20001048 Ver 2_Stormwater Info_20010102

W'\ \
Permit No.
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
V Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DW Stormwater Management Plan Review:
A complete stormwater management plan submittal includes an application form, a wet detention basin
supplei: ent for each basin, design calculations, and plans and specifications showing all basin and outlet
structure details.
1. PROJECT INFORMATION
Project Name: 1000 CGS CASE
Contact Person: T'1'1 s , 'V` Doc Phone Number: (q19 ) 71 6 - 3 q G
For projects with multiple basins, specify which basin this worksheet applies to: /90A/0 Alo ,
elevations
Basin Bottom Elevation Zq S, U ft. (floor of the basin)
Permanent Pool Elevation -2- 'g, 0 ft . (elevation of the orifice)
Temporary Pool Elevation 3 0C). 9 ft. (elevation of the discharge structure overflow)
areas
Permanent Pool Surface Area 7 Ov sq. ft. (water surface area at the orifice elevation)
Drainage Area 16,61 ac. (on-site and off-site drainage to the basin)
Impervious Area -7.0 7 ac. (on-site and off-site drainage to the basin)
volumes
Permanent Pool Volume 5 7 g 6 0 cu. ft. (combined volume of main basin and forebay)
Temporary Pool Volume ?i Z 2-b cu. ft. (volume detained above the permanent pool)
Forebay Volume O U cu. ft. (approximately 20% of total volume)
Other parameters
0
SA/DAI ?. 73 0 ° (surface area to drainage area ratio from DWQ table)
Diameter of Orifice << in. (2 to S day temporary pool draw-down required)
Design Rainfall , Q in. Ro,4 ofr (610q t?//&- .to wz sro,--.4?
Design TSS Removal 2 `$ S % (minimum 85% required)
Form SWU-102 Rev 3.99 Page 1 of 4
Footnotes:
When using the Division SA/DA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
In the 20 coastal counties, the requirement for a vegetative filter may be waived if the wet detention basin is designed to provide
90% TSS removal. The NCDENR BMP manual provides design tables for both 85% TSS removal and 90% TSS removal.
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. If a requirement has not been met, attach justification.
Applicants Initials
C_ ON, f VA a. The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
SOW- 1fV4 b. The forebay volume is approximately equal to 20% of the basin volume.
C;P IfV4 c. The temporary pool controls runoff from the design storm event.
CD 1'"
MZA d. The temporary pool draws down in 2 to 5 days.
cp t 4 e. If required, a 30-foot vegetative filter is provided at the outlet (include non-erosive flow
calculations)
off'/!?/+ f. The basin length to width ratio is greater than 3:1.
g. The basin side slopes above the permanent pool are no steeper than 3:1.
Ch f VAS h. A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
CD ffv? i. Vegetative cover above the permanent pool elevation is specified.
CIO ' f j. A trash rack or similar device is provided for both the overflow and orifice.
k. A recorded drainage easement is provided for each basin including access to nearest right-
of-way.
1. If the basin is used for sediment and erosion control during construction, clean out of the
basin is specified prior to use as a wet detention basin.
Cd Hf/?F in. A mechanism is specified which will drain the basin for maintenance or an emergency.
III. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the
vegetated filter if one is provided.
This system (check one) does 0 does not incorporate a vegetated filter at the outlet.
This system (check one) 0 does does not incorporate pretreatment other than a forebay.
Form SWU-102 Rev 3.99 Page 2 of 4
n ?W
Permit No.
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
(to be provided by DWQ)
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DW Stormwater Management Plan Review:
A complete stormwater management plan submittal includes an application form, a wet detention basin
supplement for each basin, design calculations, and plans and specifications showing all basin and outlet
structure details.
1. PROJECT INFORMATION
Project Name: -1000 CC-L_- CS& Se?L/0--1 TY -/4^,, s O.Al ?u.?Ty'
Contact Person: ?TtM - ; tS Al L DO C_ Phone Number: (91 q) "7l 6 3
For projects with multiple basins, specify which basin this worksheet applies to: _, o,?a /Vo,'Z
elevations
Basin Bottom Elevation ZqZ, 0 ft. (floor of the basin)
Permanent Pool Elevation 2 q ?. ft. (elevation of the orifice)
Temporary Pool Elevation Z q -7. 9 ft. (elevation of the discharge structure overflow)

areas
Permanent Pool Surface Area g 12 5 sq. ft. (water surface area at the orifice elevation)
Drainage Area 3, R 3 ac. (on-site and off-site drainage to the basin)
Impervious Area 2, 9 1 ac. (on-site and off-site drainage to the basin)

volumes
Permanent Pool Volume 23,000 cu. ft. (combined volume of main basin and forebay)
Temporary Pool Volume -33,500 cu. ft. (volume detained above the permanent pool)
Forebay Volume 6300 cu. ft. (approximately 20% of total volume)

Other parameters
SA/DAI -4, (surface area to drainage area ratio from DWQ table)
Diameter of Orifice (,0 in. (2 to S day temporary pool draw-down required)
Design Rainfall 1,0 in. #,-00c C6 • nq r v/t/".- ' 10 Yom- Sro?'- ??)
Design TSS Removal 2 `3 5 % (minimum 85% required)
Form SWU-102 Rev 3.99 Page 1 of 4
Footnotes:
When using the Division SA/DA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
In the 20 coastal counties, the requirement for a vegetative filter may be waived if the wet detention basin is designed to provide
90% TSS removal. The NCDENR BMP manual provides design tables for both 85% TSS removal and 90% TSS removal.
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. If a requirement has not been met, attach justification.
Applicants Initials
a. The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
b. The forebay volume is approximately equal to 20% of the basin volume.
COW1 If U54 c. The temporary pool controls runoff from the design storm event.
d. The temporary pool draws down in 2 to 5 days.
_-C !?4 e. If required, a 30-foot vegetative filter is provided at the outlet (include non-erosive flow
calculations)
f. The basin length to width ratio is greater than 3:1.
g. The basin side slopes above the permanent pool are no steeper than 3:1.
h. A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
i. Vegetative cover above the permanent pool elevation is specified.
j. A trash rack or similar device is provided for both the overflow and orifice.
k. A recorded drainage easement is provided for each basin including access to nearest right-
of-way.
1. If the basin is used for sediment and erosion control during construction, clean out of the
basin is specified prior to use as a wet detention basin.
G4e kv, m. A mechanism is specified which will drain the basin for maintenance or an emergency.
III. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the
vegetated filter if one is provided.
This system (check one) does 0 does not incorporate a vegetated filter at the outlet.
This system (check one) 0 does does not incorporate pretreatment other than a forebay.
Form SWU-102 Rev 3.99 Page 2 of 4
Maintenance activities shall be performed as follows:
1. After every significant runoff producing rainfall event and at least monthly:
a. Inspect the wet detention basin system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of the temporary pool occurs within
2 to 5 days as designed.
2. Repair eroded areas immediately, re-seed as necessary to maintain good vegetative cover, mow vegetative
cover to maintain a maximum height of six inches, and remove trash as needed.
3. Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to maintain
proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed of
in an appropriate manner and shall be handled in a manner that will not adversely impact water quality (i.e.
stockpiling near a wet detention basin or stream, etc.).
The measuring device used to determine the sediment elevation shall be such that it will give an accurate
depth reading and not readily penetrate into accumulated sediments.
When the permanent pool depth reads 2,2-5 feet in the main pond, the sediment shall be removed.
When the permanent pool depth reads 2;z5 feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
(fill in the blanks)
0 Permanent Pool Elevation ZQ S. D
Sediment R\Ele l El. 2gS,7 s 75 0
_____________ Sediment Removal Elevation 2-q2-,75'
75%
Bottom tion Z 4 5•(? % -------------------------------Z Z?--------- ---o--
Bottom Elevation 0 25 /o
FOREBAY
MAIN POND
5. Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and forebay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment through
the emergency drain shall be minimized to the maximum extent practical.
Form SWU-102 Rev 3.99 Page 3 of 4
7. All components of the wet detention basin system shall be maintained in good working order.
I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print name: ZC I,//rar., c5?o era //
Title:
Address: I oA fl, CC V e"-- 4.'V, I;we' 'W-56-- /"NC
Phone: r, 716 3'100 p'
Signature: "7.
Date:
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and a
resident of the subdivision has been named the president.
I, Qmn ICS.. m , a Notary Public for the State of )L\)&&
C- o-rai AC"
County of ?Ca?L , do hereby certify that Upi `k % OVf-N ?'I, 'E- Uc't k
personally appeared before me this o`rJ day of-3 arAV ,- u ,nk--), and acknowledge the due
execution of the forgoing wet detention basin maintenance requirements. Witness my hand and official seal,
SEAL
My commission expires 9 'S - C-)-001
Form SWU-102 Rev 3.99 Page 4 of 4
JAN i n ?orn
Permit No.
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
(to be provided by DWQ)
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DWQStormwater Management Plan Review:
A complete stonnwater management plan submittal includes an application form, a wet detention basin
supplement for each basin, design calculations, and plans and specifications showing all basin and outlet
structure details.
1. PROJECT INFORMATION
Project Name: 1 00 0 C Eu- CAS e S?w?t 1Y /4t-s ?,, Coc,- ir
Contact Person: 5(M ?w-rfr5 - NC- l) c) C- Phone Number: ( 91 `j )/?-716 -3 440
For projects with multiple basins, specify which basin this worksheet applies to: Pv,tio AVo. 3
elevations
Basin Bottom Elevation Z q z,, o ft.
Permanent Pool Elevation Z 9 S, 0 ft.
Temporary Pool Elevation z a 7. ` ft.
(floor of the basin)
(elevation of the orifice)
(elevation of the discharge structure overflow)
areas
Permanent Pool Surface Area 9300 sq. ft. (water surface area at the orifice elevation)
Drainage Area 3 7 4- ac. (on-site and off-site drainage to the basin)
Impervious Area 7 ac. (on-site and off-site drainage to the basin)
volumes
Permanent Pool Volume 6 5 7 S cu. ft. (combined volume of main basin and forebay)
Temporary Pool Volume 3 7 9 O cu. ft. (volume detained above the permanent pool)
Forebay Volume 2 w Z5 cu. ft. (approximately 20% of total volume)
Other parameters
6
SA/DA1 2.0 U ° (surface area to drainage area ratio from DWQ table)
Diameter of Orifice 0.7 7 in. (2 to 5 day temporary pool draw-down required)
Design Rainfall 1.0 in. /t-?vo("r 0q 1,111b, Y" .9 rv,._,4
Design TSS Removal Z 5; % (minimum 85% required)
Form SWU-102 Rev 3.99 Page 1 of 4
Footnotes:
When using the Division SA/DA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
In the 20 coastal counties, the requirement for a vegetative filter may be waived if the wet detention basin is designed to provide
90% TSS removal. The NCDENR BMP manual provides design tables for both 85% TSS removal and 90% TSS removal.
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. If a requirement has not been met, attach justification.
Applicants Initials
C? a.
v* b.
C.
d.
CO e.
f.
UA g.
GDN' ¢ h.
G/JH' lv? j.
CO<!? l k.
The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
The forebay volume is approximately equal to 20% of the basin volume.
The temporary pool controls runoff from the design storm event.
The temporary pool draws down in 2 to 5 days.
If required, a 30-foot vegetative filter is provided at the outlet (include non-erosive flow
calculations)
The basin length to width ratio is greater than 3:1.
The basin side slopes above the permanent pool are no steeper than 3:1.
A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
Vegetative cover above the permanent pool elevation is specified.
A trash rack or similar device is provided for both the overflow and orifice.
A recorded drainage easement is provided for each basin including access to nearest right-
of-way.
Gdl !? 1. If the basin is used for sediment and erosion control during construction, clean out of the
basin is specified prior to use as a wet detention basin.
coff ?'?" in. A mechanism is specified which will drain the basin for maintenance or an emergency.
III. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the
vegetated filter if one is provided.
This system (check one) 4 does O does not incorporate a vegetated filter at the outlet.
This system (check one) 0 does QFdoes not incorporate pretreatment other than a forebay.
Form SWU-102 Rev 3.99 Page 2 of 4
Maintenance activities shall be performed as follows:
1. After every significant runoff producing rainfall event and at least monthly:
a. Inspect the wet detention basin system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of the temporary pool occurs within
2 to 5 days as designed.
2. Repair eroded areas immediately, re-seed as necessary to maintain good vegetative cover, mow vegetative
cover to maintain a maximum height of six inches, and remove trash as needed.
3. Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to maintain
proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed of
in an appropriate manner and shall be handled in a manner that will not adversely impact water quality (i.e.
stockpiling near a wet detention basin or stream, etc.).
The measuring device used to determine the sediment elevation shall be such that it will give an accurate
depth reading and not readily penetrate into accumulated sediments.
When the permanent pool depth reads 2,25 feet in the main pond, the sediment shall be removed.
When the permanent pool depth reads 2,7- S feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
(fill in the blanks)
0 Permanent Pool Elevation 9 s• O
Sediment VElea Z R S,7S 75 o
________ Sediment Removal Elevation Z9 Z, 5 75%
BottoZ9 S,O % ---------- ----------------------------------- ------
Bottom Elevation 25%
FOREBAY
MAIN POND
5. Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and forebay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment through
the emergency drain shall be minimized to the maximum extent practical.
Form SWU-102 Rev 3.99 Page 3 of 4
7. All components of the wet detention basin system shall be maintained in good working order.
I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print name: /_), '//, 1 P9 m //
Title: c 7-1012, ON a ,iy ?rit'?.vG
Address: lIcR IA C f1Ro /,', ?? dedAX 61 i,r-W / cr7)C (. OAX fC &?/
Phone: 71!0 -7160
Signature: 7? Y
Date: GO/ 'z 1, Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and a
resident of the subdivision has been named the president.
I, ? ? I Cr, ?O .'?) t '?A? , a Notary Public for the State of A 0r'- &COk a j,p`
County of Wc?-? , do hereby certify that U MV104y1
personally appeared before me this ? day of CnLkcol and acknowledge the due
execution of the forgoing wet detention basin maintenance requirements. Witness my hand and official seal,
SEAL
My commission expires I - y ' a (Do ?
Form SWU-102 Rev 3.99 Page 4 of 4
? V
Pond #3
Detention Basin Design
Determine Surface area and volume required
Drainage Area = 3.74 Acres
Impervious area = 1.87 Acres
% Impervious 50.00 %
From Table 1.1 of NCDENR Stormwater Best Management Practices SA/DA = 2.00 %
For Depth = 3 feet Permanent Pool
Depth = 3 ft Required
Surface Area 3258.29 SF
BASIN DIMENSIONS
Length Width L/W Ratio Basin
75 25 3.00 :1 Surface Area 3999 SF
Sidcslopes 3 :1
DETERMINE STAGE-STORAGE FUNCTION
S Z
CONTOUR [NCR ACCUM
t1nT.1 rnT TD A DR A VnT T TKA-P VnT T TKAP CT A r:F
y x
In R In 7. 7, ect
FT S Q. FT CU. FT CU. FT FT FT
0 0 0
1 2511 1256 1256 1 7.135289179 0 0.99
2 3219 2865 4121 2 8.323729794 0.6931472 2.05
3 3999 3609, 7730 3 8.952799456 1.0986123 3.01
4 4851 4425 12155 4 9.405454751 1.3862944 3.97
5 5775 5313 17468 5 9.76809729 1.6094379 4.96
6 6771 6273 23741 6 10.07493773 1.7917595 5.99
From Linear Regression
Ks = 1282
b = 1.63
corr. = 0.999831124
Pond #3
Determine Volume to Be controlled by 1" storm
Calculate Rv
Rv = 0.05 + 0.009 * I
Volume to be treated
Volume = Rainfall * Rv * Drainage Area
Rainfall= 1 in
STAGE-STORAGE function
KS = 1282
b = 1.63
Set riser Z
Volume to drain
Orifice Required
Drawdown time
Say
Qo =
Rv =
V =
Say
V =
2-5 Days
Qrcq.
3.5 Days
Cd =
Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
D (in) D (ft) Qo(cfs) Drawdown (days) Remark
2 0.17 0.1789 0.44 Too Fast
0.5 0.04 0.0112 7.11 Too Slow
0.75 0.06 0.0252 3.16 OK
0.50 in/in
0.1558333 acre-ft
6788 cf
Z= 2.78026387
Z= 2.8
El (riser) = 5.8
6867 cf
0.0227077 cfs
0.6
Pond #3
Pipe to Drain Pond
Qo = Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
Riser Depth = 5.8 ft
Riser Depth Volume = 22504.826 cf
D (in) D (ft) Qo(cfs) Drawdown (hrs) Remark
4 0.33 0.7156 8.74 I OK
Determine Post Development and Pre Development Runoff Coefficients
Pre Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 0 0.00% 0.00%
Pastureland 0.3 6.88 100.00% 30.00%
Total: 6.88
]
F-- Use C= 30%19
Post Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 1.87 50.00% 47.50%
Turf 0.3 1.87 50.00% 15.00%
Total: 3.74

