Tanglewood Business Park - 17-061 Tanglewood Business Park Phase I - SWM Study

Tanglewood Business Park – Phase I

Table of Contents

Stormwater Management Narrative

Soils Map

USGS Map

Composite Runoff Curve Numbers

NOAA Rainfall Data (Precipitation Depth)

Wet Detention Pond Calculations

Watershed Model Schematic, Pond Report, and Stage Storage Discharge

1 Yr 24 Hr Stormwater Summary Report & Pre, Post, and Routed
Hydrographs (with Pond Report & TR-55 Time of Concentration
Worksheets)

50 Yr 6 Hr Stormwater Summary Report & Storm Pre, Post, and Routed
Hydrographs

100 Yr 6 Hr Stormwater Summary Report & Storm Pre, Post, and Routed
Hydrographs

Appendix

Seasonal High Water Table Study

Wetland & Stream Delineation Map

NC DEQ Notice of Exemption to NC Dam Safety Law

Exhibits

EX-1.0 Drainage Area Map – Pre-Development

EX-1.1 Drainage Area Map – Post-Development

Tanglewood Business Park – Phase I
Winston-Salem, NC

INTRODUCTION
The proposed Tanglewood Business Park is located adjacent to Idols Road in Forsyth County,
North-Carolina. The site is located just outside of the Village of Clemmons jurisdictional limits
and is approximately 1,200 linear feet southwest of the Idols Road and Dillon Industrial Drive
intersection. The site can be currently accessed by a gate and gravel drive at the end of
Topsider Drive. The 169.74 acre site is currently undeveloped and consists of predominantly
wooded ground cover.

Tanglewood Business Park will be developed in two phases and will serve as an Industrial park
with approximately six lots. The park will be accessed from Topsider Drive, which will be
extended through the property over the course of the two phases and connected to Idols Road
at the Idols Road and Foxpark Drive Intersection. The project will consist of installing a storm
drainage conveyance system that will direct stormwater runoff towards a proposed wet
detention pond that will treat the stormwater runoff. Lots that are not served by the wet
detention pond will be served by other stormwater control measures that will be designed
during the phase 2 design of the park or as each individual lot is developed. The extension of
Topsider Drive crosses a stream and will require the installation of a culvert under the proposed
roadway in order to maintain the conveyance of runoff within the existing stream channel. The
project also consists of a water main extension along Topsider Drive and the installation of a
new sanitary sewer line that will serve the park and gravity drain to the future Idols Road Pump
Station. The future Idols Road Pump Station will be located on-site along the southern property
line and is to be constructed by others under a different project.

Phase I development will consist of the Topsider Drive extension, water main extension,
sanitary sewer line installation, culvert installation, and the wet detention pond installation.
Refer to the construction drawings for the extents of all Phase I items. The proposed wet
detention pond has been designed to manage a drainage area of 68.67 acres and will treat
runoff from the Phase I development and select areas of the future phase II development. Refer
to EX-1.1 Drainage Area Map – Post-Development for a delineation of the wet detention pond
drainage area. The location of this project is within a Phase II designated area and therefore
has been designed to comply with the Phase II Post-Construction design guidelines. The
proposed wet detention pond has been designed to satisfy the wet pond requirements per the
current NCDEQ Stormwater Design manual. Additional management in regard to volume
and/or peak flow attenuation were not required for this project.

DRAINAGE BASIN
The pre-developed condition is comprised of a single drainage basin, which drains towards the
south west property line and into an existing draw that passes through an adjacent residential
property. A hydrograph was calculated for the Pre Development Area (Hydr. #3).The ground
cover for this area prior to development is mostly wooded with some smaller areas of grassed
and impervious cover. A composite pre-developed curve number was calculated for the Pre
Development Area (Hydr. #3) based on ground cover and soil type coverage of the
predeveloped area.

The post-developed area is comprised of two drainage basins, which are referred to as Post
Development Bypass (Hydr. #4) and Post Development (Hydr. #1); Post Development (Hydr.
#1) represents the drainage area to the proposed Wet Detention Pond prior to detention.

The stormwater management system was modeled by routing Post Development (Hydr. #1)
through the Wet Detention Pond. The discharge hydrograph from the Wet Detention Pond
(Hydr. #2) is then combined with Post Development Bypass (Hydr. #4) to create a combined
hydrograph (Hydr. #5), which provides post development runoff rates. This is then compared to
the pre-development rates (Hydr. #3) for the 1-year 24 Hour storm event.

SOILS AND CURVE NUMBER
Soils information was obtained from the City of Winston Salem GIS website. The City
references the U.S. Department of Agriculture, Natural Resources Conservation Service dated
2-16-2001 as the source.

Pre-developed and Post-developed curve numbers were calculated for each drainage basin
based on the SCS curve numbers. Soils present on this site have a hydrologic soils group
classification of ‘B’.

TIME OF CONCENTRATION
Several methods are available and are widely accepted for estimating time of concentration
(SCS Lag (1), Kirpich (2), and TR-55 Methods (3)). TR-55 method was used for detention
calculations. Calculated time of concentration values less than 0.1 hours (6 min.) are rounded
up to 6 minutes, as this is the minimum Tc in TR-55. Post developed time of concentration
consists of TR-55 method for overland flow added to the calculated pipe travel time. The pre
and post developed drainage maps shows the travel path used in the time of concentration
calculations. See the time of concentration section for documentation.

PRECIPITATION
Precipitation data for the study was taken from NOAA ATLAS 14, Volume 2. NOAA Atlas 14
Volume 2 contains precipitation frequency estimates for Delaware, District of Columbia, Illinois,
Indiana, Kentucky, Maryland, New Jersey, North Carolina, Ohio, Pennsylvania, South Carolina,
Tennessee, Virginia, and West Virginia. These areas were addressed together in a single
project focused on the Ohio River basin and surrounding states. The Atlas supercedes
precipitation frequency estimates contained in Technical Paper No. 40 “Rainfall frequency atlas
of the United States for durations from 30 minutes to 24 hours and return periods from 1 to 100
years” (Hershfield, 1961), NWS HYDRO-35 “Five- to 60-minute precipitation frequency for the
eastern and central United States” (Frederick et al., 1977) and Technical Paper No. 49 “Two- to
ten-day precipitation for return periods of 2 to 100 years in the contiguous United States” (Miller
et al., 1964). NOAA ATLAS 14, Volume 2 is based on more recent and extended data sets,
currently accepted statistical approaches, and improved spatial interpolation and mapping
techniques. The work was performed by the Hydrometeorological Design Studies Center within
the Office of Hydrologic Development of the National Oceanic and Atmospheric
Administration’s National Weather Service. Precipitation depths used in the study are as
follows:

Precipitation (P) – NOAA Atlas 14 Volume 2 (24-Hour)
1-Year 2.78in.

