SW6201004_Calcs_20210427

Storm wafer Management Design Calculations
April 26, 2021
Blackhawk Landing —Phase 1
Rockfish Road
Hoke County, NC
Prepared for:
Double D Engineering, PLLC
150 S. Page Street
Southern Pines, NC 28387
910-684-8646
Prepared by:
Triangle Site Design, PLLC
4004 Barrett Drive, Suite 101
Raleigh, NC 27609
[phone]
License#P-0619
TRIANGLE
S I T E D E S I G N
tr

TABLE OF CONTENTS
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This report contains the storm wafer management oo|ou|otiono for the proposed residential
development 0ookhowk Landing - Phase 1 on Rockfish Rood in Hoke County. The project
site is currently un-developed wooded area. The proposed site consists of 40.8308 acres
and approximately 23.43 acres will be disturbed on port of this project for the construction
of the site improvements. There is approximately 0.657 nonaa of surface wafer area which
results in approximately 40.1738 acres of total pn400f area,
The proposed site in located in Flood Zone `X` as shown on FEMA FIRM Panel 3710946500j
with on effective dote of 10/17/06. Flood zones are subject to change by FEMA.
There are existing stream or wefland features on the proposed properiN
The proposed storm water rnonogornenf facility /wef pond) outlined in this report has been
designed to treat the impervious or000 of the development. The wet pond has been
overdoxigned to overcompensate the off-aife drainage area to balance out the impervious
area not directly draining to the wef pond by [ofo 38-42 and [ofo 77-73. The development
of the Phone 1 site will result in on impervious area of 485,392of (11.1400 - 77.29%
impervious).
The drainage area oonoiufm of off -site oroon which includes port of Rockfish Rood, which
includes 74.866of /0.57oc\. The off-oife drainage area also includes port of on apartment
complex along Rockfish Rood, which includes 97.373af /2.234oc\. and residential areas and
open space along Markus Drive and Rockfish Rood, which includes 168.373af /3.865oc\. The
total off-sife drainage area is 290.567sf (6.67oc) The wet pond is designed to receive
100% HUA for fhoua off-aife drainage oreoo. The site grading and ofonn drainage systems
are designed to convey ofonnwofer runoff from the impervious areas of the site and off -
site to the wef pond. A wef pond will be used to provide peak flow attenuation of the
10-yeor storm event for o drainage area of 23.87 acres with on impervious area of
16.62oc. The balance of the site is comprised of the bypassed roads and sidewalk
associated with Lots 38-42 and [ofo 77-73 and open opouo and will by-pass the proposed
wet pond. The pond is designed to treat o 1.0~ ofonn event.
The County Soils Survey indicates that VVogrom and Blaney Loamy Sand soils are present on
the site.

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Conservation Service National Cooperative Soil Survey Page 3 of 4

