SW8931006_Historical File_19951002

RODERT H. DAVIS. RLS
SURVEYORS AND PLANNERS
IPA Fi75 N'GHWAY 70 EAST
NEW BERN. NORTH CAROLINA 28562
919-636-2109
October 2, 1995
Ms. Linda Lewis
Environmental Engineer
N. C. Department of EHNR
Division of Environmental Management
Water Quality Section
127 Cardinal Drive Extension
Wilmington, NC 28405-3845
Dear Ms. Lewis:
Subject: Stormwater Project No. 931006 Revision
Sand Ridge Subdivision and Multifamily
Carteret County
OCT 0 ,3 1995
TER
p [CEO U I
La D
(?Ct C 3 1995
DAM.
'' of ip 13too
C�
Thank you for your patience with this project and its many changes. Each time
the plan has been changed the actual drainage areas have changed slightly.
We have enclosed a new back to the submittal form as requested in comment #1.
After receiving your second comment in your letter of September 18, 1995, we
did not dare to try to decipher the many different approaches we have taken in
determining the total impervious areas. Instead, we recalculated the areas
off the current plan, and our notes are included. Our notes show that the
figure of 7.71 acres was correct.
We have added additional pond dimensions to our plan and sections of the pond
p.er your third comment.
With 7.71 acres of impervious surfaces, the surface area and volume of the
pond are sufficient.
Please forgive us for the many changes and reconfigurations that this project
has undergone.
Sincerely,
Robert vi
Registered Land Surveyor
Enclosures

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e7 15&
i g�s 20l ,, 3�oS
A 7/f 13f,17F A5p6a/f 48, 000
0
f00 )e 110
Tofal �v =
qo?o 755, (O.5
IT, 43_ acres - �i-►�, use 3 �'�1
I�000
ef(0)c log = 2332e 2� = -Zeumo
Green = :5,6? scoco e�
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vol u-t- e d e fiGr

State of North Carolina
Department of Envronment,Health, and Natural Reuon^es
Wilmington Regional Office
James B. Hunt, Jr. DIVISION OF ENVIRONMENTAL MANAGEMENT Jonathan B. Howes
Governor WATER QUALITY SECTION Secretary
September 18, 1995
Mr. Robert H. Davis, R.L.S.
7175 Highway 70 East
New Bern, North Carolina 28562
Subject: ADDITIONAL INFORMATION
Stormwater Project No. 931006 Revision
Sand Ridge Subdivision & Multi -Family
Carteret County
Dear Mr. Davis:
The Wilmington Regional Office received a revised Stormwater Submittal for the Sand Ridge
Subdivision & Multi -Family Area on August 28, 1995. A preliminary review of that information has
determined that the submittal for the subject project is not complete. The following information is needed
to continue the stormwater review:
1. The back of the submittal form must be completed with the built -upon area for each lot, as
done before.
2. My approach to this recombination of projects is to simply total the previously allowed
drainage areas and impervious areas and design the pond for the new total. My total
impervious area is 9.43 acres, while you use only 7.71 acres, which includes only the single
family portion of the subdivision, and completely excludes the apartments. Please revise.
3. Please add the pond dimensions to the plans.
4. Due to #2 above, the surface area and volume and deficient.
127 Cardinal Drive Extension, Wilmington, N.C. 28405-3845 • Telephone [phone] • Fax [phone]
An Equal Opportunity Affirmative Action Employer

Mr. Davis
September 18, 1995
Stormwater Project No. 931006 Revision
----------------------------------------------
Please note that this request for additional information is in response to a preliminary review. The
requested information should be received by this Office prior to October 18, 1995, or the submittal will
be returned as incomplete.
If you have any questions concerning this matter please feel free to call me at [phone].
Sincerely,
Ms. Linda Lewis
Environmental Engineer
DA/arl: S:\WQS\STORMWAnADDINFO\931006.SEP
cc: Gary Barker, P.E.
Linda Lewis
Central Files
2

