SW1200601_2020-07-22 Sanstone Storm & EC Calcs_20200722

TABLE OF CONTENTS

Storm Water & Erosion Control Narrative……...……………...……………………… 1-3

NOAA Precipitation Charts, USGS, FEMA, Soils, SHWT, and Wetlands…………..Appendix 1

Collection System Calculations…………………………………………………………Appendix 2

Hydrologic Model and BMP Design………………………………………….…………Appendix 3

Erosion Control Calculations and Specifications...……………………………………Appendix 4

NARRATIVE

Project Description
The proposed Sanstone Office & Storage Expansion is located on two adjacent parcels
(Henderson County PINs: 9632-48-7869 and 9632-48-9561) on Old Haywood Road in
Mills River, North Carolina. The development for the 6.00-acre site consists of one
office building and one storage building. The plans also incorporate a second storage
building to be constructed at a later date. Two driveway connections will be made to the
parking areas associated with the existing Sanstone office building and healthcare
facility.

This report addresses requirements to meet current NPDES Construction and Post
Construction Activities. The site is located outside of a Water Supply Watershed
Overlay District and is therefore designed based on NCDEQ design criteria.

Existing Site Conditions
The existing site is vacant and former farmland. The western half of the property is
wooded and the eastern portion along the Old Haywood Road frontage is a grass field.
The soils for the site are classified by the NRCS as Hayesville loam (HyB & HyC) and
Delanco (dillard) loam (DeB). HyB soils are classified as Hydrologic Soil Group (HSG)
Type B, whereas HyC and DeB are considered to by HSG Type C. The site primarily
drains from west to southeast to an existing drainage ditch along Old Haywood Road.
For analysis purposes, this drainage basin was split in to two areas because runoff exits
the site at two separate locations and rejoins at a common point offsite. The northern
portion of the site drains to the storm drainage system for the existing Sanstone office
building and healthcare facility.

Proposed Developed Conditions
The proposed development is considered high-density and is designed to achieve a
runoff treatment for the first inch with a piped stormwater conveyance system and a
bioretention cell. Runoff from impervious areas associated with buildings, paved drives
with curb & gutter, sidewalk, and parking are to be captured to the extent practical.
Approximately 431 SF of impervious driveway is proposed to drain to storm drainage
infrastructure associated with the existing Sanstone office and healthcare facility (The
Henderson-Beystone Parcel aka The Lodge at Mills River – SanStone Health & Rehab).
The bioretention cell is designed to accommodate approximately 9,100 SF of
impervious area for a future storage building and associated pavement adjacent to the
proposed storage building. Offsite drainage from adjacent western parcels drains to
swales located that allows this stormwater to bypass the proposed SCM.
During construction a temporary construction entrance will be located along Old
Haywood Road in order to minimize construction traffic for the existing healthcare
facility.

Purpose of Report
The purpose of this analysis is to show that the site will be in compliance with NCDEQ
stormwater regulations.

Procedure

Collection System:
The proposed collection system was sized to adequately convey the 25-year, 24-hour
storm. Drainage areas were delineated for each proposed inlet in addition to Rational
‘C’ coefficients and time of concentration based on the TR-55 method. Energy
dissipation will be handled with riprap pads sized for the 25-year storm. Refer to the
provided plan set for a drainage summary.

Water Quantity:
The SCS Method using a 24-hour, Type II storm was used to determine the pre-
developed and developed annual peak stormwater discharges generated from this site.
The HydroCAD runoff routing program was used to determine these peak flows and
storm volumes as well as routing through the detention basin and bypass areas.
Stage/discharge rates for the ponds were determined based on storage, culvert and
broad crested weir equations within Hydrocad.

Calculations for the 25-year storm event were performed to show the pond is
adequately sized to pass the 25-year storm event. A vegetated spillway with matting
has been provided along with riser/barrel outlet control structures for primary drainage
from basin areas.

Water Quality:
The Simple Method was used to determine the runoff volume for the first-inch of rainfall.
The bioretention cell was then designed to allow a maximum of one-foot of ponding
above the media mix for this design volume. The underdrain system is designed to
discharge the first inch between 2-5 days after the rainfall event.

Seasonal High Water Table (SHWT):
Per NCDEQ MDC guidelines for bioretention cells, the lowest point shall be a minimum
of two feet above the SHWT. On April 21, 2020, Land Resources Management
excavated a test pit at the location of the SCM. The pit was excavated to a depth of 75”
(6.25’) with no sign of the SHWT. Existing elevation at the pit location is approximately
2182.0’ and the proposed bottom of the bioretention underdrain system is 2178.75’.
Therefore, the bottom of the bioretention cell is at least 2’ above the SHWT.

Calculations
Drainage maps are included in the plans associated with this project. These maps
show the predeveloped and developed conditions. A summary of the entire drainage
area for the site and each individual drainage area within the site is included in this

report. Erosion Control calculations including skimmer basin design are included in
Appendix 4.

Stormwater Results
The following table shows the pre/post runoff rates for the project. There is no increase
the annual discharge for Basins 1 & 2 that drain to Old Haywood Road. There is a 0.01
CFS increase in runoff from Basin 3 draining to the storm drainage system for the
existing office and healthcare facility due to a reduction in time of concentration and
wooded area. The 25-year storm calculations show the proposed detention ponds are
adequate to pass the 25-year storm event.

Basin Name 1-Year
(cfs)
25-Year
(cfs)
25-Year Ponding
(Elevation - feet)
Existing Basin 1 2.16 10.09
To BMP #1 4.48 16.68
Out BMP #1 0.33 13.84 2182.90
BMP Bypass 1.19 4.32
Proposed Basin 1 1.19 15.60
Existing Basin 2 0.33 4.35
Proposed Basin 2 0.20 1.90
Existing Basin 3 0.08 1.94
Proposed Basin 3 0.09 0.77

Recommendations
Brooks Engineering recommends that the proposed development utilize stormwater
management facilities as outlined in this study in order to mitigate developed peak
stormwater discharges per NCDEQ regulations. Routine maintenance will need to be
performed in order for the stormwater management areas to operate as designed.