Precipitation (P) – NOAA Atlas 14 Volume 2 (6-Hour)
50-Year 4.47in.
100-Year 4.95in.
HYDROGRAPHS
Hydraflow Hydrographs by Intelisolve(4) computer software was used to automate the
hydrograph and routing procedure. Hydraflow Hydrographs uses the Unit Hydrograph Method
for calculating runoff hydrographs. More specifically, it uses the triangular D-hour Unit
Hydrograph approach as used in TR-20 (5). Hydrographs were calculated based on a peaking
(shape) factor of 484.

ROUTINGS
Storm hydrograph routing through was performed using the Storage Indication Method as
outlined in NEH-4(6).

SYSTEM CONFIGURATION
The stormwater management system proposed for this project is a wet detention pond. The
pond will be located on the south side of the Topsider Drive road extension and to the east of
the proposed phase I stream crossing. Stormwater runoff will enter the pond by the way of a
60” RCP at the downstream end of the proposed conveyance system that captures the runoff
from the project area.

The wet detention pond has a forebay area located at the entry section of the pond. The
forebay volume is approximately 20% of the of the main pool volume and is designed to pre-
treat stormwater as it enters the pond. The proposed permanent pool elevation is located at the
center of a 10 foot wide vegetated shelf. The pond is also designed to have 1 foot of sediment
storage at the pond bottom. The ponds outlet system will consist of a precast riser, trash rack,
drawdown orifice, bottom drain, and 30 inch D.I. outlet barrel. There is also a 25 foot wide
emergency spillway located 2 feet below the top of dam. The outlet barrel discharges
stormwater into a rip rap discharge channel before entering the nearby stream that ultimately
drains to the Yadkin River.

Design elevations for the pond are as follows:

Location Elevation
Top of Dam 740.50
Emergency Spillway 738.50
Top of Riser 737.00
Top of Shelf 734.50
Permanent Pool & Drawdown Orifice 734.00
Bottom of Shelf 733.50
Bottom of Pond 726.00
Bottom of Sediment Storage Zone 725.00

STUDY POINT #1 PRE / POST / ROUTED RELEASE RATES AND ELEVATION TABLE
– 24 HR STORM

Flows Represented in this Comparison are based on SCS 1-yr, 24-hr design storm.

1 yr. 24 hr.
PRE-
DEVELOPED
1yr. 24 hr.
POST
DEVELOPED
ELEVATION
*FIRST 1 in.
VOLUME
RELEASE
RATE
14.37 cfs 10.07 cfs 737.26 0.457cfs
*Drawdown time is 2.52 days-see drawdown calculations in Wet Detention Pond
Calculations Section.

NARRATIVE REFERENCES:
(1) SCS, 1972 - (Soil Conservation Service).
(2) Z. P. Kirpich, 1940.
(3) Technical Release No. 55, USDA Soil Conservation Service, December 1993
(4) Hydrowflow Hydrographs Version 2007 (9.24), Intelisolve Software
(5) TR-20: Computer Program Manual 1992
(6) National Engineering Handbook Section 4-Hydrology, USDA Soil Conservation Service,
1972
(7) NOAA Atlas 14, Volume 2, Version 3 – Point Precipitation Frequency Estimates
SOILS MAPS
Hydrologic Soil Group—Forsyth County, North Carolina
(Idols Road - Hydrologic Soil Group)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/27/2017
Page 1 of 439823003982500398270039829003983100398330039835003983700398390039841003982300398250039827003982900398310039833003983500398370039839003984100554200554400554600554800555000555200555400555600
554200 554400 554600 554800 555000 555200 555400 555600
36° 0' 1'' N 80° 23' 57'' W36° 0' 1'' N80° 22' 55'' W35° 58' 55'' N
80° 23' 57'' W35° 58' 55'' N
80° 22' 55'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 17N WGS84
0 450 900 1800 2700
Feet
0 100 200 400 600
Meters
Map Scale: 1:10,000 if printed on A portrait (8.5" x 11") sheet.
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
1:15,800.
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: Forsyth County, North Carolina
Survey Area Data: Version 16, Sep 19, 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—Mar
15, 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—Forsyth County, North Carolina
(Idols Road - Hydrologic Soil Group)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/27/2017
Page 2 of 4
Hydrologic Soil Group
Hydrologic Soil Group— Summary by Map Unit — Forsyth County, North Carolina (NC067)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
ClB Clifford sandy loam, 2 to
6 percent slopes
A 3.8 1.2%
ClC Clifford sandy loam, 6 to
10 percent slopes
A 1.9 0.6%
CoA Codorus loam, 0 to 2
percent slopes,
frequently flooded
B/D 30.7 9.7%
FaD Fairview fine sandy
loam, 10 to 15 percent
slopes
B 5.2 1.7%
OkC Oak Level loam, dark
surface, 6 to 10
percent slopes
C 7.2 2.3%
OkD Oak Level loam, dark
surface, 10 to 15
percent slopes
C 5.3 1.7%
RaB Rasalo fine sandy loam,
2 to 6 percent slopes
C 25.7 8.1%
RaC Rasalo fine sandy loam,
6 to 10 percent slopes
C 24.0 7.6%
RaD Rasalo fine sandy loam,
10 to 15 percent
slopes
C 27.9 8.8%
SmC Siloam sandy loam, 4 to
10 percent slopes
D 2.4 0.7%
SmD Siloam sandy loam, 10
to 15 percent slopes
D 12.0 3.8%
SmF Siloam sandy loam, 15
to 45 percent slopes
D 7.2 2.3%
TmB Tomlin loam, 2 to 6
percent slopes
B 58.6 18.6%
TmC Tomlin loam, 6 to 10
percent slopes
B 43.7 13.9%
TmD Tomlin loam, 10 to 15
percent slopes
B 22.5 7.1%
ToB2 Tomlin clay loam, 2 to 6
percent slopes,
moderately eroded
B 3.9 1.2%
ToC2 Tomlin clay loam, 6 to
10 percent slopes,
moderately eroded
B 6.0 1.9%
WmB Wickham fine sandy
loam, mesic, 2 to 6
percent slopes
B 27.2 8.6%
Hydrologic Soil Group—Forsyth County, North Carolina Idols Road - Hydrologic Soil Group
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/27/2017
Page 3 of 4
Hydrologic Soil Group— Summary by Map Unit — Forsyth County, North Carolina (NC067)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
Totals for Area of Interest 315.1 100.0%
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.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Forsyth County, North Carolina Idols Road - Hydrologic Soil Group
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/27/2017
Page 4 of 4
USGS MAP

