20010185 Ver 1_SW Wetland Calculations_20050701

CMFI Kiml
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We are sending you
® Attached ? Under separate cover via the following items:
? Shop drawings ? Prints/Plans ? Samples ? Specifications
? Change Orders
? Other
Copies Date NO. Description
2 Stormwater Management Plans
These are transmitted as checked below:
? For your use ? Approved as submitted ? Resubmit
? Copies for approval
? As requested ? Approved as noted ® Submit
? Copies for distribution
? For review and comment ? Returned for corrections ? Return ? Corrected prints
Remarks: Enclosed are two revised sets of Stormwater Management Plans for Plantation Point. These
plans address Sam's comments. Also, as requested, the DWQ project # is 00-1489. Please feel free to
contact me at [phone] with any questions.
Thanks,
Copy to: Signed: Jason C. Allen, El
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Stormwater Wetland Calculations
Plantation Point
Raleigh, North Carolina
Prepared for:
Cypress Equities, Inc.
©Kimley-Hom and Associates, Inc., 2005
r=Fj Kimley-Horn
and Associates, Inc

•

PLANTATION POINT
RALEIGH, NORTH CAROLINA

STORMWATER WETLAND CALCULATIONS

.. Prepared for,'
CYPRESS EQUITIES, INC
15601 DALLAS PARKWAY, SUITE 400
. ADDISON, TEXAS 75001

Prepared by:
KIMLEY-HORN AND ASSOCIATES,,INC.
P. O. BOX 33068
RALEIGH, NORTH CAROLINA 27636

. REVISED: JUNE2005
REVISED: DECEMBER 2004
REVISED: OCTOBER 2004
AUGUST 2004,
. 012298001

•
This document, together with the concepts and designs presented herein, as an instrument of service, is intended
only for the specific purpose and client for which it was prepared. Reuse of and improper reliance on this
document without written authorization and adaptation by Kimley-Horn and Associates, Inc. shall be without .
liability to Kimley-Horn and Associates, Inc.

a
TABLE OF CONTENTS
OVERVIEW
WATERSHED MAPS
USGS QUADRANGLE MAP
PRE-DEVELOPMENT DRAINAGE MAP
. POST-DEVELOPMENT DRAINAGE MAP
SOIL CLASSIFICATIONS

USDA SOIL SURVEY MAP
SOIL CLASSIFICATION SUMMARY

WATER QUALITY

. STORMWATER WETLAND DESIGN SUMMARY
NITROGEN CALCULATIONS

WATER QUANTITY
WETLAND ROUTING SUMMARY

WETLAND OUTLET RIP RAP CALCULATIONS

•

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- OVERVIEW
- Back ound
- This report contains the approach and results of a stormwater analysis conducted for the proposed Plantation
- Point shopping center development. The project site is located at the southwest quadrant of Capital
Boulevard (US-1) and Interstate-540 in Raleigh, North Carolina. The development encompasses
approximately 52 acres. Stormwater runoff, after being treated, will discharge into existing culverts under I-
540 that drain to Greshams Lake.
A Major Variance for this project was approved by the Environmental Management Committee of the North
- Carolina Department of Environment and Natural Resources ("NCDENR") Division of Water Quality
- ("DWQ"), on April 11, 2001.
Water Quality
The majority of the development (approximately 45 acres of a 52 acre site) will drain to a proposed on-site
stormwater wetland, which has been designed to mitigate the impacts of the development on stormwater
- quality and quantity (both addressed below). In addition, the wetland has been sized to accommodate
- approximately 10 acres of off-site drainage, for a total watershed of 56 acres. The approved variance for this
project called for a treatment area of 48.5 acres to be served; therefore, the proposed design exceeds
NCDENR's original requirements.
The wetland has been designed and will be constructed according to the guidelines set forth in the City of
Raleigh "Stormwater Design Manual" which refers to the latest design guidance available through the
- NCDENR DWQ, the Center for Watershed Protection, The North Carolina Cooperative Extension
("NCCE"), and other well-established programs. The design included herein is also based on the
recommendations included in the NCDENR's "Stormwater Best Management Practices" manual and the
NCCE's "Stormwater Wetland Workshop" manual.
- The vegetation planted in the wetland provides stormwater filtration that is designed to remove pollutants.
The stormwater wetland is designed to provide 85% total suspended solid (TSS) removal and to reduce
nitrogen loading rates to below 10 lbs/ac/yr per the Neuse Stormwater Rule (15A NCAC 2B .0235) of the
. "Neuse River Basin: Model Stormwater Program for Nitrogen Control," August, 1999. The wetland will
also reduce total phosphorous, ammonia-nitrogen, phosphate-phosphorous, and some metals.
A by-pass level spreader was designed according to the NCDWQ Level Spreader Design Suggestions Oct.
2001. The level spreader system includes a small detention basin and a bypass system for storms greater
than 1" per hour. The level spreaders are in series due to steep slopes in Zone 2. A series level spreader of
earth and grass will be used outside of Zone 1.
An analysis of estimated nitrogen export and offset fees, per City of Raleigh and NCDENR regulations, is
included herein. At the request of the City of Raleigh, this breakdown also accounts for additional nitrogen
- generated for the proposed extension of Ruritania Street. Storm drainage from Ruritania Street will outfall
to level spreaders.