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Water aossific9tions-,
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9/1/2020 Precipitation Frequency Data Server
NOAA Atlas 14, Volume 2, Version 3
Location name: Raeford, North Carolina, USA',N
Latitude: 34.9901°, Longitude:-79.1321°
Elevation: 205.79 ft-
9
1
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 I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency i _.�.��..)
p p p quency estimates with 90% confidence intervals (In inches)1
��� . m _ .
1 2 5 10 2 recurrence h {,Yeurs100 200 �� 50U�
IOurattoYl -
Avera a recu interval
_. 5 50 1000
- {0 50 99 ) ( 0 664 0.741 0.797 0.851 0.901 0.96
C 4A 396 0.482) (CI 85e 0 k1f p @ G4) 0 0r1 0 1.J( (0 r0ld-"0 817) (0 718 C 877) f,C 761-0 47 ia1) f0.602-0 Cog) PU 851 1 t 6) C7 087.1.11)
5-min �( 0.435 0 514 3 1.01
10 min 0.695 0 822 0 960 1.06 1.18 1 27 1.35 1 43 1 52 1.59
.. {Cl h]32-0 d871 (0 747 0 90�1p (0 W N Y () I r1 962 1 17p (1.07-1 30) I' �1 14 1 40;1 r �1.21 1„4`) � Q 1 27„1 � l 1`(1 35-1.haY [(1.40-1.75)
qo 790 0 9Gy I (ra s3s 1 14 1.34 1.50 1 61 1 71 1 80 1 92 2 00
1 0.80, " ' 1.03 -1 1 � Q 1IT102113 y � 0.22-1 48) � Q i 35. I dat l (1 45 1 7 ) 1 53_1 88) Q 1 61 1 �d 1,,, �l y„�_69 2 11)1 (V 75 + 20)
u 15-min
r ff d
30-min ,1.08119JC1,,,, 04381 (1.57 13911..(1 7695'It) (' 00224,1)l (2 8 2 6t) ,,� ( 2 628/)� (J 5 81t9fYlmm (2 0051 r1 (?,N 124ti D,,,,
I L .
q l 35 1 tr1 1 79 2.21 2 54 2 95 3 28 3 61 3 93 f 4.38 � 4 73
60-mini 1 4949 �i
®..,� I� ( /-�_(" itN �F10) � ( a>"...rc �I�'61Y. .G7 3 �Ikay e1'SO4.,3 �d5.87�.81 {'11551 )
{163191,1 81-2�Sa a a (!_ ......... ..
2-hr 1.73 2 10 2.64 3 05 3 61 4 06 4 51 4 97 5. 00 6 10
91 b6„1,,, 6) (1 89 2 6) �� {1 "57•2 J8J D2 74 :; 42) ,..(3 �q :4 05@ f3 t 1� BED). (3 99 051 � (4 ,37 5 56) � (4 88-&26) ] (5 27-6 821.
1.83 2.2 1 2.81 3 27 3.92 4.45 5.00 5.58 6.40 7.06
q1 V� 07) (:00 2 SO) (2.62�w3 169 f � r aP3 fi U8 t 4 �� �, 1 7) (3 94 4 SN�m 4 1`vI a (.Y 4i 86 6 S24@ ] C�'A-7.15,
3 hr _..w .. ( 1 4 _
6-hr, 2 19 2 65 f 3.35 3.91
4 70 5 35 6.04 6.76 7.79 8 63
6 2 44) 11 l3 02.3 "s °a 4 3Fi '�jal'0- 221 (4 7 N „ W9?di I (5 32,6,68) l (5 90"7.46) 5 (1 9 ) { (u3.71 8 r;u 17.35 9 511
12 hr �37 4 66 5.64 6 46 7.33 8��(2 33 2888) (k {3 124 i ( �4 18 5 19M (� lP2 6 G) (_a 70 7 1 F1 (6 41-8 10! !' 15 9. Y �i (F1 19-10 6J (E 0„ 11 C1E
823 8) (944 397 I ) ®„
3 03 3 67 4.66 5 45 6.53 7.41 8.31 9 24 10.5 11 6
24 hr 2-5 041" C4 ra Hfij (fi,71-7 0"v1 (La 81d-7 98) (7.60-6 c28) 1 (fk 4�3 �1 1 J) q'sd 56 11 4) q10 4 1I `s)
BR (4 3
_-
f 35-2-71 425 535 623 7.43 840 940 104 118 130
y (' 2F1 ' 7E) () 4d8 # 7`a (4, 98 5 75) (5 78 6.69) (6 87-7 98) a
2-da _ _ �i (.7W9 MOT. (8._6 101.).- (.: 3I'l.,11..,.? i10..8..1. 8J. {41.8140j
3 day 3. 4 01) � 1 7 00 � 2 . ).., # 1 {12 2 15 5),
(t 5L1 q 1 21 4 r3 (5 2664 6 54 7.78 8 78 9 80 10 9 12 3
74 4 51 5 6 04) (6 09 7 00) (7 22-8 33 8 1 1 N 3 f) (� 03 10 (9 96 11 B N (11 2 1 �q�
.. _..:
4-dayF-i4 2 9 16 10.2 11 3 12.8 14 0�
2-4 ) (1 4 770"IN ) r .5 633 2p (FII(8 0,7.31) (7 8 18.67) ('8 Y9 "/hi) { 1 4;3 10 9) ." � (10 4 12.1) ��11 7-13.2j �1 (12.7 14 9
7-day (j 4161�)p 6 51831 f (6 3 78ix') (? 2678 f ".) I {8 51 19.76) �9.51g 3.0) (10 5 2.2) (11 6�13 4) (1310-15 2) ('d4151E ;y
10-day 0 97-5 61 8,10 (B 13 9 19)� (9 41 10 7) (10 4- .B (11 4-13 .4- 4 141 16 1
5.28 6 30 7.-63 8 66 10 1 �_ ��
J
�.18 t1 (a 16 ) ) 30) (tit414:,) �('1381! J) I.(.tl4.8„172)
..:., _
Y rE� 72 72a0. (7 974 96 ( 4 0 10 6 12 01 )16 2-13 8) q'13 4 1 n 2.). ,"1 1 ( B 21 t)
�.•( 11 3 13.0 14 3 15. i
.2 1
20 da 8.85 10.4 � 'l2�2 �) 13.6 15.4 16.8 I (1418
p ,III" Ir 7 17 0 18 9
30-day Y (, ,,,, (1.61916 1) 1 (1721 4 1) I (N8 22 24 8) I,
o l
4.5-16 3i 5 6 17 Y) (17 1 19.3) (1Ei , 20 6) (20,0-2 ,
15.1
_. - 8.6 IF_ -2 1 6 24 . 24.9 26 3
y 0134 FV) I12151�), (141316Gap� (0518176j (1716-19) (19202 :§� (20.3-228)(rW 230 t) �(a31-161)l ((ns26lf)
) I
60 da I� 21.7 23 4 25 0 26 5 28 5 30 0
17.9
18 8) (1019 6 dM) (CI 6 2 9) (` 1 24..1„ �(.'..:8 3.?.....( lY 4)d8
y
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 PIMP values,
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=34.9901 &Ion=-79.1321 &data=depth&units=english&series=pds 1/4

STORMWATER MANAGEMENT CALCULATIONS

SUPPLE ENT-EZ COVER PAGE
FORMS. L0,ADII,,D
NUMBER AND TYPE OF SCMs:
11
Infiltration System ® ..... ....
.
0
12_
Bwrete.... Cell......... ... ......... ... .....
. _ ... ®.O ...... —- .....
13
Wet P. ......... ......... ......... . _
...._.... _...... ......... .................. ..... ................ ..... ...........
14
Stormwater Wetland
— — —.._ ......... ...... _...___.............. ..._.. ..
0
...-... _ _ _ ... ........
15 ,
Permeable Pavement
_ ff ....., _......... me ... ...... ----
0
._... ..� . , ...... .............m._ �_ ... ........._ ......
16
Sand Filter
0
......_.
17
.. _ _
1Rainwater Harvestm RWH)
........ --
_... 0
18
Green . ------ ....... _....
_ .....
19
Level Spreader -Filter Strip(LS-FS)
0
20
Disconnected Impervious Surface , IS)
0 �,.
21
Treatment Swale
n., ..... _
0
22
Dry Pond
0
23 .
StormFilter
........ ...... .. __ --
0
_ - .....J....
24
Silva Cell ®
w __ 0
25
Balter„
0
26 Filterra
_ —
0....
I,:DRttir S LOADED
Certification Statement:
I certify, under penalty of law that this Supplement-FZ form and all supporting information were prepared under my direction or
supervision; that the information provided in the form is, to the best of my knowledge and belief, true, accurate, and complete; and
that the engineering plans, specifications, operation and maintenance agreements and other supporting information are consistent
With the information provided here.
I OSL ner
p n
Signature of Designer
Date
1�12,t,,-2.

