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WITHERS 7 RAVEN EL
STORMWATER MANAGEMENT PLAN
TRENTON ROAD SUBDIVISION
S-38-05
Raleigh, North Carolina
Prepared For:
Five Star Developers, LLC
105 Quail Ridge Road
Wilmington, NC 28409
Prepared By:
WITHERS & RAVENEL, INC
111 MacKenan Drive
Cary, North Carolina 27511
OENR - ,?rAi E? ?a?!A? ?r
V'STLANOS ANU STORWATER BRANCH
January 2oo6
Revised March 2oo8
W&R Project No. 205o18
?'?? • S?j' ?y?i
r
IKAIL
0242 ; z
C.
Hunter C. reeman, P. E.
TRENTON ROAD SUBDIVISION (S-38-05)
STORMWATER MANAGEMENT PLAN
RALEIGH, NORTH CAROLINA
INTRODUCTION
The purpose of this study is to document pre-and post-development peak stormwater discharges
for the 2-year and 1o-year storm events and to evaluate the affect of the loo-year design storm on
the proposed stormwater management device. The goal is to provide detention structures adequate
to maintain a discharge less than or equal to the 2-year and 1o-year pre-development peak
discharges after the site has been developed.
Figure 1. Site outlined in red on USGS Quadrangle.
The site is located in the Neuse River Basin and has two streams with 50 ft buffers - one of which
makes up the northern boundary of the site and the other that bisects the western portion of the
site. Richland Creek runs on the eastern boundary of the site and was studied by the Federal
Emergency Management Agency (FEMA) for flood insurance purposes. The loo-year floodplain from
Richland Creek as delineated by FEMA has a backwater finger which extends along the northern
boundary of the site as shown in Figure 2. According to the City Ordinance 10.9023(b)(3) and the
interpretation of this ordinance by city staff, the portion of the site that discharges into the FEMA
floodplain is exempt from attenuation requirements. Therefore - only the drainage area from the
upstream limit of the FEMA floodplain is considered in this analysis as shown in Sheet 1 of the
appendix.
Trenton Road Subdivision - Revised ?. W&R Project 205018
Stormwater Management Report March 2008
Figure 2. Site outlined in red on USGS Quadrangle with FEMA Floodplain shown in blue.
There is one stormwater Best Management Practice (BMP) proposed for the site to meet peak
attenuation requirements. The proposed BMP is an extended dry detention basin, designed to draw
down the first inch of runoff over a 2 to 5 day period.
METHODOLOGY
The stormwater study was conducted using the natural drainage features as depicted by the Wake
County aerial topographic information (2-ft contours), field survey data and proposed development
within the drainage areas.
The scope of work included the following analyses:
Hydrology
? Simulation of the 2-year, io-year, and Zoo-year rainfall events for the Cary area
? Formulation of the 2-year, io-year, and loo-year flood hydrographs for the pre- and post-
development drainage areas
Hydraulic
? Routing the 2-year, io-year, and loo-year flood hydrographs for post development runoff
through the proposed stormwater BMP
The results of the hydrologic calculations are used in the hydraulic analyses. The hydraulic design
requires the development of stage-storage and stage-discharge functions for the dry detention
Trenton Road Subdivision - Revised 2 W&R Project 205018
Stormwater Management Report March 2008
TRENTON ROAD SUBDIVISION (S-38-05)
STORMWATER MANAGEMENT PLAN
RALEIGH, NORTH CAROLINA
P9
L _j
TRENTON ROAD SUBDIVISION (S-38-05)
• STORMWATER MANAGEMENT PLAN
RALEIGH, NORTH CAROLINA
basin. The rainfall/runoff hydrographs, stage-storage and stage-discharge functions have been
• compiled to create a routing computer simulation model using Haestad Methods PondPack vlo.o
software. This PondPack model was then used to assess the impact of the peak discharges for the
design rainfall events. The PondPack modeling results are provided as appendices to this report.
• HYDROLOGY
The SCS Method was used to develop runoff hydrographs for the 2-year and io-year storm events.
NOAA Atlas 14 rainfall data for Raleigh-Durham International Airport was used to determine the 24-
hour duration rainfall for the 2-year, to-year, and loo-year storm events. This method requires three
basic parameters: a curve number (CN), time of concentration (Q, and drainage area.
Curve numbers were based on soil type and land use. Soil types were delineated from the Soil
Survey of Wake County, North Carolina (November 1970). Land use data was determined using aerial
• photography and the most recent site plans for the proposed site. The curve numbers used in this
• study are listed in the appendix of this report.
Times of concentration were calculated using methods described in the SCS publication "Urban
• Hydrology for Small Watersheds, TR-55" and based on natural drainage patterns and field survey
data. The post-development basins that were routed to the detention basin were estimated to have
a time of concentration of 5 minutes to account for the small amounts of sheet flow and piping.
• HYDRAULICS
Computer simulated reservoir routing of the 2-year, to-year, and loo-year design storms utilized
• stage-storage and stage-discharge functions. Stage-storage functions were derived from the
• proposed contours for the detention basin. A non-linear regression relation for surface area versus
elevation was derived for the BMP. This relation estimates the incremental volume of the basin to
the stage or elevation of the basin. Stage-discharge functions were developed to size the outlet
• structure for the pond.