Appendix “1”
4/14/2020 Precipitation Frequency Data Server
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.4251&lon=-82.5765&data=depth&units=english&series=pds 1/4
NOAA Atlas 14, Volume 2, Version 3
Location name: Mills River, North Carolina, USA*
Latitude: 35.4251°, Longitude: -82.5765°
Elevation: 2225.91 ft**
* source: ESRI Maps
** 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 | PF_graphical | Maps_&_aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Duration Average recurrence interval (years)
1 2 5 10 25 50 100 200 500 1000
5-min 0.367
(0.331‑0.408)
0.437
(0.394‑0.484)
0.523
(0.472‑0.581)
0.589
(0.530‑0.652)
0.675
(0.602‑0.746)
0.740
(0.657‑0.818)
0.806
(0.712‑0.893)
0.872
(0.764‑0.968)
0.957
(0.829‑1.07)
1.03
(0.880‑1.15)
10-min 0.586
(0.528‑0.651)
0.698
(0.631‑0.775)
0.838
(0.755‑0.930)
0.942
(0.847‑1.04)
1.08
(0.960‑1.19)
1.18
(1.05‑1.30)
1.28
(1.13‑1.42)
1.38
(1.21‑1.54)
1.51
(1.31‑1.69)
1.62
(1.39‑1.82)
15-min 0.732
(0.660‑0.814)
0.878
(0.793‑0.974)
1.06
(0.955‑1.18)
1.19
(1.07‑1.32)
1.36
(1.22‑1.51)
1.49
(1.32‑1.65)
1.62
(1.43‑1.79)
1.74
(1.53‑1.94)
1.91
(1.65‑2.13)
2.03
(1.74‑2.28)
30-min 1.00
(0.905‑1.12)
1.21
(1.10‑1.35)
1.51
(1.36‑1.67)
1.73
(1.55‑1.91)
2.02
(1.80‑2.23)
2.25
(1.99‑2.48)
2.48
(2.19‑2.75)
2.71
(2.38‑3.02)
3.03
(2.63‑3.39)
3.29
(2.82‑3.69)
60-min 1.25
(1.13‑1.39)
1.52
(1.37‑1.69)
1.93
(1.74‑2.14)
2.25
(2.02‑2.49)
2.69
(2.40‑2.97)
3.05
(2.70‑3.37)
3.42
(3.02‑3.78)
3.81
(3.34‑4.23)
4.35
(3.77‑4.86)
4.80
(4.11‑5.39)
2-hr 1.47
(1.32‑1.63)
1.78
(1.61‑1.97)
2.25
(2.02‑2.48)
2.62
(2.34‑2.90)
3.14
(2.79‑3.48)
3.56
(3.15‑3.95)
4.01
(3.52‑4.45)
4.48
(3.90‑4.98)
5.15
(4.42‑5.74)
5.68
(4.83‑6.38)
3-hr 1.57
(1.42‑1.76)
1.90
(1.71‑2.11)
2.38
(2.14‑2.64)
2.77
(2.48‑3.08)
3.35
(2.97‑3.72)
3.83
(3.37‑4.25)
4.33
(3.79‑4.82)
4.89
(4.22‑5.44)
5.68
(4.83‑6.37)
6.33
(5.33‑7.14)
6-hr 1.97
(1.80‑2.17)
2.35
(2.14‑2.58)
2.89
(2.64‑3.18)
3.36
(3.05‑3.69)
4.04
(3.64‑4.44)
4.62
(4.12‑5.07)
5.24
(4.63‑5.77)
5.92
(5.17‑6.52)
6.90
(5.93‑7.65)
7.73
(6.56‑8.62)
12-hr 2.48
(2.29‑2.71)
2.96
(2.72‑3.23)
3.63
(3.34‑3.96)
4.17
(3.82‑4.55)
4.92
(4.49‑5.37)
5.53
(5.03‑6.04)
6.16
(5.56‑6.74)
6.82
(6.11‑7.48)
7.72
(6.85‑8.55)
8.44
(7.42‑9.41)
24-hr 2.97
(2.75‑3.21)
3.56
(3.30‑3.85)
4.37
(4.05‑4.73)
5.02
(4.64‑5.43)
5.92
(5.45‑6.39)
6.65
(6.10‑7.18)
7.40
(6.76‑7.98)
8.18
(7.43‑8.84)
9.28
(8.35‑10.0)
10.2
(9.06‑11.0)
2-day 3.53
(3.29‑3.80)
4.21
(3.92‑4.53)
5.13
(4.78‑5.51)
5.86
(5.45‑6.29)
6.87
(6.36‑7.37)
7.68
(7.09‑8.24)
8.52
(7.83‑9.15)
9.38
(8.58‑10.1)
10.6
(9.60‑11.4)
11.5
(10.4‑12.5)
3-day 3.77
(3.52‑4.04)
4.49
(4.19‑4.81)
5.43
(5.06‑5.81)
6.17
(5.74‑6.60)
7.17
(6.66‑7.67)
7.97
(7.38‑8.54)
8.79
(8.11‑9.43)
9.63
(8.84‑10.3)
10.8
(9.82‑11.6)
11.7
(10.6‑12.6)
4-day 4.01
(3.75‑4.28)
4.77
(4.47‑5.10)
5.72
(5.35‑6.11)
6.47
(6.04‑6.91)
7.48
(6.96‑7.98)
8.27
(7.67‑8.83)
9.07
(8.38‑9.70)
9.88
(9.10‑10.6)
11.0
(10.0‑11.8)
11.9
(10.8‑12.8)
7-day 4.69
(4.40‑5.02)
5.57
(5.23‑5.96)
6.68
(6.26‑7.14)
7.56
(7.07‑8.08)
8.75
(8.16‑9.35)
9.70
(9.03‑10.4)
10.7
(9.89‑11.4)
11.7
(10.8‑12.5)
13.0
(11.9‑14.0)
14.1
(12.8‑15.2)
10-day 5.38
(5.08‑5.71)
6.37
(6.01‑6.76)
7.55
(7.14‑8.02)
8.49
(8.01‑9.01)
9.76
(9.18‑10.4)
10.8
(10.1‑11.4)
11.8
(11.0‑12.5)
12.8
(11.9‑13.6)
14.2
(13.1‑15.2)
15.3
(14.1‑16.4)
20-day 7.32
(6.94‑7.73)
8.61
(8.16‑9.10)
9.99
(9.47‑10.6)
11.1
(10.5‑11.7)
12.5
(11.8‑13.2)
13.5
(12.8‑14.3)
14.6
(13.7‑15.4)
15.6
(14.6‑16.5)
16.9
(15.8‑17.9)
17.9
(16.6‑19.0)
30-day 8.98
(8.53‑9.46)
10.5
(10.0‑11.1)
12.1
(11.5‑12.7)
13.2
(12.5‑13.9)
14.6
(13.9‑15.4)
15.7
(14.9‑16.5)
16.7
(15.8‑17.6)
17.7
(16.7‑18.6)
18.9
(17.7‑19.9)
19.7
(18.5‑20.9)
45-day 11.4
(10.9‑12.0)
13.4
(12.7‑14.0)
15.0
(14.3‑15.8)
16.3
(15.5‑17.1)
17.8
(16.9‑18.7)
18.8
(17.9‑19.8)
19.8
(18.8‑20.8)
20.7
(19.6‑21.7)
21.7
(20.6‑22.9)
22.5
(21.2‑23.7)
60-day 13.7
(13.1‑14.4)
16.0
(15.3‑16.8)
17.9
(17.0‑18.8)
19.2
(18.3‑20.2)
20.8
(19.8‑21.9)
21.9
(20.9‑23.1)
22.9
(21.8‑24.1)
23.8
(22.6‑25.1)
24.9
(23.6‑26.3)
25.6
(24.2‑27.1)
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 NOAA Atlas 14 document for more information.
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Maps & aerials
Small scale terrain
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Large scale terrain
Large scale map
Large scale aerial
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4/14/2020 Precipitation Frequency Data Server
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National Oceanic and Atmospheric Administration
National Weather Service
National Water Center
1325 East West Highway
Silver Spring, MD 20910
Questions?: [e-mail]
Disclaimer
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4/14/2020 Precipitation Frequency Data Server
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NOAA Atlas 14, Volume 2, Version 3
Location name: Mills River, North Carolina, USA*
Latitude: 35.4251°, Longitude: -82.5765°
Elevation: 2225.91 ft**
* source: ESRI Maps
** 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 | PF_graphical | Maps_&_aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hour)1
Duration Average recurrence interval (years)
1 2 5 10 25 50 100 200 500 1000
5-min 4.40
(3.97‑4.90)
5.24
(4.73‑5.81)
6.28
(5.66‑6.97)
7.07
(6.36‑7.82)
8.10
(7.22‑8.95)
8.88
(7.88‑9.82)
9.67
(8.54‑10.7)
10.5
(9.17‑11.6)
11.5
(9.95‑12.8)
12.3
(10.6‑13.8)
10-min 3.52
(3.17‑3.91)
4.19
(3.79‑4.65)
5.03
(4.53‑5.58)
5.65
(5.08‑6.26)
6.46
(5.76‑7.14)
7.07
(6.28‑7.82)
7.69
(6.79‑8.51)
8.29
(7.27‑9.21)
9.08
(7.87‑10.2)
9.70
(8.31‑10.9)
15-min 2.93
(2.64‑3.26)
3.51
(3.17‑3.90)
4.24
(3.82‑4.71)
4.77
(4.28‑5.28)
5.45
(4.86‑6.03)
5.97
(5.30‑6.60)
6.48
(5.72‑7.17)
6.98
(6.12‑7.74)
7.62
(6.60‑8.52)
8.11
(6.96‑9.12)
30-min 2.01
(1.81‑2.23)
2.42
(2.19‑2.69)
3.01
(2.71‑3.34)
3.45
(3.10‑3.82)
4.04
(3.60‑4.47)
4.50
(3.99‑4.97)
4.96
(4.38‑5.49)
5.43
(4.76‑6.03)
6.07
(5.26‑6.78)