date:
EXHIBIT description:
project:
scale:
job #:
sheet of
05/21/2018 17-061
Tanglewood Business Park - Phase I
1" = 800'1 1
USGS Map (7.5 Minute Map for Advance, NC)
SITE
COMPOSITE RUNOFF CURVE NUMBERS
Project :Tanglewood Business Park Sheet : 1
Project No.:17-061 Date : 5/29/2018
Designed by:AWK
Checked by:
DRAINAGE AREA TO STUDY POINT 1
BASIN LAND USE SOIL HYDROL. AREA AREA CURVE NO CN x
NAME GROUP (AC.) ( % ) (CN)AREA
*TmB B 68.08 90.94%60 4085
0.27 0.36%98 26
*TmB B 6.52 8.70%69 450
TOTALS 74.86 100.0% 4560
WEIGHTED CN (PRE-DEVELOPED) = 61
POST-DEVELOPED CONDITIONS - To Pond
BASIN LAND USE SOIL HYDROL. AREA AREA CURVE NO CN x
NAME GROUP (AC.) ( % ) (CN)AREA
9.80 14.27%98 960
*WmB B 4.20 6.12%69 290
21.64 31.51%98 2121
*TmB B 3.82 5.56%69 263
4.78 6.96%98 469
*TmB B 0.84 1.23%69 58
3.88 5.64%98 380
*TmB B 0.68 1.00%69 47
5.49 8.00%98 538
*TmC B 2.35 3.43%69 162
2.08 3.03%98 204
*TmB B 1.36 1.99%69 94
*TmB B 3.82 5.56%69 264
2.75 4.00%98 269
*TmB B 1.18 1.71%69 81
TOTALS 68.67 100.0% 6200
WEIGHTED CN (DEVELOPED) = 90
BASIN LAND USE SOIL HYDROL. AREA AREA CURVE NO CN x
NAME GROUP (AC.) ( % ) (CN)AREA
*TmB B 15.70 20.97%60 942
0.00 0.00%98 0
*TmB B 4.64 6.20%69 320
TOTALS 20.34 27.2% 1262
WEIGHTED CN (PRE-DEVELOPED) = 62
* Dominant soil group only is listed above; refer to soil map for complete list of soil types within each area.
PRE-DEVELOPED CONDITIONS
Woods - Fair
Impervious
Open Space - Fair Co.
Lot 5 - Open Space - Fair Condition
Lot 3 - Open Space - Fair Condition
Lot 5 - Impervious
SCS RUNOFF CURVE NUMBERS
R/W - Impervious
Lot 1 - Impervious
Lot 1 - Open Space - Fair Condition
Lot 2 - Impervious
Lot 6 - Impervious
Lot 6 - Open Space - Fair Condition
Lot 2 - Open Space - Fair Condition
Lot 3 - Impervious
Woods - Fair
Impervious
Open Space - Fair Co.
POST DEVELOPED CONDITIONS - Bypass
R/W - Open Space - Fair Condition
BMP Area - Open Space - Fair Cond.
Offsite Area - Impervious
Offsite Area - Open Space - Fair Co.
NOAA RAINFALL DATA
(PRECIPITATION DEPTHS)
9/15/2017 Precipitation Frequency Data Server
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.9917&lon=-80.3850&data=depth&units=english&series=pds 1/4
NOAA Atlas 14, Volume 2, Version 3
Location name: Clemmons, North Carolina, USA*
Latitude: 35.9917°, Longitude: -80.385°
Elevation: 735.26 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 0.375
(0.346‑0.407)
0.445
(0.411‑0.484)
0.521
(0.480‑0.566)
0.573
(0.527‑0.622)
0.632
(0.579‑0.686)
0.672
(0.611‑0.729)
0.707
(0.639‑0.768)
0.737
(0.662‑0.804)
0.770
(0.684‑0.843)
0.792
(0.696‑0.870)
10-min 0.599
(0.552‑0.650)
0.711
(0.657‑0.774)
0.834
(0.769‑0.907)
0.916
(0.842‑0.995)
1.01
(0.922‑1.09)
1.07
(0.973‑1.16)
1.12
(1.01‑1.22)
1.17
(1.05‑1.27)
1.22
(1.08‑1.33)
1.25
(1.10‑1.37)
15-min 0.748
(0.690‑0.813)
0.894
(0.826‑0.973)
1.06
(0.972‑1.15)
1.16
(1.07‑1.26)
1.28
(1.17‑1.39)
1.35
(1.23‑1.47)
1.42
(1.28‑1.54)
1.47
(1.32‑1.61)
1.53
(1.36‑1.68)
1.57
(1.38‑1.72)
30-min 1.03
(0.946‑1.11)
1.24
(1.14‑1.34)
1.50
(1.38‑1.63)
1.68
(1.54‑1.82)
1.89
(1.73‑2.05)
2.04
(1.86‑2.22)
2.17
(1.97‑2.36)
2.30
(2.06‑2.50)
2.44
(2.17‑2.67)
2.54
(2.23‑2.79)
60-min 1.28
(1.18‑1.39)
1.55
(1.43‑1.69)
1.92
(1.77‑2.09)
2.19
(2.01‑2.37)
2.52
(2.31‑2.73)
2.76
(2.52‑3.00)
3.00
(2.71‑3.26)
3.22
(2.89‑3.51)
3.50
(3.11‑3.83)
3.70
(3.25‑4.07)
2-hr 1.49
(1.37‑1.61)
1.80
(1.66‑1.96)
2.25
(2.08‑2.45)
2.59
(2.38‑2.81)
3.02
(2.76‑3.28)
3.35
(3.04‑3.64)
3.68
(3.31‑3.99)
3.99
(3.56‑4.35)
4.41
(3.88‑4.82)
4.72
(4.10‑5.17)
3-hr 1.59
(1.47‑1.73)
1.93
(1.78‑2.10)
2.41
(2.23‑2.62)
2.78
(2.55‑3.01)
3.26
(2.98‑3.54)
3.63
(3.29‑3.94)
4.00
(3.60‑4.34)
4.36
(3.89‑4.74)
4.85
(4.26‑5.29)
5.21
(4.52‑5.71)
6-hr 1.93
(1.78‑2.11)
2.34
(2.16‑2.55)
2.92
(2.70‑3.19)
3.38
(3.10‑3.67)
3.99
(3.63‑4.33)
4.47
(4.04‑4.84)
4.95
(4.44‑5.37)
5.44
(4.82‑5.90)
6.10
(5.32‑6.64)
6.60
(5.69‑7.20)
12-hr 2.29
(2.12‑2.50)
2.77
(2.56‑3.03)
3.48
(3.20‑3.80)
4.04
(3.70‑4.40)
4.81
(4.36‑5.21)
5.42
(4.88‑5.86)
6.04
(5.39‑6.53)
6.69
(5.90‑7.23)
7.58
(6.57‑8.20)
8.28
(7.06‑8.96)
24-hr 2.78
(2.58‑3.00)
3.36
(3.12‑3.63)
4.21
(3.90‑4.55)
4.89
(4.52‑5.28)
5.80
(5.34‑6.27)
6.54
(6.00‑7.06)
7.29
(6.67‑7.87)
8.06
(7.35‑8.72)
9.13
(8.27‑9.89)
9.97
(8.99‑10.8)
2-day 3.23
(3.00‑3.47)
3.88
(3.62‑4.18)
4.83
(4.49‑5.19)
5.56
(5.16‑5.97)
6.54
(6.05‑7.03)
7.32
(6.75‑7.87)
8.11
(7.45‑8.72)
8.91
(8.16‑9.60)
10.0
(9.12‑10.8)
10.9
(9.86‑11.7)
3-day 3.42
(3.20‑3.68)
4.12
(3.84‑4.42)
5.10
(4.75‑5.47)
5.86
(5.45‑6.29)
6.89
(6.39‑7.39)
7.70
(7.12‑8.28)
8.53
(7.86‑9.18)
9.38
(8.61‑10.1)
10.5
(9.61‑11.4)
11.4
(10.4‑12.4)
4-day 3.62
(3.39‑3.89)
4.35
(4.07‑4.67)
5.36
(5.01‑5.75)
6.16
(5.75‑6.60)
7.24
(6.72‑7.76)
8.09
(7.49‑8.69)
8.96
(8.27‑9.64)
9.85
(9.05‑10.6)
11.1
(10.1‑12.0)
12.0
(10.9‑13.0)
7-day 4.15
(3.89‑4.44)
4.95
(4.64‑5.30)
6.02
(5.64‑6.43)
6.86
(6.42‑7.33)
8.00
(7.46‑8.56)
8.90
(8.27‑9.52)
9.81
(9.09‑10.5)
10.7
(9.92‑11.5)
12.0
(11.0‑12.9)
13.0
(11.9‑14.0)
10-day 4.72
(4.45‑5.02)
5.62
(5.30‑5.97)
6.75
(6.36‑7.18)
7.64
(7.19‑8.12)
8.83
(8.28‑9.38)
9.76
(9.13‑10.4)
10.7
(9.98‑11.4)
11.7
(10.8‑12.4)
12.9
(12.0‑13.8)
13.9
(12.8‑14.9)
20-day 6.36
(6.02‑6.71)
7.51
(7.11‑7.93)
8.88
(8.40‑9.38)
9.96
(9.41‑10.5)
11.4
(10.7‑12.1)
12.6
(11.8‑13.3)
13.7
(12.8‑14.5)
14.9
(13.9‑15.8)
16.5
(15.3‑17.5)
17.7
(16.3‑18.9)
30-day 7.87
(7.51‑8.27)
9.26
(8.82‑9.71)
10.7
(10.2‑11.3)
11.9
(11.3‑12.4)
13.4
(12.7‑14.0)
14.5
(13.7‑15.2)
15.6
(14.8‑16.4)
16.7
(15.8‑17.6)
18.2
(17.1‑19.2)
19.3
(18.0‑20.4)
45-day 9.90
(9.48‑10.4)
11.6
(11.1‑12.1)
13.2
(12.7‑13.8)
14.5
(13.9‑15.1)
16.2
(15.4‑16.9)
17.4
(16.5‑18.2)
18.6
(17.7‑19.5)
19.8
(18.7‑20.8)
21.3
(20.1‑22.4)
22.5
(21.1‑23.7)
60-day 11.8
(11.4‑12.4)
13.8
(13.3‑14.4)
15.6
(15.0‑16.2)
16.9
(16.2‑17.6)
18.6
(17.9‑19.4)
19.9
(19.1‑20.8)
21.2