CONCLUSIONS
Based on the routing study, the post development peak discharge from the entire site is less than
the pre-development peak for the 2-year and 1o-year design storms. Table 1 below summarizes the
• peak attenuation results. The pond also contained the discharge from the loo-year storm without
• overtopping the dam. Table 2 summarizes the wet detention basin design.
The resulting post development nitrogen export for the site is below the 3.6 lbs/acre/year maximum
• nitrogen loading allowed in the Neuse River Basin for residential development. The nitrogen export
calculations are provided in an appendix to this report.
• Trenton Road Subdivision - Revised 3 W&R Project 2o5oi8
• Stormwater Management Report March 2oo8
•
•
TRENTON ROAD SUBDIVISION (S-38-o5)
STORMWATER MANAGEMENT PLAN
RALEIGH, NORTH CAROLINA
TABLE 1. PEAK ATTENUATION SUMMARY FOR THE 2-YEAR, 10-YEAR, AND 100-YEAR DESIGN STORM
2-year Qpeak io-year Qpeak loo-year Qpeak
Pre-Development 26.48 cfs 69.83 cfs 136.58 cfs
[N
pment
Pond Out 1.16 cfs 5.59 cfs 30.25 cfs
Untreated 25.48 cfs 64.22 cfs 123.o6 cfs
pment Total 26.25 cfs 69.81 cfs 147.57 cfs
TABLE 2. DRY DETENTION BASIN DESIGN SUMMARY
m of Pond 346.oo'
of Dam 352.00'
wn Orifice 1" Diameter at 346.oo'
Orifice
NAttenuation 9" Diameter at 347.90'
iser 4' x 4' - Crest at 350.25'
et Barrel 24" RCP -104 LF at 2.9%
ear WSEL 351.00'
Trenton Road Subdivision - Revised 4 W&R Project 205018
Stormwater Management Report March 2008
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DISCHARGE SUMMARY
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Pre-bevelopment
0
Y
C_
0
Q
A
Pre Out
Post - Untreated
9aa???2o
To BMP
4
W
0
w
dnd 10
0
?o
A
Out 10
-N
?aP
Fi?P
To Ditch
• Type.... Master Network Summary Page 1.01
Name.. .. Waters hed
• File.. .. K:\05\05-010\05018\ H&H\trenton Mar O8.ppw
•
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MASTER DESIGN STORM SUMMARY
• Network Storm Collection: RDU NOAA 14 Desi
•
Total
Depth Rainfall
• Re turn Event in Type RNF ID
-- -----
2 --
3.4400 ---------------- ---------
Time-Depth Curve RDU NOAA -------
2yr
• 10 4.9800 Time-Depth Curve RDU NOAA 10yr
100 7.3700 Time-Depth C urve RDU NOAA 100yr
•
•
MAS TER NETWORK SUMMARY
• SCS U nit Hydrogra ph Method
• (*Node=Ou tfall; +Node =Diversion;)
• (Trun= HYG Truncation: Blank=None; L=Left; R=Rt; LR =Left&Rt)
•
• Max
Return HYG Vol Qpeak Qpeak Max WSEL Pond Storage
• Node ID Type Event ac-ft Trun hrs cfs ft ac-ft
• ----
--
-
-
*
----
---- -----
-
----
-
-----
--
-
--
--- - -
--
-
-------- ------------
OUT
1
0 JCT
2 3.419 12.4000 26.25
• *OUT 10 JCT 10 8.019 12.4000 69.81
*OUT 10 JCT 100 16.918 12.3000 147.57
•
POND 10 IN POND 2 .555 12.2000 8.70
• POND 10 IN POND 10 1.220 12.2000 17.67
• POND 10 IN POND 100 2.462 12.1000 30.82
• POND 10 OUT POND 2 .552 12.6000 1.16 348.60 .226
POND 10 OUT POND 10 1.217 12.4000 5.59 350.38 .470
• POND 10 OUT POND 100 2.459 12.2000 30.25 351.00 .574
• POST - UNTREATED AREA 2 2.867 12.4000 25.48
• POST -
POST - UNTREATED
UNT AREA 10 6.802 12.4000 64.22
REATED AREA 100 14.459 12.3000 123.06
• *
PRE OUT JCT 2 3.073 12.4000 26.48
• *PRE OUT JCT 10 7.457 12.4000 69.83
*PRE OUT JCT 100 16.086 12.4000 136.58
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Type.... Master Network Summary Page 1.02
Name.... Watershed
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
MASTER NETWORK SUMMARY
SCS Unit Hydrograph Method
(*Node=Outfall; +Node=Diversion;)
(Trun= HYG Truncation: Blank=None; L=Left; R=Rt; LR=Left&Rt)
Max
Return HYG Vol Qpeak Qpeak Max WSEL Pond Storage
Node ID Type Event ac-ft Trun hrs cfs
-------- ft ac-ft
-------- ------------
-----------------
PRE-DEVELOPMENT ----
AREA ------
2 ---------- --
3.073 ---------
12.4000 26.48
PRE-DEVELOPMENT AREA 10 7.457 12.4000 69.83
PRE-DEVELOPMENT AREA 100 16.086 12.4000 136.58
TO BMP AREA 2 .143 12.1000 2.69
TO BMP AREA 10 .319 12.1000 5.90
TO BMP AREA 100 .649 12.1000 10.14
TO DITCH AREA 2 .412 12.1000 7.92
TO DITCH AREA 10 .901 12.1000 16.79
TO DITCH AREA 100 1.813 12.1000 28.34
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PRE-DEVELOPMENT
CALCULATIONS
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Job File: K:\05\05-010\05018\H&H\TRENTON MAR 08.PPW
Rain Dir: K:\05\05-010\05018\H&H\
JOB TITLE
--------------------------