6.57
(5.63‑7.38)
60-min 1.25
(1.13‑1.39)
1.52
(1.37‑1.69)
1.93
(1.74‑2.14)
2.25
(2.02‑2.49)
2.69
(2.40‑2.97)
3.05
(2.70‑3.37)
3.42
(3.02‑3.78)
3.81
(3.34‑4.23)
4.35
(3.77‑4.86)
4.80
(4.11‑5.39)
2-hr 0.733
(0.660‑0.813)
0.890
(0.802‑0.984)
1.12
(1.01‑1.24)
1.31
(1.17‑1.45)
1.57
(1.40‑1.74)
1.78
(1.57‑1.97)
2.00
(1.76‑2.22)
2.24
(1.95‑2.49)
2.57
(2.21‑2.87)
2.84
(2.41‑3.19)
3-hr 0.524
(0.473‑0.585)
0.631
(0.569‑0.702)
0.792
(0.712‑0.879)
0.923
(0.827‑1.02)
1.12
(0.990‑1.24)
1.27
(1.12‑1.42)
1.44
(1.26‑1.60)
1.63
(1.41‑1.81)
1.89
(1.61‑2.12)
2.11
(1.77‑2.38)
6-hr 0.329
(0.301‑0.362)
0.392
(0.358‑0.431)
0.483
(0.440‑0.531)
0.562
(0.510‑0.617)
0.675
(0.607‑0.741)
0.771
(0.688‑0.846)
0.875
(0.773‑0.963)
0.988
(0.863‑1.09)
1.15
(0.990‑1.28)
1.29
(1.10‑1.44)
12-hr 0.206
(0.190‑0.225)
0.246
(0.226‑0.268)
0.301
(0.277‑0.329)
0.346
(0.317‑0.378)
0.408
(0.373‑0.446)
0.459
(0.417‑0.501)
0.511
(0.462‑0.559)
0.566
(0.507‑0.621)
0.641
(0.569‑0.709)
0.701
(0.615‑0.781)
24-hr 0.124
(0.115‑0.134)
0.148
(0.137‑0.161)
0.182
(0.169‑0.197)
0.209
(0.193‑0.226)
0.247
(0.227‑0.266)
0.277
(0.254‑0.299)
0.308
(0.282‑0.333)
0.341
(0.310‑0.368)
0.387
(0.348‑0.418)
0.423
(0.378‑0.459)
2-day 0.074
(0.069‑0.079)
0.088
(0.082‑0.094)
0.107
(0.099‑0.115)
0.122
(0.113‑0.131)
0.143
(0.132‑0.153)
0.160
(0.148‑0.172)
0.177
(0.163‑0.191)
0.195
(0.179‑0.210)
0.220
(0.200‑0.238)
0.240
(0.216‑0.260)
3-day 0.052
(0.049‑0.056)
0.062
(0.058‑0.067)
0.075
(0.070‑0.081)
0.086
(0.080‑0.092)
0.100
(0.092‑0.107)
0.111
(0.102‑0.119)
0.122
(0.113‑0.131)
0.134
(0.123‑0.144)
0.150
(0.136‑0.161)
0.163
(0.147‑0.175)
4-day 0.042
(0.039‑0.045)
0.050
(0.047‑0.053)
0.060
(0.056‑0.064)
0.067
(0.063‑0.072)
0.078
(0.072‑0.083)
0.086
(0.080‑0.092)
0.094
(0.087‑0.101)
0.103
(0.095‑0.110)
0.114
(0.105‑0.123)
0.124
(0.112‑0.133)
7-day 0.028
(0.026‑0.030)
0.033
(0.031‑0.035)
0.040
(0.037‑0.043)
0.045
(0.042‑0.048)
0.052
(0.049‑0.056)
0.058
(0.054‑0.062)
0.064
(0.059‑0.068)
0.069
(0.064‑0.074)
0.078
(0.071‑0.083)
0.084
(0.076‑0.090)
10-day 0.022
(0.021‑0.024)
0.027
(0.025‑0.028)
0.031
(0.030‑0.033)
0.035
(0.033‑0.038)
0.041
(0.038‑0.043)
0.045
(0.042‑0.048)
0.049
(0.046‑0.052)
0.053
(0.050‑0.057)
0.059
(0.055‑0.063)
0.064
(0.059‑0.068)
20-day 0.015
(0.014‑0.016)
0.018
(0.017‑0.019)
0.021
(0.020‑0.022)
0.023
(0.022‑0.024)
0.026
(0.025‑0.027)
0.028
(0.027‑0.030)
0.030
(0.029‑0.032)
0.032
(0.030‑0.034)
0.035
(0.033‑0.037)
0.037
(0.035‑0.040)
30-day 0.012
(0.012‑0.013)
0.015
(0.014‑0.015)
0.017
(0.016‑0.018)
0.018
(0.017‑0.019)
0.020
(0.019‑0.021)
0.022
(0.021‑0.023)
0.023
(0.022‑0.024)
0.025
(0.023‑0.026)
0.026
(0.025‑0.028)
0.027
(0.026‑0.029)
45-day 0.011
(0.010‑0.011)
0.012
(0.012‑0.013)
0.014
(0.013‑0.015)
0.015
(0.014‑0.016)
0.016
(0.016‑0.017)
0.017
(0.017‑0.018)
0.018
(0.017‑0.019)
0.019
(0.018‑0.020)
0.020
(0.019‑0.021)
0.021
(0.020‑0.022)
60-day 0.010
(0.009‑0.010)
0.011
(0.011‑0.012)
0.012
(0.012‑0.013)
0.013
(0.013‑0.014)
0.014
(0.014‑0.015)
0.015
(0.014‑0.016)
0.016
(0.015‑0.017)
0.017
(0.016‑0.017)
0.017
(0.016‑0.018)
0.018
(0.017‑0.019)
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 NOAA Atlas 14 document for more information.
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PF graphical
4/14/2020 Precipitation Frequency Data Server
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.4251&lon=-82.5765&data=intensity&units=english&series=pds 2/4
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Maps & aerials
Small scale terrain
4/14/2020 Precipitation Frequency Data Server
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.4251&lon=-82.5765&data=intensity&units=english&series=pds 3/4
Large scale terrain
Large scale map
Large scale aerial
+
–
3km
2mi
+
–
100km
60mi
+
–
100km
60mi
4/14/2020 Precipitation Frequency Data Server
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.4251&lon=-82.5765&data=intensity&units=english&series=pds 4/4
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US Department of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
National Water Center
1325 East West Highway
Silver Spring, MD 20910
Questions?: [e-mail]
Disclaimer
+
–
100km
60mi
Hydrologic Soil Group—Henderson County, North Carolina
(SANSTONE_BOUNDARY)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/3/2020
Page 1 of 43921180392121039212403921270392130039213303921360392139039211803921210392124039212703921300392133039213603921390356800356830356860356890356920356950356980357010357040357070357100357130
356800 356830 356860 356890 356920 356950 356980 357010 357040 357070 357100 357130
35° 25' 32'' N 82° 34' 39'' W35° 25' 32'' N82° 34' 25'' W35° 25' 25'' N
82° 34' 39'' W35° 25' 25'' N
82° 34' 25'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 17N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,650 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
1:20,000.
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: Henderson County, North Carolina
Survey Area Data: Version 19, 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: May 21, 2015—Nov
28, 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—Henderson County, North Carolina
(SANSTONE_BOUNDARY)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/3/2020
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
DeB Delanco (dillard) loam, 2
to 7 percent slopes
C 0.2 2.7%
HyB Hayesville loam, 2 to 7
percent slopes
B 3.6 59.5%
HyC Hayesville loam, 7 to 15
percent slopes
C 2.3 37.8%
Totals for Area of Interest 6.0 100.0%
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—Henderson County, North Carolina SANSTONE_BOUNDARY
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/3/2020
Page 3 of 4
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Henderson County, North Carolina SANSTONE_BOUNDARY
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/3/2020
Page 4 of 4

