20090992 Ver 1_More Info Received_20091214

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NCDER&
North Carolina Department of Environment and Natural Resource. V
Division of Water Quality 'gh4sl ?i9?.9
Beverly Eaves Perdue Coleen N. Sullins `bee Freeman
Governor Director Secretary
October 23, 2009
DWQ Project # 2009-0992
Wake County
CERTIFIED MAIL: RETURN RECEIPT REQUESTED
Wimbledon Homeowners Association Inc
Attn: Mr. Benjamin Shiver
PO Box 8005
Cary, NC 27512
Subject Property: Agassi Court Drainage Rehabilitation Project, Cary
Long Branch [030402, 27-43-2.8, WSIII, NSW]
REQUEST FOR MORE INFORMATION
Dear Mr. Shiver:
On September 16, 2009, the Division of Water Quality (DWQ) received your application dated
September 8, 2009 to impact 600 square feet (ft2) of Zone 1 protected riparian buffers and 400 square
feet (ft2) of Zone 2 protected riparian buffers to construct the proposed drainage improvements at the site.
The DWQ has determined that your application was incomplete and/or provided inaccurate information
as discussed below. The DWQ will require additional information in order to process your application to
impact protected wetlands and/or streams on the subject property. Therefore, unless we receive five
copies of the additional information requested below, we will place this project on hold as incomplete
until we receive this additional information. If we do not receive the requested information, your project
will be formally returned as incomplete. Please provide the following information so that we may
continue to review your project.
Additional Information Requested:
1. Please provide full-sized site plans showing the entire site in detail at a F'= 20' or larger scale.
2. Please provide an aerial photo or other detailed depiction of the entire drainage area contributing
to the drainage problems at this site.
Per the requirements of the Neuse Riparian Buffer Rule, any new stormwater discharges to the
buffered pond must be discharged through a correctly designed level spreader. Level spreader
design requirements are set forth in Chapter 8 of the North Carolina Stormwater BMP Manual,
available at: http://h2o.eiir.state.nc u5isu/bmp forms 11011. For any proposed level spreaders,
please provide a Level Spreader Supplement Form (available at the same web site) with all
required items.
4. Please provide the calculations to support pipe sizing as well as calculations of the discharge
velocities for the peak flow from the 10-year storm. Any discharges to natural areas must be at
non-erosive velocities for the 10-year storm.
401 Oversight/Express Review Permitting Unit
1650 Mail Service Center, Raleigh, North Carolina 27699.1650
Location: 2321 Crabtree Blvd„ Raleigh, North Carolina 27604
Phone: [phone]', FAX: [phone]
Internet: hftp:flh2o.enr.state.nc.us/ncwetlands/
One
NorthCarolina
,'Vatumlzy
An Equal Opportunity'.. Affirmative Ac6en Employer
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•
December 2, 2009
NC DENR-DWQ
Wetlands and Stormwater Branch
Attn: Cyndi Karoly
401 Oversight/Express Permitting Unit
1650 Mail Service Center
Raleigh, North Carolina 27699-1650
Subject Property: Agassi Court Drainaeg Rehabilitation Project, Cary
DWQ Project # 2009-0992
Long Branch [030402, 27-43-2.8, WSIII, NSW]
Dear Ms. Karoly,
ENGINEERING DEPARTMENT
I was asked to provide additional information for my buffer authorization request for the Agassi
Court Drainage Project. Below (or attached as specified) are my responses to this request. Please
let me know if you need additional information or clarification to these responses.
1. Please provide full-sized site plans showing the entire site in detail at a 1"=20' or larger
scale.
See attached plan sheets provided
2. Please provide an aerial photo or other detailed depiction of the entire drainage area
contributing to the drainage problems at this site.
Aerial photos of the pond drainage area and the drainage area contributing to the pipe
network are provided is this response package.
