SW8021110_COMPLIANCE_20031218

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW _�yi�/l(_)
DOC TYPE
❑CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
OMPLIANCE EVALUATION INSPECTION
DOC DATE
l.Y
YYYYMMDD

OF WATER Michael F_ Easley, Governor
Q William G. Ross Jr., Secretary
Go North Carolina Department of Environment and Natural Resources
�—� Alan W. Klimek, P.E.,Director
Division of Water Quality
Coleen H. Sullins, Deputy Director
Division of Water Quality
December 18, 2003
Mr. Matthew T. Murphy, President
Southeastern Enterprises, Inc. Managing Member
SECOF, LLC
Carolina Beach, NC 28428
NOTICE OF INSPECTION:
Rachel Gardens Subdivision
Stormwater Project No. SW8 021110
New Hanover County
Dear Mr. Murphy:
Please find attached a copy of the completed form entitled "Stormwater Compliance
lnspection Report". The report summarizes the findings of a recent inspection of the
project's stormwater controls conducted on December 15, 2003 to determine
compliance with Stormwater Permit Number SW8 021110 issued on April 15, 2003.
A summary of the findings and comments are noted under Section 4 of the report.
Please inform this Office in writing before January 29, 2004, of the specific actions that
will be undertaken and the time frame required to correct the deficiencies. Failure to
provide the requested information, when required, may initiate enforcement action. If
you have any questions please contact me at the Wilmington Regional Office, telephone
number [phone].
Sincerely,
Gary H. Beecher
Environmental Technician
RSSlghb: S:IWQSISTORMWATIINSPECT1021110.Dec03
cc: Wilmington Regional Office
Beth Wetherill ( New Hanover County )
►1S
N. C. Division of Water Quality 127 Cardinal Drive Extension [phone] Customer Service
Wilmington Regional Office Wilmington, NC 28405 [phone] Fax [phone] NCDENi

i 1 �
STORMWATER COMPLIANCE INSPECTION REPORT
Project Name: Rachel Gardens Subdivision
Project Number: SW8 021110 Control Measure: Detention Pond
Water Body: Cape Fear/ Barnards Creek Stream Classification: "C Sw"
Directions to site: 17th Street Extension,(L) on Steeple Chase, (R) on
Chippenham Drive.
2. Inspection Date: December 15, 2003
Weather Conditions: Windy, Dry and Cold
3. Compliance Issues:
Y N
❑ ❑ The drainage area (including offsite) and built -upon area to the permitted
system are per the approved plan. No unpermitted offsite drainage enters
the system.
❑ ❑ All the built -upon area associated with the project is graded such that the
runoff drains to the system.
❑ ❑ For ponds/infiltration, the outlet/bypass structure relative elevations are
per the approved plan. (Must be verified via as -built survey if in question).
❑ ❑ The inlets and outlet structure are located per the approved plans and do
not cause short-circuiting.
X ❑ A trash rack is provided over the outlet weir and orifice.
❑ X All slopes are grassed with permanent vegetation and are not eroding.
❑ ❑ Vegetated 'slopes are no steeper than 3:1.
❑ ❑ The approximate amount of permitted surface area has been provided.
(Must be verified via as -built survey or designer's certification.)
❑ ❑ Required drawdown devices are correctly sized per the approved plans.
All required design depths are provided.
❑ ❑ Allrequired parts of the system are provided, such as a vegetated shelf,
and a forebay.
❑ ❑ The designer's certification has been submitted.
❑ The required deed restrictions are correctly recorded and submitted.
❑ The number of lots or outparcels is per the permitted amount.
❑ ❑ The built -upon area on the lots or outparcels does not appear to exceed
the maximum amount (must be verified via as -built survey if in question)
❑ ❑ Curb outlet swales are constructed, located properly, are 100' long and
have dense vegetated cover.
❑ ❑ The road, cul-de-sac, parking lot and sidewalk widths are per the
approved plan.
❑ ❑ Required maintenance is being performed.
❑ ❑ Outparcels have their own offsite permit.
❑ ❑ For low density projects, roadside swales are 3:1, vegetated and stable.
00 For low density projects, there are no unpermitted pipes on the project.