July 21, 2020

Brooks Engineering Associates, PA
17 Arlington St.
Asheville, NC 28801

Attention: Mark Brooks, PE

Regarding: Report of Findings
Storm Water -Soil Evaluation
LRM Project # 70120

Dear Mr. Brooks:

Land Resource Management, PLLC (LRM) appreciates the opportunity to provide this Report of
Findings. The subject site is a proposed Storm Water Basin utilized to infiltrate storm water on
Henderson County, NC Tax ID 9632-48-7869. The background and findings are discussed below.

Background

The purpose of the study is to access the sites suitability for storm water infiltration, by providing site
specific soils information. One test pit was excavated and described in the center of the proposed
basin. The purpose of the test pit was to described the soil profile and identify if a Seasonal High-
Water Table (SHWT) existed beneath the basin.

Findings

The placement of the test pits was coordinated with Brooks Engineering Associates, PA (BEA) to be
representative of the proposed Storm Water Basin. The soil was described to a depth of 75 inches
beneath the ground surface. The soil description identified a Residual soil with a clay loam texture.
No SHWT was observed in the test pit. The full soil profile description is provided as Enclosure 1.

LRM appreciates the opportunity to provide this Report of Findings. Please do not hesitate to call
with any questions or concerns.

Sincerely,

Walker Ferguson, LSS
President, Land Resource Management, PLLC

Enclosure:
1) Soil Profile Description
Sanstone Office & Storage Expansion
Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,USDA, USGS, AeroGRID, IGN, and the GIS User Community
Wetlands
Estuarine and Marine Deepwater
Estuarine and Marine Wetland
Freshwater Emergent Wetland
Freshwater Forested/Shrub Wetland
Freshwater Pond
Lake
Other
Riverine
July 15, 2020
0 0.08 0.160.04 mi
0 0.1 0.20.05 km
1:4,735
This page was produced by the NWI mapperNational Wetlands Inventory (NWI)
This map is for general reference only. The US Fish and Wildlife Service is not responsible for the accuracy or currentness of the base data shown on this map. All wetlands related data should be used in accordance with the layer metadata found on the Wetlands Mapper web site.

Appendix “2”
13017.252181.002181.980.981.779.731.472183.450.0023.732181.292182.270.981.779.731.471.210.290.000.512183.450.0023014.992181.292182.901.613.335.780.522183.210.1724.002181.652182.961.312.594.500.310.250.060.000.352183.210.3332411.952182.152183.481.332.235.830.532183.930.32166.032183.812185.051.242.055.370.450.360.600.000.302183.930.404246.662183.812185.391.582.674.750.352185.490.07202.982189.592190.500.911.402.500.100.200.410.000.122185.490.345245.212189.592190.681.091.764.400.302190.820.11100.902198.322199.120.801.182.960.140.220.220.000.002190.820.336184.762200.332200.700.370.3413.862.992203.690.0088.862207.442207.810.370.3413.862.997.937.050.001.432203.690.007184.032209.312210.130.820.994.420.302210.390.31101.052215.372216.140.770.914.070.260.350.350.000.092210.390.398182.982215.372216.270.891.104.010.252216.380.13120.512216.582217.230.660.742.720.110.250.300.000.062216.380.379182.702216.582217.350.770.913.890.232217.480.1755.122217.132217.750.620.692.960.140.270.150.000.052217.480.3610182.542217.132217.860.730.853.820.232218.000.1867.162217.802218.400.600.672.990.140.270.180.000.102218.000.3611181.912217.802218.530.730.853.500.192218.610.1053.812218.342218.860.520.552.240.080.230.120.000.122218.610.3512181.302218.342219.000.660.743.140.152219.040.0769.832219.042219.460.430.411.750.050.210.150.000.032219.040.3513180.432220.482220.640.160.104.180.272220.910.0024.002220.962221.120.160.104.180.271.980.480.000.052220.910.0014180.512212.952213.130.180.124.390.302213.430.0023.862213.432213.600.180.124.390.301.990.470.000.062213.430.0015180.502191.172191.350.170.114.370.302191.640.0023.922191.652191.820.170.114.370.301.990.470.000.062191.640.0016182.212184.432185.380.951.183.660.212185.430.0644.042185.312185.870.560.601.880.050.210.090.000.042185.430.3525 YEARPage 1MILLS RIVER 25-YR FIXED1607/14/2020
4
D50 INTERSECT= 0.5FT
LENGTH INTERSECT L= 14FT
RIP RAP PAD PARAMETERS
L= 14 FT
W= 18 FT
d50= 0.5
depth= 14 in
25-YEAR FLOW= 17.25CFS
PIPE SIZE= 30IN.
POND RIPRAP OUTLET
ST1
4
D50 INTERSECT= 0.3FT
LENGTH INTERSECT L= 10FT
RIP RAP PAD PARAMETERS
L= 10 FT
W= 12 FT
d50= 0.3
depth= 12 in
25-YEAR FLOW= 13.84CFS
PIPE SIZE= 18IN.
POND RIPRAP OUTLET
BMP #1

Appendix “3”
Simple Method for RO Volume Rv = 0.05 + 0.9 * Ia
DV = 3630 * Rd * Rv * A
BMP #1
Rv 0.3546
Ia 0.3384
Rd (in)1.0
A (ac)4.41
Design Vol (CF)5,681
Design Vol (acre-ft)0.130
Temporary Pool Surface Area for Bioretention
BMP #1
Max. Allowable Ponding Depth (ft)1.0
Min. Required Surface Area (SF)5,681
Provided Surface Area at bottom (SF)5,873
Provided Surface Area 1 ft above bottom (SF)6,809
Calculated Ponding Depth for RO Volume (ft)0.90 --> Set Peak attentuation at 12"
Underdrain Sizing (Per NCDEQ Stormwater Design Manual Sec A-5)
Determine Flow Rate
Surface Area at top of Media 5873 SF
Hydraulic Conductivity of Media (5 in/hr)0.000116 ft/s
Flow Rate 0.680 cfs
Apply Safety Factor (2-10 times max. flow)2.00
Design Q 1.36 cfs
Calculate the Diameter of a Single Pipe needed
to carry all the water, D 8.94 in where,
D = diameter, in inches
n = Manning's roughness coefficent (0.011)
s = slope, ft/ft (0.005 ft/ft)
Q = discharge, in cfs
Per Section A-5 (Table 2) use 3 - 6" pipes for the underdrain system.
=16

⁄
IWS Drawdown Time Calculation
Use the following equations to determine the necessary orifice size to
achieve a drawdown time between 2 - 5 days.
Set Drawdown Time = 2.0 days
where:
DV = 5,681 Design Volume calculated using the simple method (CF)
t = 172,800 Drawdown Time (sec)
Q = 0.0329 Discharge rate (CFS)
Cd =0.6 orifice coefficient
g =32.2 acceleration of gravity (ft/sec2)
Ho =1.00 maximum head (ft), divide by three to model diminishing head
A =0.01183 Cross sectional Area of the orifice (ft2)
Solve for orifice diameter (A = 0.25πD2)
D =1.922 Calculated Orifice Diameter (in)
Specify orifice size, D = 1.90 in (Round down to nearest tenth)
=