Use C= 63
Pond #3
Determine Post Development and Pre Development Curve Number
Pre Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Open Space B 61 0.00
C 74 0.00
D 80 6.88 80.00
Streets & Roads B 98 0.00
(Pavement & Buildings) C 98 0.00
D 98 0.00
B 98 0.00
C
D 98
98
Totals: 6.88 80.00
Use CN: 80
Post Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Turf B 61 0.00
C 74 0.00
D 80 1.87 40.00
Streets & Roads B 98 0.00
C 98 0.00
D 98 1.87 49.00
0.00

Totals: 3.74 89.00
Use CN: 89
Pond #3
Set Crest of Riser at Water Quality Stage
Set riser at water quality stage + Permanent Pool
Stage(WQ): 2.7802639 ft
Say 2.8 Riser Elevation:
Compute Allowable Outflow:
Qpre= 13 cfs See "Peak Inflow" sheet
Qpost = 14 cfs 10 yr flood
Estimate Stormwater Storage Needed:
S = (Qpost - Qpre) * Tp *60 sec/min
If S is neg. (Qpre > Qpost)
S = 1.39 * Qpost * Tp
Determine Total Storage
Total Storage = Flood Storage + Water Quality
Total Storage =
Total Stage =
Configure Outlet
Select Riser by Orifice Equation
Cd =
li = ((0.159 * Q)/(Cd * D^2))^2
h is to Centerline of barrel
Cet nn Trinl nnA Frrnr Mhle
S=
S=
S needed =
Qp =
0.6
Tp =
Tp =
9411 cf
3.40 ft
z
D (inch) D (ft) h (ft) h + D/2 (ft)

15 1.25 4.86 5.49
24 2 0.74 1.74
12 1 11.87 12.37
Route to confirm
5.8 ft
2544 cf
825 cf
2544 of
13 cfs
Try barrel =
Riser =
68.29 min.
42.4 min.
12
18
Pond #3
Forebay Required Volume
Total Storage = 9411 cf ( Total Storage)
Fore Bay Volume = 20% Total Volume
Fore Bay Volume = 1882 of
Forebay Dimension
Try Len h Width
15 25
Area = (Length + (2 *Depth* Sideslope)) *(Width + (2 *Depth* Sideslopes)
Depth 3 ft
Area = 1419 sf
Sideslopes 3 :1
Volume = (Average Area*Depth)
Sediment Storage
From "Sediment predictions in Eastern United States"
Malcom, H.R. and Smallwood, C., (1977)
(for Urbanized ) V = 2.96 * A^0.67
V = 0.0944007 acre-ft/year
4112 of/year
Cleanout interval 2 Years
Volume= 8224 cf
Volume = 2691 CF
Where:
V = Sed. Volume (acre-ft/year
A = Area (sq. miles)
Total Volume Needed for Pond = (ceanout volume - (0.25 * Forebay volume)) = 7551 cf
Pond #3
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 10-Year, 24-Hour Depth; 10-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L= ft
H = ft
Te = 10.00 minutes
1 = 6.09 in/hr
Pre Development
SOLUTION - Tp:
A = 6.88 acres
C = 0.30
INPUT
Qp = 13 efs
OUTPUT
P = 4.97 in
CN = 80
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
S = 2.50 in
Q* = 2.87 in
Tp = 68.29 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 13 CFS
11 Tp = 68.29 MINUTES
Pond #3
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H= ft
Te = 10.00 minutes
I = 6.09 in/hr
Post Development
SOLUTION - Tp:
A = 3.74 acres
C = 0.63
INPUT
P = 4.97 in
CN = 89
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 14 cfs
OUTPUT
S = 1.24 in
Q* = 3.74 in
Tp = 42.46 minutes
L = Hydraulic Length, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 14 CFS
Tp = 42.46 MINUTES
Pond #3
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L= ft
H = ft
Te = 10.00 minutes
I = 7.30 in/hr
Pre Development
SOLUTION - Tp:
A = 6.88 acres
C = 0.30
INPUT
P = 5.82 in
CN = 80
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 15 cfs
OUTPUT
S = 2.50 in
Q* = 3.62 in
Tp = 71.93 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 15 CFS
IF Tp = 71.93 MINUTES
Pond #3
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L= ft
H = ft
OUTPUT
Tc = 10.00 minutes
I = 7.30 in/hr
Post Development
SOLUTION - Tp:
A = 3.74 acres
C = 0.63
INPUT
P = 5.82 in
CN = 89
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 17 cfs
OUTPUT
S = 1.24 in
Q* = 4.56 in
Tp = 43.17 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 17 CFS
11 Tp = 43.17 MINUTES
Pond #3
Chainsaw Routing
(REF: Malcom, 1991)
IIUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 10-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q."I' = 9 CFS Z.rsvr = 6.99 FT '1'-S.nrm = 22,675 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT WSA.max = 7,112 SQ-FT
FRBD.min = 1.01 FT V.s = 0.0 FPS T-S.max = 30,483 CU-FT
WSEL.nrm = 3.00 FT Q.s = 0 CFS WSA.nrm = 4,175 SQ-FT
SEL.max = 6.99 FT T-S.det = 14,991 CU-FT