3. Per the requirements of the Neuse Buffer Rule, any new stormwater discharges to the
buffered pond must discharge through a correctly designed level spreader. Level spreader
design requirements are set forth in chapter 8 of the North Carolina Stormwater BMP
Manual. For any proposed level spreaders. Please provide a Level Spreader Supplement
Form with all of the required items.
See Buffer Variance request and justification attached.
TOWN Of CARY
316 North Academy Street -Cary, NC 27513-PO Box 8005-Cary, NC 27512-8005
• tel [phone] • fax [phone]• www.townofcary.org
4. Please provide calculations to support pipe sizing as well as calculations of the discharge
velocities for the peak flow from the 10-year storm. Any discharges to natural areas must
be at a non-erosive velocities for the 10-year storm.
See attached Hydraulics report.
5. One data CD of full size plans in TIFF Group 4 format (black and white, not greayscale
or color).
Data CD is provided is this response package.
Thank you for your time in reviewing this submittal and have a great Christmas holiday.
Sincerely
1
RDan Clinton, PE
Town of Cary Stormwater Engineering
0
•
•
Agassi Drive Drainage Improvements
Hydraulic Report & Justification
Documentation
Prepared by: Dan Clinton, PE
Town of Cary
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Table of Contents
• Introduction
Methodology
Peak Discharge Analysis
Drainage Analysis
Pond
Cul-de-sac
Storm Drainage Pipe Alignment Alternative Analysis
Rip-Rap Dissipater Sizing
Justification for Storm Drainage Pipe Location
Summary
Supporting Documentation
Tab 1 - GIS Maps of Both Drainages
Tab 2 - Peak Discharge Calculations
Tab 3 - Drainage Analysis Calculations & Graphs
Tab 4 - Rip- Rap Dissipater Sizing Calculations
Tab 5 - Site Photos
Attachments
Full Size Plan Sheets
Larger Scale GIS Maps
0
Agassi Drive Drainage Improvements
Hydraulic Report
Prepared by: Dan Clinton, PE - Town of Cary
Introduction:
The Agassi Court Cul-de-sac in the Wimbledon subdivision in Cary is experiencing
significant flooding as a result of the current stormwater drainage system. The flooding,
as seen in the attached photos, is significant enough to limit access to and from the area
during heavy rain events (>10-yr events). This is a safety concern to both the residents
and emergency personnel. To alleviate this safety concern, the Town of Cary is
requesting authorization to modify the storm drainage in this cul-de-sac as shown.
Described in this report is supporting documentation and justification for this activity as
an allowable use for buffer impacts under "Protection of existing structures, facilities....
Methodology
In determining the appropriate solution to this problem, both the watershed for the lake
downstream of cul-de-sac and the sub-watershed of the storm drain network of the cul-
de-sac were examined. Rational equation was used to determine the peak runoff rates for
both watersheds. For the larger lake watershed, the rational equation results were
compared to USGS regression equations. USGS regression discharge rates were lower
then the rational equation so the more conservative approach was taken and the rational
equation discharge rates were used.
The cul-de-sac sub-watershed was modeled using StormCAD software. StormCAD uses
the rational equation to determine runoff rates, Manning's Equation to determine flow
rates in the storm drain pipes with standard hydraulic head losses within the system.
StormCAD software was used to execute the model.
Peak Discharge Anal
Discharges for both watersheds were calculated as follows:
Total watershed (for the downstream lake)
Q=CIA
C= 0.487 (weighted runoff coefficient)
I= 3.44 inches/hour (based on a Time of Concentration of 30 minutes from NOAA point
precipitation frequency data - see attached table)
A= 415 Acres
Q = 695 cfs
Agassi Court Sub-watershed
Q=CIA
C= 0.275 (weighted runoff coefficient)
I- 7.08 inches/hour (based on a Time of Concentration of 5 minutes - see attached table)
A= 11.1 Acres
Q=21.6 cfs
CJ
Drainage Analysis
Pond Analysis
. In addition to investigating the pipe network in Agassi Court, the lake was examined to
determine what the stage is and if it affects the flow in drainage system in Agassi Court.