surfln'lWATER
�ECEpYf�DD
SAND RIDGE 4U6 9 B 1995
DEM
!,Ror 9 112se
This project is located in the Town of Newport. It contains
approximately 23.42 +/- acres. Except for a small section developed
as an exempt area in a previously permitted section (permit #931006)
all surface waters will be collected in a storm water control pond
and treated before they are discharged to the canal on the southern
side of Bayberry Road. The property is primarily cleared at this
time. The first step of construction will be to construct the storm
water control structure in conjunction with clearing and grubbing.
Next the site will be rough graded and drainage ditches will be
constructed.. Underground utilities will then be installed and a
temporary ground cover of rye will be planted. After construction
of the apartment buildings or homesites is completed, final
landscaping and permanent vegetation will be established. It is
expected that from beginning to completion of site work will take
120 days. Construction of the buildings or homes will take 8 to 10
months from the completion of the site work.
For the ten year storm calculations 6.6 in/hr.. was utilized. For
paving and concrete a coefficient of 0.95 was used. Roof areas were
assigned 1.00. Grassed areas were assigned a "C" of 0.20. It"is
expected that volunteer vegetation will grow and provide enhanced
treatment in the forebay and safety shelf areas. The pond was
designed with SA/DA ratio in mind producing only a two foot rise
with a one inch storm. An orifice 2.75 inches in diameter will
release this storm in two and a half days.
The ten year storm requires a 48" CMP.
The area labeled DA#1 is part of a previously approved project that
used density limits and did not flow into a stormwater control. pond.
The area served by the existing filter basin has been drastically
reduced and has been diverted to DA#3 which will be collected in
surface swales and treated in the stormwater control pond. Both
DA#2 and DA#3 are collected in the stormwater control pond.
c�ts..s °
SEAL
s7so
C. gP�,
1

Stormwater Project No. 931006 Revision
Sand Ridge Subdivision and Multifamily
Carteret County
Impervious .area Calculations
Roads: 3117 if X 26' wide
Cul-de-sacs: 3 @ 3750
Total roads
2 parking lots: 68 X 128
2 parking lots: 68 X 152
Roof area apartments: 8 buildings @ 36 X 88
Pond area contribution: 130 X 240
Lots' contribution:
86 total lots
Lots 1-12, 1/3 of lots 13, 14 & 15 are not
in drainage area going to pond, therefore
73 lots enter pond
Lots 1-20 were restricted to 1950 sf by
previous exempt-� permit
2/3 X 3 lots (13, 14, 15) @ 1950 sf
5 lots (16-20) @ 1950 sf
66 lots (21-86) @ 2050 sf
81,042
11,250
92,292 sf
17,408
= 20,672
38,080 sf
25,344 sf
31,200 sf
= 3,900
sf
= 9,750
sf
= 135,300
sf
335,866
sf
= 7.71
acres
D ECEI
n k OD
OCT C 3 W5
",ol ip Q 3 OoCo

Storage Required for Stormwater Retention Pond
Q - CIA
C = Weighted runoff co -efficient
I = 1 inch per hour
A = Drainage Area in square feet
C X I
Roof Tops 1.00 .08333
Paving 0.95 .08333
Grassed Area 0.20 .08333
Determine Pond Size
x A = CF
2.46(43,560) 8,930
5.25(43,560) 18,105
15.71(43,560) 11,405
23.42 38,440
Roof Tops 2.46 Acres 7.71 = .33 impervious
Paving + 5.25 Acres 23.42
Impervious 7.71 Acres
SA/DA - > 90% TSS REMOVAL
FOR WET DETENTION WITHOUT VEGETATIVE FILTER
. per Water Quality Section NC DEHNR
-Ironer $
3.0'
3.5'
4.0'
4.5'
5.01
S 5'
6 0'
6 5'
7.01
7.5'
10
1.3
1.0
.8
.7
.6
.5
.4
.3
.2
.1
20
2.4
2.0
1.8
1.7
1.5
1.4
1.2
1.0
.9
.6
30
3.5
3.0
2.7
2.5
2.2
1.9
1.6
1.3
1.1
.8
40
4.5
4.0
3.5
3.1
2.8
2.5
2.1
1.8
1.4
1.1
50
5.6
5.0
4.3
3.9
3.5
3.1
2.7
2.3
1.9
1.5
60
7.0
6.0
5.3
4.8
4.3
3.9
3.4
2.9
2.4
1.9
70
8.1
7.0
6.0
5.5
5.0
4.5
3.9
3.4
2.9
2.3
80
9.4
8.0
7.0
6.4
5.7
5.2
4.6
4.0
3.4
2.8
90
10.7
9.0
7.9
7.2
6.5
5.9
5.2
4.6
3.9
3.3
100
12.0
10.0
8.8
8.1
7.3
6.6
5.8
5.1
4.3
3.6
Actual % = 33%
Interpolate between 30% and 40%
Pond Depth of Permanent Pool = 6.5
SA/DA must be 1.5 or greater
Minimum SA = .015 x 23.42 x 43,5.60 = 15,302 sf
2