DRAINAGE AREAS
............ � .._. _..
1 _ Is this a high denss��rolect? _ Yes
2 If so, number of drainage areas/SCMs 1
Is all/part of this project subject to previous rule
3 versions? No
DRAINAGEAREA
INFORMATION
Entire Stte
1
4
type of SCM
Wet Pond y ..
Wet Pond.
5
Total BUA in project {sq ft)
485392 sf
433196 sf
New BUA on subdivided lots (subject to permitting)
New BUA outside of subdivided lots (subject to
7
permdUnc) {sf)
8
Offslte total area fsc�ft)
i_.. 290562 sf
290562 sf
_.— .
9
..�..... m n...... �.
pffsite BUA s ft
� )
_.05 _...._..
290562 sf
�.
290562 sf
..�........... . .........
10
Breakdown of new BUA outside subdivided lots.,
Parking (sq ft)
Sidewalk (sg_ft)
17090 sf.......
15114 sf . .
...........
Roof (sq ft.)
365000 sf
330000 sf
30 ... _ ......... !
............................... ...........
Roadway fsq...ftL.. —
_._
_ 100062 sf _. .
..... _ 84842 sf
Future (s n)_
mOther,
m
please specify in the comment box
belowmsq fit_
3240 sf y.
3240 sfw
New infiltrating permeable pavement on
11
subdivided lots s ft
New infiltrating permeable pavement outside of
12
subdivided lots fsig ft) .. m_
----.
Exisitng BUA that will remain (not subject to
13........
permitting) fsq.ft). ..
. �.
14
Existing BUA that is already permitted fsq ft)
-
15
—
Existing BUA that will be removed (sq fit
....
.e.
6
Percent BUA
27.29%
69 6200
1
Design stormm(mches)
1.0 m
B !Design
volume of SCM cu ft
{
.
8614 cf
19
,
r....
g)
Calculation method for deal n volume
� �
e
I Si pie Method
^
f
..
rtrt
1 1 1 tl I I T10
-Pleases
pace to
use this provide any additional information
about the
20
drama a area(s�
Line 10 - There
.... m
is offsne BUA draining towards the SCM This includes the residential areas and open
_.... _ — �...._......
spare along Marcus PWce
Drive and
Rockfish Road, apartments along Rockfish Road and a portion of Rockfish Road This
offsite BUA will be (adored with
100% Bwld-Out
Potential in the post developatl peak now runoff to the SCM The SCM has been overdesigned
to overcompensate
hhe off -site
drainage area to balance out the impervious area not directly draining to the SCM by Lots
38-42 and Lots 72-73 The
drainage area
drainage area
+mperviaus
has decreased and without changing the see of the SCM now has a design volume
yielded a design volume of 66,693 (difference of 8,279 d) In addition mere is a postal
area
ww.wvw nww..«rwr.«wvxaa�e�arvry
of 56,614 d The previous
kbsk on site with 3240 at
s�ewx
f�

WET
POND
-inage
1
2
eu��I (c.ftnumber
Oes g o�... �.,........
um .......
u )
_ _W ..
88614 c
rreEN{�
� �� _
3�Is
t c
the SCM sized es at build -out?
�� ��to treat the SW from all surfs
Yes
_
4
�
Is the S d away from contaminated soils?
-
Yes
5
What are the side. slopes of the SCM (H:V)?
. 3 1
Does th_....., ............. ......,.,._ - _...........
e SCM have retaining wallslls,, gabion walls- or other
6
engineered side slopes?
— ..
No
_ _ .......-- _
........_
Ar — _...—. .....
e the inlets, outlets, and receiving stream protected from erosion
7
(10-year storm)?
Yes
..,. ......
o Is there an overflow orsypass forinflow volume �� � _ t_h-__—
in excess f te
8
design volume?
Yes
. .._.-
9
What is the method for dewaterrng the SCM for maintenance?
Pump
p prefe
(
10
1f applica@ethe SCM, be cleaned oaf a her construction?'
Yes
11
Goes the maintenance access comply with General MDC (8)?
Yes
......12
Dae the drainage easement comply with general MD (9)?
Yes
-- --
Willie SCM is on a)7n single family lot, does will? the fat comply with
9 Y (will?) P PY
F�
13
---
General MDC (10
,..—.—..... ...... ............... .......... ..... _
...
14
Is there an O&M Agreement that complies with General MDC (11)?
Yes
—
15
- .._ _.. _ ....,.w... ....... ....... -_____ -
Is there an O&M Plan that complies with General MDC ('12)?
- - -
Yes
16
_ -.W- .._.. .. _ ---- ---
Doos fhe SCM follow the +device specific MDC?
Yes
e—i
17
Was the nCM designed"bl an NC licensed professional a' """' __
-_._ ,._.._._
Yes
WET It
'ERMANULAM
18
Method used
SA/DA
—19
Rani a"Oslorage table been inthecalculations?-
�Yes
Elevation of the excavated main pool depth (bottom of sediment
20
removal) (fmsl)
174.5
21
Elevation of the main pool bottom -(top of sediment removal) (fmsl)
175.5
22
Elevation of the bottom of the vegetated shelf (fmsl)
84.5
� 184.5
_.....
23
l........ ........................
Elevation of the permanent pool (fmsl)
1$5.0
2....
4
Elevation of the top of the vegetated shelf (fnisl) _ f ........ M�
� �1.85.5
25'
Elevat on of the temporary pool (fmsi)
187.3
2Ci
Surface area of the main permanent pool (square feet) ......... .....
15710.0
27
V6jiiri a of the, main psmisnent pool (cubic fee if _
0i359
30
If using equation 3, main pool perimeter (feet)
485.0 R
31
If using equation 3 w Oh of submer'god ve,g. shelf (feut}
3.Oft
—
32
.......................... .. ------.______---
Volume ofthe forebay (cubic feety
15496 cf
33
Is this 15-2046 of the volume in the main pool?
Yes
—
34
..... ... ..... _- .........
Clean -out depth for forebay (inches)
60 in
35
Design volume of SCM (cu ft) — --
58614 ct'
36
Is the outlet an orifice or a w _..
Orifice
37
_air?
If orifice, orifice diameter (inches) - — _
3.50in
—
38
..,... ........._ _.....
....... ........
i __.—..ei -.. .......
If weir, weir height (inches)
-_. .. _...._ ..
39
NT wawa,"were IengtNi (incNties)
-
40
-... — ---.., .. i,p
Drswdov^an trme'for tN°re temporary pool (days,) .. e
w..... __..
2.14
Are the i..-_. in" le"'t-..'c"a,f.....m......__ ._._.w
nlet(s) and outlet located in a manner that avoids short-
__ ....
41
circuiting?
Yes
--
_.......
Are berms or haffe�p.ro._vd.odtoimpITr._o.vrthe .f�orpat—h7,e'„
._..-_._yes
�3
Depth of forebay at entrance (inches) — — — — ---
_ 72 0 in .
.-._.
44
-- forebayr' at exit (inches)
Dppth of .
�n
36 b in-
45
....._—
orebay in anon -erosive manner?
Does water flow out of the t....._ .....,......... _.....osiv .. manner?
Yes
4161i1lU1dth
of the vegetated shelf (feet) — — — — _ ....
.. 511
ft .....
48 permanent pool?
Yes
Does the pond minimize impacts to the receiving channel fromW the 1-
IT
49 yr, 24-hr storm?
Yes
.. Are fountainsmproposed? (IiY, please provide documentation that
50 MDC(9) is met.)
No
51 Is a trash rack or other device provided to protect the outlet system?
Yes
52 Are the dam and embankment planted in non -clumping turf grass?
_ _ Yes
53 Species of turf will be used on the dam and embankment
Hybrid Be
— �­.
5 ' _H.6' a pfantmg p1a Ve_6h-pr.rvir&ffEe IB6 vege to ffo
."het
ADDITIONAL INFO�w
RMATION
Please athis s
use pace to provide any additional information about
55 the wet and s
p .. -- -- -
Responses to Lines 34, 43 & 44 are for East Forebay.
West Forebay: Line 34 = 72 in, Line 43 = 84 in, Line 44 = 36 in
See Drainage Area additional information for clarification on oversizing of
SCM.
Wet Pond 1 3:19 PM 4/26/2D21