An analysis was run on the lake using Chainsaw Routing (see attached). The pond
routing result are listed below:
Pond Permanent Pool Elevation = 389.66
Max Stage for 10-yr event = 3.97-ft (393.63-ft)
Since the time of concentration is different between watershed, the lag time was
calculated for each watershed in TR-55 using a center weighted 24-hour hydrograph.
Once the lag time was determined, the Stage at that peak lag was 2.14-ft or 391.80- ft.
Supporting documentation is attached which include a copy of the hydrographs of the
two watershed showing different peak times (see attached).
Therefore, an elevation of 391.8 was used as the tailwater elevation of this pipe system.
Based on that information, several alternative designs were investigated. They are listed
below.
Cul-de-sac Analysis
The pipe system in Agassi Court was investigated to determine the cause of the
stormwater backup. Hydraulic analysis was run initially with a free outfall to see if the
source was within the pipe network itself. Profile 3 in Tab 3 of this report shows that the
• first problem with this system is that the pipes are severely undersized for the 10-yr storm
event. In all pipes, the hydraulic grade line is well above the ground surface and outside if
the system. This would explain the flooding. Due to the limited cover and location of
adjacent houses, a pipe layout analysis was undertaken to determine if enlarging the
existing pipe in place is an option. See analysis below.
PIPE LAYOUT ALTERNATIVE ANALYSIS
Two alternatives were examined.
Alternative #1- Enlarge existing system
Description: Install larger or parallel pipes along the current alignment
Conclusion: Not a practical alternative.
The current alignment takes an indirect route to the lake and has several areas
where cover is a limiting factor. Due to these cover constraints, the only way to
increase capacity is to add additional parallel pipes. In addition to the cover
constraints, the existing line runs within 1 foot of the house at 112 Agassi Court.
Adding a parallel line is not possible without significant protection measures
applied to the existing house and would still result in an additional pipe outfall.
For these reasons, this alternate is ruled out as a practical alternative.
C]
2
Alternative #2 - Reconfigure system alignment
Description: Split the existing system and run a new larger pipe system along a new
• alignment (most direct route).
Conclusion: By splitting the existing system between the existing catch basins, we are
able to:
1.) Allow the existing system to meet capacity from the western catch basin (CB#3)
to the existing outlet.
2.) Increases the capacity of the new line and allows the hydraulic grade line to
remain below the road surface.
3.) Allows for a more hydraulically efficient path to the point of discharge
4.) Allows the placement of the outlet at a higher elevation which reduced tailwater
impacts which improves hydraulics.
Cover remains an issue so parallel pipes were required to meet capacity. Sealed
(gasketted) pipe will be necessary since the Hydraulic Grade Line is above the pipe
for the majority of the system during the 10-yr event. Although the HGL is above the
pipe crown, it remains below the ground surface which is not the case with the
existing system.
Additional Calculations
See attached for the StormCAD results of the existing conditions and the proposed
conditions of the cul-de-sac drainage system.
Dissipater sizing
The proposed dissipater size will be 96"x180" (8'x15'). See attached printout of
calculation sheet.
Justification for Storm Drain Pipe Location
The proposed alignment will outlet within zone 1 of the existing pond buffer. Due to the
following reasons, there is no other practical alternative for the placement of the pipe
outlet.
1.) The elevation of the outlet is fixed due to the pond elevation and upstream ground
elevation.
a. The highest elevation the outlet can be set at to obtain positive grade in the
pipe is 390.2 feet. This elevation is limited by the cul-de-sac elevation.
The catch basin elevation in the cul-de-sac is 391.51 feet which provides
minimum cover over the storm drain pipe.
b. The permanent pool elevation of the pond is 389.6 feet.
c. The pipe slope at 0.66% provides 0.2 feet rise per 30 feet of length.
d. Tailwater (from the pond) at the time of peak of the cul-de-sac drainage is
391.8 feet.
e. Tail water will submerge the pipe outlet by 1.6 feet above the invert and
0.1 feet above the crown of the proposed pipe. And therefore would
submerge the level spreader as well and render the level spreader
ineffective.
