Williamston Subdivision - Williamston Calcs_111817

Williamston Subdivision is a proposed 9 lot residential development located off SR 1627 (New
Salem Road) approximately 600 feet south of SR 2717 (Polk Mountain Road). The site is in the
Yadkin River Basin and drains to Brandon Branch. The site is in Union County Zoning District.

The development is proposed as "low density" with a maximum built upon area of 24%. The
street cross-sections are shoulder and ditch. This combined with natural swales leaving the site
shall provide the required conveyances.

The maximum built upon area per lot shall not exceed 9,000 sf for all 9 lots.

EROSION CONTROL
CALCULATIONS

Job: Williamston Subdivision Job No. Date Sheet
Subject: REVISED TEMPORARY SEDIMENT TRAPS By Chk By
Runoff Intensity
Coeff. Tc I(10)
TRAP C (min) (in/hr)
ST-1 0.60 5 7.6
COMPOSITE RUNOFF "C" BASED ON C(DIST)=0.60 & C(UN-DIST)=0.33
DISCHARGE DETERMINED USING RATIONAL METHOD (Q=CIA)
WEIR
REQ'D DESIGN PROV'D REQ'D PROV'D WEIR BOTTOM LNTH (FT)
1580 Q(10) 1596 2880 3192 526.0 523.5 28 X 57 X 2.5 4
SURFACE AREA REQUIRED (SQ FT)= Q*435 sf/ac
VOLUME REQUIRED (CU FT)= 3600 cubic feet (Area disturbed)
VOLUMES PROVIDED BASED ON 2:1 SIDE SLOPES OF TRAP
TRAP ELEV'S DIMENSIONS
ST-1
DISTURBED
0.80 0.80
(Ac)
10 YEARDRAINAGE
AREA PEAKAREA
(Ac)
11/18/2017
KEH
TRAP
3.63
Q(10) cfs
SEDIMENT VOLUME (CF)SURFACE AREA (SF)
@ TOP OF WEIR
DITCH & DIVERSION
CALCULATIONS