Triangle Site Design, PLLC
Bethesda, Aberdeen, NC
Curve Number Calculation (CN)
Pre -Developed Conditions
Drainage Area jacresJ: 23.87
Existing Soil Groups:
Soil Grouo Map Symbol
Soil Description
Acres
Percent of DA
A WaB
Wagram Loamy Sand
10.67
45%
C BaB
Blaney Loamy Sand
13.20
55%
Existing Land Uses.,
Land Use Description
Existing SoiP Group Acres
Curve #
l4 e h1ed QN
Wooded - Good Stand
A 10.67
40
17,9
Wooded - Good Strand
C 11.77
73
36.0
Impervious Area
C 1.43
98
5.9
Cumulative Curve # =
59.7

Triangle Site Design, PLLC
Curve Number Calculation (CN)
Post -Developed Conditions to Wet Pond
2IL471Mg 4 rO , (: C ,° 23.87
5� 5oll Groins:
Soil Group Map Symbol
Soil Description
Acres
Percent of DA
".._..._
A WaB
Wa Loam Sand
ram
9 Y
10.67
45
C BaB
Blaney Loamy Sand
13.20
55%
Pro Deed L41 rf L1s,
Land Use Description
t~xisting ,Soil Crow Acres
Curve #
Weighted CN
Impervious Area
A and C 16.62
98
68.2
Open Space - Good Condition
A 4.50
45
8.5
Open Space - Good Condition
C 2.75
76
8.8
Cumulative Curve # =
85.5

Impervious Area Sumrnar
Impervious Area to Wet Pond
Road 84,842 1.948
Sidewalk 15,114 0.347
Lots 1-37/43-71 (66 Lots) 330,000 7.576
Mail Kiosk
3,240
0.074
'Total)On.-site
433,1.96
9.945
Rockfish Road
24,866
0.571
Apartments
97,323
2.234
100% BUA
Homes
168,373
3.865
100% BUA
Total -site
290,562
6.67
':
" 723,758
16 62.
Assignment #'s per Hoke County GIS Map
Homes
Homes/Open Space
168373
3.865
Total Homes
168373
3.865
Apartments
Apartment 036
22457
0.516
Apartment 035
23498
0.539
Apartment 208
20398
0.468
Apartment 206
20497
0.471
Apartment 203 1/2 lot
10473
0.240
Fotall Alpartments
97323
2.234

Proposed Wet Pond
Project Information
Project Name: Blackhawk Landing
Project #:
Designed by: CEP Date: 4/26/2021
Revised by: Date°
Checked by: Date:
ite Information
Sub Area Location: Drainage To Proposed Wet Pond
Drainage Area (DA) = 23 87' Acres 1,039,,600 sf
Impervious Area (IA) = 1662 Acres 723,758 sf
Percent Impervious I = % 69.62 %
(;equired Surface Area
Permament Pool Depth: 7,07 ft Non (;: oastall County
SA/DA = 1.32
Min Re 'd Surface Area = 13,7 sf (at Permanent Pool)
;equired WQv Storage Volume
Design Storm = 1 inch 1°4(:wi,...Coa,: t6l County
Determine Rv Value = 0.05 + .009 (1) = 0.677 in/in
Storage Volume Required = 58,614 cf (above Permanent Pool)
Elevations
Top of Pond Elevation =
19100 ft
Temporary Pool Elevation =
187,30 ft
Permanent Pool Elevation =
185.00 ft
Shelf Begining Elevation =
'185Z(") ft
Forebay Weir =
184.00 ft
Shelf Ending Elevation =
184.50 ft
Bottom Elevation =
175,50 ft
Permanent Pool Area
Area @ Top of Permanent Pool = 15,710 sf
Volume of Temporary Storage = 60,75 ' cf
Is Permenant Pool Surface Area Sufficient (yes/no)? Yes ( 15710 > 13723) sf
Volume of Storage for Design Storm = 605"e ( 60757 > 58614) cf