r
r
r
r Water Quantity
r The proposed stormwater wetland has been designed to control stormwater per NCDENR and City of
Raleigh requirements. The 1-year, 24-hour storm was analyzed per NCDENR requirements. In addition, the
r 2- and 10-year, 24-hour storm events were analyzed per City of Raleigh Stormwater requirements. Because
r the post-development peak discharge rates will not exceed the pre-development levels, it is not anticipated
that the capacity of the NCDOT culverts downstream will be adversely affected. Direct runoff from grassed
slopes not draining to the pond was neglected altogether in this analysis since pre- and post-development
r runoff coefficients and time of concentration are basically equivalent for these areas. Stormwater quantity
r from, the City of Raleigh required Ruritania Street extension was also neglected since the increase in runoff
r from the pre- to post-development condition is less than 5% for the 10-year storm (See attached
calculations).
r The proposed stormwater management system will also include City of Raleigh catch basins, concrete
r piping, lined ditches (where applicable), velocity riprap dissipaters, and level, spreaders.
r
Conclusion
The proposed stormwater wetland and other stormwater management measures were sized using methods
r prescribed by the aforementioned resources. The wetland was routed using "PondPack," a Haestad Methods
. computer software program, which utilizes TR-55 methods of calculating time of concentration and SCS
. methods of generating hydrographs. Based on the analyses provided herein, the proposed system will be
adequate to address the stormwater requirements of the City of Raleigh and NCDENR.
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. Title: USGS Quad Map (Raleigh East and Wake Forest, NC, 1987)
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F1 Project:
Stoi•mwater Analysis

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Kimley-Horn and Associates, Inc. Raleigh, North Carolina
Date: Scale: Project No. Appendix:
08/04 012298001
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Title: Soils Map (Wake County GIS, 2003)
Project:
PEPOP], m F Stormwater Analysis
Plantation Point
Kimley-Horn and Associates, Inc, Raleigh, North Carolina
Date: Scale: Project No. Appendix:
08/04 012298001

Plantation Point
Raleigh, North Carolina
Soil Classifications
Kimley-Horn and Associates, Inc.
Date: 8/30/2004
Prepared by: JCA
Checked by: JNG
Soils present in the watershed, based on Wake County GIS, 2003
Symbol Name Description Slope Group
ApB2 Appling sandy loam 2-6% eroded B
ApC2 Appling sandy loam 6-10% eroded B
ApD Appling sandy loam 10-15% B
CeB2 Cecil sandy loam 2-6% eroded B
CeC2 Cecil sandy loam 6-10% eroded B
CeD Cecil sandy loam 10-15% B
Cn Colfax sandy loam - C
LoC Louisburg loamy sand 6-10% B
LoD Louisburg loamy sand 10-15% B
WkE Wake Soils - 10-25% D
Wy Worsham sandy loam - D
Soil Group B will be used in the analysis contained herein.

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CZI . andLsociates,lnc.
Stormwater Wetland Design Summary
Per NCDENR's
Stormwater BMP Manual