1?1
3
2.) The cut necessary to install a level spreader at this location results in structural
concerns in surrounding infrastructure and pond slope.
a. The existing pond bank is currently 5:1 (390' to 392) for the first 10 feet
and 25:1 (392' to 394') for the next 50 feet with the invert of the pipe at
the edge of zone 1 being 390.4.
b. This results in a 4 foot cut out cove for the level spreader which would be
submerged during rain events limiting infiltration.
c. This cut would be over an existing sanitary sewer line and approaching
adjacent houses at either 114 or 112 Agassi Court.
Summary
In order to provide drainage of this cul-de-sac during rain events and alleviate this
existing safety problem, the Town of Cary is proposing this storm drainage retrofit. Due
to physical constraints of the surrounding area, storm drainage pipe realignment is
necessary to provide adequate drainage. Multiple options are investigated and a final
proposed alignment is presented. The Town of Cary is requesting an allowable use
exempting for the placement of this storm drainage retrofit to protect existing structures
and alleviate this safety problem.
Please provide a response to this request at your convenience.
•
•
4
LEGEND
Watershed Boundary
Approx Project Boundary
SCALE 1 "= 200'
AGASSI COURT DRAINAGE AREA AERIAL PHOTO
AGASSI COURT DRAINAGE AREA LANDUSE
Z
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UO YoC
W
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U)
K`?KSHLvkE G6;
1 A?
txlsungLanause_ZUUb Legen
Commercial
High Density Residen
Industrial
Institutional
Lake
Low Density Resident
Medium Density Resid
Mixed Density Reside
Office
- Open Space Private
Open Space Public
Rural
Undeveloped
Utilities
Very Low Density Res
P/
'O/
/Q
U1
•
LEGEND
Watershed Boundary
Approx Project Boundary
SCALE 1"= 200'
LEGEND
Watershed Boundary
• Approx Project Boundary
SCALE 1 "= 200'
AGASSI COURT DRAINAGE AREA TOPOGRAPHY
AGASSI COURT LAKE DRAINAGE AREA AERIAL PHOTO
0
•
•
SCALE 1"=1,000'
AGASSI COURT LAKE DRAINAGE AREA LANDUSE
ExistingLandUse_2006 Legend
Commercial
High Density Residen
Industrial
- Institutional
Lake
Low Density Resident
Medium Density Resid
Mixed Density Reside
Office

- Open Space Private
Open Space Public
Rural

Undeveloped
OW
t
Utilities
Very Low Density Res
AGASSI COURT LAKE DRAINAGE AREA TOPOGRAPHY
SCALE 1"=1,000'
LEGEND
Watershed
Boundary
Neuse
Stream
Buffer
2' Contours
•
•
•
Rational Method: Q=CIA Total Time of Concentration, Tc = Overland Flow Tc + Shallow Concentrated Flow Tc + C hanneUPi pe Flow Tc