--------------------------
Project Date: 3/10/2008
Project Engineer: HCF
Project Title: Trenton Road Subdivision
Project Comments:
Evaluate Pre and Post-development conditions for the 2 and 10-year
storms
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Table of Contents
i
****************** DESIGN STORMS SUMMARY *******************
RDU NOAA 14 Desi Design Storms ...................... 1.01
********************** TC CALCULATIONS *********************
PRE-DEVELOPMENT Tc Calcs ........................... 2.01
********************** CN CALCULATIONS *********************
PRE-DEVELOPMENT Runoff CN-Area ..................... 3.01
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Type.... Design Storms Page 1.01
Name.... RDU NOAA 14 Desi
File.... K:\05\05-010\05018\H&H\trenton Mar O8.ppw
Title... Project Date: 3/10/2008
Project Engineer: HCF
Project Title: Trenton Road Subdivision
Project Comments:
Evaluate Pre and Post-development conditions for the
2 and 10-year storms
DESIGN STORMS SUMMARY
Design Storm File,ID = RDU NOAA 14 Desi
Storm Tag Name = 2
Data Type, File, ID
Storm Frequency
Total Rainfall Depth
Duration Multiplier
Resulting Duration
Resulting Start Time
Time-Depth Curve RDU NOAA 2yr
2 yr
3.4400 in
1
23.9904 hrs
.0000 hrs Step= .0833 hrs End= 23.9904 hrs
Storm Tag Name = 10
Data Type, File, ID = Time-Depth Curve RDU NOAA 10yr
Storm Frequency = 10 yr
Total Rainfall Depth= 4.9800 in
Duration Multiplier = 1
Resulting Duration = 23.9904 hrs
Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9904 hrs
Storm Tag Name = 100
Data Type, File, ID
Storm Frequency
Total Rainfall Depth
Duration Multiplier
Resulting Duration
Resulting Start Time
Time-Depth Curve RDU NOAA 100yr
100 yr
7.3700 in
1
23.9990 hrs
.0000 hrs Step= .0833 hrs End= 23.9990 hrs
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Type.... Tc Calcs
Name.... PRE-DEVELOPMENT
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2. 01
...........................................................
TIME OF CONCENTRATION CALCULATOR
Segment #1: Tc: TR-55 Sheet
Mannings n .4000
Hydraulic Length 100.00 ft
2yr, 24hr P 3.6000 in
Slope .022000 ft/ft
Avg.Velocity .09 ft/sec
Segment #1 Time: .3248 hrs
------------------------------------------------------------------------
Segment #2: Tc: TR-55 Shallow
Hydraulic Length 975.80 ft
Slope .066000 ft/ft
Unpaved
Avg.Velocity 4.15 ft/sec
Segment #2 Time: .0654 hrs
------------------------------------------------------------------------
Segment #3: Tc:
Flow Area
Wetted Perimeter
Hydraulic Radius
Slope
Mannings n
Hydraulic Length
TR-55 Channel
9.0000 sq.ft
9.00 ft
1.00 ft
.047000 ft/ft
.0650
855.50 ft
Avg.Velocity 4.97 ft/sec
Segment #3 Time: .0478 hrs
------------------------------------------------------------------------
Total Tc: .4380 hrs
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Type.... Tc Calcs
Name.... PRE-DEVELOPMENT
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2.02
------------------------------------------------------------------------
Tc Equations used...
------------------------------------------------------------------------
______=----___
SCS TR-55 Sheet Flow ------- ____----
Tc = (.007 * ((n * Lf)**0.8)) / ((P**.5) * (Sf**.4))
Where: Tc = Time of concentration, hrs
n = Mannings n
Lf = Flow length, ft
P = 2yr, 24hr Rain depth, inches
Sf = Slope, o
___= SCS TR-55 Shallow Concentrated Flow _____________________________
Unpaved surface:
V = 16.1345 * (Sf**O.5)
Paved surface:
V = 20.3282 * (Sf**0.5)
To = (Lf / V) / (3600sec/hr)
Where: V = Velocity, ft/sec
Sf = Slope, ft/ft
Tc = Time of concentration, hrs
Lf = Flow length, ft
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Type.... Tc Calcs
Name.... PRE-DEVELOPMENT
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2.03
___= SCS Channel Flow _________
R = Aq / Wp
V = (1.49 * (R**(2/3)) * (Sf**-0.5)) / n
Tc = (Lf / V) / (3600sec/hr)
Where: R
Aq
Wp
V
Sf
n
Tc
Lf
Hydraulic radius
Flow area, sq.ft.
Wetted perimeter, ft
Velocity, ft/sec
Slope, ft/ft
Mannings n
Time of concentration, hrs
Flow length, ft
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Type.... Runoff CN-Area
Name.... PRE-DEVELOPMENT
Page 3.01
RUNOFF CURVE NUMBER DATA
..........................................................................