(20.2‑22.1)
22.4
(21.3‑23.4)
23.9
(22.7‑25.0)
25.0
(23.7‑26.3)
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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9/15/2017 Precipitation Frequency Data Server
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PF graphical
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Small scale terrain
9/15/2017 Precipitation Frequency Data Server
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Large scale terrain
Large scale map
Large scale aerial
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2mi
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100km
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9/15/2017 Precipitation Frequency Data Server
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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
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–
100km
60mi
WET DETENTION POND CALCULATIONS
Project:IDOLS ROAD
Project No.:17-061
Designed By:AWK
Checked By:KBG Date:9/26/2017
Revised:
DRAINAGE BASIN INFORMATION
WATERSHED INFORMATION
On-Site Drainage Area to Pond =64.75 acres Watershed =Yadkin River
On-Site Proposed Impervious Area =47.67 acres Classification =Class IV
On-Site Future Impervious Area =0.00 acres
Total On-Site Impervious Area = 47.67 acres
Offsite Drainage Area to Pond =3.92 acres
Offsite Impervious Area =2.75 acres
Offsite Future Impervious Area =0.00 acres
Total Offsite Impervious Area = 2.75 acres
Total Drainage Area = 68.67 acres
Total Impervious Area = 50.41 acres
Total Impervious % = 73.4%
DETERMINE DESIGN VOLUME (DV)
Runoff Coefficient (Rv) = 0.05 + 0.9 x IA
IA = Impervious Fraction (Impervious Area/Drainage Area)
Design Volume (DV) = 3630 x RD x RV x A, (Cubic Feet)
RD = Design Storm Depth (in)
A = Drainage Area (ac)
Design Storm Depth (in) =1.00
IA =0.734
RV =0.711
DV =177,162 Cubic Feet
WATER QUALITY POND DESIGN
Wet Pond 1
ON-SITE DATA
OFFSITE DATA
SIMPLE METHOD
Page 1 WET DETENTION POND
POND SIZING CALCULATIONS
Stage-Storage Data
Stage
(Feet)
Elevation
(Feet)
Forebay Area
(SF)
Forebay
Volume
(CF)
Cumulative
Forebay
Volume
(CF)
Main Pool
Area
(SF)
Main Pool
Volume
(SF)
Cumulative
Main Pool
Volume
(CF)
Cumulative
Combined
Volume
(CF)
0.0 726.00 1519 0 0 31025 0 0 0
2.0 728.00 5622 7141 7141 35978 67003 67003 74144
4.0 730.00 8728 14350 21491 41146 77124 144127 165618
6.0 732.00 10835 19563 41054 46528 87674 231801 272855
7.5 733.50 12542 17533 58587 50706 72926 304727 363313
8.0 734.00 14442 6746 65333 55348 26514 331240 396573
8.5 734.50 75666 32754 363994 429326
10.0 736.00 81108 117580.5 481574 546907
12.0 738.00 88563 169671 651245 716578
14.0 740.00 96242 184805 836050 901383
14.5 740.50 98227 48617.25 884667.25 950000
CHECK FOREBAY SIZE
Stage at Permanent Pool = 8
Elevation = 734.00
Forebay Volume = 65,332.75
Main Pool Volume = 331,240.00
Forebay volume shall be 15-20% of Main Pool Volume : 19.72%Forebay Size OK
CHECK MAIN POOL SIZING
HRT Method (Hydraulic Retention Time Method)
Volume of Main Pool (VMP) = 0.87 x (HRT/Ts) x DV
0.87 = Factor to adjust for the volume of the forebay
VMP = Main pool volume, not including the forebay (CF)
HRT = Required hydraulic Retention time (14 days)
TS = Average time between storm events (5 days)
DV = Design Volume (CF)
VMP =431,567 Cubic Feet Volume Too Small Per HRT Method, Check SA/DA Method
SA/DA & Average Depth Method
Average depth when shelf is submerged:
Average Depth (Davg) = (VPP - Vshelf)/Abottomofshelf
Davg = Average depth in feet
VPP = Total volume of permanent pool (CF)
Vshelf = Volume over shelf only (CF)
Abottomofshelf = Area of wet pond at the bottom of the shelf (SF)
Vshelf = 0.5 x Depthmaxovershelf x Perimeterpermpool x Width submergedshelf
Depthmaxovershelf = Depth of water at the deep side of the shelf (FT)
Perimeterpermanentpool = Perimeter of permanent pool at bottom of shelf (FT)
Widthsubmergedshelf = Width from deep side of shelf to dry side (FT)
Page 2 WET DETENTION POND
Depthmaxovershelf =0.50 FT
Perimeterpermanentpool =1046.00 FT
Widthsubmergedshelf =5.00 FT
Vshelf =1,308 Cubic Feet
Stage at Bottom of Shelf =7.50
Elevation = 733.50
Abottomofshelf =50,706.00
VPP =331,240.00 Cubic Feet
Davg =6.51 FT
3.0 4.0 5.0 6.0 7.0 8.0
10% 0.51 0.43 0.37 0.30 0.27 0.25
20% 0.84 0.69 0.61 0.51 0.44 0.40
30% 1.17 0.94 0.84 0.72 0.61 0.56
40% 1.51 1.24 1.09 0.91 0.78 0.71
50% 1.79 1.51 1.31 1.13 0.95 0.87
60% 2.09 1.77 1.49 1.31 1.12 1.03
70% 2.51 2.09 1.80 1.56 1.34 1.17
80% 2.92 2.41 2.07 1.82 1.62 1.40
90% 3.25 2.64 2.31 2.04 1.84 1.59
100% 3.55 2.79 2.52 2.34 2.04 1.75
73.4% 2.65 2.20 1.89 1.65 1.44 1.25
Required SA/DA ratio =1.54
Required surface area = 46,085.68 SF
Provided surface area = 55,348.00 SF Provided Surface Area OK per SA/DA Method
20.1% Larger than required surface area
DETERMINE DESIGN VOLUME STORAGE ELEVATION & DESIGN ORIFICE DIAMETER
Design Volume Storage Elevation DV = 177,162 Cubic Feet
Permanent Pool Elevation = 734.00 Volume = 396,573 Cubic Feet
Contour Above Permanent Pool = 738.00 Volume = 716,578 Cubic Feet
Head Difference = 4.00 ∆ =320,005 Cubic Feet
Min. DV Elevation =736.21
Design Orifice Diameter
Orifice Equation: Q = Cd x A x (2gH)0.5
Cd = Coefficient of Discharge
A = Area of Orifice Opening, Based on Diameter of Orifice
g = gravity
H = Driving Head, Use H/3 for Drawdown Calculations
Q = Orifice Discharge
Percent
Impervious
Permanent Pool Average Depth (ft)
Table 1: Piedmont and Mountain SA/DA Table (Adapted from Driscoll, 1986)
Page 3 WET DETENTION POND
Cd = 0.6
Diameter of Orifice = 6.0 in
A = 0.19635 SF
g = 32.2
H = 2.21 FT
H/3 = 0.74 FT
Q = 0.812 CFS
Determine Drawdown Time
Drawdown Time = DV/Q
Target Drawdown Time = 2 - 5 Days
DV = 177,162 Cubic Feet