Watershed Basin Number Lake Agassii Tc Overland (min) 2 0
Total Drainage Area 415 11.1 Tc Shallow Conc (min) 0.4
Subarea A (acres) 203 7.3 Tc Channel/Pipe (min) 35.1
Subarea A Runoff Coefficient 0.4 0.4 Te Total (min) 37.6
Subarea B acres 165 7.3 Surface Mammas n
Subarea B Runoff Coefficient 0.7 0.16 Overland flow Tc -- Kinematic Wave Theo Smooth Surface 0 011
Subarea C acres 62 Le th of overland flow 170.0 feet Fallow 01050
Subarea C Runoff Coefficient 0.15 Mannin s "n" for surface 0.011 Cultivated <= 201, Residue 0.060
Subarea D acres Average watershed sloe 0.012 ft./ft. Cultivated., 201b Residue 0.170
Subarea D Runoff Coefficient Constant alpha 14.8 Grass, Short 0.150
Weighted Runoff Coefficient 0.4869 0.275 Constant m 1.67 Grass, Dense 0.240
Wei htedRunoffCoefficient 0.4869 Gratis Bermuda 0A10
2-year Rainfall Intensity IDF 2.56 Woods LI ht 0.400
10- ear Rainfall Intensity IDF 3.44 7.08 Woods, Deese v.600
02 Flow 517.288 0
010 Flow (cfs) 695A 21.6 Trail Time of Duration Rainfall Intensity(IDF) Calculation of Time of Concentration
tr minutes i inches/hour tc minute s
htt:/ h . w n v/h / f rb/nc f .h ml
Shallow Conc Flow Tc 5 7.08 3.14
Sloe 0-06154 0.012 10 5.66 3.44
Length of Conc Flow 130 170 15 4.78 3.68
V (paved) 5.0 2.2 30 346 4.19 X
60 1 hour 2.25 4.97
120 2 hours 1.33 6.14
Channel/Pipe Flow Tc 180 0 hours 0.95 7.02
Slope 0.00829 0.04 360 6 hours 0.98 6.93
Length of Channel/Pi a Flow 8200 1123 720 12 hours 0.34 10.59
R o.8 0.8 1440 24 hours 0:21 12.85
n 0.03 0,93
V 3.9 8.6 Enter the Rainfall Intensity Values for the Correa ondin Times of Duration from the NWS h rlink provided.
Select the Rainfall Intensity that corresponds to the Trial Time of Duration that is equal to or less than the calculated
Time of Concentration.
Co the selected Rainfall Intensity into cell B13 or B14 as required to calculate the desired flow.
ttEF C9EFFtC1ENT
U
LAND
5E
BUSINESS:
DOWNTOWN AREAS 07-0-95 07-0.95
NEIGHBORHOOD AREAS 0.5-0 7 15-0.7
RESIDENTIAL:
SINGLE FAMILY AREAS 03-0-5 0.3-0,5
MULTI UNITS, DETACHED 0 -1 0 6 04-0 6
MULTI UNITS, ATTACHED 0.6-0.75 0-6-0.75
SUBURBAN 025 0A 0250A
(INDUSTRIAL:
LIGHT AREAS 0.5-0.8 0.?,-0.8
HEAVY AREAS 06-0,9 0-6-0.9
PARKS, CEMETARIES 0.1-0.25 (11-0.25
PLAYGROUNDS 0.2-0.35 02-0.35
RAILROAD YARD AREAS 02-0A 0.2-OA
UNIMPROVED AREAS
R
S 01 0.3 01-0.3
EETS:
T
ASPHALT 07-095 0.7-0-95
CONCRETE 0-8-0 95 08-0 95
BRICK 07 085 0.7-O.E5
DRIVES AND WALKS 0.75-0-85 0-75-0.85
ROOFS
LAWNS 0.7 -0.35 0.75.0$5
:
SANDY SOIL, FLAT, 21a 0.05-0.1. 0-05-0.1