Job Name Williamston Subdivision Job No. Date 10/20/2017 Sheet
Subject DIVERSION CHANNEL SUMMARY SHEET By KEH Chk By
<4.5f/s <1.0'Design
Diversion Drainage Average Bottom Side Slope Velocity Flow Depth for Top Width
Channel Area (Ac) Slope (%) Width(ft) ft/ft ft/s Depth (ft) Liner (ft)T (ft)
RD-1(9.0%) 0.93 9.00 0.75 3.5 3.85 0.42 1.00 7.75
RD-2(9.0%) 0.26 9.00 0.50 3.5 2.79 0.25 1.00 7.50
RD-3(8.0%) 0.40 8.00 0.50 3.5 2.99 0.32 1.00 7.50
RD-4(8.0%) 0.32 8.00 0.50 3.5 2.82 0.29 1.00 7.50
PD (5.0%) 0.80 5.00 0.50 3 3.09 0.50 1.00 6.50
SYNTHETIC MAT" TO BE NAG C125 OR EQUAL, STAPLE PATTERN "D"
STRAW WITH NET" TO BE NAG S-75 OR EQUAL, STAPLE PATTERN "A"
Liner
SYNTHETIC MAT
Temporary
SYNTHETIC MAT
SYNTHETIC MAT
SYNTHETIC MAT
SYNTHETIC MAT
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL:RD-1(9.0%)
DRAINAGE AREA: 0.93
MAX SHEAR Td allowed: 2.00
AVERAGE SLOPE: 9.00 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 7.02 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER:SYNTHETIC MAT
*MANNINGS (n) of 0.036 used for design
Calculated shear of 1.89 is less than the Permissable Shear*** of 2
Therefore can be used as a temporary liner for RD-1(9.0%)
*Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
Q=CIA Where C= 0.5 I=7.6 in/hr for channel design,Tc=5.0 min
I=5.94 in/hr for 2 year storm REF: NOAA Atlas 14 Data
***Permissable Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
v (f/s)
4.27
(Td) ****
1.89
VELOCITYDISCHARGE**Calculated Shear
Q (cfs)
2.76
SYNTHETIC MAT
d (ft)
DEPTH
0.34
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE GRASS LINER
PROPOSED GRASS LINER:TALL FESCUE
Use Retardence Class D
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL:RD-1(9.0%)
AVERAGE SLOPE: 9.00 %
MAX VELOCITY allowed: 4.00 feet/sec
MANNING'S (n) used: 0.045
MAX VR allowed: 2.2
DISCHARGE FLOW WETTED CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA AREA PERIMETER DEPTH FROUDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs) (sq ft) (ft) (ft) No. Fr VR
0.42 3.5 0.75 3.85 3.53 0.92 3.78 0.48 1.36 0.94
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 3.85 feet/sec is less than permissable velocity of 4.00 feet/sec
VR CHECK
0.94 is less than the maximum allowable VR of 2.2
Therefore TALL FESCUE can be used as a grass liner for RD-1(9.0%)
*Permissable Velocity Obtained from Table 8.05a
**VR = Velocity * Hydraulic Radius = Velocity * Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
Calculated VR
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL:RD-2(9.0%)
DRAINAGE AREA: 0.26 Acres
MAX SHEAR Td allowed: 2.00
AVERAGE SLOPE: 9.00 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 5.08 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER:SYNTHETIC MAT
*MANNINGS (n) of 0.036 used for design
Calculated shear of 1.15 is less than the Permissable Shear*** of 2
Therefore can be used as a temporary liner for RD-2(9.0%)
*Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
Q=CIA Where C= 0.5 I=7.6 in/hr for channel design,Tc=5 min
I=5.94 in/hr for 2 year storm REF: NOAA Atlas 14 Data
***Permissable Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
DISCHARGE** DEPTH
Q (cfs) d (ft) v (f/s)
SYNTHETIC MAT
VELOCITY Calculated Shear
1.15
(Td) ****
0.77 0.21 3.09
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE GRASS LINER
PROPOSED GRASS LINER:TALL FESCUE
Use Retardence Class D
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL:RD-2(9.0%)
AVERAGE SLOPE: 9.00 %
MAX VELOCITY allowed: 4.00 feet/sec
MANNING'S (n) used: 0.045
MAX VR allowed: 2.2
DISCHARGE FLOW WETTED CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA AREA PERIMETER DEPTH FROUDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs) (sq ft) (ft) (ft) No. Fr VR
0.26 3.5 0.5 2.79 0.99 0.35 2.35 0.28 1.26 0.42
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 2.79 feet/sec is less than permissable velocity of 4.00 feet/sec
VR CHECK
0.42 is less than the maximum allowable VR of 2.2
Therefore TALL FESCUE can be used as a grass liner for RD-2(9.0%)
*Permissable Velocity Obtained from Table 8.05a
**VR = Velocity * Hydraulic Radius = Velocity * Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
Calculated VR
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL:RD-3(8.0%)
DRAINAGE AREA: 0.40 Acres
MAX SHEAR Td allowed: 2.00
AVERAGE SLOPE: 8.00 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 5.46 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER:SYNTHETIC MAT
*MANNINGS (n) of 0.036 used for design
Calculated shear of 1.28 is less than the Permissable Shear*** of 2
Therefore can be used as a temporary liner for RD-3(8.0%)
*Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
Q=CIA Where C= 0.5 I=7.6 in/hr for channel design,Tc=5 min