4. Required Actions: (Explain each deficiency and what needs to be done to bring
the system back into compliance)
(a) The pond looks pretty good, there is a robust coverage of grass on most of the
slopes. The only bad spot is on the Chippenham Drive side. More grass seed
should be added to the bare spots, to ensure that the slope remains stabilized
and erosion free.
(b) I also noticed some large tire ruts that lead down the slope to the waters edge.
These deep ruts will certainly cause erosion problems in the future unless they
are grassed and stabilized now.
(c) We also need a copy of the Deed Restrictions for Rachel Gardens Subdivision
as soon as possible. Thank You
Inspector: Gary H. Beecher
Water Quality/Wilmington Regional Officel(910) 395-3900
RSSlghb: S:IWQSISTORMWATIINSPECT1021110.Dec03

WET DETENTION POND ANALYSIS
FILE NAME:
PROJECT #: SW8 021110
PROJECT NAME: Rachel Gardens Subdivision
G :1DATAIWPDATAIWQSIPOND1021110. WK1
REVIEWER: L. Lewis
DATE: 27-Mar-03
Receiving Stream: Barnards Creek Class: C Sw
Drainage Basin: Cape Fear Index No. CPF17 18-80
Site Area 3.00 acres
Drainage Area [ 30680:00, square feet Area in Acres 3.00
IMPERVIOUS AREAS
Rational C
16 lots @2300 sq. ft. per lot
36800.00 square feet
1.00
Street
14019.00 square feet
1.00
SW
2735.00 square feet
1.00
square feet
square feet
square feet
TOTAL 5354 00' square feet Rational Cc= 0.62
SURFACE AREA CALCULATION
% IMPERVIOUS 40.98%
Des. Depth 4
TSS: 90
SA/DA Ratio 3.58%
Req. SA 4676 sf ,r
Prov. SA 4i92: sf'
VOLUME CALCULATION " place a "1" in the box if Rational is used
Rational ?*
1
Des. Storm
...;1 Qtl<?
inches
Rv=
419
04119
Bottom
38.3 msl
Perm. Pool
::.......42:3A. msl
Design Pool
44.4 msl
Storage met @elev 43.52 msl
Req. Volume 712 < cf
Vol. Prov. at DP 1734: cf
ORIFICE CALCULATION
Avg. Head =
Flow Q2, cfs
Flow Q5, cfs
No. of Orifices
Diameter, inches
Drawdown =
FOREBAY
Perm. Pool Volume=
6772
Req. Forebay Volume=
1354.4
Provided Volume=
1426.00
Percent=
Elevation Area
Inc. Vol.
Acc. Vol.
42.30 4692.00
0.00
0.00
43.80 6321.00
8259.75
8259.75
44.80 7479.00
6900.00
15159.75
COMMENTS
Surface Area , Volume and Orifice are within Design Guidelines

Entity Names
http:/Iwww.secretary. state.nc.us/Corporations/soskb/Corp.asp?50604
North Carolina
Elaine F. Marshall EPARTMEN T' OF THE
Secretary SECRETARY of STATE
PO Box 29622 Raleigh, NC 27626-0622 [phone]
,*Corporations Home.'.
,*Important Notice
*Corporate Forms ,
Corporations FAQ
!New Form Notice
,Business License .
,lRegisterforE-ProcuremE
!Dept. of Revenue
999 Senate Bills
001 Bill Summaries
knnual.Reports 1997
:orporations 1997
)they Leaislation
eBy"Corporate Name
'For New Corporation
!By Reqistered Agent
Date: 1 /21 /2003
Document Filings
Corporation Names
Name Name Type
SECOF, L.L.C. Legal
Limited Liability Company Information
SOSID:
0466715
Status:
Current -Active
Date Formed:
8/4/1998
Citizenship:
Domestic
State of Inc.:
NC
._.._.Duration: .__7113/20,18........
Registered Agent
Agent Name:
Ken Coffer Construction, LLC
Registered Office Address:
#9 South Lake Park Blvd.
Carolina Beach NC 28428
Registered Mailing Address:
#9 South Lake Park Blvd.
Carolina Beach NC 28428
Principal Office Address:
1202 N. Lake Park Blvd.
Suite a
Carolina Beach NC 28428
Principal Mailing Address:
No Address
Bar -Coded Forms
For questions or comments about the North Carolina Secretary of State's web site, please send e-mail
Webmaster.
For questions or comri7ents concerning the Corporations Division, please send e-mail to Corporations Admij
Click here for help downloading forms.
1 of 1 1 /21 /2003 12:05 QM

