SWA000177_Stormwater Narrative_20230104

ENGINEERNG gz ENVIRONMENTAL SCIENCE COMPANY
3008 ANDERSON DRIVE, SUITE 102
RALEIGH, NC 27609
[phone]
September 22, 2022
Friar Julio
St Julia Catholic Church
210 Harold Hart Road
Siler City, NC 27344
RE: Stormwater Evaluation
St. Julia Catholic Church- Auxiliary Parking Lot
210 Harold Hart Road
Siler City, NC 27344
Dear Friar Julio,
Engineering & Environmental Science Company (E2S) has completed the stormwater plan
evaluation for the above referenced project. Following is a brief discussion of this project and
our evaluation.
Project Information
The subject property is located at 210 Harold Hart Road in Siler City, North Carolina (See
Figures 1 & 2). The site totals 17.75 acres. Currently located at the site is the St. Julia Catholic
Church building and associated parking areas.
Proposed for construction is an approximately 1 acre auxiliary parking area that will be accessed
from the existing asphalt paved parking area. The proposed auxiliary parking area will be gravel
surfaced. The accompanying 24"06" site drawings show the existing and proposed conditions
for the site.
The total proposed disturbance is 1.9 acres and consists of the proposed gravel parking area,
sidewalks, topsoil stockpile area, and erosion control measures. The existing ground at the
proposed parking area generally slopes downward to the southeast with mild slopes of 2 to 3%.
Minor cut and fill construction activities will be required for the proposed gravel parking area.
The project has an approved erosion control permit from NCDEQ (CHATH-2022-004).
The nearest surface water is a pond located approximately 100 ft. east from the limits of
disturbance for the project. This pond outlets to an unnamed tributary that drains to Varnell
Creek, which has `C' stream classification.

Stormwater Evaluation
The site has an existing Built -Upon Area (BUA) of 69,985 sf. The proposed construction will
add an additional 47,752 sf of BUA. The project density is 6.79%, which classifies the site as
`Low Density'. The proposed gravel parking lot will drain via sheet flow at a 1 % grade to a
sidewalk that will also act as a level spreader to promote dispersed flow to a vegetated area. The
runoff will enter the vegetated area at a non -erosive velocity.
An earthen diversion berm on the north side of the parking lot is provided to divert runoff from
the grassed area to the north of the proposed parking lot. The drainage areas are provided in
Figure 3 of Attachment A. Calculations for the combination sidewalk/level spreader and the
diversion berm are provided in Attachment B.
Closure
We appreciate serving you on this project. PIease contact us if you have any questions.
Sincerely,
Robert W. Brantly, P.E.
Project Engineer
Attachment A: Figures
Attachment B: Calculations
'�� A R Off/
oQ•` FEssro • 'yy
SEAL q
041984
�'•. FNGINE��''�"�
W.
�/11111111\
62s

Attachment A:
Figures
6's

Ills
r
,r'r, , ��f ! ,I ���J J p1 `t !! r•�\' r/f `� 0.>r J
Scale 1" = 1,000'
0
I�
2 ENGINEERING 8 ENVIRONMENTAL
GSCIENCE COMPANY
3008 ANDERSON DR., SUITE 102
RALEIGH, NORTH CAROLINA 27609
[phone]
Vicinity Map
"ATE:
St. Julia Catholic Church
9/22J22
Auxiliary Parking Lot
FIGURE NC
210 Harold I Tart Road
Siler City, NC

92630
DRAINAGE AREA FOR EARTHEN DIVERSION BERM
TOTAL 4.55 ACRES
0,17 AC. IMPERV.
4-39 AG. GRASS
75570
PROPOSED DIV RSION BERM
_ Llmits of Dlsturlbance
,•' i' fl SANG S�piSG �tEti.O
M Fence Stare Outlet #5 _
�'ti ait siocw
1 [OPS
,'} PILE AFEA.
45 Wide
Level Spreader! r I
st JUft Sidewalk
244 -a, holit'
Iiur�_.h '•r..
11702 75163 DRAINAGEAREA FOR LEVEL SPREADER
TOTAL 1.0 ACRES (ALL IMPERV., C=0.98)
Scale 1'" = 100'
ENGINEERING & ENVIRONMENTAL
SCIENCE COMPANY
a
3008 ANDERSON DR., SUITE 102
RALEIGH, NORTH CAROLINA 27609
' 11748 [phone]
DATE:
Drainage Areas Map
St Julia Catholic Church 9/22/22
Pervious Auxiliary Parking Lot
210 Harold Hart Road
Siler City, NC

Attachment B:
Calculations
62s

Diversion 2yr Rainfall Duration=60 min, Inten=3.99 in/hr
Prepared by E2S
HydroCADO 10.00-20 s/n 07329 © 2017 HydroCAD Software Solutions LLC Page 1
Summary for Subcatchment 1S: DRAINAGE AREA DIVERSION BERM
Runoff = 6.79 cfs @ 0.26 hrs, Volume= 0.492 af, Depth> 1.30"
Runoff by Rational method, Rise/Fall=1.011.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs
Rainfall Duration=60 min, Inten=3.99 inlhr
Area (sf) C Descripti
7,315
0.95 Impervious
191,319
0.35 Grass
198,634
0.37 Weighted Average
191,319
96.32% Pervious Area
7,315
3.68% Impervious Area
Tc Length
Slope
Velocity
Capacity Description
(min) (feet)
(ftlft)
(ftlsec)
(cfs)
7.4 100
0.0350
0.23
Sheet Flow,
Grass: Short n= 0.150 P2= 3.61"
7.9 620
0.0350
1.31
Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fos
15.3 720 Total