= × × 2× 3 → = /
× 2× 3
E1
Existing Basin 1
E2
Existing Basin 2
E3
Existing Basin 3
P1
Proposed to BMP
P2
BMP Bypass
P5
Proposed Basin 2
P6
Proposed Basin 3
P3
BMP 1
P4
Total Proposed Basin 1
Routing Diagram for Sanstone
Prepared by Brooks EA, Printed 7/15/2020
HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Subcat Reach Pond Link
Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 2HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Area Listing (all nodes)
Area
(acres)
CN Description
(subcatchment-numbers)
1.810 61 >75% Grass cover, Good, HSG B (E1, E2, P1, P5, P6)
0.346 61 >75% Grass cover, Good, HSG B - Offsite (P1)
0.346 61 >75% Grass cover, Good, HSG B, Offsite (E1)
3.915 74 >75% Grass cover, Good, HSG C (E1, E2, P1, P2, P5)
0.023 74 >75% Grass cover, Good, HSG C - Offsite (P1)
0.001 74 >75% Grass cover, Good, HSG C, Offsite (E1)
0.297 98 Impervious - Buildings (P1)
0.209 98 Impervious - Future Storage (P1)
0.887 98 Impervious - Pavement, Curb (P1, P6)
0.019 98 Impervious - Pavement, Curb - Offsite (P1)
0.091 98 Impervious - Sidewalk (P1)
4.440 55 Woods, Good, HSG B (E1, E2, E3, P1, P5, P6)
0.357 70 Woods, Good, HSG C (E2, P5)
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 3HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN
Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method
Runoff Area=138,603 sf 0.00% Impervious Runoff Depth>0.57"Subcatchment E1: Existing Basin 1
Flow Length=513' Tc=17.1 min CN=69 Runoff=2.16 cfs 0.152 af
Runoff Area=94,309 sf 0.00% Impervious Runoff Depth>0.22"Subcatchment E2: Existing Basin 2
Flow Length=515' Tc=15.7 min CN=58 Runoff=0.33 cfs 0.039 af
Runoff Area=43,914 sf 0.00% Impervious Runoff Depth>0.15"Subcatchment E3: Existing Basin 3
Flow Length=217' Tc=12.1 min CN=55 Runoff=0.08 cfs 0.013 af
Runoff Area=192,269 sf 33.84% Impervious Runoff Depth>0.79"Subcatchment P1: Proposed to BMP
Flow Length=649' Tc=16.9 min CN=74 Runoff=4.48 cfs 0.292 af
Runoff Area=40,018 sf 0.00% Impervious Runoff Depth>0.80"Subcatchment P2: BMP Bypass
Flow Length=345' Tc=10.1 min CN=74 Runoff=1.19 cfs 0.061 af
Runoff Area=34,170 sf 0.00% Impervious Runoff Depth>0.27"Subcatchment P5: Proposed Basin 2
Flow Length=379' Tc=13.5 min CN=60 Runoff=0.20 cfs 0.018 af
Runoff Area=11,791 sf 3.66% Impervious Runoff Depth>0.30"Subcatchment P6: Proposed Basin 3
Flow Length=161' Tc=10.6 min CN=61 Runoff=0.09 cfs 0.007 af
Peak Elev=2,182.19' Storage=7,672 cf Inflow=4.48 cfs 0.292 afPond P3: BMP 1
Outflow=0.33 cfs 0.129 af
Inflow=1.19 cfs 0.190 afLink P4: Total Proposed Basin 1
Primary=1.19 cfs 0.190 af
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 4HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment E1: Existing Basin 1
Runoff =2.16 cfs @ 12.12 hrs, Volume=0.152 af, Depth>0.57"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
20,567 61 >75% Grass cover, Good, HSG B
*15,093 61 >75% Grass cover, Good, HSG B, Offsite
92,037 74 >75% Grass cover, Good, HSG C
*23 74 >75% Grass cover, Good, HSG C, Offsite
10,883 55 Woods, Good, HSG B
138,603 69 Weighted Average
138,603 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
12.4 100 0.0691 0.13 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
4.7 413 0.0850 1.46 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
17.1 513 Total
Subcatchment E1: Existing Basin 1
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)2
1
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=138,603 sf
Runoff Volume=0.152 af
Runoff Depth>0.57"
Flow Length=513'
Tc=17.1 min
CN=69
2.16 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 5HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment E2: Existing Basin 2
Runoff =0.33 cfs @ 12.15 hrs, Volume=0.039 af, Depth>0.22"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
544 61 >75% Grass cover, Good, HSG B
4,899 74 >75% Grass cover, Good, HSG C
79,315 55 Woods, Good, HSG B
9,551 70 Woods, Good, HSG C
94,309 58 Weighted Average
94,309 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
11.0 100 0.0929 0.15 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
4.7 415 0.0875 1.48 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
15.7 515 Total
Subcatchment E2: Existing Basin 2
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)0.36
0.34
0.32
0.3
0.28
0.26
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=94,309 sf
Runoff Volume=0.039 af
Runoff Depth>0.22"
Flow Length=515'
Tc=15.7 min
CN=58
0.33 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 6HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment E3: Existing Basin 3
Runoff =0.08 cfs @ 12.12 hrs, Volume=0.013 af, Depth>0.15"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
43,914 55 Woods, Good, HSG B
43,914 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
10.8 100 0.0987 0.16 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
1.3 117 0.0926 1.52 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
12.1 217 Total
Subcatchment E3: Existing Basin 3
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)0.08
0.075
0.07
0.065
0.06
0.055
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=43,914 sf
Runoff Volume=0.013 af
Runoff Depth>0.15"
Flow Length=217'
Tc=12.1 min
CN=55
0.08 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 7HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P1: Proposed to BMP
Runoff =4.48 cfs @ 12.11 hrs, Volume=0.292 af, Depth>0.79"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
*12,953 98 Impervious - Buildings
*3,974 98 Impervious - Sidewalk
*38,203 98 Impervious - Pavement, Curb
*833 98 Impervious - Pavement, Curb - Offsite
*9,100 98 Impervious - Future Storage
43,940 61 >75% Grass cover, Good, HSG B
*15,093 61 >75% Grass cover, Good, HSG B - Offsite
30,204 74 >75% Grass cover, Good, HSG C
*1,005 74 >75% Grass cover, Good, HSG C - Offsite
36,964 55 Woods, Good, HSG B
192,269 74 Weighted Average
127,206 66.16% Pervious Area
65,063 33.84% Impervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
12.8 100 0.0640 0.13 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
2.3 236 0.1160 1.70 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
1.8 313 0.0210 2.94 Shallow Concentrated Flow, Curb Flow
Paved Kv= 20.3 fps
16.9 649 Total
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 8HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Subcatchment P1: Proposed to BMP
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)5
4
3
2
1
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=192,269 sf
Runoff Volume=0.292 af
Runoff Depth>0.79"
Flow Length=649'
Tc=16.9 min
CN=74
4.48 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 9HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P2: BMP Bypass
Runoff =1.19 cfs @ 12.03 hrs, Volume=0.061 af, Depth>0.80"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
40,018 74 >75% Grass cover, Good, HSG C
40,018 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
7.5 100 0.0877 0.22 Sheet Flow,
Grass: Dense n= 0.240 P2= 3.56"
2.6 245 0.0515 1.59 Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fps
10.1 345 Total
Subcatchment P2: BMP Bypass
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)1
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=40,018 sf
Runoff Volume=0.061 af
Runoff Depth>0.80"
Flow Length=345'
Tc=10.1 min
CN=74