Drawdown Time = 60.59 Hrs
2.52 Days
Page 4 WET DETENTION POND
WATERSHED MODEL SCHEMATIC, POND
REPORT, AND STAGE STORAGE DISCHARGE
1
2 34
5
Watershed Model Schematic Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Project: Storm Routing.gpw Tuesday, 05 / 29 / 2018
Hyd.Origin Description
Legend
1 SCS Runoff Post to Pond
2 Reservoir Wet Pond
3 SCS Runoff Pre
4 SCS Runoff Post Bypass
5 Combine Post Total
Pond Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Tuesday, 05 / 29 / 2018
Pond No. 1 - Wet Pond
Pond Data
Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 726.00 ft
Stage / Storage Table
Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)
0.00 726.00 32,544 0 0
2.00 728.00 41,600 73,952 73,952
4.00 730.00 49,874 91,340 165,291
6.00 732.00 57,363 107,139 272,431
7.50 733.50 63,248 90,413 362,844
8.00 734.00 69,790 33,243 396,087
8.50 734.50 75,666 36,351 432,437
10.00 736.00 81,108 117,545 549,982
12.00 738.00 88,563 169,599 719,582
14.00 740.00 96,242 184,733 904,315
14.50 740.50 98,227 48,612 952,926
Culvert / Orifice Structures Weir Structures
[A] [B] [C] [PrfRsr] [A] [B] [C] [D]
Rise (in)= 30.00 6.00 0.00 0.00
Span (in)= 30.00 6.00 0.00 0.00
No. Barrels = 1 100
Invert El. (ft)= 725.00 734.00 0.00 0.00
Length (ft)= 140.00 0.00 0.00 0.00
Slope (%)= 4.12 0.00 0.00 n/a
N-Value = .013 .013 .013 n/a
Orifice Coeff.= 0.60 0.60 0.60 0.60
Multi-Stage = n/a Yes No No
Crest Len (ft)= 16.00 25.00 Inactive Inactive
Crest El. (ft)= 737.00 738.50 0.00 0.00
Weir Coeff.= 3.33 3.33 3.33 3.33
Weir Type = 1 Ciplti Rect ---
Multi-Stage = Yes NoNoNo
Exfil.(in/hr)= 0.000 (by Contour)
TW Elev. (ft)= 0.00
Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).
0.0 30.0 60.0 90.0 120.0 150.0 180.0 210.0 240.0 270.0 300.0 330.0
Stage (ft)
0.00 726.00
3.00 729.00
6.00 732.00
9.00 735.00
12.00 738.00
15.00 741.00
Elev (ft)
Discharge (cfs)
Stage / Discharge
Total Q
1-YR 24 HR STORM PRE, POST, AND ROUTED
HYDROGRAPHS
1-YR 24 HR STORMWATER SUMMARY REPORT &
STORM PRE, POST, AND ROUTED
HYDROGRAPHS (WITH POND REPORT & TR-55
TIME OF CONCENTRATION WORKSHEETS)
Hydrograph Summary Report
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 SCS Runoff 202.54 2 716 416,712 ------ ------ ------ Post to Pond
2 Reservoir 9.204 2 788 398,685 1 737.26 657,182 Wet Pond
3 SCS Runoff 14.37 2 726 75,615 ------ ------ ------ Pre
4 SCS Runoff 4.706 2 726 22,623 ------ ------ ------ Post Bypass
5 Combine 10.07 2 786 421,308 2, 4 ------ ------ Post Total
Storm Routing.gpw Return Period: 1 Year Wednesday, 05 / 30 / 2018
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Tuesday, 05 / 29 / 2018
Hyd. No. 1
Post to Pond
Hydrograph type = SCS Runoff Peak discharge = 202.54 cfs
Storm frequency = 1 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 416,712 cuft
Drainage area = 68.670 ac Curve number = 90
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 6.00 min
Total precip. = 2.78 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 120 240 360 480 600 720 840 960 1080 1200 1320
Q (cfs)
0.00 0.00
30.00 30.00
60.00 60.00
90.00 90.00
120.00 120.00
150.00 150.00
180.00 180.00
210.00 210.00
Q (cfs)
Time (min)
Post to Pond
Hyd. No. 1 -- 1 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Tuesday, 05 / 29 / 2018
Hyd. No. 2
Wet Pond
Hydrograph type = Reservoir Peak discharge = 9.204 cfs
Storm frequency = 1 yrs Time to peak = 788 min
Time interval = 2 min Hyd. volume = 398,685 cuft
Inflow hyd. No. = 1 - Post to Pond Max. Elevation = 737.26 ft
Reservoir name = Wet Pond Max. Storage = 657,182 cuft
Storage Indication method used. Wet pond routing start elevation = 734.00 ft.
0 600 1200 1800 2400 3000 3600 4200 4800 5400 6000
Q (cfs)
0.00 0.00
30.00 30.00
60.00 60.00
90.00 90.00
120.00 120.00
150.00 150.00
180.00 180.00
210.00 210.00
Q (cfs)
Time (min)
Wet Pond
Hyd. No. 2 -- 1 Year
Hyd No. 2 Hyd No. 1 Total storage used = 657,182 cuft
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Tuesday, 05 / 29 / 2018
Hyd. No. 3
Pre
Hydrograph type = SCS Runoff Peak discharge = 14.37 cfs
Storm frequency = 1 yrs Time to peak = 726 min
Time interval = 2 min Hyd. volume = 75,615 cuft
Drainage area = 74.860 ac Curve number = 61
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 14.10 min
Total precip. = 2.78 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
3.00 3.00
6.00 6.00
9.00 9.00
12.00 12.00
15.00 15.00
Q (cfs)
Time (min)
Pre
Hyd. No. 3 -- 1 Year
Hyd No. 3
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Tuesday, 05 / 29 / 2018
Hyd. No. 4
Post Bypass
Hydrograph type = SCS Runoff Peak discharge = 4.706 cfs
Storm frequency = 1 yrs Time to peak = 726 min
Time interval = 2 min Hyd. volume = 22,623 cuft
Drainage area = 20.340 ac Curve number = 62
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 14.10 min
Total precip. = 2.78 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
1.00 1.00
2.00 2.00
3.00 3.00
4.00 4.00
5.00 5.00
Q (cfs)
Time (min)
Post Bypass
Hyd. No. 4 -- 1 Year
Hyd No. 4
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Tuesday, 05 / 29 / 2018
Hyd. No. 5
Post Total
Hydrograph type = Combine Peak discharge = 10.07 cfs
Storm frequency = 1 yrs Time to peak = 786 min
Time interval = 2 min Hyd. volume = 421,308 cuft
Inflow hyds. = 2, 4 Contrib. drain. area = 20.340 ac
0 600 1200 1800 2400 3000 3600 4200 4800 5400 6000
Q (cfs)
0.00 0.00
2.00 2.00
4.00 4.00
6.00 6.00
8.00 8.00
10.00 10.00
12.00 12.00
Q (cfs)
Time (min)
Post Total
Hyd. No. 5 -- 1 Year
Hyd No. 5 Hyd No. 2 Hyd No. 4
TR55 Tc Worksheet
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Hyd. No. 1
Post to Pond
Description A B C Totals
Sheet Flow
Manning's n-value = 0.011 0.011 0.011
Flow length (ft) = 100.0 0.0 0.0
Two-year 24-hr precip. (in) = 3.36 0.00 0.00