SANDY SOIL AVE.. 2-770 0.1-0 15 0-1-0.15
SANDY SOIL, STEEP. 7°n 0.15-0.2 0,15-0.2
HEAVY SOIL, FLAT, 21.0 0.13-0.17 0.13-0:17
HEAVY SOIL, AVE., 2-7% 0.18-0.22 1-18-022
HEAVY SOIL, STEEP. -r
4GRIC 025-0-35 0 25-0.35
ULTURAL LAND:
BARE PACKED SC1L
SMOOTH 0 3-0.6 03-()6
ROUGH (12-05 0.2-0.5
CULT1VATED ROWS
HEAVY 801L NO CHOP
EA 0 3-06 0.3-0.6
H
VY SOIL WITH CROP 02-0 5 0.2-0,5
SANDY SOIL NO CROP
Y 0.2-0.4 0.2-0.4
SAND
SOIL WITH CROP 0.1-0.25 0.1-0,25
PASTURE
HEAVY SOIL 0 ,15-0.45 0 16.0.45
SANDY SOIL 0 .05.0.25 0.05-0.25
,VVOODLr0Q6 0 .05.0.25 0.06.0.25
•
0
POINT PRECIPITATION
FREQUENCY ESTIMATES
` FROM NOAA ATLAS 14
RALEIGH DURHAM WSFO AP, NORTH CAROLINA (31-7069) 35.8706 N 78.7864 W 403 feet
from "Precipitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3
G.M. Bonnin, D. Martin. B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland, 2004
Extracted: Mon Feb 26 2007
Confidence Limits Seasonality Location Maps Other info. GIS data Maps 11 Help
Precipitation Intensity Estimates (in/hr)
25 7.75 6.18 5.22 3.87 2.58 1.54 1.11 0.68 0.41 0.24 0.14 0.07 0.05 0.04 0.02 0.02 0.02 0.01
50 8.27 6.58 5.56 4.18 2.83 1.71 1.25 0.76 0.46 0.27 0.15 0.08 0.05 0.04 0.03 0.02 0.02 0.01
100 8.71 6.92 5.84 4.47 3.08 1.88 1.38 0.85 0.52 0.30 0.17 0.09 0.06 0.05 0.03 0.02 0.02 0.02
200 9.10 7.21 6.06 4.72 3.31 2.04 1.52 0.94 0.57 0.33 0.18 0.10 0.06 0.05 0.03 0.02 0.02 0.02
500 9.50 7.52 6.31 5.02 3.60 2.25 1.70 1.06 0.65 0.37 0.21 0.11 0.07 0.05 0.03 0.03 0.02 0.02
1000 9.82 7.73 6.47 5.24 3.82 2.42 1.85 1.16 0.72 0.41 0.22 O.12 0.08 0.06 0.04 0.03 0.02 0.02
Text version of table j * These precipitation frequency estimates are based on a partial duration series. ARI is the Average Recurrence Interval.
Please refer to the Jommc ntatirm for more information. NOTE: Formatting forces estimates near zero to appear as zero.
ARI* 5 10 1 1 15 120 6 12
(years) min min 1 1 min min min

4.7
3 3.77 3. I S 2.16 1.34 0.78 0.55 0.33 0.20 0.12 0.07 0.04 0.03 0.02 0.01 0.01 0.01
5.53 4.42 3.71 2.56 1.61 0.93 0.66 0.40 0.24 0.14 0.08 0.05 0.03 0.02 0.02 0.01 0.01
I , 16.36 5.09 4.29 3.05 1.95 1.I5 0.81 0.49 0.29 0.18 0.10 0.06 0.04 0.03 0.02 0.02 0.01
10 7.0 5.63 4.75 .44 .24 1.32 0.94 0.57 0.34 0.21 0.12 0.06 0.04 0.03 0.02 0.02 0.01
30 60 3
1 1 F 48
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min hr hr hr h hr da y day A] day day day d ay

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CHAINSAW ROUTING To, L11
lt-c'
100-yr 10-yr
Qp = 1040.00 580.00 1040.00
Tp = 33.00 CHAINSAW RESULTS
7.857
