SW3200601_08_SpeedwaySubstation_StormwaterMemo_20200720

kimley-horn.com 421 Fayetteville Street, Suite 600, Raleigh, NC 27601 919 677 2000

SPEEDWAY SUBSTATION
STORMWATER NARRATIVE
JUNE 2020
The Speedway Substation site consists of 10.0 acres—part of an overall tract of 74.47
acres—located in Cabarrus County. The site is located at 2410 Wallace Road, 1.5 miles west
of the Town of Midlands, North Carolina and its current zoning is countryside residential.
Existing conditions include cleared agricultural fields, an electric transmission line, and
moderate to steep slopes across the site.
A gravel access road with an asphalt apron, within the right-of-way, is proposed to
provide access to gravel substation and switchyard pads. Grading is proposed to ensure
positive drainage across the proposed substation pad and access road. Due to the grading
for the proposed access road, two RCP culverts are proposed to maintain existing drainage
patterns on site. Existing drainage patterns downstream are to remain. Impacts will be
permitted through the US Army Corps of Engineers as applicable.
The site’s proposed impervious area is 13.7%, which falls within the maximum 36%
impervious low-density development standard for this project location. Therefore, no
permanent stormwater measures are proposed.

Page 2
kimley-horn.com 333 Fayetteville Street, Suite 600, Raleigh, NC 27601 919 835 1494

TABLE OF CONTENTS

STORMWATER NARRATIVE
MEMORANDUM
APPENDICES
APPENDIX A – MAPS AND FIGURES
USGS Quadrangle Map
Soils Survey Map
Aerial Map
APPENDIX B –NOAA
Precipitation Frequency Depth
Precipitation Frequency Intensity
APPENDIX C – STORMWATER CALCULATIONS
Drainage Maps
Rip-Rap Dissipater Calculations
Culvert Calculations

APPENDIX A

PROJECT
LOCATION
Hydrologic Soil Group—Cabarrus County, North Carolina
(Speedway Substation)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/20/2020
Page 1 of 4389740038974503897500389755038976003897650389770038977503897800389740038974503897500389755038976003897650389770038977503897800542670542720542770542820542870542920542970
542670 542720 542770 542820 542870 542920 542970
35° 13' 20'' N 80° 31' 52'' W35° 13' 20'' N80° 31' 39'' W35° 13' 6'' N
80° 31' 52'' W35° 13' 6'' N
80° 31' 39'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 17N WGS84
0 100 200 400 600
Feet
0 30 60 120 180
Meters
Map Scale: 1:2,120 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Cabarrus County, North Carolina
Survey Area Data: Version 18, Sep 16, 2019
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 18, 2011—Nov
25, 2017
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Cabarrus County, North Carolina
(Speedway Substation)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/20/2020
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
GoC Goldston very channery
silt loam, 4 to 15
percent slopes
D 2.9 16.8%
MsA Misenheimer channery
silt loam, 0 to 4
percent slopes
C/D 14.4 83.2%
Totals for Area of Interest 17.3 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Hydrologic Soil Group—Cabarrus County, North Carolina Speedway Substation
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/20/2020
Page 3 of 4
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Cabarrus County, North Carolina Speedway Substation
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/20/2020
Page 4 of 4
PROJECT
LOCATION
APPENDIX B