Incremental Drawdown Time
STORMWATER POND
INCREMENTAL DRAWDOWN METHOD -Water Quality Volume
Project Information
Project Nar Blackhawk Landing
Project #:
3signed by: CEP Date: 4/26/2021
iecked by: Date:
Water
kty Orifice
` Incremental Determination of Water Quality Volume Drawdown Time
Zone 2
Orifice Diameter (D) =
Cd =
Ei =
Zone 1 Range =
Zone 2 Range =
Zone 3 Range =
Q3 = 0.0437 CD " Dz (Z-D/24-Ei)A(9n)
Q$ = 0.372 CD . D`(Z-Ei)"(3n)
Em
3.5 in
0.6
185
Orifice Inv.
0.00
to 185
185
to 185.1
185.1
to 186
Incremental
Drawdown
Method
Countour
Contour
Incremental
Stage, Z
Zone
Q
Drawdown
Area
Volume
Time
s ft
cu ft
ft
cfs
min
185.00
21,940
0
0.00
2.00
0.000
--
185.50
24355
11,574
0.50
3.00
0.191
1.009
186.00
26000
12.589
0.50
3.00
0.297
707
187.00
29305
27.653
1.00
3.00
0.437
1,054
187.30
30305
8,941
0.30
3.00
0.471
316
Total J
60,757
--
--
3,086
Drawdown Time = Incremental Volume / Q / 60sec/min
Summary
Total Volume = 60,757 cf
Total Time = 3,086 min
Total Time = 2.14 days
4/26/2021 Prop Wet Pond- new design-Blackhawk 1 of 1

Project: Pond #1 Date: 3/10/2021
Mam-Pond contours -Volumes
Elevation Main -Pond Incremental Vol. Accumulated Vol.
185
15,710
7,498
101,359
A2 (Perm -Pool)
184.5
14,280
7,024
93,861
Al (Bottom_Shelf)
184
13,815
13,360
86,838
183
12,905
12,463
73,478
182
12,020
11,588
61,015
181
11,155
10,740
49,428
180
10,325
9,925
38,688
179
9,525
9,140
28,763
178
8,755
8,388
19,623
177
8,020
7,665
11,235
176
7,310
3,570
3,570
175.5
6,970
0
0
A3 (Bottom -Pond)
F rebway Contours -Volumes
Elevation
FB1
FB2
FB3
Total -Areas
Incremental Vol..
Accumulated Vol.
185
3,110
2,595
5,705
2,706
15,496
184.5
2,820
2,300
5,120
2,418
12,790
184
2,535
2,015
4,550
4,003
10,373
183
1,990
1,465
3,455
2,925
6,370
182
1,460
935
2,395
1,928
3,445
181
975
485
1,460
1,088
1,518
180
525
190
715
430
430
179
145
0
145
0
0
Forebay Volume
15.3% *Between 15% & 20%
Average Depth (Option 1)
6.57 *At least 3' average depth
Average Depth Calculation (Option 2)
Vpp
101,359
permeter of shelf
486
width of shelf
3
Al (Bottom -Shelf):
14,280
Average Depth =
7.07

Proposed Wet Pond #1
Project Information
Project Name: Blackhawk Landing
Project #:
Designed by: CEP Date: 4/6/221
Revised by: Date:
Checked by: Date:
Site Information
Sub Area Location:
Drainage
to Proposed Pond
Drainage Area (DA) =
23.87
Acres
Impervious Area (IA) =
16.62
Acres
Percent Impervious (1) =
69.62
% (Drainage Area)
Orifice Sizing
Orifice Size = 3.50 in (Diameter)
Drawdown Time = 2.14 days (Incremental Draw Down Method)
less than 5 days (yes/no) ? ergs
greater than 2 day (yes/no) ? yes
Anti -Flotation Device
4' x 4' Outlet Structure
Area:
16.0
sf
Volume:
280.0
cf
Weight:
17472
Ibs
Factor of Safety
1.20
WT Req'd of Anti -Flotation Device:
20,966
Ibs
Volume of Concrete Req'd:
139.8
cf
(Water Displaced - Top of Pond to Bottom of Pond)
(Unit WT of Concrete = 150 pcf)
Volume Provided: 165.5 cf (4'x4' riser x 8' = 128sf, 5'x5' footing x 1.5'=37.5cf)

P
Jr.
W
115
w
lip
ttR9,
I
uuu
Ili
cq
10

if' c.,
f'', �,
f.
i� t "
V„ u...

