SW5241101_Stormwater Report_20241119

Stormwater Management Report
FOREST HILLS PERMIT NO. SW5230902
Louisburg, North Carolina
August 8, 2023
Revised January 2, 2024
Revised October 29,2024
\-\ CAR0
F O• / •
•
�` �•Q�O tiq
• ••••
= SEAL s
030339
•
'# THY P 0s
Prepared By:
The Nau Company, PLLC
PO Box 810
Rolesville, North Carolina, 27571
[phone]
[e-mail]

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
INTRODUCTION
This report presents the stormwater management design for the proposed improvements at the
Forest Hills Subdivision in Franklin County, North Carolina. The site is within the Town of
Louisburg's ETJ and will be annexed into the Town of Louisburg. The site is located on Hawthorn
Street at the intersection with NC Highway 561 northeast of the Town of Louisburg.
BACKGROUND
Forest Hills Subdivision is a proposed 49.64-acre development that consists of 64 single residential
properties.The project includes construction of the water, sewer, storm drainage, and additional
site improvements. Water and sewer services will be provided by the Town of Louisburg.The
proposed subdivision (SCM) stormwater control measure meets NCDEQ requirements for
stormwater treatment for water quantity volume control, water quality treatment and peak flow
reduction.
REQUIREMENTS
Stormwater Permits for the Town of Franklinton are issued by the North Carolina Division of
Environmental Quality (NCDEQ).
The relevant NCDEQ requirements for high density projects found in 15A NCAC 02H .1003 (3) are
summarized below:
• Treatment requirements -SCMs shall be designed, constructed, and maintained so that the
project achieves either"runoff treatment" or "runoff volume match" as those terms are
defined in Rule .1002 of this Section.
• On-site stormwater-Stormwater runoff from off-site areas and existing development shall
not be required to be treated in the SCM. Runoff from off-site areas or existing
development that is not bypassed shall be included in the sizing of on-site SCMs at its full
built-out potential.
• MDC for SCMs -SCMs shall meet the relevant MDC set forth in Rules .1050 through .1062 of
this Section except in accordance with Item (6) of this Rule.
The relevant MDC for wet ponds in 15A NCAC 02H .1053 are summarized below:
• Main Pool Surface Area and Volume -The main pool of the wet pond shall be sized using
either:
o the Hydraulic Retention Time (HRT) Method; or
o the SA/DA and Average Depth Method.
• Main Pool Depth -The average depth of the main pool shall be three to eight feet below the
permanent pool elevation. The applicant shall have the option of excluding the submerged
portion of the vegetated shelf from the calculation of average depth.
• Sediment Storage -The forebay and main pool shall have a minimum sediment storage
depth of six inches.
1

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
• Location of inlet(s) and outlet-The inlet(s) and outlet shall be located in a manner that
avoids short circuiting.
• Forebay-A forebay that meets the following specifications shall be included;
o Forebay volume shall be 15 to 20 percent of the volume in the main pool;
o The forebay entrance shall be deeper than the forebay exit;
o The water flowing over or through the structure that separates the forebay from the
main pool shall flow at a nonerosive velocity; and
o If sediment accumulates in the forebay in a manner that reduces its depth to less
than 75 percent of its design depth, then the forebay shall be cleaned out and
returned to its design state.
• Vegetated shelf-The main pool shall be equipped with a vegetative shelf around its
perimeter. The minimum width of the vegetated shelf shall be six feet and the slope shall be
no steeper than 6:1 (horizontal to vertical).
• Drawdown time -The design volume shall draw down to the permanent pool level between
two and five days.
• Protection of the receiving stream -The wet pond shall discharge the runoff from the one-
year, 24-hour storm in a manner that minimizes hydrologic impacts to the receiving
channel.
• Trash rack-A trash rack or other device shall be provided to prevent large debris from
entering the outlet system.
• Vegetation -The following criteria apply to vegetation in and around the wet pond:
o The dam structure, including front and back embankment slopes, of the pond shall
be vegetated with non-clumping turf grass; trees and woody shrubs shall not be
allowed; and
o The vegetated shelf shall be planted with a minimum of three diverse species of
herbaceous, native vegetation at a minimum density of 50 plants per 200 square
feet of shelf area.
The design storm for this project is the one inch 24-hour rainfall.
This project bypasses the off-site drainage area. The proposed SCM accounts for emergency
overflow if needed, including a spillway into an existing wetland.
2

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
PROPOSED STORMWATER CONTROL MEASURE
One wet pond is proposed to meet NCDEQ requirements. Refer to the construction drawings for
details of the SCM.
METHODOLOGY
Drainage Areas and SCS Curve Numbers
Drainage areas were delineated based on proposed and existing topography using CAD software.
Land use types were measured using CAD software and SCS curve numbers were applied to each land
use type within the drainage area to calculate a weighted, composite SCS Curve Number. Curve
numbers for the various land use types were taken from NRCS TR-55 and are included as an appendix
to this report.
Times of Concentration
The minimum time of concentration used for calculation of peak flows was 5 minutes. For times of
concentration more than 5 minutes, a simplified TR-55 method was used. The simplified method
calculates the time of concentration only using sheet flow time and channel flow time—shallow
concentrated flow time is disregarded. Since channel dimensions vary along the channel flow path,
channel parameters were selected for the entire length of channel flow that yield a flow velocity of
approximately 4.5 feet per second. A flow velocity of 4.5 feet per second is greater than or equal to
actual flow velocities expected in the pipes or open channels along the flow path and therefore will
yield a runoff higher that what would be expected at the analysis point.
Runoff and Pond Routing
Runoff flowrates and volumes for the proposed SCM were calculated using the Hydrology Studio
software program. The software utilizes the SCS Methodology to determine peak flow rates and
performs routing calculations to determine detention results by the Storage-Indication method.
Rainfall Depths
The following rainfall depths used in the calculations for this report were taken from the NOAA
Precipitation Frequency Data Server (PFDS). A printout of this rainfall data is included as an
appendix to this report.
Rainfall event Rainfall Depth(inches)
Design storm 1.00
1-year,24-hour 2.83
2-year,24-hour 3.42
10-year, 24-hour 4.94
25-year, 24-hour 5.84
100-year,24-hour 7.27
3