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Project Number 02021
1114102 - Revised 12/15102, 1124/02
131069
Asite '= Asite = 3
acres
43560
0
Awetland '= Awetland = 0
acres
43560
Apond:= Asite Apond = 3
acres .....area on site draining to pond
0
Aoffsite := 43560
Aollsite = 0 acres .....offsite area draining to pond
Atotal := Apond + AoMite Atotal = 3.0089
acres ...total area draining to pond
Apatio := 100•16 Apatio - 0.04 acres .....patio
43560
Abld := 1400 16 Abld = 0,51 acres .....bldg
g g
43560
Ag arag e = 0 15 acres .....garage
Ag b arage: — 4
43560 3560
2735`a���e�saiaa�atpt,r
Aside Aside - 0.1 acres
on site sidewalk draining to pond ,�� ��PO rrr,,,� =`{
43460
20.20.16QV
Adrive '= Adrivc = 0.1 acres
.....paved drives q: tty r
43560
12346 + 1673
Aroad — 43560 load 0.32 acres
z 9524
road and curbing `ltv"N
A = A + As• + A + Ar + Ap
,lr�ep.�r`
+ A
imp Bldg ide drive oad duo garage
Aimp = 1.23 acres ...impervious areas
A A A 1 8
other := Atotal — imp other = • acres ...total area not impervious
Cpre := 0.15 ...pre -development C
Cimp := .95 ...paved area C
Cbldg 1.00 ....building area C
Aothcr Aimp (Abldg)]
Ccomp Cpre- + Cimp' + Cbldg-
Atotal Atatal Atotal
Ccomp = 0.65 ...composite C (post -development)
1_ := 400 ft ...hydraulic length
Fl := 3.8 ft ...height
RE C E INT E. D
JAW 3 0 2003
DW
pgoj # S(Au3o ( 110
1

t
' Drainage Calculations for Chippenham 2
Subdivision
Wilmington, NC
L3 .385 0
.385
Tc :— i �] 28 < 5' S' H128
I'c = 5 ...time of concentration
Intensity -Duration -Frequency Relationships:
Values of G and H*
10 252 30
50 338 33
R= Return period
*Source: City of Wilmington Technical Standards and Specifications Manual
T.= if(TG < 5,5,"I'c) I' = 5 minutes Time of duration (use 5 minutes min.)
G10:= 252
Hi0:= 30
110:= Gt0 110= 7.2 inlhr
�1110 + 1
G50:= 338 f'50:= 33
150 :- G50 150 = 8.9
(1150 + 7 )
Compute runoff rates:
Qloprc Cpre-110'(Atotal)
Q10pre = 3.25 cfs
Q50pre := Cpre-150"(AtatAl)
Q50pCe = 4.01 cfs
Q l 0 :- Ccomp' l l w (Atotal)
Q 10 = 14.03 cfs
inlhr
10 year storm intensity
.50 year storm
total pre -development runoff from 10 yr. storm
total pre -development runoff from 100 yr. storm
... post -development discharge rate to pond from 10 yr. storm
Q50:= Ccomp-150-(Atotal)
Q50 = 17.34 cfs ... post -development discharge rate to pond from 50 yr. storm
Volume of runoff from developed area of site:
Pt0 := 4.82 in 1)50 := 6.42 in Soil type = Leon Fine Sand

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
IMP% := Aimp IMP% = 0.4086
total
CN := IMP%-(98) + [(1 -- IMP%)-301 CN = 57.8
1000
S: CN — 10 S=7.3 Now compute runoff depth and time to peak for 10 yr. storm:
(PIO — 0.2 S)2
RIOdepth := Pl0 + .8•S R10depth = 1.1 in.
R10vol := Rlodepth•(Atotal)'435b()• 12TIO R10voi = 11557
R1Odepth'(Atotal) 43560, 1 1
1.39•(Q10) (12) 60
'I'10p = 9.87 ...time to peak flow
T10
Curve No.
...runoff depth
cubic feet ... runoff volume
ATIO := P AT10 = I ...time increment for routing 10 year storm
10
Now compute runoff depth and time to peak for 50 yr. storm:
(P50 — 0.2.S)2
R50depth := P50 + •8 SR50depth = 2 in. ...runoff depth
1 R50vol:= R50depth'(Atotal)•43560 12
T50p .— R50depth'(Atotal) 43560• I
1.39•(Q50) (112) 60
T50p = 15.15 ..time to peak flow
R50vo1= 21902 cubic feet ... runoff volume
T50
AT50 := p AT50 = 1.5 ...time increment for routing 50 year storm
10
Determine size of pond without vegetative filter:
depth := 4 ft
IMP% = 0.4086 i := 0.. 1
IMP%40 := .035
IMP°/a50:= .043
3

0
Drainage Calculations for Chippenham 4
Subdivision
Wilmington, NC
vx.:= x.
IMP := linterp(vx, vy, IMP%• 100)
IMP = 0.035691
DA := (Atotal).43560
SAfeq := (IMP)•DA
SACeq 4678 sq.ft. ...Required surface area
slope, := 6 ...min. slope of shelf
slope2 := 2.5 ...min, slope of pond below shelf
shelf := 2 ft. ...depth of shelf
w:= (depth - shelf)•slope2.2 + shelf-slopel•2
w = 34 ...minimum width of permanent pool
w := 34 ft. - width chosen
[.= 3-w
I = 102 ft. ...min. length of permanent pool
1 := 138 ft. - length chosen
SAprov l-W SAprov = 4692 ...sq.ft. of surface area provided must be >= SA1Cq = 4678
Determine volume of permanent pool in order to size forebay:
:= 0 .. g k := 1.. 8
A. D.:-_ corresponding depth from contour above
J J
2 ...area of contours t
629-ft .()-ft
772412 1-ft I
1 140-W 1-ftl
545•ft2 ]-ft
0•ft2 ]-ft I
Vk := `-1 + -Dk ...incremental volume
2