..........................................................................
Impervious
Area Adjustment Adjusted
Soil/Surface Description CN acres %C %UC
-- CN
------
------------------------------
Open Space; B -- ----
61 ---------
2.080 ----- --- 61.00
Impervious 98 .160 98.00
1 acre Lots; Wooded; C 76 .050 76.00
1 acre Lots; Wooded; B 64 15.240 64.00
ROW - open ditches; C 92 .600 92.00
ROW - open ditches; B 89 1.890 89.00
Woods - good; B 55 30.400 55.00
112 acre Lots; Wooded; C 77 .720 77.00
112 acre Lots; Wooded; B 65 3.130 65.00
Woods - good; C 70 8.490 70.00
COMPOSITE AREA & WEIGHTED CN -
..............................
.............................. -->
..........
.......... 62.760
..........
..........
............
............ 61.67 (62)
.............
.............
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Appendix A
Index of Starting Page Numbers for ID Names
A-1
----- P -----
PRE-DEVELOPMENT... 2.01, 3.01
----- R -----
RDU NOAA 14 Desi... 1.01
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POST DEVELOPMENT
CALCULATIONS
Job File: K:\05\05-010\05018\H&H\TRENTON MAR 08.PPW
Rain Dir: K:\05\05-010\05018\H&H\
JOB TITLE
------------
Project Date: 3/10/2008
Project Engineer: HCF
Project Title: Trenton Road Subdivision
Project Comments:
Evaluate Pre and Post-development conditions for the 2 and 10-year
storms
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Table of Contents
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****************** DESIGN STORMS SUMMARY *******************
RDU NOAA 14 Desi Design Storms ...................... 1.01
**+***********++****** TC CALCULATIONS ******+**************
POST - UNTREATED Tc Calcs ........................... 2.01
TO BMP.......... Tc Calcs ........................... 2.04
TO DITCH........ Tc Calcs ........................... 2.06
*****+*+***********++* CN CALCULATIONS **++*+***************
POST - UNTREATED Runoff CN-Area ..................... 3.01
TO BMP.......... Runoff CN-Area ..................... 3.02
TO DITCH........ Runoff CN-Area ..................... 3.03
+*****+******+**++**+** POND VOLUMES *******++**+****+++****
POND 10......... Vol: Elev-Area ..................... 4.01
******************** OUTLET STRUCTURES *********************
Outlet 1........ Outlet Input Data .................. 5.01
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Table of Contents
ii
Table of Contents (continued)
Composite Rating Curve ............. 5.04
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Type.... Design Storms Page 1.01
Name.... RDU NOAA 14 Desi
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Title... Project Date: 3/10/2008
Project Engineer: HCF
Project Title: Trenton Road Subdivision
Project Comments:
Evaluate Pre and Post-development conditions for the
2 and 10-year storms
DESIGN STORMS SUMMARY
Design Storm File,ID = RDU NOAA 14 Desi
Storm Tag Name = 2
Data Type, File, ID
Storm Frequency
Total Rainfall Depth
Duration Multiplier
Resulting Duration
Resulting Start Time
Time-Depth Curve RDU NOAA 2yr
2 yr
3.4400 in
1
23.9904 hrs
.0000 hrs Step= .0833 hrs End= 23.9904 hrs
Storm Tag Name = 10
Data Type, File, ID = Time-Depth Curve RDU NOAA 10yr
Storm Frequency = 10 yr
Total Rainfall Depth= 4.9800 in
Duration Multiplier = 1
Resulting Duration = 23.9904 hrs
Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9904 hrs
Storm Tag Name = 100
Data Type, File, ID
Storm Frequency
Total Rainfall Depth
Duration Multiplier
Resulting Duration
Resulting Start Time
Time-Depth Curve RDU NOAA 100yr
100 yr
7.3700 in
1
23.9990 hrs
.0000 hrs Step= .0833 hrs End= 23.9990 hrs
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Type.... Tc Calcs
Name.... POST - UNTREATED
File.... K:\05\05-010\05018\H&H\trenton Mar_08.ppw
TIME OF CONCENTRATION CALCULATOR
Segment #1: Tc: TR-55 Sheet
Mannings n .4000
Hydraulic Length 100.00 ft
2yr, 24hr P 3.6000 in
Slope .022000 ft/ft
Avg.Velocity .09 ft/sec
Segment #1 Time: .3248 hrs
------------------------------------------------------------------------
Segment #2: Tc: TR-55 Shallow
Hydraulic Length 975.80 ft
Slope .066000 ft/ft
Unpaved
Avg.Velocity 4.15 ft/sec
Segment #2 Time: .0654 hrs
------------------------------------------------------------------------
Segment #3: Tc: TR-55 Channel
Flow Area 9.0000 sq.ft
Wetted Perimeter 9.00 ft
Hydraulic Radius 1.00 ft
Slope .047000 ft/ft
Mannings n .0650
Hydraulic Length 855.50 ft
Avg.Velocity 4.97 ft/sec
Segment 43 Time: .0478 hrs
------------------------------------------------------------------------
Total Tc: .4380 hrs
Page 2.01
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Type.... Tc Calcs
Name.... POST - UNTREATED
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2.02
------------------------------------------------------------------------
Tc Equations used...