STAGE STORAGE TABLE
STAGE ELEVATION CONTOUR INCREMENTAL TOTAL
(FT) (FT) AREA (SF) STORAGE (CF) STORAGE (CF)
0.0
185.0
21940
0
0
0.5
185.5
24355
11574
11574
1.0
186.0
26000
12589
24163
2.0
187.0
29305
27653
51815
2.3
187.3
30305
8942
60757 (WQv)
2.5
187.5
30975
6128
66885
3.0
188.0
32980
15989
82873
4.0
189.0
36255
34618
117491
5.0
190.0
39585
37920
155411
6.0
191.0
42960
41273
196683
7.0
192.0
46390
44675
241358
8.0
193.0
49875
48133
289491
STOR WATER MANAGEMENT DESIGN
WET DETENTION POND
RIVER BASIN:
CAPE FEAR
RECEIVING STREAM:
BEAVER CREEK
STREAM INDEX:
18-31-19-5
STREAM CLASS:
C
HUC:
03030004
DRAINAGE AREA TO POND: 23.87 ACRES
SITE IMPERVIOUS AREA TO POND: 9.95 ACRES
QEF SITE DESIGN IMPER14OUS AREA TO MD. 6.67 ACID ------
TOTAL DESIGN IMPERVIOUS AREA TO POND: 16.62 ACRES
PRE -DEVELOPED POST -DEVELOPED POST DEVELOPED
DRAINAGE AREA: 23.87 AC 23.87 AC
CURVE NUMBER: 59.7 85.5
TIME OF CONCENTRATION: 19.0 MIN 12 MIN
V STORM EVENT:
2.999 CFS
0.222 CFS
1-YEAR STORM EVENT: 5.094 CFS
56.88 CFS
3.375 CFS
10-YEAR STORM EVENT: 39.71 CFS
129.58 CFS
37.33 CFS
100-YEAR STORM EVENT: 96.31 CFS
216.08 CFS
110.04 CFS

12
M
e
N
rmm

4
U%,IUKL NOT JnW"n FOR CLARIN
1CCESS)
RISER STRUCTURE ~-..
4' PVC SCREW CAP
FOR CLEANING ACCESS
12" MIN. EXTEND 4"
PVC THROUGH
RISER
STRUCTURE
4"x4" PVC TEE
PERM. POND ELEV. 185.0
12" MIN.
4"DIA. HOLE DRILLED
INTO BOTTOM CAP
PVC DRAIN OUTLET
SCALL: N. 1.5.

SPILLWAY CREST
ELEV=190.9B.
3
U
TOP OF EMBANKMENT ELEV=193.0
I 8' 1
3
1� D
LEVEL
SPILLWAY
CREST
COMPACTED
SUBGRADE
3� 1
SPILLWAY A B
BASIN 15 FT 2.1 FT
CONCRETE SECTION
OF
2 A E BAN 193.0
SPILLWAY
B II.EY= 190 9
1I' III; II�IVk-
2'-0' ,— 3CY CLASS B RIP —RAP
S' THICK 4000 PSI --•I t " �;
CONC. W/ 6K8, 10/10I
WWF 2' FROM TOP !
...............
CONCRETE SPILLWAY CLASS B
RIP —RAP d 50 MEDIAN
DUL=B' ON FILTER
FABRIC

Pond Reports
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066 Monday, Apr 26, 2021
Pond No. 1 - Wet Pond
Pond Data
Contours - User -defined contour areas. Average end area method used for volume calculation. Begining Elevation = 185.00 ft
Stage / Storage Table
Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cult) Total storage (cult)
0.00
185.00
21,940
0
0
0.50
185.50
24,355
11,574
11,574
1.00
186.00
26,000
12,589
24,163
2.00
187.00
29,305
27,653
51,815
2.30
187.30
30,305
8,942
60,757
2.50
187.50
30,975
6,128
66,885
3.00
188.00
32,980
15,989
82,873
4.00
189.00
36,255
34,618
117,491
5.00
190.00
39,585
37,920
155,411
6.00
191.00
42,960
41,273
196,683
7.00
192.00
46,390
44,675
241,358
8.00
193.00
49,875
48,133
289,491
Culvert / Orifice Structures
Weir Structures
[A]
[B]
[C]
[PrfRsr]
[A] [B]
[C] [D]
Rise (in)
= 30.00
3.50
Inactive
Inactive
Crest Len (ft)
= 3.00 15.00
Inactive Inactive
Span (in)
= 30.00
3.50
0.00
0.00
Crest El. (ft)
= 187.70 190.90
0.00 0.00
No. Barrels
= 1
1
0
0
Weir Coeff.
= 3.33 2.60
3.33 3.33
Invert El. (ft)
= 185.00
185.00
0.00
0.00
Weir Type
= Rect Broad
---
Length (ft)
= 42.00
0.50
0.00
0.00
Multistage
= Yes No
No No
Slope (%)
= 2.38
1.00
0.00
n/a
N-Value
= .013
.013
.013
n/a
Orifice Coeff.
= 0.60
0.60
0.60
0.60
Exfil.(in/hr)
= 0.000 (by Contour)
Multistage
= n/a
No
No
No
TW Elev. (ft)
= 0.00
Stage (ft)
8.00
6.00
4.00
2.00
0.00 -A-
0.0
Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s)
Stage / Discharge
20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0
Total Q
Elev (ft)
193.00
191.00
189.00
187.00
s....,... 185.00
180.0
Discharge (cfs)

Hydrograph Summary Rep yc raflow Hydrographs Extension for AutoCADO Civil 3DO 2009 by Autodesk, Inc. v6.066
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
5.094
2
728
28,980
------
-._,
_aw
Pre -Developed -Overall Site
2
SCS Runoff
56.88
2
720
147,486
....--
-
Post Developed to Pond
3
Reservoir
3.375
2
798
142,051
2
188.13
87,340
Post Through Pond
5
SCS Runoff
2.999
2
154
16,551
_--
1.0 Post -Developed to Pond
6
Reservoir
0.222
2
372
14,523
5
185.62
14,679
1.0inPost Through Pond
j 1 r 26, 202 ackhawk_pond.gpw B Return Period: 1 Year Monday, p -