0
Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Vpond:_ I V ...total volume equals the sum of the incremental volumes
Vpond = 6772 ft3 ...total volume in permanent pool
Vrequired := •20'Vpond ...forebay volume equals 20% of total pool volume minimum
Vrequired = 1354 113 ...eu.ft. required in forebay
Determine volume in forebay:
m := 0.. 8 n := L. 8
area :=
depm = corresponding depth from contour below
m ...area of contours
0•ftl
0-ft2
67.5-ft2
t
I •ft
180•ft2
I
] ft
583-ft2
I
1 •ft
1190.112
1
1 ft
area + area
n—I n
vine := depn ...incremental volume
n 2
Vforebay:= Nine ...total volume in forebay equals the sum of the incremental volumes
V {forebay = 1426 fl3 ...total volume in forebay must be >= Vrequired = 1354 ft3
Vforebay.
forebay := 100 forebay = 21.1
...per cent forebay volume is of total pond volume
Vpond
Develop stage -storage function:
m := 0.. 8 n := 1 ,. 8 eontour0 := 42.30
increment := .5 ...ft
contour := contourn_I + increment
contour = ...contours of proposed pond
am := ...area of proposed pond contours (sq.ft.)
42.3
692
42.8
5217
43.3
5760
43.8
6321
44.3
6900
44.8
7497
45.3
8112
45.8
8745
4E3.3
9396
5

an -I + an
vn2
• (contour n -- contour n-
S0:= 0 ...initial storage
Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
.incremental volume (cubic ft.)
Sn Sn-I + vn ...cumulative storage (cubic ft.)
stagcn := contour - conlouro
InZn := In(stagcn)
la!
n
-0.6931
0
0.4055
0.6931
0.9163
1.0986
12528
1.3863
stage =
0.5
1
1,5
2
2.5
3
3.5
4
...natural log of stage
S
In
0
2477
5222
8242
11547
15146
19049
23263
27798
InSn := In(Sn)
InS
n
7.8149
8.5605
9.017
9.3542
9.6255
9.8547
10.054fi
102327
v
m
0
2477.25
2744.25
3020.25
3305.25
3599.25
3902.25
4214.25
4535.25
...natural log of storage
L

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
x:= submatrix(ln%,2,6,0,0)
y:= submatrix(InS,2,6,0,0)
slope := slope(x,y) slope = 1.19
b := intercept(x,y) b = 8.55
K, := eh Ks = 5166
I
S slope
Zestm := m ...stage -storage function
Ks
L.estm =
Should compare closely with : stagem =
0
0
0.54
0.5
1.01
1
1A9
1.5
1.98
2
2.5
2.5
3.03
3
3.59
3.5
4.18
4
Determine storage volume required for treatment of first inch of runoff:
Ccomp = 0.65
1
V := 32 (Atowl)-43560•Ccomp
V = 7076 cubic feet of storage required
Solve for depth "d" to provide required storage for first inch of runoff:
d := 1.5 ...guess value
I•w + (1 + 6•d)•(w + 6•d)
1'(d) := .d ...function of d for rectangular pond w/3:1 side slopes
2
g(d) = V
d := root[ (f(d) — g(d)), dl
d = 1.31 ft. - depth required to provide required storage for 1 inch with site fully developed
_ V
2day'� 2•24.60.60 2day—
— 0.0409
V
Q5day 5.24.60.60 Q5day = 0.0164
g := 32.2 Cdo := .6
cfs ...Max discharge for 2 day drawdown
cfs ...Max discharge for 5 day drawdown
.orifice coefficient
7