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
Pre-Development and Post-Development Drainage Areas
Drainage area maps showing the pre-development and post-development drainage areas are
included as an attachment to this report. Note that the drainage areas are based field topography
where available and GIS topography outside the limits of field topography.
ANALYSIS POINTS
The analysis point for the project was selected based on the location where surface flow leaves the site.
The analysis point for this project is located on the far eastern corner of the parcel where the stream
crosses under Highway NC561.
RESULTS
Runoff Volume
Two runoff volumes were calculated as part of this design. One runoff volume the Water Quality
Volume which is for the entire area that drains to the SCM and the other volume is the Runoff
Treatment Volume which is the volume from the net increase in BUA
The runoff volumes for this project were calculated by the simple method and are summarized below.
Runoff Volume Drainage area Impervious area Impervious% Runoff volume
Water Quality 39.25 ac 20.25 ac 51.6% 73,282 CF
Volume
Runoff Treatment 8.26 ac 8.26 ac 100% 28,470 CF
Volume
4

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
Peak Flow Attenuation
Although peak flow attenuation is not required for this project, pre-development and post-
development flows were calculated for several storm events for reference. The table below
summarizes the pre-development and post-development data for selected storm events. Detailed
routing information can be found in the appendix to this report.
ANALYSIS POINT DRAINAGE AND RUNOFF DATA
Development Condition Drainage area SCS CN Time of Q(1) Q(2) Q(10)
concentration
Pre-Development 53.68 acres 73 21.3 minutes 40.8 cfs 64.1 cfs 132.5 cfs
Post-Development to 39.25 acres 86 17.4 minutes 72.2 cfs 96.3 cfs 159.7 cfs
SCM
Post-Development SCM 14.43 acres 76 10.0 minutes 20.5 cfs 30.2 cfs 57.6 cfs
bypass
Post-Development SCM 25.7 cfs 37.5 cfs 139.0 cfs
outfall flowrate
Post-Development 29.0 cfs 45.2 cfs 161.9 cfs
Pond Surface Area
The required pond surface area was determined based on NCDEQ Stormwater Design Manual for
the Piedmont and Mountain area. The impervious percentage of the onsite drainage area was used
to determine the required surface area. The pond surface area data is summarized in the table
below.
SCM1
Drainage area 14.32 acres
Impervious area 8.11 acres
Impervious percentage 27.7%
Pond average depth 3.0 feet
Required surface area 12,531 SF
Surface area provided 18,833 SF
*Pond surface area calculations are included in the Appendix to this report.
5

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
SCM Dewatering Time
The required pond dewatering time was based on the NCDEQ Stormwater Design Manual and was
calculated using the falling head equation assuming vertical pond sides. The pond dewatering time
is summarized in the table below.
SCM1
Required dewatering time 2 to 5 days
Design storm 1 inch
Calculated dewatering time 3.1 days
Pond dewatering time calculations are included in the Appendix to this report.
Pond Average Depth and Forebay Volume
Pond average depth was calculated using equations 2 and 3 in the NCDEQ Stormwater Design
Manual for Wet Ponds. The interior of the ponds were graded so that the forebays are between
15%and 20%of the main pool volume. The results of the average depth and forebay volume
calculations are summarized below. Calculations are included in the appendix to the report.
Pond Average Depth
Pond ID Average Depth
SCM1 3.3 feet (by equation 2)
SCM1 4.1 feet (by equation 3)
Pond Forebay Volumes
Pond ID Forebay Volume
SCM1 19.5% (total of both forebays)
Erosion at Pond Inlets and Outlets
Flows into and out of the stormwater control measures should not produce erosion for the 10-year
storm. Riprap energy dissipaters are used to eliminate erosion at the pond inlets and outlets. Data
for the riprap dissipaters are summarized below. Calculations are included in the appendix to the
report.
Location Length Width Thickness Riprap size
Inlet pipe on north 20.0' 7.5' 22" Class I
side of pond
Inlet pipe on south 28.0' 10.5' 122" Class I
side of pond
Pond outlet 12.0' 6.0' 22" Class B
6

Stormwater Management Report
October 29, 2024
Forest Hills—SW5230902
Pond Freeboard
The pond is required to have at least 1 foot of freeboard between the 100-year water surface
elevation in the pond and the top of the embankment. The table below summarizes the freeboard
for each pond.
Pond ID Top of berm elevation 100-year WSEL Freeboard
SCM1 220.0 218.9 1.1 feet
Riser Anti-Flotation Device
An anti-flotation device was designed to counteract the buoyant forces on the pond riser. The riser
anti-flotation block was sized to provide a factor of safety for buoyancy of at least 1.5. Calculations
for the anti-flotation block are included in the Appendix to the report.
Nutrient Loading
Nutrient loading calculations for this project were performed with the SNAP Tool v4.2 provided by
NCDEQ. The output from this tool is included in the appendix to this report.
The output calculated by the spreadsheet for nutrient loading is summarized in the table below:
Post-BMP TN Loading 2.27 Ib/ac/yr
Post-BMP TP Loading 0.46 lb/ac/yr
CONCLUSION
Based on the analysis there are no negative downstream impacts as the result of this development.
7

APPENDICES
Appendix A Drainage Area Maps
Appendix B Hydrology Studio Output
Appendix C Wet Pond Supporting Calculations
Appendix D Energy Dissipater/Riprap apron Calculations
Appendix E SNAP Tool Output
Appendix F Supporting Documentation

APPENDIX A
DRAINAGE AREA MAPS

a Hydrologic Soil Group—Franklin County,North Carolina
F (USDA Soils Map)
744000 744100 744200 744300 744400 744500 744600 744700 744800 744900 745000 745100
36°7 8"N , 1 36°7 8"N
H
I _
�r , "_ _ .. . WeC C-hA
01.r ar4�wncf) ,. ChAi"
WeC
7 .HeB
kof -
it,
4
VaB ,
c f
s, ,......„ -0- '
Cottrell Dr .C., WeC
81 3 ,
v
1 - -c:.,. SITE
'1 r Z1 : t
fir,g .. . ChA
t 4
6' ' WeC Q '
ti
d(.
.6
,,1.SCE`
"Thornton
111111111114._WaB �k _ � aiWr
' '
36°6'42"N • A— 36°6'42"N
744000 744100 744200 744300 744400 744500 744600 744700 744800 744,,900 745000 745100
3 3
F Map Scale:1:5,460 if printed on A landscape(11"x 8.5")sheet. ,-9
Meters
m N 0 50 100 200 300
Feet
0 250 500 1000 1500
Map projection:Web Mercator Corner coordinates:WG584 Edge tics:UTM Zone 17N WG5584
USDA Natural Resources Web Soil Survey 10/31/2024
1011. Conservation Service National Cooperative Soil Survey Page 1 of 4