2
Hydrograph
Report
HydraFlow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 1
Pre -Developed -Overall Site
Hydrograph type
= SCS Runoff
Peak discharge
= 5.094 cfs
Storm frequency
= 1 yrs
Time to peak
= 728 min
Time interval
= 2 min
Hyd. volume
= 28,980 cuft
Drainage area
= 23.870 ac
Curve number
= 59.7
Basin Slope
= 0.0 %
Hydraulic length
= 0 ft
Tc method
= USER
Time of conc. (Tc)
= 19.00 min
Total precip.
- 3.03 in
Distribution
= Type II
Storm duration
24 hrs
Shape factor
= 484
Pre -Developed -Overall Site

3
Hydrograph
Repoft
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 2
Post Developed to Pond
Hydrograph type
= SCS Runoff
Peak discharge
= 56.88 cfs
Storm frequency
= 1 yrs
Time to peak
= 720 min
Time interval
= 2 min
Hyd. volume
= 147,486 cuft
Drainage area
= 23.870 ac
Curve number
= 85.5
Basin Slope
= 0.0 %
Hydraulic length
= 0 ft
Tc method
= USER
Time of conc. (Tc)
= 12.00 min
Total precip.
= 3.03 in
Distribution
= Type II
Storm duration
= 24 hrs
Shape factor
= 484
Post Developed to Pond
Q (cfs) Hyd. No. 2 -- 1 Year Q (cfs)
60.00 .. .......---- ------ 60.00
50.00 w.. ...... . .........m 50.00
i
40.00 .... _........... ............ 40.00
30.00 ............ m ........................_ .................. ........... ------ 30.00
20.00 .._....._. ....- . ....... 20.00
10.00 ..... .............................._ ................................ �.................. ........... 10.00
0.00
0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
.........°° Hyd No. 2 Time (min)

Hydrograph Report
Hydraflow Hydrographs Extension forAutoCAD® Civil 3D® 2009 byAutodesk, Inc. v6.066
Hyd. No. 3
Post Through Pond
Hydrograph type = Reservoir
Storm frequency = 1 yrs
Time interval = 2 min
Inflow hyd. No. = 2 - Post Developed to Pond
Reservoir name = Wet Pond
Storage Indication method used.
Post Through Pond
Peak discharge
Time to peak
Hyd. volume
Max. Elevation
Max. Storage
4
Monday, Apr 26, 2021
= 3.375 cfs
= 798 min
= 142,051 tuft
= 188.13 ft
= 87,340 tuft

6
lydrograph
Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 31DO 2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 5
1.0 Post -Developed to Pond
Hydrograph type
= SCS Runoff
Peak discharge
= 2.999 cfs
Storm frequency
= 1 yrs
Time to peak
= 154 min
Time interval
= 2 min
Hyd. volume
= 16,551 cuft
Drainage area
= 23.870 ac
Curve number
= 85.5
Basin Slope
= 0.0 %
Hydraulic length
= 0 ft
Tc method
= USER
Time of conc. (Tc)
= 12.00 min
Total precip.
= 1.00 in
Distribution
= SCS 6-Hr
Storm duration
= 6.00 hrs
Shape factor
= 484
Q (cfs)
3.00
2.00
1.00
w
1.0 Post -Developed to Pond
Hyd. No. 5 -- 1 Year
60 120 180 240 300 360
mmm Hyd No. 5
Q (cfs)
3.00
2.00
1.00
0.00
420
Time (min)

7
ydrograh
Repoft
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D®2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 6
1.OinPost Through Pond
Hydrograph type
= Reservoir
Peak discharge
= 0.222 cfs
Storm frequency
= 1 yrs
Time to peak
= 372 min
Time interval
= 2 min
Hyd. volume
= 14,523 cuft
Inflow hyd. No.
= 5 - 1.0 Post -Developed to Pond
Max. Elevation
= 185.62 ft
Reservoir name
= Wet Pond
Max. Storage
= 14,679 cuft
Storage Indication method used.
Q (cfs)
3.00
2.00
w
600 1200
Hyd No. 6
1.0inPost Through Pond
Hyd. No. 6 -- 1 Year
1800 2400
Hyd No. 5
3000 3600 4200 4800 5400
Total storage used = 14,679 cuft
Q (cfs)
3.00
2.00
1.00
0.00
6000
Time (min)

Hydrograph Summary e p y "flow Hydrographs Extension for AutoCADO Civil 3D® 2009 by Autodesk, Inc. v6.066
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)
(cult)
(ft)
(cuft)
1
SCS Runoff
39.71
2
726
134,235
------
___u_.
_....__-
Pre -Developed -Overall Site
2
SCS Runoff
129.58
2
720
342,899--
-
------
Post Developed to Pond
3
Reservoir
37.33
2
734
337,368
2
190.25
165,350
Post Through Pond
5
SCS Runoff
0.000
2
n/a
0
------
------
—
1.0 Post -Developed to Pond
6
Reservoir
0.000
2
n/a
0
5
185.00
0.000
1.0inPost Through Pond
_pond.gpw Return Period: 10 Year Monday Apr 26, 2021
Blackhawk. .. .. .....

10
ydrograph
Repoit
HydraFlow Hydrographs Extension for AutoCADO Civil 3DO 2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 1
Pre -Developed -Overall Site
Hydrograph type
= SCS Runoff
Peak discharge
= 39.71 cfs
Storm frequency
= 10 yrs
Time to peak
=, 726 min
Time interval
= 2 min
Hyd. volume
= 134,235 cuft
Drainage area
= 23.870 ac
Curve number
= 59.7
Basin Slope
= 0.0 %
Hydraulic length
= 0 ft
Tc method
= USER
Time of conc. (Tc)
= 19.00 min
Total precip.
= 5.45 in
Distribution
= Type II
Storm duration
= 24 hrs
Shape factor
= 484
Pre -Developed -Overall Site
Q (cfs) Hyd. No. 1 -- 10 Year Q (cfs)
40.00 - ,-..__. ------- ------ _ ____ ---------------- __----- _ . I 40.00
30.00 m,.-__ _ ......... 30.00
20.00 - — — - - .....—. ........................ .. 20.00
10.00 ........ ... -......,, 10.00
0.00 _ 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hyd No. 1