INPUT
Qp = 14 CPS N.r = 1 ClV.S = 3.00
Tp = 42.40 MIN Cw.r = 3.30 Ct.s = 2.45
d'l'= 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :I
ICs = 1282
b = 1.63 D.r = 1.50 FT
EL.s = 7.00 IT
N.b = I
FLA= = 8.00 FT Cd.b = 0.60 EL.r = 5.80 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.80 FT
OUTPUT
A B C D E F G H 1
Time Inflow
1 Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CPS
0 0 7684 3.UU U INA [Nil IN/\ v.V
4 0 7684 3.00 0.00 0.0 0.0 6.0 0.0
8 1 7757 3.02 0 OA 0.0 6.0 0.0
12 3 8044 3.09 0 0.0 0.0 6.1 0.0
16 4 8665 3.23 0 0.0 0.0 6.2 OA
20 6 9714 3.46 0 0.0 0.0 6.5 OA
24 8 11245 3.79 0 0.0 0.0 6.8 0.0
28 10 13271 4.19 0 0.0 0.0 7.3 0.0
32 12 15762 4.66 0 0.0 0.0 7.7 OA
36 13 18647 5.17 0 0.0 0.0 8.2 0.0
40 14 21822 5.69 0 0.0 0.0 8.6 0.0
44 14 25155 6.21 4 4.1 5.4 9.0 0.0
48 13 27524 6.56 7 10.3 7.4 9.3 0.0
52 12 28959 6.77 8 14.9 8.4 9.5 0.0
56 11 29901 6.90 9 18.0 8.9 9.6 0.0
Pond #3
60 10 30375 6.97 9 19.7 9.2 9.6 0.0
64 9 30483 6.99 9 20.1 9.3 9.6 0.0
68 8 30309 6.96 9 19.5 9.2 9.6 0.0
72 7 29921 6.91 9 18.1 8.9 9.6 0.0
76 6 29377 6.83 9 16.3 8.6 9.5 0.0
80 5 28724 6.74 8 14.1 8.2 9.4 0.0
84 5 28003 6.63 8 11.8 7.8 9.3 0.0
88 4 27251 6.52 7 9.5 7.2 9.3 0.0
92 4 26498 6.41 7 7.4 6.6 9.2 0.0
96 3 25771 6.30 6 5.5 6.0 9.1 0.0
100 3 25209 6.22 4 4.2 5.5 9.0 0.0
104 3 24880 6.17 3 3.5 5.2 9.0 0.0
108 2 24648 6.13 3 3.0 4.9 9.0 0.0
112 2 24463 6.10 3 2.6 4.7 8.9 0.0
116 2 24306 6.08 2 2.3 4.5 8.9 0.0
120 2 24168 6.06 2 2.1 4.3 8.9 0.0
124 1 24043 6.04 2 1.8 4.2 8.9 0.0
128 1 23930 6.02 2 1.6 4.0 8.9 0.0
132 1 23826 6.01 1 1.5 3.9 8.9 0.0
136 1 23731 599 1 1.3 3.7 8.8 0.0
140 1 23643 5.98 1 1.2 3.6 8.8 0.0
144 1 23561 5.97 1 1.0 3.5 8.8 0.0
148 1 23486 5.95 1 0.9 3.3 8.8 0.0
152 1 23417 5.94 1 0.8 3.2 8.8 0.0
156 1 23353 5.93 1 0.8 3.1 8.8 0.0
160 0 23294 5.92 1 0.7 3.0 8.8 0.0
164 0 23239 5.92 1 0.6 2.9 8.8 0.0
168 0 23188 5.91 1 0.5 2.8 8.8 0.0
172 0 23142 5.90 0 0.5 2.7 8.8 0.0
176 0 23098 5.89 0 0.4 2.6 8.8 0.0
180 0 23058 5.89 0 0.4 2.5 8.8 0.0
184 0 23021 5.88 0 0.4 2.4 8.8 0.0
188 0 22986 5.88 0 0.3 2.3 8.8 0.0
192 0 22954 5.87 0 0.3 2.3 8.8 0.0
196 0 22924 5.87 0 0.3 2.2 8.7 0.0
200 0 22897 5.86 0 0.2 2.1 8.7 0.0
204 0 22871 5.86 0 0.2 2.0 8.7 0.0
208 0 22847 5.85 0 0.2 2.0 8.7 0.0
212 0 22825 5.85 0 0.2 1.9 8.7 0.0
216 0 22805 5.85 0 0.2 1.9 8.7 0.0
220 0 22786 5.84 0 0.1 1.8 8.7 0.0
224 0 22768 5.84 0 0.1 1.7 8.7 0.0
228 0 22752 5.84 0 0.1 1.7 8.7 0.0
232 0 22737 5.84 0 0.1 1.6 8.7 0.0
236 0 22722 5.83 0 0.1 1.6 8.7 0.0
240 0 22709 5.83 0 0.1 1.5 8.7 0.0
244 0 22697 5.83 0 0.1 1.5 8.7 0.0
248 0 22685 5.83 0 0.1 1.4 8.7 0.0
252 0 22675 5.83 0 0.1 1.4 8.7 0.0
Pond #3
Chainsaw Routing
(REF.- Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 25-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 13 CFS Z.rsvr = 7.34 FT T-S.nrm = 22,704 CU-FT
Q.pr = 4 CFS Z.s = 0.34 FT W SA.max = 7,338 SQ-FT
FRBD.min = 0.66 FT V.s = 1.7 FPS T-S.max = 33,058 CU-FT
WSEL.nrm = 3.00 FT Q.s = 4 CFS WSA.nrm = 4,175 SQ-FT
SEL.max = 7.34 FT T-S.det = 15,020 CU-FT'

INPUT
Qp = 17 CFS N.r = l Cw.s = 3.00
Tp = 43.17 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks = 1282
b = 1.63 D.r = 1.50 FT
EL.s = 7.00 FT
N.b = 1
EL.dam = 8.00 FT Cd.b = 0.60 EL.r = 5.80 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.80 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CFS
0 0 7684 J.UO V NA 114A IA V.V
4 0 7684 3.00 0.00 0.0 0.0 6.0 0.0
8 1 7770 3.02 0 0.0 0.0 6.0 0.0
12 3 8106 3.10 0 0.0 0.0 6.1 0.0
16 5 8836 3.27 0 0.0 0.0 6.3 0.0
20 8 10069 3.54 0 0.0 0.0 6.6 0.0
24 10 11874 3.92 0 0.0 0.0 7.0 0.0
28 12 14271 4.39 0 0.0 0.0 7.4 0.0
32 14 17229 4.92 0 0.0 0.0 7.9 0.0
36 16 20671 5.51 0 0.0 0.0 8.4 0.0
40 17 24480 6.11 3 2.6 4.7 8.9 0.0
44 17 27871 6.61 8 11.4 7.7 9.3 0.0
48 16 30107 6.93 9 18.8 9.1 9.6 0.0
52 15 31889 7.18 11 25.3 10.0 9.8 1.3
56 14 32913 7.32 13 29.2 10.5 9.9 3.2
Pond #3
60 12 33058 7.34 13 29.8 10.6 9.9 3.5
64 Il 32749 7.30 13 28.6 10.4 9.8 2.8
68 10 32281 7.24 12 26.8 10.2 9.8 1.9
72 8 31751 7.16 11 24.8 9.9 9.7 1.1
76 7 31180 7.08 10 22.6 9.6 9.7 0.4
80 7 30571 7.00 9 20.4 9.3 9.6 0.0
84 6 29927 6.91 9 18.1 9.0 9.6 0.0
88 5 29190 6.80 9 15.6 8.5 9.5 0.0
92 5 28396 6.69 8 13.0 8.0 9.4 0.0
96 4 27581 6.57 7 10.5 7.5 9.3 0.0
100 4 26772 6.45 7 8.2 6.9 9.2 0.0
104 3 25996 6.34 6 6.1 6.2 9.1 0.0
108 3 25303 6.23 4 4.4 5.6 9.0 0.0
112 3 24927 6.18 4 3.6 5.2 9.0 0.0
116 2 24676 6.14 3 3.0 4.9 9.0 0.0
120 2 24484 6.11 3 2.7 4.7 8.9 0.0
124 2 24324 6.08 2 2.3 4.5 8.9 OA
128 2 24185 6.06 2 2.1 4.4 8.9 0.0
132 1 24060 6.04 2 1.9 4.2 8.9 0.0
136 1 23946 6.03 2 1.7 4.0 8.9 0.0
140 1 23843 6.01 1 1.5 3.9 8.9 0.0
144 1 23747 5.99 1 1.3 3.7 8.9 0.0
148 1 23659 5.98 1 1.2 3.6 8.8 0.0
152 1 23578 5.97 1 1.1 3.5 8.8 0.0
156 1 23503 5.96 1 1.0 3.4 8.8 0.0
160 1 23433 5.95 1 0.9 3.2 8.8 0.0
164 1 23369 5.94 1 0.8 3.1 8.8 0.0
168 0 23310 5.93 1 0.7 3.0 8.8 0.0
172 0 23254 5.92 1 0.6 2.9 8.8 0.0
176 0 23203 5.91 1 0.6 2.8 8.8 0.0
180 0 23156 5.90 1 0.5 2.7 8.8 0.0
184 0 23112 5.90 0 0.5 2.6 8.8 0.0
188 0 23071 5.89 0 0.4 2.5 8.8 0.0
192 0 23034 5.88 0 0.4 2.5 8.8 0.0
196 0 22999 5.88 0 0.3 2.4 8.8 0.0
200 0 22966 5.87 0 0.3 2.3 8.8 0.0
204 0 22936 5.87 0 0.3 2.2 8.7 0.0
208 0 22908 5.86 0 0.2 2.1 8.7 0.0
212 0 22882 5.86 0 0.2 2.1 8.7 0.0
216 0 22858 5.86 0 0.2 2.0 8.7 0.0
220 0 22835 5.85 0 0.2 1.9 8.7 0.0
224 0 22814 5.85 0 0.2 1.9 8.7 0.0
228 0 22795 5.85 0 0.2 1.8 8.7 0.0
232 0 22777 5.84 0 0.1 1.8 8.7 0.0
236 0 22760 5.84 0 0.1 1.7 8.7 0.0
240 0 22745 5.84 0 0.1 1.7 8.7 0.0
244 0 22730 5.84 0 0.1 1.6 8.7 0.0
248 0 22716 5.83 0 0.1 1.6 8.7 0.0
252 0 22704 5.83 0 0.1 1.5 8.7 0.0
Temporary Sediment Trap.
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year Design Storm
OBJECTIVE: Design a Weir for Detention Pond Forebay
Determine the weir length, capacity & freeboard of the forebay
SOLUTION - Qp: Use the calculated Time of Concentration and the Rational Method to determine
the peak inflow from the design storm.
INPUT OUTPUT
L= ft
H= ft Tc = 10.00 minutes
I = 6.09 in/hr
A = 3.74 acres
C = 0.63 Qp = 14 cfs
SOLUTION - Lw: Use Trial & Error with Weir Length (Lw) & Driving Head (H) to make Qp <= Qw
INPUT OUTPUT
Cw = 3.00 Qp = 14.3 cfs
Lw = 6 ft. Qw = 18.00 cfs
H= 1 ft. Freeboard = 0.50 ft.
DIMENSIONS: A.disturb = 0.50 acres x 1800 cf / acre
S-Trap.H = 4.50 ft.
S-Trap.D = 3.00 ft. Volume = 900 cf
S-Trap.W = 25.00 ft. cf
S-Trap.L = 15.00 ft. Capacity = 1125 cf
TERMINOLOGY: Cw = Weir Coefficient L= Watershed Hydraulic Length, (ft)
Lw = Weir Length, (ft.) Hv = Watershed Vertical Relief, (ft)
H= Driving Head, (ft.) a= Statistical Rainfall Variable
Qp = Peak Inflow, (cfs) b= Statistical Rainfall Variable
Qw = Peak Discharge, (cfs) A= Watershed Area, (acres)
A.disturb = Disturbed Area, (acres) C= Rational Runoff Coefficient
Freeboard = Freeboard of Weir, (ft.) Tc = Time of Concentration
Cap.-R. = Required Trap Capacity, (cf) 1= Rainfall Intensity, (in./hr.)
Cap.-D. = Design Trap Capacity, (cf)
S-Trap.H = Sediment Trap Height, (ft.) S-Trap.W = Sediment Trap Width, (ft.)
S-Trap.D = Sediment Trap Depth, (ft.) S-Trap.L = Sediment Trap Length, (ft.)
REFERENCES: (DRINK, 1988; Malcom, 1991)
Anti-Flotation Calculations
Riser in Detention Pond #3
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Max. WSEL = 7.34 FT
Riser Invert = 0.00 FT
Riser Diameter = 18.0 INCHES
Riser Volume = 13.0 CF Riser Buoyancy = 809 LBS
Barrel Diameter = 12.0 INCHES
Barrel Length = 8.0 FT
Barrel Volume = 6.3 CF Barrel Buoyancy = 392 LBS
Slab Length = 4.00 FT
Slab Width = 4.00 FT
Slab Thickness = 1.50 FT Slab Buoyancy = 1498 LBS
Slab Volume = 24.0 CF Slab Weight = 3480 LBS
Unit Wt. of Water = 62.4 LBS/CF
it Wt. of Concrete = 145.0 LBS/CF Total Buoyancy = 2699 LBS
Total Weight = 3480 LBS
Factor of Safety = 1.29 (OK)
NOTE: Factor of Safety must be at least 1.1