Hydrologic Soil Group—Franklin County, North Carolina
(USDA Soils Map)
MAP LEGEND MAP INFORMATION
Area of Interest(AOI) p c The soil surveys that comprise your AOI were mapped at
Area of Interest(AOI) 1:24,000.
0 C/D
Soils • D Warning:Soil Map may not be valid at this scale.
Soil Rating Polygons
0 A p Not rated or not available Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
n A/D Water Features line placement.The maps do not show the small areas of
Streams and Canals contrasting soils that could have been shown at a more detailed
n B scale.
Transportation
Q B/D
r4-1. Rails Please rely on the bar scale on each map sheet for map
n C measurements.
ti Interstate Highways
C/D US Routes Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
0 D Major Roads Coordinate System: Web Mercator(EPSG:3857)
n Not rated or not available Local Roads
Maps from the Web Soil Survey are based on the Web Mercator
Soil Rating Lines Background projection,which preserves direction and shape but distorts
• • A distance and area.A projection that preserves area,such as the
1111 Aerial Photography Albers equal-area conic projection,should be used if more
• • A/D accurate calculations of distance or area are required.
^r B This product is generated from the USDA-NRCS certified data as
.v B/D of the version date(s)listed below.
• r C Soil Survey Area: Franklin County,North Carolina
Survey Area Data: Version 28,Sep 9,2024
• • C/D
Soil map units are labeled(as space allows)for map scales
• • D 1:50,000 or larger.
• w Not rated or not available Date(s)aerial images were photographed: Apr 25,2022—May
Soil Rating Points 20,2022
p A The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
O A/D imagery displayed on these maps.As a result,some minor
• B shifting of map unit boundaries may be evident.
• B/D
USDA Natural Resources Web Soil Survey 10/31/2024
Conservation Service National Cooperative Soil Survey Page 2 of 4

Hydrologic Soil Group—Franklin County,North Carolina USDA Soils Map
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
AaA Altavista sandy loam,0 C 14.5 9.5%
to 3 percent slopes,
rarely flooded
ApB Appling loamy sand,2 to B 2.7 1.8%
6 percent slopes
ChA Chewacla and B/D 25.9 17.1%
Wehadkee soils,0 to
3 percent slopes,
frequently flooded
HeB Helena sandy loam,2 to D 2.6 1.7%
6 percent slopes
RoA Roanoke-Warne C/D 14.4 9.5%
complex,0 to 3
percent slopes,
occasionally flooded
Ud Udorthents,loamy C 0.4 0.3%
VaB Vance sandy loam,2 to C 9.9 6.5%
6 percent slopes
W Water 2.1 1.4%
WaB Wake-Saw-Wedowee D 5.2 3.5%
complex,2 to 8
percent slopes,rocky
WeB Wedowee sandy loam,2 B 53.7 35.3%
to 6 percent slopes
WeC Wedowee sandy loam,6 B 20.5 13.5%
to 10 percent slopes
Totals for Area of Interest 152.0 100.0%
usm Natural Resources Web Soil Survey 10/31/2024
Conservation Service National Cooperative Soil Survey Page 3 of 4

Hydrologic Soil Group—Franklin County, North Carolina USDA Soils Map
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
USDA Natural Resources Web Soil Survey 10/31/2024
Conservation Service National Cooperative Soil Survey Page 4 of 4

National Flood Hazard Layer FI RMette FEMA Legend
78°17'16"W 36°7'5"N SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
pIT = Without Base Flood Elevation(BFE)
Zone A,V,ASS
SPECIAL FLOOD With BFE or Depth Zone AE,AO,AR,VE,AR
HAZARD AREAS Regulatory Floodway
1 •
e 0.2%Annual Chance Flood Hazard,Areas
of 1%annual chance flood with average
• depth less than one foot or with drainage
TOWN OF LOUISBURG r areas of less than one square mile zonex
EXTRATERRITORIAL JURISDICTION Future Conditions 1%Annual
_ 111Chance Flood Hazard zonex
• LOUISBURGgjg �" Area with Reduced Flood Risk due to
0, 370098 OTHER AREAS OF Levee.See Notes.zonex
i - FLOOD HAZARD Area with Flood Risk due to Leveezone D
mil .
NO SCREEN Area of Minimal Flood Hazard zonex
IP
i 1114 . it lip Effective LOMRs
' OTHER AREAS Area of Undetermined Flood Hazard ZoneD
lik 14 1 I GENERAL -
- Channel,Culvert,or Storm Sewer
` : STRUCTURES I I•I I I Levee,Dike,or Floodwall
a ; 'AREA OF MINIMAL FLOOD HAZARD 7
' 1� Zone Tx -- . 0 20.2 Cross Sections with 1%Annual Chance
1Z•s Water Surface Elevation
f - �► - :-_
� e— — — Coastal Transect
f -•••••513---- Base Flood Elevation Line(BFE)_ - Limit of Study
- II 1 ---
3/2028 160W ` \ Jurisdiction Boundary
eff. 1/16/2004 Y
ti Coastal Transect Baseline
•4.
OTHER - - Profile Baseline
FEATURES Hydrographic Feature
•
- - ( Digital Data Available N
i r `,. ` r� ?08F�F :::::ata
Available
a` MAP PANELS
TOWN OF LOUISBURG r FFT
3 The pin displayed on the map is an approximate
41 LOUISBURG9
',. point selected by the user and does not represent
lip an authoritative property location.
370098 CI,' zone AE
-i: 2vnp,, This map complies with FEMA's standards for the use of
eF�t`E digital flood maps if it is not void as described below.
! --
{ 41.6.
t The basemap shown complies with FEMA's basemap
.F r accuracy standards
rr ill It - The flood hazard information is derived directly from the
- Y C authoritative NFHL web services provided by FEMA.This map
...it J `, 1 was exported on 10/31/2024 at 1:26 PM and does not
Y' r =�, _ .,� reflect changes or amendments subsequent to this date and
r _ time.The NFHL and effective information may change or
- litk • . :1111t.w.....----.07.„------
��-_ become superseded by new data over time.
�-3 -one AE This map image is void if the one or more of the following map
or .
+ 20 �� elements do not appear:basemap imagery,flood zone labels,
fl • �Q,J �y S�.FT .# legend,scale bar,map creation date,community identifiers,
I FIRM panel number,and FIRM effective date.Map images for
Feet 78°16'39"W 36°6'36"N unmapped and unmodernized areas cannot be used for
0 250 500 1,000 1,500 2,000 1 6'DOO regulatory purposes.
Basemap Imagery Source:USGS National Map 2023