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
h := d h = 0.66 ft ...avg. head
2
Q2day
AoriGce 5 Aorifice = 0.011 Square ft.
Cdo•(2•P'h)
.5
1)2 (4. Aorifice • 12 D2 = 1.4 in. - for 2 day drawdown
3.14
Q5day = 0.0164 cfs
Aorifcc •= Q5day 5 AoriGce = 0.004 Square ft.
Cdo-(2-g•h)
�,5.Aorificc
D5 := 4 12 D5 = 0.9 in - for 5 day drawdown
3.14
Select drawdown orifice size:
Do:= 1.125 in.
Stage Discharge for Riser/Barrel Spillway with Emergency Weir:
g := 32.2 ...acceleration due to gravity
dia := 0 ...diameter of riser (ft.) (enter 0 if rectangular)
len := 4 ...length of opening if rectangular (ft.) (enter 0 if circular)
wid := 4 ...width of opening if rectangular (ft.) (enter 0 if circular)
grate := 16 ...area of openings in grate if rectangular (enter 0 for circular)
L:= i(dia * 0,7r-dia,2-(len + wid)] ...perimeter of riser (ft.)
(dia)2
A:= i dia O,xc• ii(gratc # 0,grate, len•wid)
4
A = 16 ...area of riser as orifice (sq.ft.)
Ltop := contour() + d Ltop = 43.61 ...minimum elevation of top of riser (ft.)
1'., = 44.40 ...chosen elevation for top of riser
lop
Cwr := 3.33 ...weir coefficient for riser
CA,.:= 0.60 —Orifice coefficient of discharge for riser
Nh := 1 ...Number of barrels
Values for Orifice Coefficient of discharge:
Dh := 15 ...diameter of barrel (in.)
Entrance Condition
CA
Typical default value
0.60
Eb := 42.3 ...invert elevation of barrel must be a= contour, =
42.3 Square -edged entrance
0.59
my 0
Concrete pipe, grooved end
0.65
Cdb := 0.60 ...Orifice coefficient of discharge for barrel
Corr mtl pipe, mitred to slope
0.52
corr mtl pipe projecting from fill
0.51
S

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Check drawdown time when water level is at top of discharge structure:
"oinv contour0
1)0
Elocl := contour0 +
12
li :_
(1'top — Eocl)
2
Eocl = 42.3 ...elevation of center line of orifice
h = 1.027 ...avg. head
do :_ o ft. -diameter of orifice
12
d 2
Aorificc := 3.14' 2 Aorifice - 0,0069 ...sq. ft.
I
q2:= Cdo'Aoriiicc'(2'g'h) 2 q2 = 0.0337 cfs
Vtop KS {1 top — 1Ao,nv)slopc ft3 Vtnp - 12365 ft3 - volume of storage when water level Is at top of
discharge structure - from stage -storage function
q2 := q2-cf.5 q2 = 0.03 cfs
drawdown:=
Vtop
q2
drawdown = 4.25 day Must be greater than or equal to 2 days and less than or equal to 5 days
Check drawdown time of first inch when water level is at top of discharge structure:
d = 1.31 ft. - depth required to provide required storage for 1 inch with site fully developed (from above)
top — Eocl dactual l
dactual - 2.05 .,.actual storage depth from orifice to top of discharge structure
dremaining dactual — d
dremaining = 0.74 ...depth remaining after 1 inch of storage has discharged
III�dremainin} + d h, = 1.4 ft... average head
2
1
q3 := Cdo'Aoritice'(2'g'h1) 2 q3 = 0.0393 cfs ...discharge rate
V := V-ft3 V = 7076 ft' - volume of storage when water level is at top of
discharge structure (from above)
��
drawdown V
1 g3•cfs
drawdown, = 2.09day Must be greater than or equal to 2 days and less than or equal to 5 days ...O.K.
0

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Size overflow spillway to pass 50 year peak flow:
Mew := .5 ..driving head over emergency weir (ft.)
Cw := 3.0 ...weir coefficient for emergency weir
_ Q50
.5
Cw' Hew'
Lv = 8.2 ...ft. (minimum)
Lw.= 10 ...ft. length chosen
I-cr := 47.52 ...crest elevation of emergency weir
inc := .2 ...amount to increment elevation (ft)
I'topofbankmin Ecr + Ilew + 5 1=topotbankmin = 48.52 ft. minimum
1'topofbank = 48.52 ....selected top of bank elevation
u := 0.. 25 v := l .. 25
elev0:= contour0 elevv:= clew-, + ine
Calculate discharge through riser:
hwu := clevu - l.top ...driving head for riser acting as a weir
hou (clevu - Etop) ...driving head when riser is acting as orifice
3
rwu := i elevu - Etop S 0, 0, Cw,.•1. rhwu) 2
rout= if[(elevu) - I top <O,O,Cdr•A•`` 2•g•hou
Calculate discharge through barrel:
I
D 2
barrel U:= i elevu 5 1 top,O,Nb•0.0437Cdb•Db2 elevu - �4 - Ebinv)
Calculate discharge through orifice:
For Z < or equal to Eo.inv: Q1 :=. 0 3
For Eo.inv <= Z <= D112 + Eo.inv Q2u := i elevu - Eoinv 5 0,0,0.372•Cdo•l)o (elevu - Eoinv) 2
1
I)o 2 1)o 2
For Z > D112 + Eo.inv: Q3u := i �elevu - 24 - Eoinv S 0,0,0.0437•Cdo•D0 elevu - 24 - Eoinv
10

