9.73 0.45 7.41 0.069 1.95 31 Synthetic Mat ✓ TD #4A 0.52 0.60 7.44 336.0 2.00 1.00 9.00 2 0.036 120.79 2.32 0.32 4.36 0.085 1.72 20 Synthetic Mat ✓ TD #4B 2.42 0.60 7.44 2200. 2.00 1.00 9.00 2 0.025 130.71 10.80 0.67 6.96 0.048 1.99 8 Synthetic Mat ✓ TD #5A / PD #5A 0.54 0.35 7.44 260.00 1.50 0.00 9.00 3 0.033 54.17 1.41 0.38 3.22 0.050 1.19 9 Straw with Net ✓ TD #5B / PD #5B 1.18 0.35 7.44 292.00 1.50 0.00 9.00 3 0.078 31.92 3.07 0.62 2.63 0.097 3.77 19 Rip Rap D50 (12") ✓ PD#6A 1.32 0.35 7.44 308.00 2.00 0.00 1200. 3 0.033 52.17 3.44 0.72 2.20 0.010 0.45 3 Straw with Net ✓ TD #6B / PD #6B 2.57 0.35 7.44 193.00 2.00 0.00 1200. 3 0.078 81.70 6.69 0.78 3.64 0.137 6.69 18 Rip Rap D50 (12") x Wanning's values area based on channel lining and design flow depth as shown in NC DENR Table 8.05e. **Shear Stress is NA if design velocity is less than 2 fps and temporary seeding is used as a liner. Per NC DENR linings are not required if velocity is less than 2 fps. "'Assumed 18" check dam PIPIPWAKIYA Precipitation Frequency Data Server NOAA Atlas 14, Volume 2, Version 3 Location name: Shelby, North Carolina, USA* � 'in° Latitude: 35.312*, Longitude:-81.5914° . Elevation: 840.96 ft** *source: ESRI Maps w,�w ^ y� -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/hourp Duration Average recurrence interval (years) 1 2 5 10 25 50 1 100 100 200 500 1000 5-min 4.76 (4.34-5.23) 5.64 (5.16-6.18) 11 6.66 (6.06-7.30) 1 7.44 8.42 1 (7.61-9.22) 9.14 1 (8.22-10.0) 9.88 1 (8.84-10.8) 10.6 1 (9.42-11.6) 11.6 1 (10.2-12.7) 12.3 1 (10.7-13.6) 3.81 4.51 5.33 5.95 6.71 7.28 7.85 8.41 9.14 9.70 10-min (3.47-4.18) 1 (4.85-5.84) 11 (5.40-6.51) 11 (6.06-7.34) 1 (6.54-7.97) 1 (7.02-8.60) 1 (7.46-9.22) 1 (8.03-10.1) 1 (8.43-10.7) 3.17 3.78 4.50 5.02 5.67 6.15 6.62 7.08 7.67 8.11 15-min (2.89-3.48) (3.46-4.14) 11 (4.10-4.93) 11 (4.56-5.49) 11 (5.12-6.20) 1 (5.52-6.72) 1 (5.92-7.25) 1 (6.28-7.76) 1 (6.74-8.44) 1 (7.05-8.97) 2.18 2.61 3.19 3.64 4.20 4.63 5.07 5.51 6.10 6.57 30-min (1.98-2.39) 11 (2.39-2.86) 11 (2.91-3.50) (3.30-3.98) 11 (3.79-4.59) 1 (4.16-5.06) 1 (4.53-5.55) 1 (4.89-6.04) 1 (5.36-6.72) 1 (5.71-7.26) 1.36 1.64 2.05 2.37 2.80 3.14 3.49 3.86 4.38 4.79 60-min (1.24-1.49) 11 (1.50-1.80) (1.87-2.24) 1 (2.53-3.06) 1 (2.82-3.43) 1 (3.12-3.82) 1 (3.43-4.24) 1 (3.85-4.82) 1 (4.17-5.30) 0.792 F 0.960 1.21 1.40 1.68 1.90 2.14 2.40 2.76 3.07 2-hr (0.728-0.866) (0.882-1.05) 1 1 (1.28-1.53) 11 (1.53-1.83) 1 (1.72-2.07) 1 (1.92-2.34) 1 (2.13-2.62) 1 (2.43-3.04) 1 (2.67-3.38) 0.563 0.681 0.858 1.00 111 1.39 1.57 1.78 2.08 2.34 3-hr (0.515-0.621) (0.624-0.752) (0.784-0.945) (0.912-1.10) (1.09-1.33) 1 (1.24-1.53) 1 (1.40-1.73) 1 (1.57-1.96) 1 (1.81-2.30) 1 (2.01-2.60) 0.347 0.419 0.525 0.612 