U.S/�� U.S.DEPARTMENT OF THE INTERIOR 11„NalosilMy LOUISBURG QUADRANGLE
NORTH CA
sYvbeal.,S...Y U.S.GEOLOGICAL SURVEY 1jr US Topo 'L FRANKLIN
SM NUTESE COUNTY
SERIES
-78.3750 .)8.1500
la.11so• 38 19 40 41 42 43 44 45 46 47 al
•
.\ J G or.me l_ x 01
c-,1„;
00
w
(.0
�� ✓ ¢ � �
99 �i a+oerc� ` / p \ s P4F 1'�f

r 1
/ / V O w y Ln
\. 7� / Cam- p
�v �/ �/ // i/ l I 1 f
1 v N a
CZ'
--: --- �•� A �� �=-�^ n ai
/i i / % i /��--�� �J ♦ Ai ��\ V AV / \ g raj N
i i
/ / / . i , // d i \ / I I i I C.-.) X 0,_1
0/,/ , / I
,
.-.'-'-- —\ I ',.\i',_:_____ 2----1 ---:----_- '31 g
��►AA�► _ _ - - fir /\
i- Av -- — A A
\\ \\\.4 , / ',. / ,,t 7 i d
----' \\\\'' /030 07//// "04 oi i // ,,*
\ (—)
\N\\\:1 i::ill// /1/7//..z/7:'--(a.-\:1::N
°"% ;
/ ,./:::-\1
\\\\\A\si\z."'
-, 4'../ ,..,:."0//
1� / / 04/1°/000‘)/0. _ ntA N v ': / // /
o
41/\i/tTiIi \
t ' /'
NSIT ONLY) /�/ ( -,_ ` i -A , \\\\ \ , ,
17- , .. ,
(OFFSITE ONLY) -
12.97 AC :r4////://0///,/
/ r t J�-,���
‘ il!!!! ! !!°;" 100
40/4°0:;/:#41t° OlIP''
/ ,..,,,,,,..:,‘
Lz
-------\ 11 ,)4 / ///// /, l, ,.$
, :
,*,17j:,,11'
_.:__:::::._, \ .., i.,,. 4/ // i :// / t , , " /// s
e".... I -------"- \ u_i u H
y// 01,H/
t. 4, . Ifrylle,/: :
�\ ///,40,77,//f
Jr /p%f. ! \� \ l u.l
\\\\\t:
Lii
N.,,,, cc
,.....
N ,,..,,, _ :-_,-;:._72,--"-- ..,,,, --_-------_________:_,
7 .... 2
7 .. ,, , , ,\
,,,_
i ,, // ,) , / , ,
7,-, / ,_, \
__ .,_ __.7,-,- -,,,,;,„,,-__ -7 7 ../ / r
� I 1 . -'A Le—I G_�% �� // / '� / SEAL
\ -::
°<7.<;111 4# 1fitAff- ,
\ I- % i \ ,,%-j---,?...:y,"'K'("' I i \ a- / / / /10,0 ,O.is
/ � .v V
i A \ / v/ I \ PROJECT NO:
/— �— ��� \V I / // / I --� i� /� ---�' \ \ DESIGN BY: TNC
/ --\ \\\ \ / / / i // \ `�\ DRAWN BY:
1 \ \\ I I 1
__ --- �vv SCALE.
(\ (\ — A A A / // / — ii �— /--� A / / / DATE:
__ A A / ' / v / / / 100 0 so 100 200 zoza-os-la
I I
SCALE 1"=100' SHEET NO.
SCM1.1
401
PERMIT NO.SW5230902

gi E s-Itri
r 1
_____ ,___ ,,, _, \ V___I--""
i j % A/ / / / / ------ )
Av vv�� A K( --- N� :1 I
\ ( / \ — , -
0.0
/ / 1 1 1 ) ) ) \ \\ ) /1 il \ ,_____ _________, ------------___________ \
/77 __----i/7/----------- ---\ --)
_ -- _ji ) J ) l_ i i/// (_____ /7-7----———--—--------_--———----\ ) i)z/) 2/ / i
/ (
�_�� per,"
a
/ —�— 111\'�11� �i__"�! 1 i�� I�I I�u I II ���y \��_� / \ L fu i
�0,w
� _ _--� 1■1��!. i\1; 1i: �ll i111111!:!!""1!!!!! 1:11ll1111� 1 11 �� \ \\ \ H mom
�� ��, �. 11111
I �I� II���l�I�� 1�1'► 111 �1 1III1 P
. PI
� SCM BYPASS i i/�� \\,_ Z a�z____/:_z-----------
��r�� �1�i! I,er III' ---
-- \ -._7_: -0
/ .---z.'"'•-- - x-- -xWA,V,, ,;.$4,10474-7-7-reg-tr,;::`Z , ( ki
=- - ' -----:\\ k\i\.7 **, ;1;•;:krfar..-4 ).„‘.11 fir "rd,,,---=-Z-,4'.7-7.fr,;i -=.!!%4t...:.0%
/�� ZV
\\\\ \ ‘�il���%i �i Ili.°,���I���1�i/i �ls���/iw���o;�%� � / ' \� i,2
— N_ 1 ) ( —
Pik
l� �il,�'/"'�j�F l�jl�lijl� :Witp�l / / \, (
___ \ frAls; �df� 1111 � ', --7 "-F-AtiStf,•74# ll
��/ �la� A I d� 1 i i i 1 -_,---------/ , 7,
;� % '!►����I ��l�adl`11,ipi � '11�11II1f�I�1 � 1 i i
-�.�ia�.�j�hlll�i ��s'�.r�II�'�1 ��►�����`�T- I/ii���j�lp I � v � � � �
Off "i �a,ll; i�� ��//d, p� IIQ� M'/ II � � T
/ -
N.\k\\/\
. � ►,11. � I � � 1 ! II I�I v
�V \\ S\ii\fileV'17-ililjj:,4:/,:4%,",##0;:i0;:L;fte,fe::-
3ii1����IlPllllll � il�� rt�� �,�� j �II�I�I Ili / .,,
, � J ,4 �! s �I{ ✓� ,al► /►11�_��,� uI�/f/ i�il{' ,r tl�ki :'/� i1/ 1 I �1�► ��0�►�� � / _
���� ���►� � ►��O ��P ��, \/ �%�'��� i�� �ONSITE ONLY) ! j � A%�' '������p���o���+►A��\ ��� \ j —�-�
Imo_ ��i�I%��1� _ it," '' ,;ss„\sitiipssst:::::4,,,tstski:$
������.,®0� • � _
I� ►=�►'► /� 26.29 AC � j" >oo �� v-
SCM2.BYPASS I ►• _ �OFFSITE ONLY �d :��!�! � 'Ii0 •�� ���0110001
I�t � �� ///IIR�f� �J,l,.►► ii ..� . SCM BYPASS , , ) , , ,-
\----_, \
{)\/* \ ►/� P;4 IAt ��— ,0° ►/®i t t� / %a \mow\\ \ i' ��i_.�/ Q
r ��''�`+' 0P n - s� I��� i� 14.43 ACih '/�
II�/'/�I� III>y yv-
/41 �1►o # �-`.4 .:;, , i�p ��i I :1:;- .';*
3;0,„Ay .
�� W'r"diiit, 440,41",,eilictt:0,,,� �J°I / \ �` - _ / %'�y� tip N� Q
��I / I ,e) . ,-$4,i %� — C �i�/ /� ���� i a J zZ
ik
11►�o.� I� �5�`'✓ ►►4`� � � ������ .t: � ,em �� ���fi�� 4°9 �J / _.�' v " Z ., Q
V �IP��� i ���C ,l/���1� �����j f ��I�'I ��i � 0�� ). Arai%'/� � 1— : 0
� � (n
API �wS�r®A�% i�����/ / 9';''' ♦ �IO,P��. � ��► Lu
l
oCi
4/7..
gl
, �'?//4 ��4 � 'il.�iil� �� ♦t�I, i /jam alll��01 /ill���� : •'� :�j�'/ •
s\ _ o
— — Ivi,a k;_s .. .ter►. /,/ , ♦i ♦o� �� p.. �1 . ,;. \ ) ) \\* --\) cc
w
0.
♦��� 0t.��V 04 r v AA*�Il►�` cl 0.� I. Ali
+e�1111•1" It�0.���r1�; r..—.._..J 1 \� PtLss�O
\__,:-
030339
\` 1 \\ 1 \ � � 00.45,401TgarilM,
' ail� ' I �� 1 ` �� ` / / ` /,, / irt,
61.
SEA
tf\ 11 \ 1 , \\
.' VHI N
/ , —1 OW lb,
` . ( S1/4 __\)) )
PROJECT NO:
i, , __—__ ' \ 1� 2,000 .-i0,0
\ I 1 :::::
:
lTNC
-___/7_:: , 1 ./ \ , , \ ) ; i SCALE:
I / iI
/
\ /---------______,‘ / /i / / V / ' \ `. ' DATE: 2024.D 14
Kv \ / I Do a so 0o zoo
I I
SCALE:1"=100. SHEET NO
SCM2.1 /
PROJECT NO.SW5230902