Land slope (%) = 0.39 0.00 0.00
Travel Time (min) = 2.27 + 0.00 + 0.00 = 2.27
Shallow Concentrated Flow
Flow length (ft) = 359.00 0.00 0.00
Watercourse slope (%) = 7.39 0.00 0.00
Surface description = Unpaved Paved Paved
Average velocity (ft/s) =4.39 0.00 0.00
Travel Time (min) = 1.36 + 0.00 + 0.00 = 1.36
Channel Flow
X sectional flow area (sqft) = 3.14 7.07 15.90
Wetted perimeter (ft) = 6.28 9.43 14.14
Channel slope (%) = 1.00 1.00 1.00
Manning's n-value = 0.013 0.013 0.013
Velocity (ft/s) =7.20
9.45
12.40
Flow length (ft) ({0})507.0 639.0 14.1
Travel Time (min) = 1.17 + 1.13 + 0.02 = 2.32
Total Travel Time, Tc .............................................................................. 6.00 min
TR55 Tc Worksheet
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Hyd. No. 3
Pre
Description A B C Totals
Sheet Flow
Manning's n-value = 0.011 0.011 0.011
Flow length (ft) = 100.0 0.0 0.0
Two-year 24-hr precip. (in) = 3.36 0.00 0.00
Land slope (%) = 0.30 0.00 0.00
Travel Time (min) = 2.53 + 0.00 + 0.00 = 2.53
Shallow Concentrated Flow
Flow length (ft) = 217.00 0.00 0.00
Watercourse slope (%) = 2.90 0.00 0.00
Surface description = Unpaved Paved Paved
Average velocity (ft/s) =2.75 0.00 0.00
Travel Time (min) = 1.32 + 0.00 + 0.00 = 1.32
Channel Flow
X sectional flow area (sqft) = 3.00 0.00 0.00
Wetted perimeter (ft) = 6.32 0.00 0.00
Channel slope (%) = 2.20 0.00 0.00
Manning's n-value = 0.026 0.015 0.015
Velocity (ft/s) =5.16
0.00
0.00
Flow length (ft) ({0})3166.0 0.0 0.0
Travel Time (min) = 10.23 + 0.00 + 0.00 = 10.23
Total Travel Time, Tc .............................................................................. 14.10 min
TR55 Tc Worksheet
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Hyd. No. 4
Post Bypass
Description A B C Totals
Sheet Flow
Manning's n-value = 0.011 0.011 0.011
Flow length (ft) = 100.0 0.0 0.0
Two-year 24-hr precip. (in) = 3.36 0.00 0.00
Land slope (%) = 0.30 0.00 0.00
Travel Time (min) = 2.53 + 0.00 + 0.00 = 2.53
Shallow Concentrated Flow
Flow length (ft) = 217.00 0.00 0.00
Watercourse slope (%) = 2.90 0.00 0.00
Surface description = Unpaved Paved Paved
Average velocity (ft/s) =2.75 0.00 0.00
Travel Time (min) = 1.32 + 0.00 + 0.00 = 1.32
Channel Flow
X sectional flow area (sqft) = 3.00 0.00 0.00
Wetted perimeter (ft) = 6.32 0.00 0.00
Channel slope (%) = 2.20 0.00 0.00
Manning's n-value = 0.026 0.015 0.015
Velocity (ft/s) =5.16
0.00
0.00
Flow length (ft) ({0})3166.0 0.0 0.0
Travel Time (min) = 10.23 + 0.00 + 0.00 = 10.23
Total Travel Time, Tc .............................................................................. 14.10 min
50-YR 6 HR STORMWATER SUMMARY REPORT &
STORM PRE, POST, AND ROUTED
HYDROGRAPHS
Hydrograph Summary Report
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 SCS Runoff 194.73 2 144 786,849 ------ ------ ------ Post to Pond
2 Reservoir 77.21 2 158 775,365 1 738.34 751,156 Wet Pond
3 SCS Runoff 54.15 2 154 281,424 ------ ------ ------ Pre
4 SCS Runoff 15.89 2 154 80,832 ------ ------ ------ Post Bypass
5 Combine 92.62 2 156 856,197 2, 4 ------ ------ Post Total
Storm Routing.gpw Return Period: 50 Year Wednesday, 05 / 30 / 2018
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 1
Post to Pond
Hydrograph type = SCS Runoff Peak discharge = 194.73 cfs
Storm frequency = 50 yrs Time to peak = 144 min
Time interval = 2 min Hyd. volume = 786,849 cuft
Drainage area = 68.670 ac Curve number = 90
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 6.00 min
Total precip. = 4.47 in Distribution = SCS 6-Hr
Storm duration = 6.00 hrs Shape factor = 484
0 60 120 180 240 300 360 420
Q (cfs)
0.00 0.00
30.00 30.00
60.00 60.00
90.00 90.00
120.00 120.00
150.00 150.00
180.00 180.00
210.00 210.00
Q (cfs)
Time (min)
Post to Pond
Hyd. No. 1 -- 50 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 2
Wet Pond
Hydrograph type = Reservoir Peak discharge = 77.21 cfs
Storm frequency = 50 yrs Time to peak = 158 min
Time interval = 2 min Hyd. volume = 775,365 cuft
Inflow hyd. No. = 1 - Post to Pond Max. Elevation = 738.34 ft
Reservoir name = Wet Pond Max. Storage = 751,156 cuft
Storage Indication method used. Wet pond routing start elevation = 734.00 ft.
0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880 3120
Q (cfs)
0.00 0.00
30.00 30.00
60.00 60.00
90.00 90.00
120.00 120.00
150.00 150.00
180.00 180.00
210.00 210.00
Q (cfs)
Time (min)
Wet Pond
Hyd. No. 2 -- 50 Year
Hyd No. 2 Hyd No. 1 Total storage used = 751,156 cuft
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 3
Pre
Hydrograph type = SCS Runoff Peak discharge = 54.15 cfs
Storm frequency = 50 yrs Time to peak = 154 min
Time interval = 2 min Hyd. volume = 281,424 cuft
Drainage area = 74.860 ac Curve number = 61
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 14.10 min
Total precip. = 4.47 in Distribution = SCS 6-Hr
Storm duration = 6.00 hrs Shape factor = 484
0 60 120 180 240 300 360 420
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
Q (cfs)
Time (min)
Pre
Hyd. No. 3 -- 50 Year
Hyd No. 3
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 4
Post Bypass
Hydrograph type = SCS Runoff Peak discharge = 15.89 cfs
Storm frequency = 50 yrs Time to peak = 154 min
Time interval = 2 min Hyd. volume = 80,832 cuft
Drainage area = 20.340 ac Curve number = 62
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 14.10 min
Total precip. = 4.47 in Distribution = SCS 6-Hr
Storm duration = 6.00 hrs Shape factor = 484
0 60 120 180 240 300 360 420
Q (cfs)
0.00 0.00
3.00 3.00
6.00 6.00
9.00 9.00
12.00 12.00
15.00 15.00
18.00 18.00
Q (cfs)
Time (min)
Post Bypass
Hyd. No. 4 -- 50 Year
Hyd No. 4
100-YR 6 HR STORMWATER SUMMARY REPORT
& STORM PRE, POST, AND ROUTED
HYDROGRAPHS