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
U
orificcu := i elevu 5 Eoinv, Q 1, i elevu <-(12
- + Eoinv Q2u' Q3u
11
Calculate discharge through Principal spillway:
Prince:= igelevuS Etop,O,min{rwc,rou,barrel u}}
Calculate discharge over emergency weir:
3
weir u:= i elevu < Ecr,O,cN l-w•(elevu - Ecr)2
Calculate total discharge:
discharge := Prineu + weir + orifice
11

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Print results:
ft cfs cfs cfs cfs cfs cfs Cfs
elevu
rwu -
roll =
barrel
=
orifice
=
Princu
=
weir
=
dischargeu
=
42.3
0
0
0
0
0
0
0
42.5
0
0
0
0.013
0
0
0.01
421
0
0
0
0.02
0
0
0.02
42.9
0
0
0
0.025
0
0
0.02
43.1
0
0
0
0.029
0
0
0.03
43.3
43.5
0
0
0
0.032
0
0
0.03
0
0
0
0.036
0
0
0.04
43.7
0
0
0
0.039
0
0
0.04
43.9
0
0
0
0.041
0
0
0.04
44.1
0
0
0
0.044
0
0
0.04
44.3
0
0
0
0.046
0
0
0.05
44.5
1.68
24.36
7.4
0.049
1.68
0
1.73
44.7
8.75
42.2
7.9
0.051
7.86
0
7.91
44.9
18.84
54.48
8.3
0.053
8.29
0
8.34
45.1
31.2
64.46
8.7
0.055
8.7
0
8.76
45.3
45.49
73.09
9.1
0.057
9.09
0
9.15
45.5
61.47
80.8
9.5
0.059
9.47
0
9.53
45.7
78.97
87.84
9.8
0.061
9.83
0
9.89
45.9
97.88
94.35
10.2
0.063
10.18
0
10.24
46.1
118.1
100.45
10.5
0.064
10.51
0
10.58
46.3
139.54
106.19
111.64
10.8
0.066
10.84
0
10.9
46.5
162.14
11.2
0.068
11.15
11.46
0
11.22
46.7
185.85
116.84
11.5
0.069
0
11.53
46.9
210.61
121.81
11.8
0.071
11.76
0
11.83
47.1
236.38
126.59
12.1
0.072
12.05
0
12.13
47.3
263.12
131.19
12.3
0.074
12.34
0
12.41
12

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
COMPOSFIT STAGE- DISCHARGE,
280
260
240
220
200
180
100
80
60
40
20
0
42 42.5 43 43.5 44 44.5 45 45.5 46 46.5 47 47.5
STAGE {ft}
— riser as weir
I-.""""' riser as orifice
------- barrel
""-'-'- overflow weir
13

47.5
47
46.5
46
,, 45.5
45
W
C7
Q
44.5
44
43.5
43
42-5
42
0
Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
NET STAGE DISCHARGE
2 4 6 8 10 12 14
DISCII&RGG (efs)
14

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Set up matrix to do 10 year storm routing:
XF := ATI O Q := Q10 Tp := T1Op
iter := 60 ...number of iterations
u := 0.. iter m := 0.. 10
M = sal
u,m'
M <-- 0
0, m
clev, <-- contour,
while s 5 iter
IV+--S
.set variables for storm to be rotated
My 0 M(v--1 0) + AT
— 1.3•
Mv,o
'r
My I < if My , < 0,0,i My , 5 1.25•'rp, Q 1 �- cos v'O ,4.34•Q•e p
2 rp
My2 iCMV-1,I—Mv-1,7)-Nh'60+My-1,2<O'0'(Mv—],I—MV-1,7)-AT•60+My-1,21
M slope
My 3 <— i �Mv 2) O,contouro, v'2 + contour,
' Ks
rwV ilJ My 3 — Etop <— 0,0,cwr•L•(Mv 3—'-top)I.51
roV F iVMv 3) — Etop < 0,0,Cdr•A' 2•g My 3 11— Etop
2 Dh �0.5]
barrels +--it My 3 S Etop,0,Nh•0.0437•Cdb•Db (Mv,3 - 24 — Ebinv
Q2 <— iM — I;o• <_ 0 0,0.372•C D (M Eo• )1.51
v v,3 inv do o v,3 _ my J
0.5
Q3v i (Mv,3 — D4 — Eoir, < 0,0,0.0437•Cdo•Do2(Mv3 — 24) — Eoinv
My4<— i My3S Eoinv,Ql,i My3T)o
122 + Foinv Q2v' Q3v
II
My 5 if(My 3 S l top,O,minrrwv,roy,barrelV))
`
My 6 i�My 3 <Ecr,0,Cw•Lw. My 3 — Ecr)1.51
My 7�My 4+My 5+Mv 6
s+—s+ I
M
u, m
15