APPENDIX C

TT
STORAGE SHED
SILO SINGLE STORY
WOOD FRAME
WALLACE ROA
D
©
POA DATA TABLES
LEGEND
DRAINAGE AREA TABLE
POA FLOW RATE TABLE
PRE-DEVELOPMENT DRAINAGE MAP
KHA PROJECT NO: 018950009
DATE: 06/12/2020
SPEEDWAY SOLAR
NORTH
TT
STORAGE SHED
SILO SINGLE STORY
WOOD FRAME
WALLACE ROA
D
©
POA DATA TABLES
LEGEND
DRAINAGE AREA TABLE
POA FLOW RATE TABLE
CONSTRUCTION DRAINAGE MAP
KHA PROJECT NO: 018950009
DATE: 06/12/2020
SPEEDWAY SOLAR
NORTH
TT
STORAGE SHED
SILO SINGLE STORY
WOOD FRAME
WALLACE ROA
D
©
POA DATA TABLES
LEGEND
DRAINAGE AREA TABLE
POA FLOW RATE TABLE
POST-DEVELOPMENT DRAINAGE MAP
KHA PROJECT NO: 018950009
DATE: 06/12/2020
SPEEDWAY SOLAR
NORTH
Project Information
Project Name:
KHA Project #:
Designed by:Date:5/26/2020
Revised by:Date:
Checked by:Date:5/26/2020
18" TYP. PIPE OUTLET
Pipe Diameter d=18 in
Number of Pipes #=1 total
Pipe Slope s=1.46 %
Manning's number n=0.013
Flow Q=12.73 cfs Assumes Full Flow
Velocity V=7.20 ft/s Velocity of flow entering rip rap apron
Dissipator Dimensions *Zone =1
Stone Filling Class =A
D0 =1.50 ft
Entry Width ( 3 X D0 ) =4.5 ft
Length ( 4 X D0 ) =6.0 ft
Width (La + D0) =7.5 ft
Min. Thickness =12 inches
Min. Stone Diameter=3 inches
4.5 7.5
* All units are in feet
** Dissipator pad designed for full flow of pipe
6.0
EROSION CONTROL CALCS (RIP-RAP CALCULATIONS -TYPICAL RCP)
Speedway Substation
SAS
DMS
18950009
A_Rip_Rap_Calcs_Spreadsheet_RCP.xls 5/26/2020 Page 1 of 2
PARCEL 2
IRA B. HOWELL JR.
PIN: 55432835280000
DB. 303 PG. 36
IRA B. HOWELL JR.
PIN: 55431997310000
DB: 5980 PG. 144
IRF 5
8 "
IRF 5
8 "
IRF 5
8 "
©CULVERT DRAINAGE EXHIBIT
KHA PROJECT NO: 018950009
DATE: 06/12/2020
SPEEDWAY SOLAR
NORTH
LEGEND
X Y Display Graph
Design Culvert Diameter 18 in Discharge X 5.349808 3.845669 5.349808 3.845669 5.349808 2.655375
Number of Pipes 1 6.612342 3.640731 5.349808 10.53485
Design Flow Rate 2.04 cfs X Y cfs n 9.441356 3.181517 6.612342 3.06414
Entrance Type 3 Flow Rate Low 6.612342 3.629155 2 3 9.984426 3.181517 6.612342 10.51227
Flow Rate High 6.612342 3.959894 3 4 10.50224 3.181517 9.441356 3.15111
9.441356 9.819714
X Y Δ cfs Δ x-y 9.984426 3.275581
Flow Rate X 6.612342 3.640731 1 0.330739 9.984426 10.23684
Headwater-Depth #N/A ft 10.50224 3.212204
Headwater #N/A ft m 10.50224 10.10626
Tailwater (full flow)1.50 ft Design Line -0.16232
Outlet Velocity*5.96 ft
X Y
*Calculated per Manning's equation; 1% max slope.Turn Line 9.441356 3.181517
X Y HW-D n Δ HW-D Δ x-y
ET 1 9.441356 3.181517 0.503324 0.05 0.457349
ET1 Low 9.441356 3.15111 0.5 1
ET1 High 9.441356 3.608459 0.55 2
X Y HW-D Δ HW-D Δ x-y
ET 2 9.984426 3.181517 #N/A #N/A #N/A
ET1 Low 9.984426 #N/A #N/A #N/A
ET1 High 9.984426 #N/A #N/A #N/A
X Y HW-D Δ HW-D Δ x-y
ET 3 10.50224 3.181517 #N/A #N/A #N/A
ET1 Low 10.50224 #N/A #N/A #N/A
ET1 High 10.50224 #N/A #N/A #N/A
Culvert 1
3 - groove end projecting
2 - groove end with headwall
1 - square edge with headwall
0.55 Total Drainage Area (Acres)User entry
5 Time of Concentration (Min)Calculated Value
0.50 Rational C
10 Design Storm (Year)Q10
7.40 Design Storm Intensity (in/hr)
2.04 Peak Flow (cfs) from 10 YEAR
25 Design Storm (Year)Q25
8.16 Design Storm Intensity (in/hr)
2.24 Peak Flow (cfs) from 25 YEAR
NOTES PRIOR TO USE:
1. UPDATE STORM INTENSITY DATA
Culvert 1
Sheet Flow 1:
Surface description* =Managed Grass * See TR-55 Table 3-1
Roughness, n =0.15
Length, L =100 ft
US Elevation =569.41 ft
DS Elevation =565.58 ft
Average slope, s =0.038 ft/ft
Two-year 24-hour rainfall, P2 =3.77 in