Hydrograph Summary Report
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 SCS Runoff 220.16 2 144 894,599 ------ ------ ------ Post to Pond
2 Reservoir 92.77 2 158 883,103 1 738.75 788,488 Wet Pond
3 SCS Runoff 71.53 2 154 354,776 ------ ------ ------ Pre
4 SCS Runoff 20.74 2 154 101,326 ------ ------ ------ Post Bypass
5 Combine 113.04 2 156 984,429 2, 4 ------ ------ Post Total
Storm Routing.gpw Return Period: 100 Year Wednesday, 05 / 30 / 2018
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 1
Post to Pond
Hydrograph type = SCS Runoff Peak discharge = 220.16 cfs
Storm frequency = 100 yrs Time to peak = 144 min
Time interval = 2 min Hyd. volume = 894,599 cuft
Drainage area = 68.670 ac Curve number = 90
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 6.00 min
Total precip. = 4.95 in Distribution = SCS 6-Hr
Storm duration = 6.00 hrs Shape factor = 484
0 60 120 180 240 300 360 420
Q (cfs)
0.00 0.00
30.00 30.00
60.00 60.00
90.00 90.00
120.00 120.00
150.00 150.00
180.00 180.00
210.00 210.00
240.00 240.00
Q (cfs)
Time (min)
Post to Pond
Hyd. No. 1 -- 100 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 2
Wet Pond
Hydrograph type = Reservoir Peak discharge = 92.77 cfs
Storm frequency = 100 yrs Time to peak = 158 min
Time interval = 2 min Hyd. volume = 883,103 cuft
Inflow hyd. No. = 1 - Post to Pond Max. Elevation = 738.75 ft
Reservoir name = Wet Pond Max. Storage = 788,488 cuft
Storage Indication method used. Wet pond routing start elevation = 734.00 ft.
0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640
Q (cfs)
0.00 0.00
30.00 30.00
60.00 60.00
90.00 90.00
120.00 120.00
150.00 150.00
180.00 180.00
210.00 210.00
240.00 240.00
Q (cfs)
Time (min)
Wet Pond
Hyd. No. 2 -- 100 Year
Hyd No. 2 Hyd No. 1 Total storage used = 788,488 cuft
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 3
Pre
Hydrograph type = SCS Runoff Peak discharge = 71.53 cfs
Storm frequency = 100 yrs Time to peak = 154 min
Time interval = 2 min Hyd. volume = 354,776 cuft
Drainage area = 74.860 ac Curve number = 61
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 14.10 min
Total precip. = 4.95 in Distribution = SCS 6-Hr
Storm duration = 6.00 hrs Shape factor = 484
0 60 120 180 240 300 360 420
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
Q (cfs)
Time (min)
Pre
Hyd. No. 3 -- 100 Year
Hyd No. 3
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 4
Post Bypass
Hydrograph type = SCS Runoff Peak discharge = 20.74 cfs
Storm frequency = 100 yrs Time to peak = 154 min
Time interval = 2 min Hyd. volume = 101,326 cuft
Drainage area = 20.340 ac Curve number = 62
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = TR55 Time of conc. (Tc) = 14.10 min
Total precip. = 4.95 in Distribution = SCS 6-Hr
Storm duration = 6.00 hrs Shape factor = 484
0 60 120 180 240 300 360 420
Q (cfs)
0.00 0.00
3.00 3.00
6.00 6.00
9.00 9.00
12.00 12.00
15.00 15.00
18.00 18.00
21.00 21.00
Q (cfs)
Time (min)
Post Bypass
Hyd. No. 4 -- 100 Year
Hyd No. 4
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2016 by Autodesk, Inc. v10.5 Wednesday, 05 / 30 / 2018
Hyd. No. 5
Post Total
Hydrograph type = Combine Peak discharge = 113.04 cfs
Storm frequency = 100 yrs Time to peak = 156 min
Time interval = 2 min Hyd. volume = 984,429 cuft
Inflow hyds. = 2, 4 Contrib. drain. area = 20.340 ac
0 240 480 720 960 1200 1440 1680 1920
Q (cfs)
0.00 0.00
20.00 20.00
40.00 40.00
60.00 60.00
80.00 80.00
100.00 100.00
120.00 120.00
Q (cfs)
Time (min)
Post Total
Hyd. No. 5 -- 100 Year
Hyd No. 5 Hyd No. 2 Hyd No. 4
APPENDIX