APPENDIX B
HYDROLOGY STUDIO OUTPUT

Basin Model Project Name:
Hydrology Studio v 3.0.0.29 01-02-2024
Pre AP1 Post DA1.1 Post DA1.2
17171
Post SCM
+I ► `'t ' PostAP1

Hydrograph by Return Period Project Name:
Hydrology Studio v 3.0.0.29 01-02-2024
Hyd. Hydrograph Hydrograph Peak Outflow(cfs)
No. Type Name 1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr
1 NRCS Runoff Pre AP1 40.79 64.06 132.5 249.7
2 NRCS Runoff Post DA1.1 72.21 96.26 159.7 257.5
3 Pond Route Post SCM 25.73 37.45 139.0 248.1
4 NRCS Runoff Post DA1.2 20.52 30.17 57.55 102.9
5 Junction PostAP1 29.03 45.23 161.9 315.9

Hydrograph 1 -yr Summary Project Name:
Hydrology Studio v 3.0.0.29 01-02-2024
Hyd. Hydrograph Hydrograph Peak Time to Hydrograph Inflow Maximum Maximum
No. Type Name Flow Peak Volume Hyd(s) Elevation Storage
(cfs) (hrs) (cuft) (ft) (cuft)
1 NRCS Runoff Pre AP1 40.79 12.12 148,486 ----
2 NRCS Runoff Post DA1.1 72.21 12.07 213,797 ----
3 Pond Route Post SCM 25.73 12.32 207,599 2 217.13 94,917
4 NRCS Runoff Post DA1.2 20.52 12.00 47,264 ----
5 Junction Post AP1 29.03 12.30 254,863 3,4

Hydrograph 2-yr Summary Project Name:
Hydrology Studio v 3.0.0.29 01-02-2024
Hyd. Hydrograph Hydrograph Peak Time to Hydrograph Inflow Maximum Maximum
No. Type Name Flow Peak Volume Hyd(s) Elevation Storage
(cfs) (hrs) (cuft) (ft) (cuft)
1 NRCS Runoff PreAP1 64.06 12.12 221,558 ----
2 NRCS Runoff Post DA1.1 96.26 12.07 285,618 ----
3 Pond Route Post SCM 37.45 12.30 279,058 2 217.88 120,612
4 NRCS Runoff Post DA1.2 30.17 12.00 68,492 ----
5 Junction Post AP1 45.23 12.10 347,551 3,4

Hydrograph 10-yr Summary Project Name:
Hydrology Studio v 3.0.0.29 01-02-2024
Hyd. Hydrograph Hydrograph Peak Time to Hydrograph Inflow Maximum Maximum
No. Type Name Flow Peak Volume Hyd(s) Elevation Storage
(cfs) (hrs) (cuft) (ft) (cuft)
1 NRCS Runoff Pre AP1 132.5 12.10 439,404 ----
2 NRCS Runoff Post DA1.1 159.7 12.07 480,475 ----
3 Pond Route Post SCM 139.0 12.13 473,642 2 218.52 145,886
4 NRCS Runoff Post DA1.2 57.55 11.98 130,228 ----
5 Junction Post AP1 161.9 12.12 603,869 3,4

Hydrograph 100-yr Summary Project Name:
Hydrology Studio v 3.0.0.29 01-02-2024
Hyd. Hydrograph Hydrograph Peak Time to Hydrograph Inflow Maximum Maximum
No. Type Name Flow Peak Volume Hyd(s) Elevation Storage
(cfs) (hrs) (cuft) (ft) (cuft)
1 NRCS Runoff PreAP1 249.7 12.10 820,179 ----
2 NRCS Runoff Post DA1.1 257.5 12.05 792,421 ----
3 Pond Route Post SCM 248.1 12.10 785,318 2 218.94 162,964
4 NRCS Runoff Post DA1.2 102.9 11.98 235,635 ----
5 Junction Post AP1 315.9 12.05 1,020,953 3,4