dT = 1.00 PEAK O/FLOW 1731 cfs
MAX STAGE 397.52 ft., msl
Ks = 84147,00 AREA FLOODED 2.82 acres
b = 1.13
Or ice N = 1.00 0.0000
Cd = 0.60 0.6000
A = 14.60 11.6000
Zi = 2.00 0.0000
Weir Cw = 3.00 POND INV. EL 389.66 ft., msl
L = 26.20 7.3000 3.54
Zcr = 0.00
CHAINSAW ROUTING
1 2 3 4 5 6 7 Inflow
TIME INFLOW STORAGE STAGE OUTFLOW Weir Orifice
(min) (cfs) (cu ft) (ft) (cfs) (cfs) (cfs)
0 .00 0.00 0.00 0.0000 389.66 0.00 0.00 0.00
1 2 0.00 0.0000 389.66 0 0.00
2 9 141.28 0.0034 389.66 0 0.02
3 21 704.15 0.0143 389.67 0 0.13
4 37 1959.89 0.0355 389.70 1 0.53
5 58 4163.23 0.0693 389.73 1 1.44
6 83 7545.45 0.1176 389.78 3 3.17
7 111 12308.25 0.1815 389.84 6 6.08
8 144 18618.69 0.2621 389.92 11 10.55
9 179 26605.36 0.3598 390.02 17 16.96
10 218 36355.82 0.4747 390.13 26 25.71
11 260 47915.39 0.6066 390.27 37 37.13
12 304 61287.35 0.7547 390.41 52 51.54
13 350 76434.25 0.9182 390.58 69 69.16
14 397 93280.37 1.0958 390.76 90 90.16
15 446 111715.12 1.2860 390.95 115 114.63
16
174 k 495
D i-t4?- 131597.04
152758
42 1.4873
1
6978 391.15
391
36 143
174 142.57
173
8

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4 . . . .
8 210.76
59 175010.13 1.9 5 6._. 3.91_.58 208 208.40 241.43
119 643 _ 198146.56 2 1388_ 391.8 0 246 245.86 269.25 Top of weir
20 690 221950.47 2.3655 392.03 286 285.96 294.83
21 736 246197.68 2.5935 392.25 318 328.29 318.50
22 780 271248.90 2.8265 392.49 341 373.50 340.98
23 822 297589.89 3.0689 392.73 363 422.56 362.90
• 24
25 861
896 325113.46
353689.38 3.3196
3.5773 392.98
393.24 384
405 475.38
531.81 384.26
405.05 TOP OF DAM
26 929 383166.81 3.8408 393.50 425 591.63 425.25
27 957 413376.64 4.1084 393.77 445 654.54 444.83
28 982 444133.78 4.3787 464 720.18 463.77
29 1003 475239.41 4.6499 482 788.11 482.02
30 1019 506483.28 4.9203 500 857.84 499.56
31 1031 537646.12 5.1881 516 928.83 516.34
32 1038 568501.98 5.4516 532 1000.48 532.33
33 1040 598820.75 5.7089 548 1072.15 547.50
34 1038 628370.59 5.9583 562 1143.16 561.81
35 1031 656920.45 6.1980 575 1212.84 575.23
36 1019 684242.55 6.4263 588 1280.47 587.73
37 1003 710114.82 6.6416 599 1345.34 599.28
38 982 734323.38 6.8422 610 1406.75 609.84
39 957 756664.80 7.0267 619 1464.03 619.39
929 776948.44 7.1937 628 1516.52 627.91
41 896 794998.57 7.3418 635 1563.61 635.38
42 863 810656.38 7.4700 642 1604.75 641.77
43 830 823924.54 7.5785 647 1639.82 647.12
44 798 834871.42 7.6678 652 1668.89 651.50
45 767 843632.9 7.7392 655 1692.25 654.98
46 737 850337.3 7.7938 658 1710
18 657
63
4.7.' 709 855105.9 7.8325 660 .
1722.96 .