1.19 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 10HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P5: Proposed Basin 2
Runoff =0.20 cfs @ 12.11 hrs, Volume=0.018 af, Depth>0.27"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
5,294 61 >75% Grass cover, Good, HSG B
3,397 74 >75% Grass cover, Good, HSG C
19,464 55 Woods, Good, HSG B
6,015 70 Woods, Good, HSG C
34,170 60 Weighted Average
34,170 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
10.0 100 0.1191 0.17 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
3.5 279 0.0724 1.35 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
13.5 379 Total
Subcatchment P5: Proposed Basin 2
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)0.22
0.21
0.2
0.19
0.18
0.17
0.16
0.15
0.14
0.13
0.12
0.11
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=34,170 sf
Runoff Volume=0.018 af
Runoff Depth>0.27"
Flow Length=379'
Tc=13.5 min
CN=60
0.20 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 11HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P6: Proposed Basin 3
Runoff =0.09 cfs @ 12.06 hrs, Volume=0.007 af, Depth>0.30"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-yr Rainfall=2.97"
Area (sf)CN Description
*431 98 Impervious - Pavement, Curb
8,479 61 >75% Grass cover, Good, HSG B
2,881 55 Woods, Good, HSG B
11,791 61 Weighted Average
11,360 96.34% Pervious Area
431 3.66% Impervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
9.6 100 0.0475 0.17 Sheet Flow,
Grass: Dense n= 0.240 P2= 3.56"
1.0 61 0.0205 1.00 Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fps
10.6 161 Total
Subcatchment P6: Proposed Basin 3
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)0.1
0.095
0.09
0.085
0.08
0.075
0.07
0.065
0.06
0.055
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
Type II 24-hr
1-yr Rainfall=2.97"
Runoff Area=11,791 sf
Runoff Volume=0.007 af
Runoff Depth>0.30"
Flow Length=161'
Tc=10.6 min
CN=61
0.09 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 12HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Pond P3: BMP 1
Inflow Area =4.414 ac,33.84% Impervious, Inflow Depth > 0.79" for 1-yr event
Inflow =4.48 cfs @ 12.11 hrs, Volume=0.292 af
Outflow =0.33 cfs @ 13.79 hrs, Volume=0.129 af, Atten= 93%, Lag= 100.7 min
Primary =0.33 cfs @ 13.79 hrs, Volume=0.129 af
Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Peak Elev= 2,182.19' @ 13.79 hrs Surf.Area= 7,002 sf Storage= 7,672 cf
Plug-Flow detention time= 224.1 min calculated for 0.128 af (44% of inflow)
Center-of-Mass det. time= 131.0 min ( 951.2 - 820.2 )
Volume Invert Avail.Storage Storage Description
#1 2,181.00'21,991 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet)(sq-ft)(cubic-feet)(cubic-feet)
2,181.00 5,873 0 0
2,182.00 6,809 6,341 6,341
2,183.00 7,809 7,309 13,650
2,184.00 8,873 8,341 21,991
Device Routing Invert Outlet Devices
#1 Primary 2,177.75'18.0" Round Culvert
L= 42.0' CPP, projecting, no headwall, Ke= 0.900
Inlet / Outlet Invert= 2,177.75' / 2,177.00' S= 0.0179 '/' Cc= 0.900
n= 0.011 HDPE, Flow Area= 1.77 sf
#2 Primary 2,182.25'5.0' long x 18.5' breadth Broad-Crested Rectangular Weir
Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63
#3 Device 1 2,182.00'48.0" Vert. Orifice/Grate C= 0.600
Primary OutFlow Max=0.33 cfs @ 13.79 hrs HW=2,182.19' (Free Discharge)
1=Culvert (Passes 0.33 cfs of 12.91 cfs potential flow)
3=Orifice/Grate (Orifice Controls 0.33 cfs @ 1.49 fps)
2=Broad-Crested Rectangular Weir ( Controls 0.00 cfs)
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 13HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Pond P3: BMP 1
Inflow
Primary
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)5
4
3
2
1
0
Inflow Area=4.414 ac
Peak Elev=2,182.19'
Storage=7,672 cf
4.48 cfs
0.33 cfs
Type II 24-hr 1-yr Rainfall=2.97"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 14HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Link P4: Total Proposed Basin 1
Inflow Area =5.333 ac,28.01% Impervious, Inflow Depth > 0.43" for 1-yr event
Inflow =1.19 cfs @ 12.03 hrs, Volume=0.190 af
Primary =1.19 cfs @ 12.03 hrs, Volume=0.190 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Link P4: Total Proposed Basin 1
Inflow
Primary
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)1
0
Inflow Area=5.333 ac
1.19 cfs
1.19 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 15HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN
Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method
Runoff Area=138,603 sf 0.00% Impervious Runoff Depth>2.42"Subcatchment E1: Existing Basin 1
Flow Length=513' Tc=17.1 min CN=69 Runoff=10.09 cfs 0.641 af
Runoff Area=94,309 sf 0.00% Impervious Runoff Depth>1.52"Subcatchment E2: Existing Basin 2
Flow Length=515' Tc=15.7 min CN=58 Runoff=4.35 cfs 0.275 af
Runoff Area=43,914 sf 0.00% Impervious Runoff Depth>1.31"Subcatchment E3: Existing Basin 3
Flow Length=217' Tc=12.1 min CN=55 Runoff=1.94 cfs 0.110 af
Runoff Area=192,269 sf 33.84% Impervious Runoff Depth>2.87"Subcatchment P1: Proposed to BMP
Flow Length=649' Tc=16.9 min CN=74 Runoff=16.68 cfs 1.054 af
Runoff Area=40,018 sf 0.00% Impervious Runoff Depth>2.87"Subcatchment P2: BMP Bypass
Flow Length=345' Tc=10.1 min CN=74 Runoff=4.32 cfs 0.220 af
Runoff Area=34,170 sf 0.00% Impervious Runoff Depth>1.68"Subcatchment P5: Proposed Basin 2
Flow Length=379' Tc=13.5 min CN=60 Runoff=1.90 cfs 0.110 af
Runoff Area=11,791 sf 3.66% Impervious Runoff Depth>1.76"Subcatchment P6: Proposed Basin 3
Flow Length=161' Tc=10.6 min CN=61 Runoff=0.77 cfs 0.040 af
Peak Elev=2,182.90' Storage=12,865 cf Inflow=16.68 cfs 1.054 afPond P3: BMP 1
Outflow=13.84 cfs 0.878 af
Inflow=15.60 cfs 1.098 afLink P4: Total Proposed Basin 1
Primary=15.60 cfs 1.098 af
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 16HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment E1: Existing Basin 1
Runoff =10.09 cfs @ 12.10 hrs, Volume=0.641 af, Depth>2.42"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
20,567 61 >75% Grass cover, Good, HSG B
*15,093 61 >75% Grass cover, Good, HSG B, Offsite
92,037 74 >75% Grass cover, Good, HSG C
*23 74 >75% Grass cover, Good, HSG C, Offsite
10,883 55 Woods, Good, HSG B
138,603 69 Weighted Average
138,603 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
12.4 100 0.0691 0.13 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
4.7 413 0.0850 1.46 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
17.1 513 Total
Subcatchment E1: Existing Basin 1
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)11
10
9
8
7
6
5
4
3
2
1
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=138,603 sf
Runoff Volume=0.641 af
Runoff Depth>2.42"
Flow Length=513'
Tc=17.1 min
CN=69
10.09 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 17HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment E2: Existing Basin 2
Runoff =4.35 cfs @ 12.09 hrs, Volume=0.275 af, Depth>1.52"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
544 61 >75% Grass cover, Good, HSG B
4,899 74 >75% Grass cover, Good, HSG C
79,315 55 Woods, Good, HSG B
9,551 70 Woods, Good, HSG C
94,309 58 Weighted Average
94,309 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
11.0 100 0.0929 0.15 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
4.7 415 0.0875 1.48 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
15.7 515 Total