APPENDIX C
STORMWATER CONTROL MEASURE SUPPORTING CALCULATIONS
FOREST HILLS
SCM #1 - Wet Pond
SPREADSHEET v1.00

PRE-DEVELOPMENT Drainage Area ID1
FOREST HILLS Drainage are to analysis point on southeast side of
site
January 2, 2024
Hydrologic Soil Group C
ONSITE LAND COVERS ONSITE DRAINAGE AREA
IMPERVIOUS LAND COVERS Area
SCS CN Avg%Imp [sq ft] [ac] Weighted CN
Road (pavement only) 0 0.00 0
Parking 0 0.00 0
Roof 0 0.00 0
Driveway 0 0.00 0
Sidewalk 98 0 0.00 0
Deck/patio 0 0.00 0
Other impervious 0 0.00 0
Other impervious 0 0.00 0
PERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Lawn/grass/open space 74 0 0.00 0
Grass(within R/W) 74 0 0.00 0
Woods 70 1,730,525 39.73 68
Natural wetland 70 0 0.00 0
Riparian buffer 70 0 0.00 0
Other pervious 0 0 0.00 0
Other pervious 0 0 0.00 0
COMPOSITE LAND COVERS Area
SCS CN Avg%Imp [sq ft] [ac] Weighted CN
Commercial area 94 85 0 0.00 0
Industrial area 91 72 0 0.00 0
Residential area (1 acre lots) 79 20 42,850 0.98 2
Residential (1/4 acre lot) 83 38 0 0.00 0
Residential (1/3 acre lot) 81 30 0 0.00 0 _
OTHER ONSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
SCM 0 0.00 0
Open Water 0 0.00 0
ONSITE TOTALS 1,773,375 40.71 70
TOTAL ONSITE IMPERVIOUS 0 0.00
OFFSITE LAND COVERS OFFSITE DRAINAGE AREA
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Impervious 98 0 0.00 0
Pervious 74 0 0.00 0
Woods 70 0 0 0.00 0
Riparian buffer 70 0 0 0.00 0
60' Road R/W 84 40 0 0.00 0
Roof 98 100 0 0.00 0
Driveway/sidewalk 98 100 0 0.00 0
Residential (1/2 acre lot) 80 25 564,825 12.97 80
Residential (1/3 acre lot) 84 40 0 0.00 0
OFFSITE TOTALS 564,825 12.97 80
Area
TOTAL DRAINAGE ARA [sq ft] [ac] Composite CN
2,338,200 53.68 73

POST-DEVELOPMENT TOTAL POND DA Drainage Area ID1
FOREST HILLS DA to pond
January 2, 2024
Hydrologic Soil Group C
ONSITE LAND COVERS ONSITE DRAINAGE AREA
IMPERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Road (pavement only) 113,600 2.61 10
Parking 0 0.00 0
Roof 145,425 3.34 12
Driveway 36,750 0.84 3
Sidewalk 98 21,500 0.49 2
Deck/patio 0 0.00 0
All impervious 0 0.00 0
Other impervious 0 0.00 0
PERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Lawn/grass/open space 74 759,725 17.44 49
Grass(within R/W) 74 0 0.00 0
Woods 70 0 0.00 0
Natural wetland 70 0 0.00 0
Riparian buffer 70 0 0.00 0
Other pervious 0 0 0.00 0
Other pervious 0 0 0.00 0
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Commercial area 94 85 0 0.00 0
Industrial area 91 72 0 0.00 0
Residential area (1 acre lots) 79 20 0 0.00 0
Residential (1/4 acre lot) 83 38 42,850 0.98 3
Residential (1/3 acre lot) 81 30 0 0.00 0
OTHER ONSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
SCM 25,175 0.58 0
Open Water 0 0.00 0
ONSITE TOTALS 1,145,025 26.29 79
TOTAL ONSITE IMPERVIOUS 317,275 7.28
OFFSITE LAND COVERS OFFSITE DRAINAGE AREA
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Impervious 98 0 0.00 0
Pervious 74 0 0.00 0
Woods 70 0 0 0.00 0
Riparian buffer 70 0 0 0.00 0
60' Road R/W 84 40 0 0.00 0
Roof 98 100 0 0.00 0
Driveway/sidewalk 98 100 0 0.00 0
Residential (1/2 acre lot) 98 100 564,825 12.97 98
Residential (1/3 acre lot) 84 40 0 0.00 0
OFFSITE TOTALS 564,825 12.97 98
Area
TOTAL DRAINAGE ARA [sq ft] [ac] Composite CN
1,709,850 39.25 86

POST-DEVELOPMENT TOTAL POND DA Drainage Area ID2
FOREST HILLS Pond Bypass
January 2, 2024
Hydrologic Soil Group C
ONSITE LAND COVERS ONSITE DRAINAGE AREA
IMPERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Road (pavement only) 0 0.00 0
Parking 0 0.00 0
Roof 42,050 0.97 7
Driveway 300 0.01 0
Sidewalk 98 0 0.00 0
Deck/patio 0 0.00 0
All impervious 0 0.00 0
Other impervious 0 0.00 0
PERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Lawn/grass/open space 74 586,025 13.45 69
Grass(within R/W) 74 0 0.00 0
Woods 70 0 0.00 0
Natural wetland 70 0 0.00 0
Riparian buffer 70 0 0.00 0
Other pervious 0 0 0.00 0
Other pervious 0 0 0.00 0
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Commercial area 94 85 0 0.00 0
Industrial area 91 72 0 0.00 0
Residential area (1 acre lots) 79 20 0 0.00 0
Residential (1/4 acre lot) 83 38 0 0.00 0
Residential (1/3 acre lot) 81 30 0 0.00 0 _
OTHER ONSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
SCM 0 0.00 0
Open Water 0 0.00 0
ONSITE TOTALS 628,375 14.43 76
TOTAL ONSITE IMPERVIOUS 42,350 0.97
OFFSITE LAND COVERS OFFSITE DRAINAGE AREA
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Impervious 98 0 0.00 0
Pervious 74 0 0.00 0
Woods 70 0 0 0.00 0
Riparian buffer 70 0 0 0.00 0
60' Road R/W 84 40 0 0.00 0
Roof 98 100 0 0.00 0
Driveway/sidewalk 98 100 0 0.00 0
Residential (1/2 acre lot) 98 100 0 0.00 0
Residential (1/3 acre lot) 84 40 0 0.00 0
OFFSITE TOTALS 0 0.00 0
Area
TOTAL DRAINAGE ARA [sq ft] [ac] Composite CN
628,375 14.43 76