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
discharge := Mu 7 Q 1 Omax:= max(discharge)
stage := Mu 3 Ql Ostage := max(stage)
Q1 Omax = 0.05 cfs ...must be <= Q10pre = 3.2
Ql Ostage = 44.3 ft.
Check mass balance of matrix talcs;
Storage := Miter, 2 Storage = 11451
iter l
Inflowtotal := I F(Mv-1, 1)-[(A1).60]11 lnflowtotal = 11556
v=l
iter Outflowtotal:= I[[(Mv-1,5+Mv-1,6+Mv-1,4)-F(Xr)-60]J_Il1
Outflowtotal= 135
v= 1
Inflowtotal - Outflowtotal = 11451 MIST BE REASONABLY CLOSE TO Storage = 11451 O.K.
Display a portion of routing results:
tirneu Mu 0 inflow := Mu 1 storage := Mu 2 stage := Mu 3 orificeIt:= Mu 4 culvertu := Mu 5
weir := Mu 6 discharge := Mu �
a
(See next page for display)
cfs O. K.
16

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Partial
TIME
minutes
time
display of
INFLOW
=
10 year
cfs
inflow =
0
0.3
1.3
2.9
4.8
7
9.2
11.1
12.7
13.7
14
13.7
12.7
11.2
9.9
8.7
7.6
6.7
5.9
5.2
4.5
4
3.5
3.1
2.7
2.4
2.1
1.8
1.6
1.4
1.2
1.1
1
0.81
0.7
0.6
storm routing results:
STORAGE
cubic feet
storage =
0
0
20
100
271
558
973
1516
2175
2926
3736
4565
5375
6125
6788
7371
7882
8331
8724
9069
9372
9638
9870
10074
10253
10410
10547
10668
10773
10865
10945
11016
11077
11131
11178
11218
STAGE
ft
stagcu =
0
42.3
42.31
42.33
42.38
42.45
42.54
42.65
42.78
42.92
43.06
43.2
43.33
43.46
43.56
43.65
43.73
43.8
43.86
43.91
43.96
44
44.03
44.06
44.09
44.11
44.13
44.15
44.17
44.18
44.19
44-21
44.21
44.22
44.23
44.23
ORIFICE CULVERT
cfs
orifiiccu =
0
0
0
0
0.01
0.01
0.01
0.02
0.02
0.03
0.03
0.03
0.03
0.03
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
604
0.04
0.04
0.05
0.05
0.05
0.05
0.05
0.05
cfs
culvert =
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
WEIR
cfs
weir -
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
DISCHARGE
cfs
discharge _
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
2
3
3.9
4.9
5.9
6.9
7.9
8.9
9.9
10.9
11.8
12.8
13.8
14.8
15.8
16.8
17.8
18.8
19.7
20.7
21.7
22.7
23.7
24.7
25.7
26.7
27.6
28.6
29.6
30.6
31.6
32.6
33.6
34.6
17

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Cl IAINSAW ROUTING FOR 10 YI AR STORM
15
14
13
12
11
10
9
6
5
4
3
2
1
0 - -- - ----- -- - - - -------------------- - -
0 10 20 30 40 50 60
TIME (minutes)
inflow
------- outflow
18

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Change variables to do 50 year storm routing:
AT:= A'I'50 Q := Q50 Tp := 'I'50p
M = s<--1
u,m'
MO mF0
clev0 <-- contour0
while s 5 iter
IV<—s
...set variables for storm to be routed
My 0 <- M(v-1,0) + AT
- rp
l.3•
M"
My 1 <- i My 0 < 0,0, i My 0 S 1.25-"1'P, Q • 1 -cos v'0 ,4.34•Q•e
2 Tp
))
My 2 <-- flM V--I 1 - My-1 7)•A"I'•60 + My-1, 2 5 0,0,(Mv-1, I - My-1, 7)•A"I'•60 + My -I 21
1
M 2 slope
My 3 <- i (Mv 2) S O,contour0' v, + contour0
' Ks
rwv ill My 3 - Etop <- 0,0,Cwr'I: rMv,3 - Eta )1.51
LL ` I' J
rov <- if��Mv 3} - Et5 O, 0, Cdr-A• 2 g My 3 - Etop
2 Db 0.5
barrel y <- i My 3 5 Etop,O,Nb•0.0437•Cdb•Db (Mv 3 - 24 - Ehinv)
Q2 <-- if[
M - Eo <- 0 0 0.372•C D •(M Eoe, )1.51
v v, 3 my > > do• o v 3 - nv
1)0 2.
1)o 0.5
Q3v +- i My 3 - 24 - Eoit, 5 0,0,0.0437•Cdo•Do (Mv 3 24 - Eoinv
1
I)o 1
My 4 <- i My 3 5 Eoinv,Ql,' My 3 5 (12 + Eoinv1,Q2v'Q3v
11
My 5 F if(Mv 3 -< Etop10,min(rwv,rovIbarrel v))
My 6 +- iItMv 3 < Ecr,0,Cw I -W. (Mv, 3 - Ecr)1.5]
My 7<-Mv 4+Mv 5+Mv 6
s<--s+1
I Mu, m
discharge := Mu, 7
Q50max:= max(discharge) Q50max = 7.9 Cfs
_
stage ' u, 3 Q50stage : = max(stage) Q50stage = 44.71 ft.
19