I=5.94 in/hr for 2 year storm REF: NOAA Atlas 14 Data
***Permissable Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
SYNTHETIC MAT
1.19
v (f/s)
0.26 3.31 1.28
d (ft)Q (cfs)(Td) ****
Calculated ShearDISCHARGE** DEPTH VELOCITY
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE GRASS LINER
PROPOSED GRASS LINER:TALL FESCUE
Use Retardence Class D
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL:RD-3(8.0%)
AVERAGE SLOPE: 8.00 %
MAX VELOCITY allowed: 4.00 feet/sec
MANNING'S (n) used: 0.045
MAX VR allowed: 2.2
DISCHARGE FLOW WETTED CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA AREA PERIMETER DEPTH FROUDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs) (sq ft) (ft) (ft) No. Fr VR
0.32 3.5 0.5 2.99 1.52 0.51 2.80 0.34 1.22 0.54
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 2.99 feet/sec is less than permissable velocity of 4.00 feet/sec
VR CHECK
0.54 is less than the maximum allowable VR of 2.2
Therefore TALL FESCUE can be used as a grass liner for RD-3(8.0%)
*Permissable Velocity Obtained from Table 8.05a
**VR = Velocity * Hydraulic Radius = Velocity * Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
Calculated VR
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL:RD-4(8.0%)
DRAINAGE AREA: 0.32 Acres
MAX SHEAR Td allowed: 2.00
AVERAGE SLOPE: 8.00 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 5.15 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER:SYNTHETIC MAT
*MANNINGS (n) of 0.036 used for design
Calculated shear of 1.16 is less than the Permissable Shear*** of 2
Therefore can be used as a temporary liner for RD-4(8.0%)
*Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
Q=CIA Where C= 0.5 I=7.6 in/hr for channel design,Tc=5 min
I=5.94 in/hr for 2 year storm REF: NOAA Atlas 14 Data
***Permissable Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
d (ft) v (f/s) (Td) ****
0.95 0.23
DEPTH
3.12
Calculated Shear
1.16
VELOCITY
SYNTHETIC MAT
DISCHARGE**
Q (cfs)
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE GRASS LINER
PROPOSED GRASS LINER:TALL FESCUE
Use Retardence Class D
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL:RD-4(8.0%)
AVERAGE SLOPE: 8.00 %
MAX VELOCITY allowed: 4.00 feet/sec
MANNING'S (n) used: 0.045
MAX VR allowed: 2.2
DISCHARGE FLOW WETTED CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA AREA PERIMETER DEPTH FROUDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs) (sq ft) (ft) (ft) No. Fr VR
0.29 3.5 0.5 2.82 1.22 0.43 2.59 0.31 1.21 0.47
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 2.82 feet/sec is less than permissable velocity of 4.00 feet/sec
VR CHECK
0.47 is less than the maximum allowable VR of 2.2
Therefore TALL FESCUE can be used as a grass liner for RD-4(8.0%)
*Permissable Velocity Obtained from Table 8.05a
**VR = Velocity * Hydraulic Radius = Velocity * Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
Calculated VR
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject PERMANENT DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL:PD (5.0%)
DRAINAGE AREA: 0.80 Acres
MAX SHEAR Td allowed: 2.00
AVERAGE SLOPE: 5.00 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 5.66 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER:SYNTHETIC MAT
*MANNINGS (n) of 0.036 used for design
Calculated shear of 1.26 is less than the Permissable Shear*** of 2
Therefore can be used as a temporary liner for PD (5.0%)
*Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
Q=CIA Where C= 0.5 I=7.6 in/hr for channel design,Tc=5 min
I=5.94 in/hr for 2 year storm REF: NOAA Atlas 14 Data
***Permissable Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
DISCHARGE** DEPTH VELOCITY
v (f/s) (Td) ****d (ft)
Calculated Shear
SYNTHETIC MAT
2.38 0.40 3.43 1.26
Q (cfs)
Job Name Williamston Subdivison Job No. Date 10/20/2017 Sheet
Subject PERMANENT DITCHES By KEH Chk By
DETERMINE GRASS LINER
PROPOSED GRASS LINER:TALL FESCUE
Use Retardence Class D
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL:PD (5.0%)
AVERAGE SLOPE: 5.00 %
MAX VELOCITY allowed: 4.50 feet/sec
MANNING'S (n) used: 0.045
MAX VR allowed: 2.2
DISCHARGE FLOW WETTED CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA AREA PERIMETER DEPTH FROUDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs) (sq ft) (ft) (ft) No. Fr VR
0.50 3 0.5 3.09 3.04 0.98 3.63 0.50 1.03 0.84
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 3.09 feet/sec is less than permissable velocity of 4.50 feet/sec
VR CHECK
0.84 is less than the maximum allowable VR of 2.2
Therefore TALL FESCUE can be used as a grass liner for PD (5.0%)
*Permissable Velocity Obtained from Table 8.05a
**VR = Velocity * Hydraulic Radius = Velocity * Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
Calculated VR
STORM DRAINAGE
CALCULATIONS