Subcatchment E2: Existing Basin 2
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)4
3
2
1
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=94,309 sf
Runoff Volume=0.275 af
Runoff Depth>1.52"
Flow Length=515'
Tc=15.7 min
CN=58
4.35 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 18HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment E3: Existing Basin 3
Runoff =1.94 cfs @ 12.06 hrs, Volume=0.110 af, Depth>1.31"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
43,914 55 Woods, Good, HSG B
43,914 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
10.8 100 0.0987 0.16 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
1.3 117 0.0926 1.52 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
12.1 217 Total
Subcatchment E3: Existing Basin 3
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)2
1
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=43,914 sf
Runoff Volume=0.110 af
Runoff Depth>1.31"
Flow Length=217'
Tc=12.1 min
CN=55
1.94 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 19HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P1: Proposed to BMP
Runoff =16.68 cfs @ 12.09 hrs, Volume=1.054 af, Depth>2.87"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
*12,953 98 Impervious - Buildings
*3,974 98 Impervious - Sidewalk
*38,203 98 Impervious - Pavement, Curb
*833 98 Impervious - Pavement, Curb - Offsite
*9,100 98 Impervious - Future Storage
43,940 61 >75% Grass cover, Good, HSG B
*15,093 61 >75% Grass cover, Good, HSG B - Offsite
30,204 74 >75% Grass cover, Good, HSG C
*1,005 74 >75% Grass cover, Good, HSG C - Offsite
36,964 55 Woods, Good, HSG B
192,269 74 Weighted Average
127,206 66.16% Pervious Area
65,063 33.84% Impervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
12.8 100 0.0640 0.13 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
2.3 236 0.1160 1.70 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
1.8 313 0.0210 2.94 Shallow Concentrated Flow, Curb Flow
Paved Kv= 20.3 fps
16.9 649 Total
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 20HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Subcatchment P1: Proposed to BMP
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=192,269 sf
Runoff Volume=1.054 af
Runoff Depth>2.87"
Flow Length=649'
Tc=16.9 min
CN=74
16.68 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 21HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P2: BMP Bypass
Runoff =4.32 cfs @ 12.02 hrs, Volume=0.220 af, Depth>2.87"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
40,018 74 >75% Grass cover, Good, HSG C
40,018 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
7.5 100 0.0877 0.22 Sheet Flow,
Grass: Dense n= 0.240 P2= 3.56"
2.6 245 0.0515 1.59 Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fps
10.1 345 Total
Subcatchment P2: BMP Bypass
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)4
3
2
1
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=40,018 sf
Runoff Volume=0.220 af
Runoff Depth>2.87"
Flow Length=345'
Tc=10.1 min
CN=74
4.32 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 22HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P5: Proposed Basin 2
Runoff =1.90 cfs @ 12.07 hrs, Volume=0.110 af, Depth>1.68"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
5,294 61 >75% Grass cover, Good, HSG B
3,397 74 >75% Grass cover, Good, HSG C
19,464 55 Woods, Good, HSG B
6,015 70 Woods, Good, HSG C
34,170 60 Weighted Average
34,170 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
10.0 100 0.1191 0.17 Sheet Flow,
Woods: Light underbrush n= 0.400 P2= 3.56"
3.5 279 0.0724 1.35 Shallow Concentrated Flow,
Woodland Kv= 5.0 fps
13.5 379 Total
Subcatchment P5: Proposed Basin 2
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)2
1
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=34,170 sf
Runoff Volume=0.110 af
Runoff Depth>1.68"
Flow Length=379'
Tc=13.5 min
CN=60
1.90 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 23HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Subcatchment P6: Proposed Basin 3
Runoff =0.77 cfs @ 12.03 hrs, Volume=0.040 af, Depth>1.76"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Type II 24-hr 25-yr Rainfall=5.92"
Area (sf)CN Description
*431 98 Impervious - Pavement, Curb
8,479 61 >75% Grass cover, Good, HSG B
2,881 55 Woods, Good, HSG B
11,791 61 Weighted Average
11,360 96.34% Pervious Area
431 3.66% Impervious Area
Tc Length Slope Velocity Capacity Description
(min)(feet)(ft/ft)(ft/sec)(cfs)
9.6 100 0.0475 0.17 Sheet Flow,
Grass: Dense n= 0.240 P2= 3.56"
1.0 61 0.0205 1.00 Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fps
10.6 161 Total
Subcatchment P6: Proposed Basin 3
Runoff
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
Type II 24-hr
25-yr Rainfall=5.92"
Runoff Area=11,791 sf
Runoff Volume=0.040 af
Runoff Depth>1.76"
Flow Length=161'
Tc=10.6 min
CN=61
0.77 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 24HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Pond P3: BMP 1
Inflow Area =4.414 ac,33.84% Impervious, Inflow Depth > 2.87" for 25-yr event
Inflow =16.68 cfs @ 12.09 hrs, Volume=1.054 af
Outflow =13.84 cfs @ 12.18 hrs, Volume=0.878 af, Atten= 17%, Lag= 5.1 min
Primary =13.84 cfs @ 12.18 hrs, Volume=0.878 af
Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Peak Elev= 2,182.90' @ 12.18 hrs Surf.Area= 7,708 sf Storage= 12,865 cf
Plug-Flow detention time= 77.9 min calculated for 0.875 af (83% of inflow)
Center-of-Mass det. time= 30.2 min ( 823.6 - 793.4 )
Volume Invert Avail.Storage Storage Description
#1 2,181.00'21,991 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet)(sq-ft)(cubic-feet)(cubic-feet)
2,181.00 5,873 0 0
2,182.00 6,809 6,341 6,341
2,183.00 7,809 7,309 13,650
2,184.00 8,873 8,341 21,991
Device Routing Invert Outlet Devices
#1 Primary 2,177.75'18.0" Round Culvert
L= 42.0' CPP, projecting, no headwall, Ke= 0.900
Inlet / Outlet Invert= 2,177.75' / 2,177.00' S= 0.0179 '/' Cc= 0.900
n= 0.011 HDPE, Flow Area= 1.77 sf
#2 Primary 2,182.25'5.0' long x 18.5' breadth Broad-Crested Rectangular Weir
Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63
#3 Device 1 2,182.00'48.0" Vert. Orifice/Grate C= 0.600
Primary OutFlow Max=13.65 cfs @ 12.18 hrs HW=2,182.89' (Free Discharge)
1=Culvert (Passes 6.73 cfs of 14.08 cfs potential flow)
3=Orifice/Grate (Orifice Controls 6.73 cfs @ 3.22 fps)
2=Broad-Crested Rectangular Weir (Weir Controls 6.92 cfs @ 2.15 fps)
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 25HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Pond P3: BMP 1
Inflow
Primary
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Inflow Area=4.414 ac
Peak Elev=2,182.90'
Storage=12,865 cf
16.68 cfs
13.84 cfs
Type II 24-hr 25-yr Rainfall=5.92"Sanstone
Printed 7/15/2020Prepared by Brooks EA
Page 26HydroCAD® 10.00-24 s/n 05122 © 2018 HydroCAD Software Solutions LLC
Summary for Link P4: Total Proposed Basin 1
Inflow Area =5.333 ac,28.01% Impervious, Inflow Depth > 2.47" for 25-yr event
Inflow =15.60 cfs @ 12.16 hrs, Volume=1.098 af
Primary =15.60 cfs @ 12.16 hrs, Volume=1.098 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs
Link P4: Total Proposed Basin 1
Inflow
Primary
Hydrograph
Time (hours)
201918171615141312111098765Flow (cfs)17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Inflow Area=5.333 ac
15.60 cfs
15.60 cfs