659.50
48 681 858053.6 7.8565 1731 1730.88
49 655 795076.4 7.3425 1564 1563.81
50 630 740544.2 6.8936 1423 1422.64
51 605 692964.3 6.4990 1302 1302.25
52 582 651148.8 6.1497 1199 1198.67
53 559 614144.8 5.8384 1109 1108.83
54 538 581182.4 5.5594 1030 1030.30
55 517 551635.3 5.3078 961 961.15
56 497 524990.7 5.0796 900 899.83
57 478 500826.8 4.8715 845 845.11
58 459 478794.1 4.6807 796 795.97
59 442 458602.2 4.5051 752 751.59
60 425 440008.5 4.3426 711 711.28
61 408 422809.1 4.1916 675 674.51
62 392 406832.3 4.0507 641 640.78
63 377 391932.8 3.9187 610 609.72
64 363 377987.2 3.7947 581 581.01
65 349 364890.0 3 .6777 554 554.36
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User Input Data
Calculated Value
Reference Data
Designed By: DCinton Date: 11/3/2005
Checked By: Date:
Company:
Project Name: Agassi Court
Project No.:
Site Location (City/Town) Raleigh
Culvert Id. 101
Total Drainage Area (acres) 14
Step 1. Deternime the tatlwater depth from channel characteristics below the
pipe outlet for the design capacity of the pipe If the tail atet depth is less
than halt"the outlet pipe chameter- it is classified tninutnnn tatlwater condition.
If it is greater than half the pipe diameter, it is classified nmxioitan condition.
Pipes that outlet curio wiale flat areas with no defined channel are assruned
to have a muumuu i taihvater condition unless reliable flood stage eie ahons
shore otherwise.
Outlet pipe diameter, Do (in.) 18
Tailwater depth (in.) 19.2
Minimum/Maximum tatlwater? Max TW (Fig. 8.06b)
Discharge (cfs) 11.1
Velocity (tt./s) 6.43
Step 2. Based on the tatlwater condition,, detetmmed in step 1.. enter Fig tie
8 06a or Figure 8.06b, and determine d,t, riprap size and innurnum apron leng,11
(L, The d,> size is the median atone _:ize to a well graded riprap apron.
Step 3_ Detenu me apron tandtln an the pipe outlet_ the apron shape and the
ap€own width at the outlet end from the a=me figure used in Step
Minimum TW Maximum TW
kuure 8d06 a Eieure S-06
b ,
Ri prap d50, (ft.) 0.2
Minimum apron length, La (11.) 15
Apron width at pipe outlet (ft.) 4.5 4.5
Apron shape
Apron width at outlet end (fl.) 1.5 7.5
Step 4. Determine the maxirntmz stone diameter
d,,a, _ 15 x d,;a
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 0 0.3
Step 5. Determine the apron tlucktress:
Apron thickness = 1 5 x r19,
Minimum TW Maximum TW
Apron Thickness(tt.) 0 0.45
Step 6. Fit the riprap apron to the sire by making it level for the ruinimrnu
length, L, from Figtue 8.06a or Figure 8.06b. Extend the apron farther
downstream and along channel banks until stability is assuied Keep the
apron as straight as prssible_ and align it with the flow of tine receiving streatn.
Make any necessary aligns ent bends near the pipe ontlet so that the entrance
into the reteivin€t strewn is stiai<^ht.
Some le
cations mat reyume lining of the entire chatnnel cross section, to assure
stability.
2.4 inches
180 inches
54 inches
90 inches
3.6 inches
5.4 inches
It may be necessary to increase the size of ripral.i where protecnon of the
channel side slopes is necessary (ppv,_ri; 8.0.5). Vlnete ovetfalk exist at
pipe outlets or floras we excessive. a plunge pool should be considered, see
page 8.06.8.
•

Figure l: Map of Agassi Court Cul-de-sac
Note: Red line- existing storm drain line, Green line - sanitary sewer, Shaded Blue Area - Buffer (100-
foot shown around pond (includes Cary buffer)) Dashed Pink Line - Proposed drain

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Figure 2: Photo just after a heavy rain event (Photo taken from the north end of the project - 107
Agassi Court)
0
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Figure 3. Pond during a heavy rain event. Note the existing pond outlet is submerged near the Alder
tree/bush. Proposed outlet will be near where the whitewater is located approximately 50-feet away
a j
.r' i fit ?t
Figure 3. Relatively steep slope around the pond.
is
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¦rl"lu'f. U AINtIUg uuuet is nau sunmerged when pond is at permanent pool elevation.