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Project Information
Project Name: Plantation Point
KHA Project #: 012298001
Designed by: JCA Date: 10/25/2004
Revised by: JCA Date: 6/6/2005
Checked by: JJW Date: 6/6/2005
Site Information
Drainage Area (DA): 55.01 Acres (Includes Post-1, Offsite Old Wake Forest, and Offsite Capital)
Impervious Area (IA): 43.89 Acres (see Watershed and CN Summary)
Percent Impervious (1): 79.79
Required Surface Area at Permanent Pool
Depth Range = 0 - 1.5 feet Avg. Depth = 0.75 feet
TSS Removal= 85 %
SA/DA = 3.35 % (from Table 1.1 in BMP Manual)
SA = 80,274 SF = 1.8 Ac
Provided Surface Area
SA= 81,968 SF
Required Treatment Volume: (Simple Method - prefered)
Design Storm = 1 inches
Determine Rv Value= 0.05 +.009 (1) _
Volume Required= 153,373 CF
Volume = Design Rainfall*Rv*DA
Req'd Depth of Temp. Pool:
Permanent Pool Volume: _
Required Forebay Volume:
1.9 Ac
0.77 in/in
(Drawn over a period of 2-5 days)
1.91 ft above permanent pool
3.41 ft above pond bottom
60,205 cf (assuming avg. depth = 0.75')
16,257 cf (15% of Permanent Pool)
* Additional storage (detention) volume provided for Water Quantity
** This depth is approximate; final depth to be calculated based on average end area of wetland contours
Surface Area Breakdown
Surface Area Required = 80,274 SF
Surface Area Provided = 81,968 SF
Description Area
Forebays 16,257
Micropools 12,373
Marsh 66,542
Total 95,172
Marsh Area Breakdown Area
Uplands 4,267
High Marsh (0-0.75' Deep) 32,085
Low Marsh (0.75-1.5' Deep) 25,465
Deep Pools (>1.5' Deep) 4,725
Total 66,542
C?/? KimleyHom
? and Associates, Inc.
Stormwater Wetland Design Summary
- Per NCDENR's
Stormwater BMP Manual
•

- Orifice Sizing (2-5 Day Bleed Down Orifice)
d
Q2day= own)
0.89 cfs (Flowrate req. for 2 day draw
. Q5day= 0.36 cfs (Flowrate req. for 5 day drawdown)
Orifice Diameter = 5 in => Area= 0.14 sf
Average Head= 0.85 ft a= CdA(2gh)^0.5= 0.61 cfs
Drawdown Time = 70.34 hrs
- 2.93 days
. Anti-Floatation Calculations
- Strucure 1 (to 1-540 60" RCP) '
d
Area: )
85.5 sf (Water Displace
- Volume: 512.9 cf (Water Displaced)
Factor of Safety: 1.3
Weight: 32.007 Ibs (Water Displaced)
Wt. Req'd of Anti-Floatation Device: 41,610 Ibs
. Weight of Structure: 46,800 Ibs
Therefore no additional antifloatation is required.
• Strucure 2 (to 1-540 72" RCP) '
Area: 20.0 sf (Water Displaced)
Volume: 154.0 cf (Water Displaced)
Factor of Safety: 1.3
Weight: 9,610 lbs(Water Displaced)
. Wt. Req'd of Anti-Floatation Device: 12,492 Ibs
Weight of Structure: 24,640 lbs
Therefore no additional antifloatation is required.
" See Detail for all dimensions

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Stormwater Wetland Calculations
Plantation Point
Raleigh, North Carolina
Prepared for:
Cypress Equities, Inc.
©Kimley-Horn and Associates, Inc., 2005
? ? ? Kimley-Horn
i and Associates, Inc.
T *h
0

. PLANTATION POINT
RALEIGH, NORTH CAROLINA
STORMWATER WETLAND CALCULATIONS

. Prepared for:
CYPRESS EQUITIES, INC
15601 DALLAS PARKWAY, SUITE 400
- ADDISON, TEXAS 75001

• Prepared by:
KIMLEY-HORN AND ASSOCIATES, INC.
- P. O. BOX 33068
RALEIGH, NORTH CAROLINA 27636
•

- REVISED: JUNE 2005
REVISED: DECEMBER 2004
REVISED: OCTOBER 2004,
AUGUST 2004
012298001

This document, together with the concepts and designs presented herein, as an instrument of service, is intended •
only for the specific purpose and client for which it was prepared. Reuse of and improper reliance on this -
document without written authorization and adaptation by. Kinley-Horn and Associates, Inc. shall be without
liability to Kimley-Horn and Associates, Inc.