POST-DEVELOPMENT TOTAL POND DA Totals
FOREST HILLS Total drainage areas
January 2, 2024
Hydrologic Soil Group C
ONSITE LAND COVERS ONSITE DRAINAGE AREA
IMPERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Road (pavement only) 113,600 2.61 6
Parking 0 0.00 0
Roof 187,475 4.30 10
Driveway 37,050 0.85 2
Sidewalk 98 21,500 0.49 1
Deck/patio 0 0.00 0
All impervious 0 0.00 0
Other impervious 0 0.00 0
PERVIOUS LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Lawn/grass/open space 74 1,345,750 30.89 56
Grass(within R/W) 74 0 0.00 0
Woods 70 0 0.00 0
Natural wetland 70 0 0.00 0
Riparian buffer 70 0 0.00 0
Other pervious 0 0 0.00 0
Other pervious 0 0 0.00 0
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Commercial area 94 85 0 0.00 0
Industrial area 91 72 0 0.00 0
Residential area (1 acre lots) 79 20 0 0.00 0
Residential (1/4 acre lot) 83 38 42,850 0.98 2
Residential (1/3 acre lot) 81 30 0 0.00 0
OTHER ONSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
SCM 25,175 0.58 0
Open Water 0 0.00 0
ONSITE TOTALS 1,773,400 40.71 78
TOTAL ONSITE IMPERVIOUS 359,625 8.26
OFFSITE LAND COVERS OFFSITE DRAINAGE AREA
COMPOSITE LAND COVERS Area
SCS CN Avg% Imp [sq ft] [ac] Weighted CN
Impervious 98 0 0.00 0
Pervious 74 0 0.00 0
Woods 70 0 0 0.00 0
Riparian buffer 70 0 0 0.00 0
60' Road R/W 84 40 0 0.00 0
Roof 98 100 0 0.00 0
Driveway/sidewalk 98 100 0 0.00 0
Residential (1/2 acre lot) 98 100 564,825 12.97 98
Residential (1/3 acre lot) 84 40 0 0.00 0
OFFSITE TOTALS 564,825 12.97 98
Area
TOTAL DRAINAGE ARA [sq ft] [ac] Composite CN
2,338,225 53.68 83

RUNOFF VOLUME BY SIMPLE METHOD

WATER QUALITY RUNOFF VOLUME
FOREST HILLS SCM #1 -Wet Pond
Runoff Volume by the Simple Method taken from NCDEQ Storm water Design Manual Part B
Input Data
Onsite Impervious area 7.28 acres
Offsite Impervious area 12.97 acres
Total Impervious area 20.25 acres
Drainage area A 39.25 acres
Impervious fraction la 0.516
Design storm rainfall depth Rd 1.00 inches
Output
Runoff coefficient Rv 0.51
Runoff volume V 73,282 cubic feet
R„ = 0.05 + 0.9xIA
V = 3630 x RD x RV xA

RUNOFF TREATMENT VOLUME

RUNOFF TREATMENT VOLUME January 2, 2024
FOREST HILLS SCM #1 -Wet Pond
Runoff Volume by the Simple Method taken from NCDEQ Storm water Design Manual Part B
Input Data
Existing BUA 0.00 acres
Proposed BUA 8.26 acres
Net BUA Increase 8.26 acres
Impervious fraction la 1.000
Design storm rainfall depth Rd 1.00 inches
Output
Runoff coefficient Rv 0.95
Runoff volume V 28,470 cubic feet
R„ = 0.05 + 0.9XIA
V = 3630 x RD X RV XA

WET POND SURFACE AREA REQUIREMENT

REQUIRED WET POND SURFACE AREA January 2, 2024
FOREST HILLS SCM #1 -Wet Pond
Drainage area 26.29 acres
Percent impervious 27.7%
Permanent pool depth 3.0 ft
Required pond surface area 0.29 acres
Required pond surface area 12,531 sq.ft.
Permanent Pool Average Depth (ft)
Impervious 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 1
100 3.55 2.79 2.52 2.34 2.04 1.75
Interpolation
Average Depth
Impervious 3.0 3 3.0
20 0.84 0.84 0.84
27.709002 1.09 1.09 1.17
30 1.17 1.17 1.17
Notes:
SA/DA values taken from NCDEQ Stormwater Design Manual Section C-3, page 7 (revised 4/18/2017)
Per wet pond guidance MDC 1,the required surface area does not include the area of the forebay(s)

WATER SURFACE ELEVATION FOR DESIGN RUNOFF VOLUMES

DESIGN VOLUME WATER SURFACE ELEVATIONS January 2, 2024
FOREST HILLS SCM #1 -Wet Pond
Elevation at WQ Volume 216.50
Calculated pond surface area at above elevation 32,692 SF
Calculated pond volume at above elevation 73,427 CF
Calculated WQ Volume from simple method 73,282 CF
Elevation at Runoff Treatment Volume 215.06
Calculated pond surface area at above elevation 28,332 SF
Calculated pond volume at above elevation 29,842 CF
Calculated Runoff Treatment Volume 28,470 CF
POND ELEVATION AND CONTOUR DATA
214.0 25,165 SF 0.0 0 0
216 31,141 SF 2.0 56,306 CF 56,306 CF
218 37,344 SF 4.0 68,485 CF 124,791 CF
220 43,773 SF 6.0 81,117 CF 205,908 CF

DEWATERING TIME CALCULATION

POND DEWATERING TIME January 2, 2024
FOREST HILLS SCM #1 -Wet Pond
Dewatering time calculated by the falling head equation
Input Data
Pond surface area 25,165 sq.ft.
Orifice diameter 6.00 in.
Orifice coefficient 0.60
Orifice elevation 214.00
Initial elevation 216.50
Results
Orifice area 0.1963 sq.ft.
Dewatering time 4,535.7 min.
Dewatering time 75.6 hours
Dewatering time 3.1 days
Dewatering time = Areapond — (.✓Initial pond elevation x s/final pond elevation) x 12
Areaorifice x Cd g

AVERAGE DEPTH AND FOREBAY VOLUME

FOREBAY VOLUME & AVERAGE DEPTH CALCULATIONS January 2, 2024
FOREST HILLS SCM #1 -Wet Pond
DATA FOR MAIN POOL FROM BOTTOM OF POND TO BOTTOM OF SHELF
Elev Area [SF] Incr vol [CF]
208 3,837 0
210 7,895 11,732
Enter data up to and including 212 12,240 20,135
the bottom of the shelf 213 14,521 13,381
MAIN POOL TOTAL VOLUME(UP TO BOTTOM OF SHELF) 45,248
DATA FOR MAIN POOL FROM BOTTOM OF SHELF TO TOP OF SHELF(NOT INCLDUDING FOREBAYS)
Bottom of shelf 213 1 14,521 0
Permanent pool elev 214 18,833 16,677
Top of shelf 214 18,833 0
TOTAL VOLUME OF POND SHELF(BETWEEN TOP AND BOTTOM OF SHELF) 16,677
DATA FOR FOREBAY#1 FROM BOTTOM OF FOREBAY TO TOP OF SHELF
Elev Area [SF] Incr vol [CF]
211 200 0
212 1,031 616
213 1,428 1,230
214 2,092 1,760
Total Volume of Forebay#1 3,605
DATA FOR FOREBAY#2 FROM BOTTOM OF FOREBAY TO TOP OF SHELF
Elev Area [SF] Incr vol [CF]
210 100 0
212 2,251 2,351
213 2,904 2,578
214 4,239 3,572
Total Volume of Forebay#2 8,500
DATA FOR FOREBAY#3 FROM BOTTOM OF FOREBAY TO TOP OF SHELF
Elev Area [SF] Incr vol [CF]
Total Volume of Forebay#3 0
Total Volume of Forebays 12,105 CF Average Depth by Equation 3
Main Pool Volume 61,925 CF Perimeter of perm pool 715 FT
Forebay%of main pool 19.5% Width of shelf 6.00 FT
Max depth over shelf 1.00 FT
Average Depth by Equation 2 Vol over shelf 2,145 CF
Vol at Permanent Pool 61,925 CF SA at bottom of shelf 14,521 CF
SA at Permanent Pool 18,833 SF Vol at Permanent Pool 61,925 CF
Average Depth 3.29 FT Average depth 4.12 FT