Diversion 10yr Rainfall Durafion=60 min, Inten=5.08 in/hr
Prepared by E2S
HydroCADO 10.00-20 sln 07329 © 2017 HydroCAD Software Solutions LLC Page 1
Summary for Subcatchment 1S: DRAINAGE AREA DIVERSION BERM
Runoff = 8.64 cfs @ 0.26 hrs, Volume= 0.627 af, Depths 1.65"
Runoff by Rational method, Rise/Fall=1.0/1.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs
Rainfall Duration=60 min, Inten=5.08 inlhr
Area (sf) C Description
7,315
0.95
Impervious
191,319
0.35
Grass
198,634
0.37
Weighted Average
191,319
96.32% Pervious Area
7,315
3.68% Impervious Area
Tc Length
Slope
Velocity Capacity
Description
(min) (feet)
(ftlft)
(ftlsec) (cfs)
7.4 100
0.0350
0.23
Sheet Flow,
Grass: Short n= 0.150 P2= 3.61"
7.9 620
0.0350
1.31
Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fns
15.3 720 Total

Diversion 25yr Rainfall Duration=60 min, lnten=5.56 in/hr
Prepared by E2S
HydroCAD® 10.00-20 s/n 07329 O 2017 HydroCAD Software Solutions LLC Page 1
Summary for Subcatchment 1S: DRAINAGE AREA DIVERSION BERM
Runoff = 9.46 cfs @ 0.26 hrs, Volume= 0.686 af, Depths 1.81"
Runoff by Rational method, Rise/Fall=1.011.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs
Rainfall Duration=60 min, Inten=5.56 in/hr
Area (sf) C Description
7,315
0.95 Impervious
191,319
0.35 Grass
198,634
0.37 Weighted Average
191,319
96.32% Pervious Area
7,315
3.68% Impervious Area
Tc Length
Slope
Velocity
Capacity Description
(min) (feet)
(ft/ft)
(ft/sec)
(cfs) _
7.4 100
0.0350
0.23
Sheet Flow,
Grass: Short n= 0.150 P2= 3.61"
7.9 620
0.0350
1.31
Shallow Concentrated Flow,
Short Grass Pasture Kv= 7.0 fps
15.3 720 Total

U
S
U
U
O
U
T
w
Cn
m
m
E
..
Z
Z
Q
t
E
O
❑
U
U
a
a
a)
Z
co
O
C6
N
:a
co
uj
cu
r
co
co
O
7E
^L^,,
4-
M N
C .
.c U_
c o cu
�r OC 0
E
O
N
44 Jn '0 Cij
6�
�4
w
6
O a
a G
Nm
,+
m
`d Q
d, 0
IVqj
A
twj
dJ
�
«
o
dj
do di
d
w u
4 6f1
aj 4
>� ~
g qj o
M
a
aqq�
' a
te+
o
qj
d
Grp
L4
tu
Z
Or
Q b
.�
V •
u
H
'�
GI 01
i
.6

®RD
selaG,ea QS
wo
>10
wO
CY)\
n� `selS If6
/
/
$
6
d
6
�
§
E
»
J
.2
peRO
Apedeg
aO
NO
¥O
wO
k
O`Alpe dea
ƒ
/
ƒ
y
2
a
9uueQ)
n�
a
\
»
6
a
_
_
0
\
F
�� 9A
aJAW
U
§
\
A'A� 9A /
\
\
'IT
/
2
R �!u ue&
a
o
2
c
u luRG 00
ag$ N
CD.
/
/
r_
[
%Bmuuez
%qe
CD
6
\
k
\
5
e
2
a `s nip e H
gg7e'!
o
®
w
c
f
co
o
7
2
G nE p!H
6
6
o
d
E
@
d 'J°° -� �
qg�
7
\
co
?
%
pled M
a
®
%
v ea ,e
&
_
Ruope
qg�
2
$
7
r
ss2 g
w
3
m
¥
\
I \*!ado
qg
$
/
7
®
co
&
\
e
0
7
\
`qldeg aea
�
qg$ e a
\
7
3
6
\
0
$
o
0
-
w
zz
o
0
0
0
2
'e q� p g
a
a
a
w
q
C�
�
E
CD,�
g� pS
gso,e !]
n
m
r
r
�
o
�
Q)
�_
$
CD
E
00
��
o £
�00
z
f
D
5
G
4
—�-
E /
/
E
Lm
$
��
k
\
\
\
%
0
�
D�
U�
71
1 1
1
w I
a I%
\

St Julia Catholic Church- Auxiliary Parking Lot
Combination Sidewalk/Level Spreader
10-year design storm
Tc<5 minutes
Q=CIA
C=0.98 (gravel and concrete sidewalk)
1=7.3 in/hr
A= 1.0 ac.
Q=(0.98)(7.3 inlhr)(1.0 ac.)=7.2 cfs
h=(Q/CL)1(213)
Q=7.2 cfs
C=2.5
L=45 ft.
h=(7.2/(2.5*45))^(213)=0.16 ft.
V=Q/A=(7.21(0.16*45))=1.0 ft/sec