Appendix “4”

Total:Disturbed:Top:Bottom:Top:Bottom:
1 5.10 3.10 0.48 7.06 8.87 17.37 21.82 5,644.5 5,580.0 2178.0'130.0 117.0 78.0 65.0 8,873.0 3.25 28,835.6
Skimmer Sediment Basin Design Notes:
1. Sediment Basins have been designed in accordance with the North Carolina Erosion
and Sediment Control Planning and Design Manual Standard (Revision number
6/06) Standard number 6.64
2. Maximum Drainage Area = 10 Acres
3. Minimum Volume = 1800 ft3 per Acre of Disturbed Area.
4. Minimum Surface Area = 325 ft2 per Q10 (cfs) of peak inflow.
5. Dewatering time is from 24 to 72 hours
6. Each basin requires 3 baffles
Basin
#:Drainage area (ac.)Weighted
C:
50yr
intensity:
Drainage Area / Flow Calcs.:
10yr
intensity:
Q50
(cfs):
Depth
(ft.):
Length (ft):Width (ft.):Area (ft2):
Q10
(cfs):
Min. Surface
Area (ft2)
Min. Volume
(ft3)
Volume
(ft3):
SKIMMER SEDIMENT BASIN SIZING CHART
Sanstone Office & Storage Expansion
Bottom
Elevation:
Min. Size Calcs.:Basin Storage Dimensions:
1
Basin
#:
48 hours 1 2.0 in 1.8in 2181.25'2181.75'11.0' X 2.0'1.98 0.82 1.93 2184.0'
General Notes:
Date: 04/14/20
Calculations By: BMT
Dewatering
Time (hrs.):
Emergency
Spillway V(f/s):
Emergency
Spillway Dim.:
Top of
Dam El.:
Free-board
(ft):
Emergency
Spillway El.:
Skimmer
Orifice Size:
Ponding
Elevation:
Spillway Calcs.:
Skimmer
Size:
Number of
Skimmers:
Water
Depth (ft):
PIPE CHART PIPE CALCULATIONS
Road Pipe Road Up Down Pipe Pipe DRAINAGE UPSTREAM FLOW DESIGN FLOW RESULTS OUTLET PROTECTION CALCS
Station Name Elevation Invert Invert Size Material Length Slope Da to Inlet Da to Inlet C Value TOC 10yr I q inlet nf structure Upstream q Total q Flow Depth Velocity d50 Stone Size Apron Thickness Pad Length Pad Width
10+20 B 2224.0'2220.5'2220.0'18.0 in HDPE 64 ft 0.8%2,187 sf 0.05 ac 0.30 5 min 7.28 0.11 cfs 0.011 SW2 0.75 cfs 0.86 cfs 3.6 in 3.5 fps 6 in 9 in 10 ft 15 ft
Swale Swale Swale Up Down Side btm width
Number Name Type Invert Invert Slope - Z b(ft)Length Slope Da to Inlet Da to Inlet C Value TOC 10yr I q swale nf Flow Depth Velocity Sheer Stress
1 SW1 GRASS 2228.6'2220.0'2.0 0.5 ft 235 ft 3.7%17,036 sf 0.39 ac 0.30 11 min 5.64 0.66 cfs 0.030 2.9 in 2.8 fps 0.50 NAG C700BN (temporary)
2 SW2 GRASS 2228.6'2220.5'2.0 0.5 ft 185 ft 4.4%18,766 sf 0.43 ac 0.30 10 min 5.80 0.75 cfs 0.030 3.0 in 3.0 fps 0.60 NAG C700BN (temporary)
RESULTS
Reinforcement
SWALE CALCULATIONS
DRAINAGE
SWALE CHART
DESCRIPTION
The permanent erosion control blanket shall be a machine-produced
mat of 100% UV stable polypropylene fiber. The matting shall be of
consistent thickness with the synthetic fibers evenly distributed over
the entire area of the mat. The matting shall be covered on the top
side with black heavyweight UV-stabilized polypropylene netting
having ultraviolet additives to delay breakdown and an approximate
0.50 x 0.50 inch (1.27 x 1.27 cm) mesh. The bottom net shall also be UV-
stabilized polypropylene with a 0.63 x 0.63 inch (1.57 x 1.57 cm) mesh
size. The blanket shall be sewn together on 1.5 inch (3.81 cm) centers
with non-degradable thread. All mats shall be manufactured with a
colored thread stitched along both outer edges as an overlap guide for
adjacent mats. The P300 shall meet Type 5A, 5B, specification
requirements established by the Erosion Control Technology Council
(ECTC) and Federal Highway Administration’s (FHWA) FP-03
Section 713.18
Material Content
Matrix 100% UV stable
Polypropylene Fiber
0.7 lbs/sq yd
(0.38 kg/sm)
Netting
Top: UV-stabilized Polypropylene
Bottom: UV-stabilized Polypropylene
5 lbs/1000 sq ft
(24.4 g/sm)
3 lbs/1000 sq ft
(14.7 g/sm)
Thread Polypropylene, UV stable
Standard Roll Sizes
Width 6.5 ft (2.0 m)8 ft (2.44 m)
Length 108 ft (32.92 m) 112 ft (35.14 m)
Weight ± 10%61 lbs (27.66 kg) 76.25 lbs (34.59 kg)
Area 80 sq yd (66.0 sm) 100 sq yd (83.61 sm)
Slope Design Data: C Factors
Slope Gradients (S)
Slope Length (L)≤ 3:1 3:1 – 2.1 ≥ 2:1
≤ 20 ft (6 m)0.001 0.029 0.082
20-50 ft 0.036 0.060 0.086
≥ 50 ft (15.2 m)0.070 0.090 0.110
Index Property Test Method Typical
Thickness ASTM D6525 0.47 in.
(11.94 mm)
Resiliency ASTM D6524 91.5%
Density ASTM D792 0.916 g/cm3
Mass/Unit Area ASTM 6566 13.03 oz/sy
(443 g/m2)
UV Stability ASTM D4355/
1000 hr 90%
Porosity ECTC Guidelines 95.89%
Stiffness ASTM D1388 0.94 in-lb
(1085378 mg-cm)
Light Penetration ASTM D6567 17.9%
Tensile Strength - MD ASTM D6567 438 lbs/ft
(6.49 kN/m)
Elongation - MD ASTM D6818 28.1%
Tensile Strength - TD ASTM D6818 291.9 lbs/ft
(4.32 kN/m)
Elongation - TD ASTM D6818 26.7%
Biomass Improvement ASTM D7322 497%
Design Permissible Shear Stress
Short Duration Long Duration
Phase 1: Unvegetated 3.0 psf (144 Pa)2.0 psf (96 Pa)
Phase 2: Partially Veg.8.0 psf (383 Pa)8.0 psf (383 Pa)
Phase 3: Fully Veg.8.0 psf (383 Pa)8.0 PSF (383 Pa)
Unvegetated Velocity 9.0 fps (2.7 m/s)
Vegetaged Velocity 16 fps (4.9 m/s)
Roughness Coefficients – Unveg.
Flow Depth Manning’s n
≤ 0.50 ft (0.15 m)0.034
0.50 – 2.0 ft 0.034-0.020
≥ 2.0 ft (0.60 m)0.020
Specification Sheet – EroNet™ P300 ® Permanent Erosion Control Blanket
Tensar International Corporation warrants that at the time of delivery the product furnished
hereunder shall conform to the specification stated herein. Any other warranty including
merchantability and fitness for a particular purpose, are hereby executed. If the product
does not meet specifications on this page and Tensar is notified prior to installation, Tensar
will replace the product at no cost to the customer. This product specification supersedes
all prior specifications for the product described above and is not applicable to any
products shipped prior to January 1, 2012.
©2013, Tensar International Corporation
Tensar International Corporation
2500 Northwinds Parkway
Suite 500
Alpharetta, GA 30009
800-TENSAR-1
tensarcorp.com EC_RMX_MPDS_P300_5.13