DESIGN OF POND
SA @ 24' elevation = 18,000 sf
SA @ 26' elevation = 22,896 sf
Pond has slope of 4:1 above 24' elevation, assuming 2' rise
calculate storage of pond using average end area method to
determine volume.
Calculated volume = 40,896 cf
Required volume = 38,440 cf
OK by storage volume and SA/DA surface area calculations.
DESIGN OF ORIFICE
Q(2 days) = 38,440/172,800 = .2225
Area = [.2225/.642.(32.2)1]1.44 = 6.65
Radius 1.455"
Diameter = 2.91"
Q(5 days) = 38,440/432,000 = .0890
Area = [.0890/. 6 22 (32.2) 1] 144 = 2.66
Radius = 42.66/n _ .847"
Diameter = 1.69"
Use orifice 2.75" diameter
Actual drawdown time 53 hours 46 minutes OK
3

Outlet Design
Time of Concentration 6.6 inches/hour
Q = CIA
C = Weighted
runoff co -efficient
I = 6.6 inches
per hour
A = Drainage
Area in acres
C x
I
x A
- CFS
Roof Tops
1.00
6.6
2.46
16.2
Paving
0.95
6.6
5.25
32.9
Grassed Area
0.20
6.6
15.71
20.7
69.8
Figure 4-18
pg. 161 ARMCO Handbook
of Steel
Drainage
See copy on
next page
Use 48" CMP
Invert 24.0'
+ 4' of head = 28.0'
max
elevation of pond
4

HYDRAULICS OF CULVERTS
-lee
-e,000
LOSS COEFFICIENT Ke (1) i
FOR VARIOUS ENTRANCE (g)
9.000
TYPES g•
4.000
SCALE EWIRANCE b. S, .
la!
- a.000
D TYPE COEFFICIENT
- It0
p
f11 Heodwoll,p..dpeiorEnd 0.! ` =*" - b 6
lenlornHnO �e f111
b
- 1,000
sec �lO^
P e
- IOe
_
It) Mporad to conform 10 dope 0,1,
pe
13) Prolecllnp (rent fal
-96
1.000
- 84
soo
- 600
To use scale (2) or (0)p rolul '
herleonloay Is,
-- 600
"to (11, s on
use slraiphs Inclined Ilne Ihrouph
D ettd O Icele4 Or rewrN to
- 7!
- 40.0
RlosneMd.
aoo
900
e I,e
- 60
-
- 100
e0
L3
- s0
xIx 5
42
a
- 60
6b 1.0
- 40
EXAMPLE
.
- a6
: a0
Dlem.l01-.Ieln...1A
O
- as
- - _ - O _70 c6
,--
_
Scale Hyy Hw •6 .6 i
- !7
- 10
(1) 1.0 4.0ff. •g '
(2) 1.0 4.0
- 44
-
-6
E
21
- 4
HEADWATER DEPTH FOR
+ It
CORRUGATED STEEL PIPE CULVERTS
WITH INLET CONTROL
Furesig. 4-18. Inlet control nomoffi h for corru�stad steal Ripe culverts. The manufac.
then 1 recommend keAping HW/D to a maximum of I. and preferably to no more
then 1.0.
cJ

DESIGN OF OUTLET DITCH
Assume 4' bottom width and 4:1 side slopes
A = 4d2 + 4d
WP = 245d2 + 4
R = (4d2 + 4d) / { 215d2 + 41
S = slope in feet/foot
V (1.486/n) (R2f3) (S112)
Try d 2.5
A = 4 (2.52) + 4(2.5) = 35 sf
WP = (245 (2.52) + 4 = 15.18
R = {4(2.52) + 4(2.5))/{2 5((2.52) + 4) = 2.31
S = 0.3/300 = .001
V = (1.486/.04) (2.312/3) (.0011/2) = 2.05 fps
Q = AV = (35 sf)(2.05fps) = 71 cfs
0

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