Riprap Velocity Dissipator Pad
Outlet of Stormwater Pond No. 3
HUA No. DC9902 - 1000 Cell Close Security Prison
Anson County, NC
Design Storm: 10-year, 10-min.
BACKGROUND: Use the E&S Control Planning & Design Manual, Section 8.06.
At the outlet : flow is 9 cfs , V = 10.6 fps
REFERENCE: (NCDEHNR, 1993)
Step 1. Minimum Tailwater Condition
Step 2. D-o = 12 in.
D-o = 1 ft.
Q-10 = 9 cfs
d-50 = 0.5 ft.
L-a = 16 ft.
Step 3. 3*D-o = 3 ft.
W = 17 ft.
Step 4. d-max 0.75 ft.
d-max 9 in.
Step 5. Thickness = 0.8 ft.
Thickness = 9 in.
Figure 8.06 a
Figure 8.06 a
USE: 4 ft.
USE: 18 ft.
Maximum Stone Diameter (1.5*d-50)
USE: Class "1" Rip-Rap
Apron Thickness With Filter Fabric (1.5*d-50)
USE: 12 in.
TERMINOLOGY: Q10 = 10-Year Design Storm, Peak Discharge, (cfs)
D-o = Pipe Diameter, (in. & ft.)
d-50 = Mean Stone Diameter of Rip-Rap, (ft.)
L-a = Length of Rip-Rap Apron, (ft.)
3*D-o = Width of Rip-Rap Apron @ Pipe Outlet, (ft.)
W = Width of Rip-Rap Apron @ End of Apron, (ft.)
d-max = Maximum Stone Diameter of Rip-Rap, (ft. & in.)
Thickness = Thickness of Rip-Rap Apron With Filter Fabric, (ft. &in.)
Pond #1
Detention Basin Design
Determine Surface area and volume required
Drainage Area = 16.61 Acres
Impervious area = 7.07 Acres
% Impervious 42.56 %
From Table I.1 of NCDENR Stormwater Best Management Practices SA/DA = 1.80 %
For Depth = 3 feet Permanent Pool
Depth = 3 ft Required
Surface Area 13023.57 SF
BASIN DIMENSIONS
Length Width L/W Ratio Basin
165 55 3.00 :1 Surface Area 13359 SF
Sideslopes 3 :1
DETERMINE STAGE-STORAGE FUNCTION
S Z
CONTOUR INCR ACCUM
COMTOT M A R F A Vf)T T TMR VC)T.T TMR VTA nF.
Y x
In C In 7 7, est
FT S Q. FT CU. FT CU. FT FT FT
0 0 0
1 10431 5216 5216 1 8.55939024 0 0.97
2 11859 11145 16361 2 9.702625172 0.6931472 2.08
3 13359 12609 28970 3 10.27399883 1.0986123 3.06
4 14931 14145 43115 4 10.67161465 1.3862944 3.99
5 16575 15753 58868 5 10.98304443 1.6094379 4.92
6 18291 17433 76301 6 11.24243477 1.7917595 5.85
From Linear Regression Ks = 5482
b = 1.49
corr. = 0.99910167
Pond #1
Determine Volume to Be controlled by 1" storm
Calculate Rv
Rv = 0.05 + 0.009 * I
Volume to be treated
Volume = Rainfall * Rv * Drainage Area
Rainfall= 1 in
STAGE-STORAGE function
KS = 5482
b = 1.49
Set riser Z
Volume to drain
Orifice Required
Drawdown time
Say
Qo =
Rv =
V=
Say
V =
2-5 Days
Qreq.
3.5 Days
Cd =
Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
D (in) D (ft) Qo(cfs) Drawdown (days) Remark
2 0.17 0.1804 1.72 Too Fast
0.5 0.04 0.0113 27.49 Too Slow
1.5 0.13 0.1015 3.05 IOK
0.43 in/in
0.5994583 acre-ft
26112 cf
Z = 2.85083253
Z = 2.9
El (riser) = 5.9
26786 cf
0.0885789 cfs
0.6
Pond #1
Pipe to Drain Pond
Qo = Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
Riser Depth = 5.9 ft
Riser Depth Volume = 77180.667 cf
D (in) D (ft) Qo(cfs) Drawdown (hrs) Remark
6 0.50 1.62381 1 13.20 I OK
Determine Post Development and Pre Development Runoff Coefficients
Pre Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 0 0.00% 0.00%
Pastureland 0.3 18.43 100.00% 30.00%
Total: 18.43

Use C= 30%
Post Development
Use C Area (ac) % Area % * C

Pavemt/Bld 0.95 7.07 42.56% 40.44%
Turf 0.3 9.54 57.44% 17.23%
Total: 16.61

Use C= 58%
Pond #1
Determine Post Development and Pre Development Curve Number
Pre Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Open Space B 61 0.00
C 74 0.00
D 80 18.43 80.00
Streets & Roads 98 0.00
(Pavement & Buildings) 98 0.00
PD 98 0.00
98 0.00

D 98
98
Totals: 18.43 80.00
Use CN: 80
Post Development
Catchment No. 1
Land Use HSG CN _
Area Wt. CN
(ACRES)
Turf B 61 0.00
C 74 0.00
D 80 _
9.54 45.95
Streets & Roads B 98 0.00
C 98 _ 0.00
D 98 7.07 41.71
0.00

Totals: 16.61 87.66
Use CN: 88
Pond #1
Set Crest of Riser at Water Quality Stage
Set riser at water quality stage + Permanent Pool
Stage(WQ): 2.8508325 ft
Say 2.9 Riser Elevation
Compute Allowable Outflow:
Qpre= 34 cfs See "Peak Inflow" sheet
Qpost = 59 cfs 10 yr flood
Estimate Stormwater Storage Needed:
S = (Qpost - Qpre) * Tp *60 sec/min
If S is neg. (Qpre > Qpost)
S = 1.39 * Qpost * Tp
Determine Total Storage
Total Storage = Flood Storage + Water Quality
Total Storage =
Total Stage =
Configure Outlet
Select Riser by Orifice Equation
Cd =
li = ((0.159 * Q)/(Cd * D^2))^2
h is to Centerline of barrel
Cat nn Trial and Rrrnr tahla
Tp =
Tp =
94076 cf
6.74 ft
0.6
Z
D (inch) D (ft) h (ft) h + D/2 (ft)

15 1.25 33.25 33.88
24 2 5.07 6.07
18 1.5 16.04 16.79
S=
S=
S needed =
Qp =
5.9 ft
67290 cf
3679 cf
67290 cf
34 cfs
68.29 min.
44.86 min.
Try barrel = 18
Route to confirm Riser = 30
Pond #I
Forebay Required Volume
Total Storage = 94076 of ( Total Storage)
Fore Bay Volume = 20% Total Volume
Fore Bay Volume = 18815 of
Forebay Dimension
Try Len h Width
60 55
Area = (Length + (2 *Depth* Sideslope)) * (Width + (2 *Depth* Sideslopes)
Depth 4 ft
Area = 6636 sf
Sideslopes 3 :1
Volume = (Average Area*Depth)
Volume = 19872 CF
Sediment Storage
From "Sediment predictions in Eastern United States"
Malcom, H.R. and Smallwood, C., (1977)
Where:
(for Urbanized) V = 2.96 * A^0.67 V = Sed. Volume (acre-ft/year
A = Area (sq. miles)
V = 0.2563296 acre-ft/year
11166 cf/year
Cleanout interval 2 Years
Volume= 22331 cf
Total Volume Needed for Pond = (cleanout volume - (0.25 * Forebay volume)) = 17363 of
Pond #I
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L= ft
H = ft
Tc = 10.00 minutes
1 = 6.09 in/hr
Pre Development
SOLUTION - Tp:
TERMINOLOGY:
A = 18.43 acres
C = 0.30
INPUT

P = 4.97 in
CN = 80
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 34 cfs
OUTPUT
S = 2.50 in
Q* = 2.87 in
Tp = 68.29 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 34 CFS
Tp = 68.29 MINUTES
Pond #1
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L= ft
H= ft
Tc = 10.00 minutes
I = 6.09 in/hr
Post Development
SOLUTION - Tp:
A = 16.61 acres
C = 0.58
INPUT
P = 4.97 in
CN = 88
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 59 cfs
OUTPUT
S = 1.36 in
Q* = 3.64 in
Tp = 44.86 minutes
L = Hydraulic Length, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 59 CFS
11 Tp = 44.86 MINUTES
Pond #I
Peak Inflow
DESIGN STORM
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H= ft
Tc = 10.00 minutes
I = 7.30 in/hr
Pre Development
SOLUTION - Tp:
TERMINOLOGY:
A = 18.43 acres
C = 0.30
INPUT
P = 5.82 in
CN = 80
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 40 cfs
OUTPUT
S = 2.50 in
Q* = 3.62 in
Tp = 71.93 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 40 CFS?
Tp = 71.93 MINUTES