Job: Williamston Subdivision Job No. Date 10/20/2017 Sheet
Subject: Tc Calcs - Road Culvert By KEH Chk By
DRAINAGE AREA = 5.45 acs
PRE-DEVELOPED
SHEET FLOW
Segment ID:A
Surface description (table 3-12):Dense Grass
Manning's roughness coeff., n:0.24
Flow length, L (total L<300') (ft):190.00
2yr 24 hour rainfall, P (in):3.59 NOAA Atlas 14 - Monroe
Land slope, s (ft/ft):0.037
Tc=0.007 (nL) ^0.8 Tc=0.29 hours
P^0.5 x s^0.4
SHALLOW CONCENTRATED FLOW
Segment ID:B
Flow length, L (ft):500.00
Watercourse slope, s (ft/ft):0.010
Average velocity, V (fig3-5) (ft/s):1.60
Tc=L / (3600xV) Tc=0.087 hours
CHANNEL FLOW
Segment ID:C
Assume velocity, V (ft/s):7.00
Flow length, L (ft):370.00
Tc=L / (3600xV) Tc=0.015 hours
Total Tc path = 0.396 hours = 23.7 minutes
USE 20 minutes for Analysis
APRON
CALCULATIONS

Job: Williamston Subdivision Job No. Date 10/20/2017 Sheet
Subject: Apron By KEH Chk By
APRON:(24" RCP)
Pipe Diameter, Do 24 Inches or 2 Feet
Apron Length, L=12 Feet (from Fig 8.06a)
Channel Width, b=0.5 Feet
Side Slope, M:1 = 2 :1
H (2/3 Pipe Dia): =1.3 Feet
Apron Width, W1 =6 Feet (3 * Pipe Dia.)
Apron Width, W2 =5.9 Feet
d50 Stone Size = 0.5 Feet (from Fig 8.06a) =6 inches
Apron Thickness, t=13.5 inches
RECEIVING OUTLET (CHANNEL / SHEET FLOW): CHANNEL
SUPPORTING
DATA

Hydrologic Soil Group—Union County, North Carolina
(Williamston Subdivision)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2017
Page 1 of 438836703883720388377038838203883870388392038839703883670388372038837703883820388387038839203883970553520553570553620553670553720553770553820553870553920553970554020
553520 553570 553620 553670 553720 553770 553820 553870 553920 553970 554020
35° 5' 50'' N 80° 24' 46'' W35° 5' 50'' N80° 24' 25'' W35° 5' 39'' N
80° 24' 46'' W35° 5' 39'' N
80° 24' 25'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 17N WGS84
0 100 200 400 600
Feet
0 35 70 140 210
Meters
Map Scale: 1:2,420 if printed on A landscape (11" x 8.5") 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: Union County, North Carolina
Survey Area Data: Version 16, Sep 20, 2016
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Feb 11, 2011—Feb
13, 2011
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—Union County, North Carolina
(Williamston Subdivision)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2017
Page 2 of 4
Hydrologic Soil Group
Hydrologic Soil Group— Summary by Map Unit — Union County, North Carolina (NC179)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
GsB Goldston-Badin
complex, 2 to 8
percent slopes
D 1.0 10.6%
TaC Tarrus gravelly silt loam,
8 to 15 percent slopes
B 4.6 47.6%
TbB2 Tarrus gravelly silty clay
loam, 2 to 8 percent
slopes, moderately
eroded
B 4.0 41.9%
Totals for Area of Interest 9.6 100.0%
Hydrologic Soil Group—Union County, North Carolina Williamston Subdivision
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2017
Page 3 of 4
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.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Union County, North Carolina Williamston Subdivision
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2017
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SUPPORTING DATA