T t =0.116 hr
Shallow Concentrated Flow 1:
Surface =Unpaved ** See TR-55 Figure 3-1
Length, L =63.4864 ft
US Elevation =565.58 ft
DS Elevation =561.97 ftAverage slope, s =0.057 ft/ft Tt =L / 3600V
Velocity** =3.85 fps
T t = 0.0046 hr
Channel Flow 1:
Cross Sectional Flow Area, A =19 ft2 Velocity =
Wetted Perimeter, Pw =17.58 ft
Hydraulic Radius, r = A / Pw =1.08 ft Velocity =7.08 fps
US Elevation =561.97 ft
DS Elevation =549.51 ft
Channel slope, s =0.025 ft/ft
Roughness, n =0.035 Tt =L / 3600V
Flow Length, L =499.3559 ft T 2 = 0.0196 hr
Total Time Tc = Tt1 + Tt2 + Tt3 + …..+ Ttm Tc =0.1402 hr
=8.41 min
1.49 r0.667 s0.5
n
Time of Concentration Calculation (Tc)
Culvert 1
Tt =
0.007(nL)0.8
(P2)0.5 s0.4
Surface description* =Roadside Ditch
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Tuesday, May 26 2020
X Y Display Graph
Design Culvert Diameter 18 in Discharge X 5.349808 3.845669 5.349808 3.845669 5.349808 2.655375
Number of Pipes 1 6.612342 5.234448 5.349808 10.53485
Design Flow Rate 14.50 cfs X Y cfs n 9.441356 8.346348 6.612342 3.06414
Entrance Type 3 Flow Rate Low 6.612342 4.941519 10 11 9.984426 8.346348 6.612342 10.51227
Flow Rate High 6.612342 5.266707 15 12 10.50224 8.346348 9.441356 3.15111
9.441356 9.819714
X Y Δ cfs Δ x-y 9.984426 3.275581
Flow Rate X 6.612342 5.234448 5 0.325188 9.984426 10.23684
Headwater-Depth 2.09 ft 10.50224 3.212204
Headwater 3.13 ft m 10.50224 10.10626
Tailwater (full flow)1.50 ft Design Line 1.099994
Outlet Velocity*5.96 ft
X Y
*Calculated per Manning's equation; 1% max slope.Turn Line 9.441356 8.346348
X Y HW-D n Δ HW-D Δ x-y
ET 1 9.441356 8.346348 2.490209 0.2 0.224086
ET1 Low 9.441356 8.245274 2.4 23
ET1 High 9.441356 8.46936 2.6 24
X Y HW-D Δ HW-D Δ x-y
ET 2 9.984426 8.346348 2.022926 0.2 0.201297
ET1 Low 9.984426 8.323273 2 21
ET1 High 9.984426 8.524571 2.2 22
X Y HW-D Δ HW-D Δ x-y
ET 3 10.50224 8.346348 2.086389 0.2 0.188842
ET1 Low 10.50224 8.264778 2 21
ET1 High 10.50224 8.45362 2.2 22
Culvert 2
3 - groove end projecting
2 - groove end with headwall
1 - square edge with headwall
4.90 Total Drainage Area (Acres)User entry
10 Time of Concentration (Min)Calculated Value
0.50 Rational C
10 Design Storm (Year)Q10
5.92 Design Storm Intensity (in/hr)
14.50 Peak Flow (cfs) from 10 YEAR
25 Design Storm (Year)Q25
6.50 Design Storm Intensity (in/hr)
15.93 Peak Flow (cfs) from 25 YEAR
NOTES PRIOR TO USE:
1. UPDATE STORM INTENSITY DATA
Culvert 2
Sheet Flow 1:
Surface description* =Managed Grass * See TR-55 Table 3-1
Roughness, n =0.15
Length, L =100 ft
US Elevation =570.28 ft
DS Elevation =567.07 ft
Average slope, s =0.032 ft/ft
Two-year 24-hour rainfall, P2 =3.77 in
T t = 0.1245 hr
Shallow Concentrated Flow 1:
Surface =Unpaved ** See TR-55 Figure 3-1
Length, L =750.6506 ft
US Elevation =567.07 ft
DS Elevation =548.48 ftAverage slope, s =0.025 ft/ft Tt =L / 3600V
Velocity** =2.54 fps
T t = 0.0821 hr
Channel Flow 1:
Cross Sectional Flow Area, A =19 ft2 Velocity =
Wetted Perimeter, Pw =17.58 ft
Hydraulic Radius, r = A / Pw =1.08 ft Velocity =3105.90 fps
US Elevation =548.48 ft
DS Elevation =548.00 ft
Channel slope, s =4800.000 ft/ft
Roughness, n =0.035 Tt =L / 3600V
Flow Length, L =0.0001 ft T 2 =9E-12 hr
Total Time Tc = Tt1 + Tt2 + Tt3 + …..+ Ttm Tc =0.2066 hr
=12.40 min
1.49 r0.667 s0.5
n
Time of Concentration Calculation (Tc)
Culvert 2
Tt =
0.007(nL)0.8
(P2)0.5 s0.4
Surface description* =Roadside Ditch
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Tuesday, May 26 2020