Pond #I
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H= ft
Te = 10.00 minutes
I = 7.30 in/hr
Post Development
SOLUTION - Tp:
P = 5.82 in
CN = 88
TERMINOLOGY:
A = 16.61 acres
C = 0.58
INPUT
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
1 = Rainfall Intensity, (in/hr)
Qp = 70 cfs
OUTPUT
S = 1.36 in
Q* = 4.45 in
Tp = 45.77 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 70 CFS
Tp = 45.77 MINUTES
Pond #I
Chainsaw Routing
(REF: Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 10-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 24 CFS Z.rsvr = 8.95 FT T-S.nrm = 78,583 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT WSA.max = 23,911 SQ-FT
FRBD.min = 1.30 FT V.s = 0.0 FPS T-S.max = 143,674 CU-FT
WSEL.nrm = 3.00 FT Q.s = 0 CPS WSA.nrm = 13,993 SQ-FT
SEL.max = 8.95 FT T-S.det = 50,409 CU-FT

INPUT
Qp = 59 CPS N.r = I Cw.s = 3.00
"I'p = 44.86 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :I
Ks = 5482
b = 1.49 D.r = 2.50 FT
EL.s = 9.00 FT
N.b = 1
EL.dam = 10.25 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 18 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT 1'T CPS CFS CFS CFS CFS
0 0 28174 S.UU U NIX 1141% IN/ IL UA)
4 1 28174 3.00 0.00 0.0 0.0 12.7 0.0
8 5 28450 3.02 0 0.0 0.0 12.8 0.0
12 10 29532 3.10 0 0.0 OA 13.0 0.0
16 17 31889 3.26 0 0.0 0.0 13.5 0.0
20 25 35887 3.53 0 0.0 0.0 14.2 0.0
24 33 41768 3.91 0 0.0 0.0 15.1 0.0
28 41 49625 4.39 0 0.0 0.0 16.2 0.0
32 48 59397 4.95 0 0.0 0.0 17.4 0.0
36 54 70875 5.57 0 0.0 0.0 18.7 0.0
40 57 83715 6.23 5 4.9 13.6 19.9 0.0
44 59 96286 6.84 21 23.8 23.0 21.0 0.0
48 58 105400 7.27 22 41.7 27.7 21.7 0.0
52 55 114183 7.67 22 61.2 31.5 22.4 0.0
56 50 122111 8.03 23 80.4 34.5 22.9 0.0
Pond #I
60 45 128724 8.32 23 97.3 36.7 23.4 0.0
64 40 133915 8.54 24 111.1 38.4 23.7 0.0
68 36 137843 8.71 24 121.9 39.6 24.0 0.0
72 32 140656 8.83 24 129.7 40.4 24.1 0.0
76 28 142490 8.90 24 134.8 40.9 24.3 0.0
80 25 143461 8.94 24 137.6 41.2 24.3 0.0
84 22 143674 8.95 24 138.2 41.3 24.3 0.0
88 20 143222 8.93 24 136.9 41.1 24.3 0.0
92 18 142187 8.89 24 134.0 40.9 24.2 0.0
96 16 140642 8.83 24 129.6 40.4 24.1 0.0
100 14 138653 8.74 24 124.1 39.8 24.0 0.0
104 13 136278 8.64 24 117.6 39.1 23.9 0.0
108 11 133568 8.53 24 110.2 38.3 23.7 0.0
112 10 130570 8.40 23 102.2 37.3 23.5 0.0
116 9 127325 8.26 23 93.7 36.3 23.3 0.0
120 8 123871 8.10 23 84.8 35.1 23.0 0.0
124 7 120240 7.94 23 75.7 33.8 22.8 0.0
128 6 116461 7.78 23 66.6 32.4 22.5 0.0
132 6 112562 7.60 22 57.4 30.8 22.2 0.0
136 5 108566 7.42 22 48.5 29.1 21.9 0.0
140 4 104495 7.23 22 39.8 27.2 21.6 0.0
144 4 100368 7.04 21 31.4 25.2 21.3 0.0
148 4 96202 6.84 21 23.6 22.9 21.0 0.0
152 3 92014 6.64 16 16.5 20.3 20.6 0.0
156 3 88816 6.48 12 11.5 18.0 20.3 0.0
160 2 86717 6.38 9 8.6 16.4 20.2 0.0
164 2 85246 6.31 7 6.7 15.1 20.0 0.0
168 2 84162 6.25 5 5.4 14.0 19.9 0.0
172 2 83330 6.21 5 4.5 13.2 19.9 0.0
176 2 82670 6.18 4 3.8 12.5 19.8 0.0
180 1 82131 6.15 3 3.3 11.8 19.7 0.0
184 1 81681 6.13 3 2.8 11.3 19.7 0.0
188 1 81298 6.11 2 2.5 10.8 19.7 0.0
192 1 80967 6.09 2 2.2 10.4 19.6 0.0
196 1 80676 6.08 2 1.9 10.0 19.6 0.0
200 1 80419 6.07 2 1.7 9.6 19.6 0.0
204 1 80189 6.05 2 1.6 9.3 19.6 0.0
208 1 79982 6.04 1 1.4 8.9 19.5 0.0
212 1 79794 6.03 1 1.3 8.6 19.5 0.0
216 0 79624 6.02 1 1.1 8.3 19.5 0.0
220 0 79467 6.02 1 1.0 8.1 19.5 0.0
224 0 79324 6.01 1 0.9 7.8 19.5 0.0
228 0 79192 6.00 1 0.9 7.6 19.5 0.0
232 0 79070 6.00 1 0.8 7.3 19.5 0.0
236 0 78958 5.99 1 0.7 7.1 19.4 0.0
240 0 78853 5.99 1 0.6 6.9 19.4 0.0
244 0 78756 5.98 1 0.6 6.7 19.4 0.0
248 0 78666 5.98 1 0.5 6.5 19.4 0.0
252 0 78583 5.97 0 0.5 6.3 19.4 0.0
Pond # I
Chainsaw Routing
(REF.• Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 25-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 37 CFS Z.rsvr = 9.71 FT T-S.nrm = 78,827 CU-FT
Q.pr = 12 CFS Z.s = 0.71 FT WSA.max = 24,876 SQ-FT
FRBD.min = 0.54 FT V.s = 2.4 FPS T-S.max = 162,042 CU-FT
WSEL.nrm = 3.00 FT Qs = 12 CFS WSA.nrm = 13,993 SQ-FT
SEL.max = 9.71 FT T-S.det = 50,653 CU-FT

INPUT
Qp = 70 CFS N.r = 1 Cw.s = 3.00
Tp = 45.77 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :I
Ks= 5482
b = 1.49 D.r = 2.50 FT
EL.s = 9.00 FT
N.b = I
EL.dam = 10.25 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 18 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CPS CFS CFS
0 0 28174 J.UU U NA NA NA U.U
4 1 28174 3.00 0.00 0.0 0.0 12.7 0.0
8 5 28489 3.02 0 0.0 0.0 12.8 0.0
12 11 29724 3.11 0 0.0 0.0 13.1 0.0
16 19 32415 3.30 0 0.0 0.0 13.6 0.0
20 28 36992 3.60 0 0.0 0.0 14.3 0.0
24 38 43739 4.03 0 0.0 0.0 15.4 0.0
28 47 52782 4.57 0 0.0 0.0 16.6 0.0
32 55 64070 5.21 0 0.0 0.0 17.9 0.0
36 62 77390 5.91 0 0.0 2.4 19.3 0.0
40 67 92364 6.66 17 17.0 20.5 20.6 0.0
44 70 104429 7.23 22 39.6 27.2 21.6 0.0
48 70 115978 7.75 22 65.4 32.2 22.5 0.0
52 67 127284 8.25 23 93.6 36.2 23.3 0.0
56 62 137742 8.70 24 121.6 39.6 24.0 0.0
Pond #I
60 55 146805 9.08 25 147.1 42.2 24.5 0.4
64 49 154093 9.38 29 168.4 44.1 25.0 4.2
68 44 158925 9.58 34 182.9 45.3 25.2 8.5
72 39 161391 9.68 37 190.4 45.9 25.4 11.2
76 35 162042 9.71 37 192.3 46.1 25.4 12.0
80 31 161486 9.68 37 190.7 46.0 25.4 11.3
84 28 160192 9.63 35 186.7 45.6 25.3 9.9
88 25 158459 9.56 33 181.5 45.2 25.2 8.0
92 22 156464 9.48 31 175.5 44.7 25.1 6.2
96 20 154304 9.39 29 169.1 44.1 25.0 4.4
100 18 152026 9.30 28 162.3 43.6 24.8 2.8
104 16 149648 9.20 26 155.4 42.9 24.7 1.5
108 14 147165 9.10 25 148.2 42.2 24.5 0.5
112 13 144550 8.99 24 140.7 41.5 24.4 0.0
116 11 141727 8.87 24 132.7 40.7 24.2 0.0
120 10 138620 8.74 24 124.0 39.8 24.0 0.0
124 9 135269 8.60 24 114.8 38.8 23.8 0.0
128 8 131711 8.45 24 105.2 37.7 23.6 0.0
132 7 127978 8.28 23 95.4 36.5 23.3 0.0
136 6 124098 8.11 23 85.4 35.2 23.1 0.0
140 6 120096 7.94 23 75.4 33.7 22.8 0.0
144 5 115997 7.76 22 65.5 32.2 22.5 0.0
148 5 111821 7.57 22 55.7 30.5 22.2 0.0
152 4 107588 7.37 22 46.3 28.7 21.9 0.0
156 4 103313 7.18 22 37.3 26.7 21.5 0.0
160 3 99012 6.97 21 28.8 24.5 21.2 0.0
164 3 94701 6.77 21 21.0 22.0 20.8 0.0
168 3 90391 6.56 14 13.9 19.2 20.5 0.0
172 2 87674 6.43 10 9.9 17.1 20.2 0.0
176 2 85847 6.34 7 7.5 15.6 20.1 0.0
180 2 84544 6.27 6 5.9 14.4 20.0 0.0
184 2 83572 6.22 5 4.8 13.4 19.9 0.0
188 1 82819 6.19 4 4.0 12.6 19.8 0.0
192 1 82219 6.16 3 3.4 11.9 19.8 0.0
196 1 81727 6.13 3 2.9 11.4 19.7 0.0
200 1 81315 6.11 2 2.5 10.8 19.7 0.0
204 1 80964 6.09 2 2.2 10.4 19.6 0.0
208 1 80661 6.08 2 1.9 9.9 19.6 0.0
212 1 80395 6.06 2 1.7 9.6 19.6 0.0
216 1 80160 6.05 2 1.5 9.2 19.6 0.0
220 1 79950 6.04 1 1.4 8.9 19.5 0.0
224 1 79761 6.03 1 1.2 8.6 19.5 0.0
228 0 79589 6.02 1 1.1 8.3 19.5 0.0
232 0 79434 6.02 1 1.0 8.0 19.5 0.0
236 0 79291 6.01 1 0.9 7.8 19.5 0.0
240 0 79161 6.00 1 0.8 7.5 19.5 0.0
244 0 79041 6.00 1 0.8 7.3 19.5 0.0
248 0 78930 5.99 1 0.7 7.1 19.4 0.0
252 0 78827 5.98 1 0.6 6.9 19.4 0.0
Temporary Sediment Trap.
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year Design Storm
OBJECTIVE: Design a Weir for Detention Pond Forebay
Determine the weir length, capacity & freeboard of the forebay
SOLUTION - Qp: Use the calculated Time of Concentration and the Rational Method to determine
the peak inflow from the design storm.
INPUT
L = ft
H= ft
Tc = 10.00 minutes
I = 6.09 in/hr
A = 16.61 acres
C = 0.58 Qp = 59 cfs
SOLUTION - Lw: Use Trial & Error with Weir Length (Lw) & Driving Head (H) to make Qp <= Qw
INPUT OUTPUT
Cw = 3.00
Lw = 20 ft.
H= 1 ft.
DIMENSIONS: A.disturb = 3.30 acres
TERMINOLOGY:
S-Trap.H = 5.50 ft.
S-Trap.D = 4.00 ft.
S-Trap. W = 55.00 ft.
S-Trap.L = 60.00 ft.
Cw = Weir Coefficient
Lw = Weir Length, (ft.)
H = Driving Head, (ft.)
Qp = Peak Inflow, (cfs)
Qw = Peak Discharge, (cfs)
A.disturb = Disturbed Area, (acres)
Freeboard = Freeboard of Weir, (ft.)
Cap.-R. = Required Trap Capacity, (cf)
Cap.-D. = Design Trap Capacity, (cf)
S-Trap.H = Sediment Trap Height, (ft.)
S-Trap.D = Sediment Trap Depth, (ft.)
REFERENCES: PEHNR, /988; Malcom, 1991)
OUTPUT
Qp = 58.7 cfs
Qw = 60.00 cfs
Freeboard = 0.50 ft.
X 1800 cf / acre
Volume = 5940 cf
cf
Capacity = 13200 cf
L = Watershed Hydrailic Length, (ft)
Hv = Watershed Vertical Relief, (ft)
a = Statistical Rainfall Variable
b = Statistical Rainfall Variable
A = Watershed Area, (acres)
C = Rational Runoff Coefficient
Tc = Time of Concentration
I = Rainfall Intensity, (in./hr.)
S-Trap.W = Sediment Trap Width, (ft.)
S-Trap.L = Sediment Trap Length, (ft.)
AMM\c:\exce1\a1an\C09501\Pondl 5/18/00 7:58 AM Page 17 of 16