11
Hydrograph
Report
Hydraflow Hydrographs Extension for AutoCADO Civil 3DO 2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 2
Post Developed to Pond
Hydrograph type
= SCS Runoff
Peak discharge
= 129.58 cfs
Storm frequency
= 10 yrs
Time to peak
= 720 min
Time interval
= 2 min
Hyd. volume
= 342,899 cuft
Drainage area
= 23.870 ac
Curve number
= 85.5
Basin Slope
= 0.0 %
Hydraulic length
= 0 ft
Tc method
= USER
Time of conc. (Tc)
= 12.00 min
Total precip.
= 5.45 in
Distribution
= Type II
Storm duration
= 24 hrs
Shape factor
= 484
Q (cfs)
140.00
120.00
100.00
40.00
20.00
Q (cfs)
140.00
120.00
100.00
40.00
20.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 2 Time (min)

Iydrographw Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066
Hyd. No. 3
Post Through Pond
Hydrograph type = Reservoir
Storm frequency = 10 yrs
Time interval = 2 min
Inflow hyd. No. = 2 - Post Developed to Pond
Reservoir name = Wet Pond
Storage Indication method used.
Q (cfs)
140.00
120.00
100.00
40.00
20.00
1 1 1 � ww, ��'mr�A�ii iuuuimiaou�sAm��u���r
12
Monday, Apr 26, 2021
Peak discharge = 37.33 cfs
Time to peak
= 734 min
Hyd. volume
= 337,368 cuft
Max. Elevation
= 190.25 ft
Max. Storage
= 165,350 cuft
Q (cfs)
140.00
120.00
100.00
[:�1111I7
40.00
20.00
<TiTil•
240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880 3120
YII Time (min)
Hyd No. 3 - Hyd No. 2 �I. I LIED Total storage used = 165,350 cult

15
Hydrograph Summary Re r flow Hydrographs Extension for AutoCADO Civil 3DO 2009 by Autodesk, Inc. v6.066
Hyd.
No.
Hydrograph
type
(origin)
Peak
now
(cfs)
Time
interval
(min)
Time to
peak
(min)
Hyd.
volume
(cuft)
Inflow
hyd(s)
Maximum
elevation
(ft)
Total
strge used
(cuft)
Hydrograph
description
1
SCS Runoff
96.31
2
724
306,139
------
......
--
Pre -Developed -Overall Site
2
SCS Runoff
216.08
2
720
587,286
Post Developed to Pond
3
Reservoir
110.04
2
730
581,705
2
192.18
249,191
Post Through Pond
5
SCS Runoff
0.000
2
n/a
0
--
----.--
......
1.0 Post -Developed to Pond
6
Reservoir
0.000
2
n/a
0
5
185.00
0.000
1.OinPost Through Pond
Blackhawk_pond.gpw
Return Period:
100
Year
Monday, Apr
26, 2021

16
Hydrograph
Repoft
Hydraflow Hydrographs Extension forAutoCAD® Civil 3D® 2009 byAutodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 1
Pre -Developed -Overall Site
Hydrograph type
= SCS Runoff
Peak discharge
= 96.31 cfs
Storm frequency
= 100 yrs
Time to peak
= 724 min
Time interval
= 2 min
Hyd. volume
= 306,139 cuft
Drainage area
= 23.870 ac
Curve number
= 59.7
Basin Slope
= 0.0 %
Hydraulic length
= 0 ft
Tc method
= USER
Time of conc. (Tc)
= 19.00 min
Total precip.
= 8.31 in
Distribution
= Type II
Storm duration
= 24 hrs
Shape factor
= 484
Q (cfs)
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
Q (cfs)
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
i_..... J, P.. �,m 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 1 Time (min)
���

Hydrogr;pl Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066
Hyd. No. 2
Post Developed to
Pond
Hydrograph type
= SCS Runoff
Storm frequency
= 100 yrs
Time interval
= 2 min
Drainage area
= 23.870 ac
Basin Slope
= 0.0 %
Tc method
= USER
Total precip.
= 8.31 in
Storm duration
= 24 hrs
Q (cfs;
240.00
210.00
180.00
150.00
120.00
30.00
17
Monday, Apr 26, 2021
Peak discharge = 216.08 cfs
Time to peak
= 720 min
Hyd. volume
= 587,286 cuft
Curve number
= 85.5
Hydraulic length
= 0 ft
Time of conc. (Tc)
= 12.00 min
Distribution
= Type II
Shape factor
= 484
Post Developed to Pond
Hyd. No. 2 -- 100 Year
Q (cfs)
240.00
210.00
180.00
150.00
120.00
30.00
0.00 —... .....,. .. � ,�... m__--- 11m-1-11mmm .,. �, �J-. 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
— Hyd No. 2 Time (min)

18
Hydrogra h
Repoft
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066
Monday, Apr 26, 2021
Hyd. No. 3
Post Through Pond
Hydrograph type
= Reservoir
Peak discharge
= 110.04 cfs
Storm frequency
= 100 yrs
Time to peak
= 730 min
Time interval
= 2 min
Hyd. volume
= 581,705 cuft
Inflow hyd. No.
= 2 - Post Developed to Pond
Max. Elevation
= 192.18 ft
Reservoir name
= Wet Pond
Max. Storage
= 249,191 cuft
Storage Indication method used.
Q (cfs)
240.00
210.00
180.00
150.00
W11 K112
90.00
.1 11
KI 11
Q (cfs)
240.00
210.00
180.00
150.00
120.00
•1 11
.1 11
30.00
0.00 ..L... -&. ....m , ..-- 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
•µ°°°°°°° Hyd No. 3 Hyd No. 2 1.11 II II q...� Total storage used = 249,191 cult