------------------------------------------------------------------------
SCS TR-55 Sheet Flow ==========---------- ========--======----- --------
Tc = (.007 * ((n * Lf)**0.8)) / ((P**.5) * (Sf**.4))
Where: Tc = Time of concentration, hrs
n = Mannings n
Lf = Flow length, ft
P = 2yr, 24hr Rain depth, inches
Sf = Slope, %
_=== SCS TR-55 Shallow Concentrated Flow ====------=-------------
Unpaved surface:
V = 16.1345 * (Sf**0.5)
Paved surface:
V = 20.3282 * (Sf**0.5)
Tc = (Lf / V) / (3600sec/hr)
Where: V = Velocity, ft/sec
Sf = Slope, ft/ft
Tc = Time of concentration, hrs
Lf = Flow length, ft
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Name.... POST - UNTREATED
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Page 2.03
==== SCS Channel Flow ====------=======
R = Aq / Wp
V = (1.49 * (R**(2/3)) * (Sf**-0.S)) / n
Tc = (Lf / V) / (3600sec/hr)
Where: R
Aq
Wp
V
Sf
n
Tc
Lf
Hydraulic radius
Flow area, sq.ft.
Wetted perimeter, ft
Velocity, ft/sec
Slope, ft/ft
Mannings n
Time of concentration, hrs
Flow length, ft
SIN: DOYXYWH3NLBE Withers & Ravenel
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Type.... Tc Calcs
Name.... TO BMP
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2.04
........................................................................
........................................................................
TIME OF CONCENTRATION CALCULATOR
........................................................................
........................................................................
Segment #1: Tc: User Defined
Segment #1 Time: .0833 hrs
------------------------------------------------------------------------
Total Tc: .0833 hrs
Calculated Tc < Min.Tc:
Use Minimum Tc...
Use Tc = .0833 hrs
------------------------
S/N: DOYXYWH3NLBE
PondPack (10.00.015.00)
8:06 AM
Withers & Ravenel
3/11/2008
Type.... Tc Calcs
Name.... TO BMP
File.... K:\05\05-010\05018\H&H\trenton Mar O8.ppw
Page 2.05
------------------------------------------------------------------------
Tc Equations used...
------------------------------------------------------------------------
User Defined ==========-- ----------------------
Tc = Value entered by user
Where: Tc = Time of concentration
SIN: DOYXYWH3NLBE Withers & Ravenel
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Type.... Tc Calcs
Name.... TO DITCH
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2.06
........................................................................
........................................................................
TIME OF CONCENTRATION CALCULATOR
........................................................................
........................................................................
Segment #1: Tc: User Defined
Segment #1 Time: .0833 hrs
------------------------------------------------------------------------
Total Tc: .0833 hrs
Calculated Tc < Min.Tc:
Use Minimum Tc...
Use Tc = .0833 hrs
S/N: DOYXYWH3NLBE Withers & Ravenel
PondPack (10.00.015.00) 8:06 AM 3/11/2008
Type.... Tc Calcs
Name.... TO DITCH
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 2.07
------------------------------------------------------------------------
Tc Equations used...
------------------------------------------------------------------------
User Defined ===---------- =--==========--====--===========--
Tc = Value entered by user
Where: Tc = Time of concentration
S/N: DOYXYWH3NLBE Withers & Ravenel
PondPack (10.00.015.00) 8:06 AM 3/11/2008
Type.... Runoff CN-Area
Name.... POST - UNTREATED
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 3. 01
RUNOFF CURVE NUMBER DATA
..........................................................................
..........................................................................
Impervious
Area Adjustment Adjusted
Soil/Surface Description
------------ CN acres %C %UC CN
------------------
Impervious -- ----
98 ---------
.160 ----- ----- ------
98.00
1 acre Lots; Wooded; C 76 2.580 76.00
1 acre Lots; Wooded; B 64 23.370 64.00
ROW - open ditches; C 92 .600 92.00
ROW - open ditches; B 89 1.430 89.00
Woods - good; B 55 17.920 55.00
1/2 acre Lots; Wooded; C 77 .710 77.00
112 acre Lots; Wooded; B 65 2.630 65.00
Woods - good; C 70 5.160 70.00
COMPOSITE AREA & WEIGHTED CN -
..............................
.............................. -->
..........
.......... 54.560
..........
..........
............
............ 63.46 (63)
.............
.............
SIN: DOYXYWH3NLBE
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8:06 AM
Withers & Ravenel
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Type.... Runoff CN-Area
Name.... TO BMP
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 3.02
RUNOFF CURVE NUMBER DATA
..........................................................................
..........................................................................
Impervious
Area Adjustment Adjusted
Soil/Surface Description CN acres %C %UC CN
-------------------------------- ---- --------- ----- ----- ------
Right of Way; B 89 .160 89.00
1 acre Lots; Wooded;B 64 2.050 64.00
COMPOSITE AREA & WEIGHTED CN ---> 2.210 65.81 (66)
...........................................................................
...........................................................................
SIN: DOYXYWH3NLBE Withers & Ravenel
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Type.... Runoff CN-Area
Name.... TO DITCH
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 3.03
RUNOFF CURVE NUMBER DATA
..........................................................................
..........................................................................