Anti-Flotation Calculations
Riser in Detention Pond #1
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Max. WSEL = 9.71 FT
Riser Invert = 0.00 FT
Riser Diameter = 30.0 INCHES
Riser Volume = 47.7 CF Riser Buoyancy = 2974 LBS
Barrel Diameter = 18.0 INCHES
Barrel Length = 8.0 FT
Barrel Volume = 14.1 CF Barrel Buoyancy = 882 LBS
Slab Length = 5.50 FT
Slab Width = 5.50 FT
Slab Thickness = 2.00 FT Slab Buoyancy = 3775 LBS
Slab Volume = 60.5 CF Slab Weight = 8773 LBS
Unit Wt. of Water = 62.4 LBS/CF
it Wt. of Concrete = 145.0 LBS/CF Total Buoyancy = 7632 LBS
Total Weight = 8773 LBS
Factor of Safety = 1.15 (OK)
NOTE: Factor of Safety must be at least 1.1

Riprap Velocity Dissipator Pad
Outlet of Stormwater Pond No. I
HUA No. DC9902 -1000 Cell Close Security Prison
Anson County, NC
Design Storm: 10-year, 10-min.
BACKGROUND: Use the E&S Control Planning & Design Manual, Section 8.06.
At the outlet : flow is 24 cfs , V = 11.7 fps
REFERENCE: (NCDEHNR, 1993)
Step 1. Minimum Tailwater Condition
Step 2. D-o = 18 in.
D-o = 1.5 ft.
Q-10 = 24 cfs
d-50 = 0.8 ft.
L-a = 20 ft.
Step 3. 3*D-o = 4.5 ft.
W = 21.5 ft.
Step 4. d-max 1.2 ft.
d-max 14.4 in.
Step 5. Thickness = 1.2 ft.
Thickness = 14 in.
Figure 8.06 a
Figure 8.06 a
USE: 6 ft.
USE: 22 ft.
Maximum Stone Diameter (1.5*d-50)
USE: Class "2" Rip-Rap
Apron Thickness With Filter Fabric (1.5*d-50)
USE: 15 in.
TERMINOLOGY: Q10 = 10-Year Design Storm, Peak Discharge, (cfs)
D-o = Pipe Diameter, (in. & ft.)
d-50 = Mean Stone Diameter of Rip-Rap, (ft.)
L-a = Length of Rip-Rap Apron, (ft.)
3*D-o = Width of Rip-Rap Apron @ Pipe Outlet, (ft.)
W = Width of Rip-Rap Apron @ End of Apron, (ft.)
d-max = Maximum Stone Diameter of Rip-Rap, (ft. & in.)
Thickness = Thickness of Rip-Rap Apron With Filter Fabric, (ft. &in.)
HOBBS, UPCHURCH & ASSOCIATES, PA
Consulting Engineers
300 SW BROAD STREET
P.O. BOX 1737
SOUTHERN PINES, NC 28387/28388 \
PHONE: [phone] W\\
FAX: [phone]
To: Division of Water Quality - NC DENR
4401 Reedy Creek Road
Raleigh, NC 27607
LETTER OF TRANSMITTAL
Date: 1/9/01 Job No.: DC9902
Attn.: Mr. Todd St.John
Ref.: Stormwater Management Plans
1000 Cell Close Security Prison
NC DOC
,.: ;;`'Anson County Site
We are sending you
Attached
o Under separate cover VIA
The Following Item(s) :
D Shop Drawings D Prints ? Plans o Specifications
D Copy of Letters D Change Orders ? Forms & Calculations
Copies Date Item Description
1 set 12/13/00 prints Revised Drawings, sheets C.B.3, C.133A, C.B.313 and C.D3B -
indicating stormwater management ponds
1 1/2/01 4 pages Wet Detention Basin Supplement, Pond No. 1
1 set - 17 pages Pond No. 1 design calculations spreadsheets
1 1/2/01 4 pages Wet Detention Basin Supplement, Pond No. 2
1 set - 17 pages Pond No. 2 design calculations spreadsheets
1 1/2/01 4 pages Wet Detention Basin Supplement, Pond No. 3
1 set - 17 pages Pond No. 3 design calculations spreadsheets

These are Transmitted as Checked Below :
For Approval N E T k
For Your Use
o As Requested
O For Review and Comment
o For Bids Due
o xcepL on a en
Correct As Noted
Revise and Resubmit
Remarks:
Copy To:
Resubmit for Approval
Submit for Distribution
Return Corrected Prints
Prints Returned After Loan to Us
Submitting for stormwater management plan approval due to wetlands impacts.
Mr. Jim Gates, NC DOC
Ms Jennifer Pownall, Law
Signed: co Charles D. (Chuck) Heiser, PE
Maintenance activities shall be performed as follows:
1. After every significant runoff producing rainfall event and at least monthly:
a. Inspect the wet detention basin system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of the temporary pool occurs within
2 to 5 days as designed.
2. Repair eroded areas immediately, re-seed as necessary to maintain good vegetative cover, mow vegetative
cover to maintain a maximum height of six inches, and remove trash as needed.
3. Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to maintain
proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed of
in an appropriate manner and shall be handled in a manner that will not adversely impact water quality (i.e.
stockpiling near a wet detention basin or stream, etc.).
The measuring device used to determine the sediment elevation shall be such that it will give an accurate
depth reading and not readily penetrate into accumulated sediments.
When the permanent pool depth reads Z•?-7 feet in the main pond, the sediment shall be removed.
When the permanent pool depth reads 3,0 feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
(fill in the blanks)
Permanent Pool Elevation Zggr O
Sediment Re oval El. ? ??•s ? 75 0
Sediment Removal Elevation L9 5-' 75- 75%
-----
Bottom Ele ation 4q, S % --------------------------------------------- f-
Bottom Elevation Z9 , 0 25%
FOREBAY
MAIN POND
5. Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and forebay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment through
the emergency drain shall be minimized to the maximum extent practical.
Form SWU-102 Rev 3.99 Pagc 3 of 4
7. All components of the wet detention basin system shall be maintained in good working order.
I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print name: e'10;11;n ' W. ?5?o?n??
Title: &'q e, foR d 4? b? , •? e,-x11 g
Address:.---/ oAlA Cluo%?, 4:y f cP Cn"c°c ud '1:2/G C. /?.NC 276f-9-%?16
Phone: [phone],00
Signature: n.
Date: ?a.V . -? , ,?CO/
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and a
resident of the subdivision has been named the president.
I, Vq_r? iC, \?/- . ? 11:OQQ , a Notary Public for the State of
County of D C , do hereby certify that ?l I l i 0.1 t) . ?-_hc> U C'J
personally appeared before me this _ day of -SQ J OD , and acknowledge the due
execution of the forgoing wet detention basin maintenance requirements. Witness my hand and official seal,
SEAL
My commission expires q ^,S - ON--AD ?
Form SWU-102 Rev 3.99 Page 4 of 4

Pond #2
ern.
Detention Basin Design
Determine Surface area and volume required
Drainage Area = 3.93 Acres
Impervious area = 2.91 Acres
% Impervious
74.05 %
From Table I.1 of NCDENR Stormwater Best Management Practices SA/DA = 3.00 %
For Depth = 3 feet Permanent Pool
Depth = 3 ft
BASIN DIMENSIONS
Length Width L/W Ratio
100 30 3.33 :1
Sideslopes 3 :1
DETERMINE STAGE-STORAGE FUNCTION
S Z
CONTOUR INCR ACCUM
.nr. crnr rr7 A-0 Wni iTNAT QTAr.P
Required
Surface Area 5135.72 SF
Basin
Surface Area 5664 SF
y x
In C In Z Z est
FT SQ. FT CU. FT CU. FT FT FT
0 0 0
1 3816 1908 1908 1 7.553810852 0 0.98
2 4704 4260 6168 2 8.727129915 0.6931472 2.06
3 5664 5184 11352 3 9.337149219 1.0986123 3.03
4 6696 6180 17532 4 9.771783062 1.3862944 3.99
5 7800 7248 24780 5 10.11779216 1.6094379 4.97
6 8976 8388 33168 6 10.40934083 1.7917595 5.98
From Linear Regression Ks = 1968
b = 1.58
corr. = 0.999675148
Pond #2
Determine Volume to Be controlled by 1" storm
Calculate Rv
Rv = 0.05 + 0.009 * I
Volume to be treated
Volume = Rainfall * Rv * Drainage Area
Rainfall= 1 in
STAGE-STORAGE function
KS = 1968
b = 1.58
Set riser Z
Volume to drain
Orifice Required
Drawdown time
Say
Qo =
Rv =
V =
Say
V =
2-5 Days
Qreq.
3.5 Days
Cd =
Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
D (in) D (ft) Qo(cfs) Drawdown (days) Remark
2 0.17 0.1804 0.68 Too Fast
0.5 0.04 0.0113 10.86 Too Slow
1 0.08 0.0451 2.72 OK
0.72 in/in
0.234625 acre-ft
10220 cf
Z = 2.83666642
Z = 2.9
El (riser) = 5.9
10583 of
0.0349971 efs
0.6
Pond #2
Pipe to Drain Pond
Qo = Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
Riser Depth = 5.9 ft
Riser Depth Volume = 32506.579 cf
D (in) D (ft) Qo(cfs) Drawdown (hrs) Remark
4 0.33 0.72_ 12.51 OK
Determine Post Development and Pre Development Runoff Coefficients
Pre Development
Use C Area (ac) % Area % * C