0.740 F 0.848 F 0.965 1.09 1.28 1.45 6-hr (0.320-0.381) (0.385-0.459) (0.481-0.574) (0.559-0.669) (0.671-0.808) (0.763-0.926) (0.861-1.06) (0.966-1.20) 1 (1.12-1.41) 1 (1.24-1.59) 0.210 0.254 0.318 0.371 0.448 0.512 0.582 0.659 0.772 F 0.869 12-hr (0.193-0.229) (0.233-0.278) (0.292-0.348) (0.339-0.405) (0.407-0.488) (0.462-0.558) (0.521-0.633) (0.582-0.717) (0.673-0.842) (0.747-0.951) 0.127 0.154 0.194 0.225 0.269 0.305 0.342 0.380 0.435 0.479 24-hr (0.118-0.137) (0.143-0.166) (0.180-0.208) (0.209-0.242) (0.249-0.289) (0.280-0.327) (0.313-0.366) (0.347-0.408) (0.394-0.466) (0.431-0.514) 0.076 0.091 0.114 0.132 0.157 0.177 0.198 0.220 0.251 0.276 2-day (0.070-0.081) (0.084-0.098) (0.106-0.123) (0.122-0.142) (0.145-0.169) (0.163-0.191) (0.182-0.213) (0.201-0.237) (0.227-0.270) (0.248-0.297) 0.054 0.064 0.080 0.092 0.109 0.123 0.137 0.151 0.172 0.188 3-day (0.050-0.057) (0.060-0.069) (0.074-0.086) (0.086-0.099) (0.101-0.117) (0.113-0.132) (0.126-0.147) (0.139-0.162) (0.156-0.184) (0.170-0.201) 0.043 0.051 0.063 0.073 0.085 0.096 0.106 0.117 0.132 0.143 4-day (0.040-0.046) (0.048-0.055) (0.059-0.067) (0.068-0.078) (0.079-0.091) (0.089-0.102) (0.098-0.113) (0.108-0.125) (0.121-0.141) (0.131-0.154) 0.028 0.034 0.041 0.047 0.055 0.061 0.068 0.074 0.084 0.091 7-day (0.026-0.030) (0.032-0.036) (0.039-0.044) (0.044-0.050) (0.051-0.058) (0.057-0.065) (0.063-0.072) (0.069-0.079) (0.077-0.089) (0.083-0.097) 0.022 0.027 0.032 0.036 0.042 0.046 0.051 0.056 0.062 0.067 10-day (0.021-0.024) (0.025-0.028) (0.030-0.034) (0.034-0.039) (0.040-0.045) (0.044-0.049) (0.048-0.054) (0.052-0.059) (0.057-0.066) (0.062-0.071) 0.015 0.018 0.021 0.023 0.027 0.029 0.032 0.035 0.038 0.041 20-day (0.014-0.016) (0.017-0.019) (0.020-0.022) (0.022-0.025) (0.025-0.028) (0.028-0.031) (0.030-0.034) (0.033-0.037) (0.036-0.041) (0.038-0.044) 0.012 0.014 0.017 0.019 0.021 0.023 0.025 0.026 0.029 0.031 30-day (0.012-0.013) (0.014-0.015) (0.016-0.018) (0.018-0.019) (0.020-0.022) (0.022-0.024) (0.023-0.026) (0.025-0.028) (0.027-0.030) (0.029-0.032) 0.010 0.012 0.014 0.015 0.017 0.018 0.019 0.021 0.022 0.023 45-day (0.010-0.011) (0.012-0.013) (0.013-0.014) (0.014-0.016) (0.016-0.017) (0.017-0.019) (0.018-0.020) (0.019-0.021) (0.021-0.023) (0.022-0.024) 0.009 0.011 0.012 0.013 0.015 0.016 0.017 0.018 0.019 0.020 60-day (0.009-0.010) (0.010-0.011) (0.012-0.013) (0.013-0.014) (0.014-0.015) (0.015-0.016) (0.016-0.017) (0.017-0.018) (0.018-0.020) (0.019-0.021) 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 NOAA Atlas 14 document for more information. Back to Top PF graphical https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?Iat=35.3120&Ion=-81.5914&data=intensity&units=english&series=pds 1 /4