Impervious
Area Adjustment Adjusted
Soil/Surface Description
------------------ CN acres %C %UC CN
------------
Lots - 1 acre; B -- ----
64 ---------
4.880 ----- ----- ------
64.00
Lots - 1 acre; C 76 .810 76.00
Right of Way; B 89 .300 89.00
COMPOSITE AREA & WEIGHTED CN -
..............................
.............................. -->
..........
.......... 5.990
..........
..........
............
............ 66.87 (67)
.............
.............
SIN: DOYXYWH3NLBE
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Type.... Vol: Elev-Area
Name.... POND 10
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 4
Elevation Planimeter Area Al+A2+sgr(Al*A2) Volume Volume Sum
(ft)
------ (sq.in) (sq.ft)
--------------------- (sq.ft)
---------------- (ac-ft)
---------- (ac-ft)
-------------
------
346.00 ----- 2598 0 .000 .000
347.00 ----- 3483 9089 .070 .070
348.00 ----- 4438 11853 .091 .160
349.00 ----- 5452 14809 .113 .274
350.00 ----- 6523 17939 .137 .411
351.00 ----- 7650 21237 .163 .573
352.00 ----- 8833 24703 .189 .762
POND VOLUME EQUATIONS
* Incremental volume computed by the Conic Method for Reservoir Volumes.
Volume = (1/3) * (EL2-EL1) * (Areal + Area2 + sq.rt.(Areal*Area2))
where: ELI, EL2 = Lower and upper elevations of the increment
Areal,Area2 = Areas computed for ELI, EL2, respectively
Volume = Incremental volume between ELl and EL2
SIN: DOYXYWH3NLBE Withers & Ravenel
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Type.... Outlet Input Data
Name.... Outlet 1
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 5. 01
REQUESTED POND WS ELEVATIONS:
Min. Elev.= 346.00 ft
Increment = .10 ft
Max. Elev.= 352.00 ft
OUTLET CONNECTIVITY
---> Forward Flow Only (Upstream to DnStream)
<--- Reverse Flow Only (DnStream to UpStream)
<---> Forward and Reverse Both Allowed
Structure
----------------- No.
---- Outfall E1, ft E2, ft
Orifice-Circular
01 -------
---> CO ---------
347.900 ---------
352.000
Inlet Box RO ---> CO 350.250 352.000
Orifice-Circular 00 ---> CO 346.000 352.000
Culvert-Circular CO ---> TW 346.000 352.000
TW SETUP, DS Channel
SIN: DOYXYWH3NLBE Withers & Ravenel
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Type.... Outlet Input Data
Name.... Outlet 1
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 5.02
OUTLET STRUCTURE INPUT DATA
Structure ID = O1
Structure Type = Orifice-Circular
------------------------------------
# of Openings = 1
Invert Elev. = 347.90 ft
Diameter = .7500 ft
Orifice Coeff. _ .600
Structure ID = RO
Structure Type = Inlet Box
-
-
-------------------
# of Openings = ---
------------
1
Invert Elev. = 350.25 ft
Orifice Area = 16.0000 sq.ft
Orifice Coeff. _ .600
Weir Length = 16.00 ft
Weir Coeff. - 3.100
K, Reverse = 1.000
Mannings n = .0000
Kev,Charged Riser = .000
Weir Submergence = No
Structure ID = 00
Structure Type = Orifice-Circular
------------------------------------
# of Openings = 1
Invert Elev. = 346.00 ft
Diameter = .0830 ft
Orifice Coeff. _ .600
SIN: DOYXYWH3NLBE Withers & Ravenel
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Type.... Outlet Input Data
Name.... Outlet 1
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
Page 5.03
OUTLET STRUCTURE INPUT DATA
Structure ID = CO
Structure Type
------------------ = Culvert-Circular
------------------
No. Barrels = 1
Barrel Diameter = 2.0000 ft
Upstream Invert = 346.00 ft
Dnstream Invert = 343.00 ft
Horiz. Length = 104.00 ft
Barrel Length = 104.04 ft
Barrel Slope = .02885 ft/ft
OUTLET CONTROL DATA...
Mannings n - .0130
Ke = .5000
Kb = .012411
Kr = .5000
HW Convergence = .001
(forward entrance loss)
(per ft of full flow)
(reverse entrance loss)
+/- ft
INLET CONTROL DATA...
Equation form = 1
Inlet Control K = .0098
Inlet Control M = 2.0000
Inlet Control c = .03980
Inlet Control Y = .6700
TI ratio (HW/D) = 1.146
T2 ratio (HW/D) = 1.292
Slope Factor = -.500
Use unsubmerged inlet control Form 1 equ. below T1 elev.
Use submerged inlet control Form 1 equ. above T2 elev.
In transition zone between unsubmerged and submerged inlet control,
interpolate between flows at T1 & T2...
At T1 Elev = 348.29 ft ---> Flow = 15.55 cfs
At T2 Elev = 348.58 ft ---> Flow = 17.77 cfs
Structure ID = TW
Structure Type = TW SETUP, DS Channel
------------------------------------
FREE OUTFALL CONDITIONS SPECIFIED
CONVERGENCE TOLERANCES ...