Pavemt/Bld 0.95 0 0.00% 0.00%
Pastureland 0.3 4.5 100.00% 30.00%
Total: 4.5

Use C= 30%
Post Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 2.54 64.63% 61.40%
Turf 0.3 1.39 35.37% 10.61%
Total: 3.93

Use C= 72%
Pond #2
Determine Post Development and Pre Development Curve Number
Prc Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Open Space B 61 0.00
C 74 0.00
D 80 4.50 80.00
Streets & Roads B 98 0.00
(Pavement & Buildings) C 98 0.00
D 98 0.00
B 98 0.00
C
D 98
98
Totals: 4.50 80.00
Use CN: 80
Post Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Turf B 61 0.00
C 74 0.00
D 80 1.39 28.30
Streets & Roads B 98 0.00
C 98 0.00
D 98 2.54 63.34
0.00

Totals: 3.93 91.63
Use CN: 92
4
Pond #2
Set Crest of Riser at Water Quality Stage
Set riser at water quality stage + Permanent Pool
Stage(WQ): 2.8366664 ft
Say 2.9 Riser Elevation:
Compute Allowable Outflow:
Qpre= 10 cfs See "Peak Inflow" sheet
Qpost = 17 cfs 10 yr flood
Estimate Stormwater Storage Needed:
S = (Qpost - Qpre) * Tp *60 sec/min
S=
If S is neg. (Qpre > Qpost)
S = 1.39 * Qpost * Tp
Determine Total Storage
Total Storage = Flood Storage + Water Quality
Total Storage =
Total Stage =
Configure Outlet
Select Riser by Orifice Equation
Cd =
1i _ ((0.159 * Q)/(Cd * D^2))^2
h is to Centerline of barrel
CPt nn Trial and F.rror tahle
S=
S needed =
Qp =
27509 cf
5.31 ft
0.6
Z
D (inch) D (ft) h (ft) h + D/2 (ft)

15 1.25 2.88 3.50
24 2 0.44 1.44
12 1 7.02 7.52
Route to confirm
Tp =
Tp =
5.9 ft
16926 cf
952 cf
16926 cf
10 cfs
Try barrel =
Riser =
57.61 min.
40.3 min.
12
18
Pond #2
Forebay Required Volume
Total Storage = 27509 cf ( Total Storage)
Fore Bay Volume = 20% Total Volume
Fore Bay Volume = 5502 of
Forebay Dimension
Try Length Width
40 30
Area = (Length + (2 *Depth* Sideslope)) *(Width + (2 *Depth* Sideslopes)
Depth 3 ft
Area = 2784 sf
Sideslopes 3 :1
Volume = (Average Area*Depth)
Volume = 5976 CF
Sediment Storage
From "Sediment predictions in Eastern United States"
Malcom, H.R. and Smallwood, C., (1977)
Where:
(for Urbanized) V = 2.96 * A^0.67 V = Sod. Volume (acre-ft/year
A = Area (sq. miles)
V = 0.0975875 acre-ft/year
4251 cf/year
Cleanout interval 2 Years
Volume= 8502 cf
Total Volume Needed for Pond = (ceanout volume - (0.25 * Forebay volume)) = 7008 cf
Pond #2
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H= ft
Tc = 5.00 minutes
I = 7.22 in/hr
Pre Development
SOLUTION - Tp:
A = 4.5 acres
C = 0.30
INPUT
P = 4.97 in
CN = 80
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 10 cfs
OUTPUT
S = 2.50 in
Q* = 2.87 in
Tp = 57.61 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 10 CFS
11 Tp = 57.61 MINUTES
Pond #2
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 10-Year, 24-Hour Depth; 10-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT
L= R
H = ft
OUTPUT
Tc = 10.00 minutes
I = 6.09 in/hr
Post Development
SOLUTION - Tp:
A = _ 3.93 acres
C = 0.72
INPUT
P = 4.97 in
CN = 92
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 17 cfs
OUTPUT
S = 0.87 in
Q* = 4.06 in
Tp = 40.30 minutes
L = Hydraulic Length, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: ? Qp = 17 CFS
11 Tp = 40.30 MINUTES
Pond #2
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L= ft
H= ft
Tc = 5.00 minutes
I = 8.24 in/hr
Pre Development
SOLUTION - Tp:
A = 4.5 acres
C = 0.30
INPUT
P = 5.82 in
CN = 80
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 11 cfs
OUTPUT
S = 2.50 in
Q* = 3.62 in
Tp = 63.72 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 11 CFS
Tp = 63.72 MINUTES
Pond #2
Peak Inflow
DESIGN STORM
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L= ft
H = ft
Te = 10.00 minutes
1 = 7.30 in/hr
Post Development
SOLUTION - Tp:
TERMINOLOGY:
A = 3.93 acres
C = 0.72
INPUT
P = 5.82 in
CN = 92
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 21 cfs
OUTPUT
S = 0.87 in
Q* = 4.89 in
Tp = 40.52 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 21 CFS
11 Tp = 40.52 MINUTES
Pond #2
Chainsaw Routing
(REF: Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 10-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 9 CFS Z.rsvr = 7.00 FT T-S.nrm = 32,772 CU-1'T
Q.pr = 0 CFS Z.s = 0.00 FT WSA.max = 9,613 SQ-F-r
FRBD.min = 1.00 FT V.s = 0.1 FPS T-S.max = 42,592 CU-F-r
WSEL.nrm = 3.00 FT Q.s = 0 CPS WSA.nrm = 5,880 SQ-FT
SEL.max = 7.00 FT T-S.det = 21,607 CU-FT

INPUT
Qp = 17 CFS N.r = 1 Cw.s = 3.00
Tp = 40.30 MIN Cw.r = 3.30 CLs = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :I
Ks = 1968
b = 1.58 D.r = 1.50 FT
EL.s = 7.00 FT
N.b = I
EL.dam = 8.00 FT Cd.b = 0.60 EL.r = 5.90 F"r
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
'l'ime
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CPS CU-FT FT CFS CPS CFS CFS CPS
0 0 11165 3.0U U INA INA INA v.v
4 0 11165 3.00 0.00 0.0 0.0 6.0 0.0
8 2 11263 3.02 0 0.0 0.0 6.0 0.0
12 3 11647 3.08 0 0.0 0.0 6.1 0.0
16 6 12477 3.22 0 0.0 0.0 6.2 0.0
20 8 13868 3.44 0 0.0 0.0 6.5 0.0
24 11 15884 3.75 0 0.0 0.0 6.8 0.0
28 13 18527 4.13 0 0.0 0.0 7.2 0.0
32 15 21739 4.57 0 0.0 0.0 7.6 0.0
36 17 25407 5.05 0 0.0 0.0 8.1 0.0
40 17 29374 5.53 0 0.0 0.0 8.5 0.0
44 17 33453 6.01 1 0.6 2.8 8.9 0.0
48 16 37316 6.44 6 6.1 6.2 9.2 0.0
52 14 39566 6.68 8 10.7 7.5 9.4 0.0
56 12 41070 6.84 8 14.2 8.3 9.5 0.0
Pond #2
60 11 41998 6.94 9 16.5 8.7 9.6 0.0
64 9 42474 6.99 9 17.6 8.9 9.6 0.0
68 8 42592 7.00 9 17.9 8.9 9.6 0.0
72 7 42425 6.98 9 17.5 8.9 9.6 0.0
76 6 42037 6.94 9 16.5 8.7 9.6 0.0
80 6 41478 6.88 8 15.2 8.4 9.5 0.0
84 5 40794 6.81 8 13.5 8.1 9.5 0.0
88 4 40024 6.73 8 11.8 7.7 9.4 0.0
92 4 39200 6.64 7 9.9 7.3 9.4 0.0
96 3 38352 6.55 7 8.2 6.9 9.3 0.0
100 3 37505 6.46 6 6.5 6.4 9.2 0.0
104 3 36683 6.37 5 5.0 5.8 9.1 0.0
108 2 36103 6.31 4 4.0 5.4 9.1 0.0
112 2 35684 6.26 3 3.3 5.1 9.1 0.0
116 2 35360 6.22 3 2.8 4.8 9.0 0.0
120 2 35096 6.19 2 2.5 4.6 9.0 0.0
124 1 34873 6.17 2 2.2 4.4 9.0 0.0
128 1 34679 6.15 2 1.9 4.2 9.0 0.0
132 1 34507 6.13 2 1.7 4.1 9.0 0.0
136 1 34353 6.11 1 1.5 3.9 8.9 0.0
140 1 34215 6.09 1 1.3 3.7 8.9 0.0
144 1 34089 6.08 1 1.2 3.6 8.9 0.0
148 1 33973 6.07 1 1.1 3.5 8.9 0.0
152 1 33868 6.06 1 1.0 3.4 8.9 0.0
156 0 33771 6.04 1 0.9 3.2 8.9 0.0
160 0 33683 6.03 1 0.8 3.1 8.9 0.0
164 0 33601 6.02 1 0.7 3.0 8.9 0.0
168 0 33525 6.02 1 0.6 2.9 8.9 0.0
172 0 33456 6.01 1 0.6 2.8 8.9 0.0
176 0 33391 6.00 0 0.5 2.7 8.9 0.0
180 0 33332 5.99 0 0.5 2.6 8.9 0.0
184 0 33277 5.99 0 0.4 2.5 8.8 0.0
188 0 33226 5.98 0 0.4 2.4 8.8 0.0
192 0 33179 5.98 0 0.3 2.4 8.8 0.0
196 0 33136 5.97 0 0.3 2.3 8.8 0.0
200 0 33095 5.97 0 0.3 2.2 8.8 0.0
204 0 33058 5.96 0 0.2 2.1 8.8 0.0
208 0 33023 5.96 0 0.2 2.1 8.8 0.0
212 0 32991 5.96 0 0.2 2.0 8.8 0.0
216 0 32961 5.95 0 0.2 1.9 8.8 0.0
220 0 32934 5.95 0 0.2 1.9 8.8 0.0
224 0 32908 5.95 0 0.2 1.8 8.8 0.0
228 0 32884 5.94 0 0.1 1.8 8.8 0.0
232 0 32862 5.94 0 0.1 1.7 8.8 0.0
236 0 32841 5.94 0 0.1 1.7 8.8 0.0
240 0 32822 5.94 0 0.1 1.6 8.8 0.0
244 0 32804 5.93 0 0.1 1.6 8.8 0.0
248 0 32787 5.93 0 0.1 1.5 8.8 0.0
252 0 32772 5.93 0 0.1 1.5 8.8 0.0
Pond #2
Chainsaw Routing
(REF: Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 25-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = I I CFS Z.rsvr = 7.60 FT T-S.nrm = 32,803 CU-FT
Q.pr = 0 CFS Z.s = 0.10 FT WSA.max = 10,082 SQ-FT
FRBD.min = 0.90 FT V.s = 0.9 FPS T-S.max = 48,489 CU-FT
WSEL.nrm = 3.00 FT Q.s = 0 CFS WSA.nrm = 5,880 SQ-FT
SEL.max = 7.60 FT T-S.det = 21,638 CU-FT