ANTI-FLOTATION BLOCK CALCULATIONS

ANTI FLOTATION BLOCK January 2, 2024
FOREST HILLS SCM #1 -Wet Pond
Constants
Unit weight of water 62.4 lb/cf
Unit weight of concrete 144.0 lb/cf
Riser Data
Length Width Area
Inside domensions 4.00 ft 4.00 ft 16.0 SF
Outside dimensions 5.00 ft 5.00 ft 25.0 SF
Cross sectional riser area 9.0 SF
Riser inside height 4.0 ft
Volume of concrete in riser 36 CF
Riser base area 25.0 SF (same as riser outside dimensions)
Riser base thickness 0.5 ft
Volume of concrete in base 13 CF
Total volume of concrete in riser+base 49 CF
Total bouyant weight of riser 3,958 lbs
Water displaced by riser 100 CF
Weight of water displaced 6,240 lbs
Anti-Flotation Block Data
Length of anti-flotation block 6.0 ft
Width of anti-flotation block 6.0 ft
Thickness of anti-flotation block 1.5 ft
Volume of anti-flotation block 54 CF
Total weight of anti-flotation block 7,776 lbs
Factor of Safety
Weight of riser+anti-flotation block 11,734 lbs
Weight of water displaced by riser 6,240 lbs
Factor of safety against flotation 1.88

APPENDIX D
ENERGY DISSIPATER/RIPRAP APRON CALCS

Forest Hills Subdivision DESIGN OF RIPRAP OUTLET PROTECTION
FES 100
August 8, 2023
OUTLET FLOWRATE 58.4 cfs
PIPE DIAMETER 42 inches
OUTLET PIPE SLOPE 1.50 %
NUMBER OF PIPES 1
PIPE SEPARATION 0 feet
ZONE FROM GRAPH 3
PIPE AREA 9.62 sq. ft.
FLOW VELOCITY 11.1 ft/sec
MATERIAL NCDOT Class I riprap
LENGTH 28.00 feet
WIDTH 10.50 feet
STONE DIAMETER 13 inches
THICKNESS 22 inches
Zone Material Diameter Thickness Length Width
1 Class A 3 9 4 x D(o) 3 x D(o)
2 Class B 6 22 6 x D(o) 3 x D(o)
3 Class I 13 22 8 x D(o) 3 x D(o)
4 Class I 13 22 8 x D(o) 3 x D(o)
5 Class II 23 27 10 x D(o) 3 x D(o)
6 Class II 23 27 10 x D(o) 3 x D(o)
7 Special study required
1. Calculations based on NY DOT method - Pages 8.06.05 through 8.06.06 in NC Erosion Control Manual
2. Outlet velocity based on full-flow velocity
6 -
• i
�. ' Ili , --
t .\; , . I1 ; Tom' I I
1 ; I ; I • • 1 -T- 4-
,� , 1I , , , { ,
IK' ae 6 .rd " 1 i
0• S 10 15' 20 25
DIAMETER (Ft.)

Forest Hills Subdivision DESIGN OF RIPRAP OUTLET PROTECTION
FES 200
OUTLET FLOWRATE 24.3 cfs
PIPE DIAMETER 30 inches
OUTLET PIPE SLOPE 2.80 %
NUMBER OF PIPES 1
PIPE SEPARATION 0 feet
ZONE FROM GRAPH 3
PIPE AREA 4.91 sq. ft.
FLOW VELOCITY 11.4 ft/sec
MATERIAL NCDOT Class I riprap
LENGTH 20.00 feet
WIDTH 7.50 feet
STONE DIAMETER 13 inches
THICKNESS 22 inches
Zone Material Diameter Thickness Length Width
1 Class A 3 9 4 x D(o) 3 x D(o)
2 Class B 6 22 6 x D(o) 3 x D(o)
3 Class I 13 22 8 x D(o) 3 x D(o)
4 Class I 13 22 8 x D(o) 3 x D(o)
5 Class II 23 27 10 x D(o) 3 x D(o)
6 Class II 23 27 10 x D(o) 3 x D(o)
7 Special study required
1. Calculations based on NY DOT method - Pages 8.06.05 through 8.06.06 in NC Erosion Control Manual
2. Outlet velocity based on full-flow velocity
6 -
• i
t .\, ' I i I ` .?A
; , . I1 ; Tom' r I
I ; I ; I • • 1 -T- 4-
5 ), Ii ' ii11 I . I : i
'K' ae 6 .rd " 1 i
0' S 10 15' 20 25
DIAMETER (Ft.)

Forest Hills Subdivision DESIGN OF RIPRAP OUTLET PROTECTION
SCM1
OUTLET FLOWRATE 140.0 cfs
PIPE DIAMETER 24 inches
OUTLET PIPE SLOPE 1.00 %
NUMBER OF PIPES 1
PIPE SEPARATION 0 feet
ZONE FROM GRAPH 2
PIPE AREA 3.14 sq. ft.
FLOW VELOCITY 11.4 ft/sec
MATERIAL NCDOT Class B riprap
LENGTH 12.00 feet
WIDTH 6.00 feet
STONE DIAMETER 6 inches
THICKNESS 22 inches
Zone Material Diameter Thickness Length Width
1 Class A 3 9 4 x D(o) 3 x D(o)
2 Class B 6 22 6 x D(o) 3 x D(o)
3 Class I 13 22 8 x D(o) 3 x D(o)
4 Class I 13 22 8 x D(o) 3 x D(o)
5 Class II 23 27 10 x D(o) 3 x D(o)
6 Class II 23 27 10 x D(o) 3 x D(o)
7 Special study required
1. Calculations based on NY DOT method - Pages 8.06.05 through 8.06.06 in NC Erosion Control Manual
2. Outlet velocity based on full-flow velocity
6 —
• i
Ililf --
I 1 ; Tom' r I
1I
; I I • • 1 ; -T- 4-
,� , 1I , , , { ,
'K' ae 6 .rd " 1 i
0• S 10 15' 20 25
DIAMETER (Ft.)