Maxi mum Iterations= 40
Min. TW tolerance = .01 ft
Max. TW tolerance = .01 ft
Min. HW tolerance = .01 ft
Max. HW tolerance = .01 ft
Min. Q tolerance = .00 cfs
Max. Q tolerance = .00 cfs
SIN: DOYXYWH3NLBE Withers & Ravenel
PondPack (10.00.015.00) 8:06 AM 3/11/2008
Type.... Composite Rating Curve
Name.... Outlet 1
File.... K:\05\05-010\05018\H&H\trenton Mar 08.ppw
WS Elev, Total Q
----------------
Elev. Q
ft cfs
346.00
346.10
346.20
346.30
346.40
346.50
346.60
346.70
346.80
346.90
347.00
347.10
347.20
347.30
347.40
347.50
347.60
347.70
347.80
347.90
348.00
348.10
348.20
348.30
348.40
348.50
348.60
348.70
348.80
348.90
349.00
349.10
349.20
349.30
349.40
349.50
349.60
349.70
.00
.01
.O1
.01
.01
.02
.02
.02
.02
.02
.02
.03
.03
.03
.03
.03
.03
.03
.03
.03
.06
.15
.28
.46
.67
.90
1.16
1.42
1.58
1.72
1.85
1.97
2.09
2.19
2.29
2.39
2.49
2.58
***** COMPOSITE OUTFLOW SUMMARY ****
Notes
-------- Converge -------------------------
'Pia 71 O.> 7 ----
ft +/-ft
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Free Outfall
Contributing Structures
(no Q: O1,R0,O0,C0)
OO,CO (no Q: O1,R0)
O0,C0 (no Q: 01,RO)
OO,CO (no Q: O1,R0)
OO,CO (no Q: 01,RO)
OO,CO (no Q: O1,R0)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,R0)
OO,CO (no Q: Ol,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
OO,CO (no Q: 01,RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
O1,O0,C0 (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,C0 (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
01,00,CO (no Q: RO)
Page 5.04
SIN: DOYXYWH3NLBE
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8:06 AM
Withers & Ravenel
3/11/2008
Type.... Composite Rating Curve
Name.... Outlet 1
Page 5.05
***** COMPOSITE OUTFLOW SUMMARY ****
WS Elev, Total Q Notes
-------- -------- ------ -- Converge
-------------
------------
Elev. Q TW Elev Error
ft
-------- cfs
------- ft +/-ft
----- Contributing Structures
349.80
2.67 -
Free -- -----
Outfall --------------
01,00,CO (no ------------
Q: RO)
349.90 2.76 Free Outfall 01,00,CO (no Q: RO)
350.00 2.84 Free Outfall 01,00,CO (no Q: RO)
350.10 2.92 Free Outfall 01,00,CO (no Q: RO)
350.20 3.00 Free Outfall 01,00,CO (no Q: RO)
350.25 3.03 Free Outfall 01,00,CO (no Q: RO)
350.30 3.63 Free Outfall O1,R0,O0,C0
350.40 6.02 Free Outfall O1,R0,O0,C0
350.50 9.41 Free Outfall O1,R0,O0,C0
350.60 13.56 Free Outfall O1,R0,O0,C0
350.70 18.04 Free Outfall O1,R0,O0,C0
350.80 22.76 Free Outfall 01,RO,O0,C0
350.90 27.55 Free Outfall Ol,R0,O0,C0
351.00 30.24 Free Outfall RO,CO (no Q: 01,00)
351.10 30.65 Free Outfall O1,R0,O0,C0
351.20 31.05 Free Outfall RO,CO (no Q: 01,00)
351.30 31.45 Free Outfall RO,CO (no Q: 01,00)
351.40 31.84 Free Outfall RO,CO (no Q: 01,00)
351.50 32.23 Free Outfall RO,CO (no Q: 01,00)
351.60 32.62 Free Outfall RO,CO (no Q: 01,00)
351.70 32.99 Free Outfall RO,CO (no Q: 01,00)
351.80 33.37 Free Outfall RO,CO (no Q: 01,00)
351.90 33.74 Free Outfall RO,CO (no Q: 01,00)
352.00 34.10 Free Outfall RO,CO (no Q: 01,00)
SIN: DOYXYWH3NLBE Withers & Ravenel
PondPack (10.00.015.00) 8:06 AM 3/11/2008
Appendix A
Index of Starting Page Numbers for ID Names
A-1
----- O -----
Outlet 1... 5.01, 5.04
----- P
POND 10... 4.01
POST - UNTREATED... 2.01, 3.01
----- R -----
RDU NOAA 14 Desi... 1.01
----- T
TO BMP... 2.04, 3.02
TO DITCH... 2.06, 3.03
SIN: DOYXYWH3NLBE Withers & Ravenel
PondPack (10.00.015.00) 8:06 AM 3/11/2008
NITROGEN
CALCULATIONS
Trenton Road Subdivision
Total Nitrogen Export Calculations
Pre-Development
Exhibit 3-1 Method 1 for Quantifying TN Export from
Residential Developments when Building and Driveway
Footprints are Not Shown
Step 1: Detetmine area for each type of land use and enter in
Column (2),
Step 2: Total the areas for each type of land use and enter at the
bottom of Column (2).
Step 3: Determine the TN export coefficient associated with right-
of-way using f=igure 3-1.
Step 4: Determine the TN export coefficient associated with lets
using Figure 3.2.