INPUT
Qp = 21 CFS N.r = I Cw.s = 3.00
Tp = 40.52 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :I
Ks = 1968
b = 1.58 D.r = 1.50 FT
EL.s = 7.50 FT
N.b = I
El-dam = 8.50 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.90 FT
OUTPUT
A 13 C D E 1' G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
Os
MIN CPS CU-FT FT CFS CFS CFS CPS CPS
0 0 11165 S.UU U NA ANA INA v.v
4 1 11165 3.00 0.00 0.0 0.0 6.0 0.0
8 2 11285 3.02 0 0.0 0.0 6.0 0.0
12 4 11755 3.10 0 0.0 0.0 6.1 0.0
16 7 12769 3.27 0 0.0 0.0 6.3 0.0
20 10 14472 3.54 0 0.0 0.0 6.6 0.0
24 14 16941 3.91 0 0.0 0.0 7.0 0.0
28 16 20181 4.36 0 0.0 0.0 7.4 0.0
32 19 24124 4.89 0 0.0 0.0 7.9 0.0
36 20 28634 5.44 0 0.0 0.0 8.4 0.0
40 21 33521 6.02 1 0.6 2.9 8.9 0.0
44 21 38412 6.56 7 8.3 6.9 9.3 0.0
48 19 41706 6.91 9 15.7 8.5 9.6 0.0
52 17 44285 7.18 10 22.4 9.6 9.8 0.0
56 15 46104 7.36 10 27.4 10.3 9.9 0.0
Pond #2
60 13 47359 7.49 10 31.1 10.7 10.0 0.0
64 12 48154 7.57 10 33.4 11.0 10.0 0.3
68 10 48489 7.60 11 34.4 11.1 10.1 0.5
72 9 48425 7.59 10 34.2 11.1 10.1 0.4
76 8 48077 7.56 10 33.2 11.0 10.0 0.2
80 7 47527 7.50 10 31.6 10.8 10.0 0.0
84 6 46808 7.43 10 29.5 10.5 9.9 0.0
88 5 45899 7.34 10 26.9 10.2 9.9 0.0
92 5 44829 7.23 10 23.9 9.8 9.8 0.0
96 4 43621 7.11 9 20.6 9.3 9.7 0.0
100 4 42384 6.98 9 17.4 8.8 9.6 0.0
104 3 41148 6.85 8 14.4 8.3 9.5 0.0
108 3 39937 6.72 8 11.6 7.7 9.4 0.0
112 3 38772 6.60 7 9.0 7.1 9.3 0.0
116 2 37670 6.48 6 6.8 6.5 9.2 0.0
120 2 36649 6.37 5 4.9 5.8 9.1 0.0
124 2 35931 6.29 4 3.7 5.3 9.1 0.0
128 2 35445 6.23 3 3.0 4.9 9.0 0.0
132 1 35091 6.19 2 2.5 4.6 9.0 0.0
136 1 34817 6.16 2 2.1 4.4 9.0 0.0
140 1 34595 6.14 2 1.8 4.1 9.0 0.0
144 1 34409 6.12 2 1.6 4.0 8.9 0.0
148 1 34250 6.10 1 1.4 3.8 8.9 0.0
152 1 34110 6.08 1 1.2 3.6 8.9 0.0
156 1 33986 6.07 1 1.1 3.5 8.9 0.0
160 1 33874 6.06 1 1.0 3.4 8.9 0.0
164 0 33774 6.04 1 0.9 3.2 8.9 0.0
168 0 33682 6.03 1 0.8 3.1 8.9 0.0
172 0 33599 6.02 1 0.7 3.0 8.9 0.0
176 0 33522 6.02 1 0.6 2.9 8.9 0.0
180 0 33452 6.01 1 0.6 2.8 8.9 0.0
184 0 33387 6.00 0 0.5 2.7 8.9 0.0
188 0 33328 5.99 0 0.4 2.6 8.8 0.0
192 0 33273 5.99 0 0.4 2.5 8.8 0.0
196 0 33222 5.98 0 0.4 2.4 8.8 0.0
200 0 33176 5.98 0 0.3 2.4 8.8 0.0
204 0 33132 5.97 0 0.3 2.3 8.8 0.0
208 0 33092 5.97 0 0.3 2.2 8.8 0.0
212 0 33055 5.96 0 0.2 2.1 8.8 0.0
216 0 33021 5.96 0 0.2 2.1 8.8 0.0
220 0 32989 5.96 0 0.2 2.0 8.8 0.0
224 0 32959 5.95 0 0.2 1.9 8.8 0.0
228 0 32932 5.95 0 0.2 1.9 8.8 0.0
232 0 32906 5.95 0 0.2 1.8 8.8 0.0
236 0 32882 5.94 0 0.1 1.8 8.8 0.0
240 0 32860 5.94 0 0.1 1.7 8.8 0.0
244 0 32840 5.94 0 0.1 1.7 8.8 0.0
248 0 32821 5.94 0 0.1 1.6 8.8 0.0
252 0 32803 5.93 0 0.1 1.6 8.8 0.0

Temporary Sediment Trap.
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year Design Storm
OBJECTIVE: Design a Weir for Detention Pond Forebay
Determine the weir length, capacity & freeboard of the forebay
SOLUTION - Qp: Use the calculated Time of Concentration and the Rational Method to determine
the peak inflow from the design storm.
INPUT
L= A
H= ft
Tc = 10.00 minutes
I = 6.09 in/hr
A = 3.93 acres
C = 0.72 Qp = 17 cfs
SOLUTION - Lw: Use Trial & Error with Weir Length (Lw) & Driving Head (H) to make Qp <= Qw
INPUT OUTPUT
Cw = 3.00
Lw = 15 ft.
H = 1 ft.
DIMENSIONS:
TERMINOLOGY:
A.disturb = 3.93 acres
S-Trap.H = 4.50 ft.
S-Trap.D = 3.00 ft.
S-Trap.W = 30.00 ft.
S-Trap.L = 40.00 ft.
Cw = Weir Coefficient
Lw = Weir Length, (ft.)
H = Driving Head, (ft.)
Qp = Peak Inflow, (cfs)
Qw = Peak Discharge, (cfs)
A.disturb = Disturbed Area, (acres)
Freeboard = Freeboard of Weir, (ft.)
Cap.-R. = Required Trap Capacity, (cf)
Cap.-D. = Design Trap Capacity, (cf)
S-Trap.H = Sediment Trap Height, (ft.)
S-Trap.D = Sediment Trap Depth, (ft.)
OUTPUT
Qp = 17.2 cfs
Qw = 45.00 cfs
Freeboard = 0.50 ft.
X 1800 cf / acre
Volume = 7074 cf
cf
Capacity = 3600 cf
L = Watershed Hydrailic Length, (ft)
Hv = Watershed Vertical Relief, (ft)
a = Statistical Rainfall Variable
b = Statistical Rainfall Variable
A = Watershed Area, (acres)
C = Rational Runoff Coefficient
Tc = Time of Concentration
I = Rainfall Intensity, (in./hr.)
S-Trap.W = Sediment Trap Width, (ft.)
S-Trap.L = Sediment Trap Length, (ft.)
REFERENCES: PEHNR, 1988; Malcom, /991)

Anti-Flotation Calculations
Riser in Detention Pond #2
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Max. WSEL = 7.60 FT
Riser Invert = 0.00 FT
Riser Diameter = 18.0 INCHES
Riser Volume = 13.4 CF Riser Buoyancy = 838 LBS
Barrel Diameter = 12.0 INCHES
Barrel Length = 8.0 FT
Barrel Volume = 6.3 CF Barrel Buoyancy = 392 LBS
Slab Length = 4.00 FT
Slab Width = 4.00 FT
Slab Thickness = 1.50 FT Slab Buoyancy = 1498 LBS
Slab Volume = 24.0 CF Slab Weight = 3480 LBS
Unit Wt. of Water = 62.4 LBS/CF
it Wt. of Concrete = 145.0 LBS/CF Total Buoyancy = 2728 LBS
Total Weight = 3480 LBS
Factor of Safety = 1.28 (O1)
NOTE: Factor of Safety must be at least 1.1

Riprap Velocity Dissipator Pad
Outlet of Stormwater Pond No. 2
HUA No. DC9902 -1000 Cell Close Security Prison
Anson County, NC
Design Storm: 10-year, 10-min.
BACKGROUND: Use the E&S Control Planning & Design Manual, Section 8.06.
At the outlet : flow is 9 cfs , V = 10.6 fps
REFERENCE: (NCDEHNR, 1993)
Step 1. Minimum Tailwater Condition
Step 2. D-o = 12 in.
D-o = 1 ft.
Q-10 = 9 cfs
d-50 = 0.5 ft.
Ira = 16 ft.
Step 3. 3*D-o = 3 ft.
W = 17 ft.
Step 4. d-max 0.75 ft.
d-max 9 in.
Step 5. Thickness = 0.8 ft.
Thickness = 9 in.
Figure 8.06 a
Figure 8.06 a
USE: 4 ft.
USE: 18 ft.
Maximum Stone Diameter (1.5*d-50)
USE: Class "1" Rip-Rap
Apron Thickness With Filter Fabric (1.5*d-50)
USE: 12 in.
TERMINOLOGY: Q10 = 10-Year Design Storm, Peak Discharge, (cfs)
D-o = Pipe Diameter, (in. & ft.)
d-50 = Mean Stone Diameter of Rip-Rap, (ft.)
L-a = Length of Rip-Rap Apron, (ft.)
3*D-o = Width of Rip-Rap Apron @ Pipe Outlet, (ft.)
W = Width of Rip-Rap Apron @ End of Apron, (ft.)
d-max = Maximum Stone Diameter of Rip-Rap, (ft. & in.)
Thickness = Thickness of Rip-Rap Apron With Filter Fabric, (ft. &in.)