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
20
time :=
Mu 0 inflow
:= Mu
t storage := Mu 2 stage := MU 3
orifice := Mu 4
culvert := Mu 5 weir := Mu
6
discharge := Mu
7
Partial display
of 50 year storm
routing results:
TIME
INFLOW
STORAGE
STAGE
ORIFICE
CULVERT
WEIR
DISCHARGE
minutes
cis
cubic feet
ft
cfs
cfs
cfs
cfs
time =
inflow
=
storage =
stageu =
orifice =
culvert =
weir =
dischargec =
0
0
0
0
0
0
0
0
1.5
0.4
0
42.3
0
0
0
0
3
1.7
39
42.3
0
0
0
0
4.5
3.6
189
42.4
0
0
0
0
6.1
6
513
42.4
0.01
0
0
0
7.6
8.7
1057
42.6
0.02
0
0
0
9.1
11.3
1843
42.7
0.02
0
0
0
10.6
13.8
2873
42.9
0.02
0
0
0
12.1
15.7
4122
43.1
0.03
0
0
0
13.6
16.9
5544
43.4
0.03
0
0
0
15.1
17.3
7078
43.6
0.04
0
0
0
16.7
16.9
8651
43.8
0.04
0
0
0
18.2
15.7
10184
44.1
0.04
0
0
0
19.7
13.9
11605
44.3
0.05
0
0
0
21.2
12.2
12863
44.5
0.05
1.02
0
1.1
22.7
10.7
13874
44.6
0.05
5.34
0
5.4
24.2
9.4
14357
44.7
0.05
7.82
0
7.9
25.8
8.3
14495
44.7
0.05
7.87
0
7.9
27.3
7.2
14526
44.7
0.05
7.88
0
7.9
28.8
6.4
14464
44.7
0.05
7.86
0
7.9
30.3
5.6
14323
44.7
0.05
7.81
0
7.9
31.8
4.9
14117
44.7
0.05
6.67
0
6.7
33.3
4.3
13952
44.6
0.05
5.76
0
5.8
34.8
3.8
13815
44.6
0.05
5.04
0
5.1
36.4
3.3
13697
44.6
0. 55
4.44
0
4.5
37.9
2.9
13591
44.6
0.05
3.92
0
4
39.4
2.6
13495
44.6
0.05
3.47
0
3.5
40.9
2.2
13408
44.5
0.05
3.08
0
3.1
42.4
2
13328
44.5
0.05
2.74
0
2.8
43.9
1.7
13254
44.5
0.05
2.43
0
2.5
45.4
1.5
13186
44.5
0.05
2.16
0
2.2
47
1.3
13124
44.5
0.05
1.92
0
2
48.5
1.2
13067
44.5
0.05
1.71
0
1.8
4451.52
"0013014
0
1.6

Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
CHAINSAW ROUTING FOR 50 YEAR STORM
18
16
14
12
6
4
2
0
0 10 20 30 40 50 60 70 80 90 100
TIME (minutes)
— inflow
"'- outflow
21

W
Drainage Calculations for Chippenham
Subdivision
Wilmington, NC
Determine outlet apron dimensions and riprap size for pipe discharge to pond
from SD MH 2:
1):= 2 ...ft - diameter of pipe
Voutict := 2.8 fps - from pipe sizing chart
From Figure 8.06.b.1 and Figure 8.06.b.2 choose Zone 1.
I -a := 4•1) I,a = 8 ft - minimum length of apron from figure 8.06b2
W := 3.1) W = 6 ft - minimum width of apron from figure 8.06b2
dia := 6 diameter of stone in inches
dmax.= 1.5•dia dmax = 9 max stone diameter
t := 18 in. min. thickness of apron in inches
Determine outlet apron dimensions and riprap size for pipe discharge to pond
from Curb Inlet 4:
D := 1.25 ...ft - diameter of pipe
Voutict :- 3•3 fps - from pipe sizing chart
From Figure 8.06.b.1 and Figure 8.06.b.2 choose Zone 1.
I -a := 4-D La = 5 ft - minimum length of apron from figure 8.06b2
W := 3•D W = 3.8 ft - minimum width of apron from figure 8.06b2
dia := 6 diameter of stone in inches
dmax:= 1.5•dia dmax = 9 max. stone diameter
t := I8 in. min. thickness of apron in inches
Note: References to chart nos., table nos., and page nos. refer to Erosion and Sediment Control
Planning and Design Manual unless noted otherwise
M

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