Stop 5., Multipty the areas in Column (2) by the TN export
coefficients in Column (3) and enter in Column (4).
Step 6: Total the TN exports for each type of land use and enter at
the bottom of Column (4).
Step 7: Determine the export coefficient for site by dividing the total
TN export from uses at the bottom of Column (4) by the
total area at the bottom of Column (2) and enter it in at the
bottom of Column (5).
(1) (2) (3) (4) (5)
Type of Land Cover site TN Export TN Export TN Export
Area coeff.. by Land Use From Site
ACraS (b5/aC f 3} Ibslactvr)
Permanently preserved undisturbed
0
6
pan space forest, unmown Meadowv 33.85 . 20.31
Permanently preserved managed 1.2
o n s ace ram, landsq 'n ,etc, :
(tight-of-Tray (read TN export from ' i
Figure 1)
Lots (read TN export from Figure 2)
.i -
Total 33.85
x, . 20.31
h
Average for Site • '? W ' 0.60
City of Raleigh January 1 002
Storrm"'arer Resigo Manual Page 79
Trenton Road Subdivision
Total Nitrogen Export Calculations
Post-Development
Exhibit 3.1 Method 1 for Quantifying TN Export from
Residential Developments when Building and Driveway
Footprints are Not Shown
Step 1: Determine area for each type of land use and enter in
Column (2).
Step 2: Total the areas for each type of land use and enter at tho
bottom of Column (2).
Step 3: Determine the TN export coefficient associated with right-
of-way using Figure 3-1.
Step 4: Determine the TN export coefficient associated with lots
using Figure 3.2.
Step 5: Multiply the areas in Column (2) by the TN export
coefficients in Column (3) and enter in Column (4).
Step 6: Total the TN exports for each type of land use and enter at
the bottom of Cohn (4).
Step 7: Determine the export coefficient for site by dividing the teat
T export from uses at the bottom of Column (4) by the
total area at the bottom of Column (2) and enter it in at the
bottom of Column (5).
(1 (2) (3) (`t)
Type of Land Cover Site TN Expert TN Export TN Export
Area COW by Land Use From Site
Acres tbsiac (lbiglyr) lbslaclyr)
Permanently preserved undisturbed
5
38
0.6
3
23
en space forest, unmown meadow . . -
Permanently preserved managed 2
1 4 ;
open space (grass. landscaing etc,) .
Right-of-war (read TN export from
2
97
10
9
32
37 ' Y s
ire 1) . . .
Lots (read TN export from Figure 2) 25.50 2.8 70.13
otal 33.85 105.73
-
--
Average for Site r '?' > -;r ?5`x
T,f J , c - 3.12
City of Raleigh Ijnudry 2Uo
Starr ?» clter i? srgrt Manual Page 79
J
W
N
OC y
Z
W`°
W
l
+.
N
0
+
+ V
N o
+ W Z ?
+ v r
+ + u l + d
+ +
+ A/ '^ Y
+ + W W
+
+ = V o
W
+
+
Y
+ T
T
+
+
+
+ +
+ + + + v I
+ + + Z
+ O
+
+ + +
+ + + a Q
+ + 3
+ ° U
Z
+ Q O
+
+
" U
H
+ w
+ O Z
+ ?
+ X
+ w
w p
+ Z Q
+ w w
OQ
+ + I + Z
+
+ +
+ + +
+ + + +
+ + + Z
+ + + + O
+ +
+ + + j
+ + +
+ + + + + + m
+ + + +
+ Q
++++
+ O
++
+ + + Z
+ w
+ 3 cR +
IM r
PA:
v?+
w u
+ ? o
? 'roy ?o z e
+ a + g
? Z
+ + o
+ +
+++++
+
li, 1 lu
Lit
\ a+ +
+ + m
BMP
CALCULATIONS
Project Name: Trenton Road Subdivision
City/State: Raleigh, NC
STORMWATER BMP #1 - EXTENDED DRY DETENTION BASIN
Land Use Area
(ac) % IA Imp. Area
(ac)
Lots - 1 acre 7.74 20 1.5
Right of Way (Offsite) 0.46 60 0.3
Totals 8.2 1.8
Total % Impervious Surface Area = 22.2 %
Proiect #:
Date:
BMP 081105
205018
1 1-Mar-08
1-Inch Runoff Volume Calculation
Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987)
Rv = 0.05 + 0.009(1) where, Rv = Runoff coefficient, in./in.
I = Percent impervious
Rv = 0.25 in./in.
Total runoff volume from 1-inch precipitation:
Runoff volume, S = (Design rainfall) (Rv) (Drainage Area)
S = 0.171 acre-ft
7447 cu. ft.
Water quality pool elevation=
Storage volume provided =
Orifice Calculations
Q =Cd*A*(2gh)''(1/2)
Variables
WQ Volume: 0.17096667 Acre-ft
Head: 2.23 ft
Draw down time: 74 hrs
Orifice Area = 0.00549836 sq. ft
Orifice Diameter = 1.00404511 in
347.90 feet
0.172 acre-ft
7492 cu. ft.
Constants
7447.308 cf g = 32.2 ft/s2
1.115 ft Cd= 0.6
266400 s
0.7917644 sq. in
USE 1" DIAMETER ORIFICE