SEASONAL HIGH WATER TABLE STUDY
WETLAND & STREAM DELINEATION MAP
LEGEND
Site Boundary
Intermittent Stream
Perennial Stream
Ephemeral Swale
Wetland
Culvert
Data Point
Verification Changes
THE LOCATIONS OF FEATURES SHOWN ON THIS MAP ARE APPROXIMATE.THEY WERE VERIFIED BY MS.JEAN
GIBBY WITH THE USACAE AND MS.SUE HOMEWOOD WITH THE NCDEQ-DWR ON JUNE 7,2017.THE
LOCATIONS OF FEATURES SHOWN ON THIS MAP HAVE NOT BEEN SURVEYED OR GEOLOCATED.
FLAG NUMBERS/INFO
WETLAND FLAGS =
STREAM FLAGS =
Stream/Pond Flags = Origins only
Wetland Flags = 235
Total Flags = 235
Wetland Map
Idols Road
Approximate 169.5 Acre Tract
Clemmons, Forsyth County, NC
Pilot Project 1899.2
Drawing 5
Aerial Imagery from ESRI
and Pilot Field Notes
Scale: 1” = 500’
Date: 6.7.17
WA 1-8
WAA 1-5
DP-1
DP-2
WA 10-20
WAA 5-10
ISCA
WB 1-35
WB 36-102
WB 103-117
WCA 6-12
WC 1-7
WCA 1-5
WB
WD 1-69
WB 1-12
ISCB 1-2
DP-1
WB 1-12
NCDEQ NOTICE OF EXEMPTION TO NC DAM
SAFETY LAW

EXHIBITS
EX-1.0 DRAINAGE AREA MAP – PRE-
DEVELOPMENT
EX-1.1 DRAINAGE AREA MAP – POST-
DEVELOPMENT