TABLE OF CONTENTS
OVERVIEW
WATERSHED MAPS
USGS QUADRANGLE MAP
PRE-DEVELOPMENT DRAINAGE MAP
POST-DEVELOPMENT DRAINAGE MAP

•
a

SOIL CLASSIFICATIONS
USDA SOIL SURVEY MAP
SOIL CLASSIFICATION SUMMARY
WATER QUALITY
STORMWATER WETLAND DESIGN SUMMARY
NITROGEN CALCULATIONS
WATER QUANTITY
WETLAND ROUTING SUMMARY
WETLAND OUTLET RIP RAP CALCULATIONS
a
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a
• Background
OVERVIEW
This report contains the approach and results of a stormwater analysis conducted for the proposed Plantation
Point shopping center development. The project site is located at the southwest quadrant of Capital
Boulevard (US-1) and Interstate-540 in Raleigh, North Carolina. The development encompasses
approximately 52 acres. Stormwater runoff, after being treated, will discharge into existing culverts under I-
540 that drain to Greshams Lake.
A Major Variance for this project was approved by the Environmental Management Committee of the North
Carolina Department of Environment and Natural Resources ("NCDENR") Division of Water Quality
. ("DWQ"), on April 11, 2001.
Water Quality
• The majority of the development (approximately 45 acres of a 52 acre site) will drain to a proposed on-site
stormwater wetland, which has been designed to mitigate the impacts of the development on stormwater
quality and quantity (both addressed below). In addition, the wetland has been sized to accommodate
. approximately 10 acres of off-site drainage, for a total watershed of 56 acres. The approved variance for this
project called for a treatment area of 48.5 acres to be served; therefore, the proposed design exceeds
NCDENR's original requirements. _
. The wetland has been designed and will be constructed according to the guidelines set forth in the City of
Raleigh "Stormwater Design Manual" which refers to the latest design guidance available through the
NCDENR DWQ, the Center for Watershed Protection, The North Carolina Cooperative Extension
. ("NCCE"), and other well-established programs. The design included herein is also based on the
recommendations included in the NCDENR's "Stormwater; Best Management Practices" manual and the
NCCE's "Stormwater Wetland Workshop" manual.
• The vegetation planted in the wetland provides stormwater filtration that is designed to remove pollutants.
The stormwater wetland is designed to provide 85% total suspended solid (TSS) removal and to reduce
nitrogen loading rates to below 10 lbs/ac/yr per the Neuse Stormwater Rule (15A NCAC 2B .0235) of the
"Neuse River Basin: Model Stormwater Program for Nitrogen Control," August, 1999. The wetland will
. also reduce total phosphorous, ammonia-nitrogen, phosphate-phosphorous, and some metals.
A by-pass level spreader was designed according to the NCDWQ Level Spreader Design Suggestions Oct.
2001. The level spreader system includes a small detention basin and a bypass system for storms greater
than 1" per hour. The level spreaders are in series due to steep slopes in Zone 2. A series level spreader of
earth and grass will be used outside of Zone 1.
• An analysis of estimated nitrogen export and offset fees, per City of Raleigh and NCDENR regulations, is
included herein. At the request of the City of Raleigh, this breakdown also accounts for additional nitrogen
generated for the proposed extension of Ruritania Street. Storm drainage from Ruritania Street will outfall
. to level spreaders.

•
•
• Water Quantity
The proposed stormwater wetland has been designed to control stormwater per NCDENR and City of
Raleigh requirements. The 1-year, 24-hour storm was analyzed per NCDENR requirements. In addition, the
• 2- and 10-year, 24-hour storm events were analyzed per City of Raleigh Stormwater requirements. Because
the post-development peak discharge rates will not exceed the pre-development levels, it is not anticipated
that the capacity of the NCDOT culverts downstream will be adversely affected. Direct runoff from grassed
slopes not draining to the pond was neglected altogether in this analysis since pre- and post-development
runoff coefficients and time of concentration are basically equivalent for these areas. Stormwater quantity
• from the City of Raleigh required Ruritania Street extension was also neglected since the increase in runoff
from the pre- to post-development condition is less than 5% for the 10-year storm (See attached
calculations).
The proposed stormwater management system will also include City of Raleigh catch basins, concrete
piping, lined ditches (where applicable), velocity riprap dissipaters, and level spreaders.
•
Conclusion
The proposed stormwater wetland and other stormwater management measures were sized using methods
prescribed by the aforementioned resources. The wetland was routed using "PondPack," a Haestad Methods
computer software program, which utilizes TR-55 methods of calculating time of concentration and SCS
methods of generating hydrographs. Based on the analyses provided herein, the proposed system will be
adequate to address the stormwater requirements of the City of Raleigh and NCDENR.
•
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mF1 Project:
Stormwater Analysis
= Plantation Point
Kimley-Horn and Associates, Inc. Raleigh, North Carolina
Date: Scale: Project No. Appendix:
08/04 012298001
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- WATERSHED BOUNDARY
TIME OF CONCENTRATION
_ FLOW PATH
SF SHEET FLOW
SHALLOW CONCENTRATED
SC FLOW
CF CHANNEL/PIPE FLOW
OFFSITE - OFF-SITE WATERSHED
PRE - ON-SITE WATERSHED
PLANTATION POINT
of /A RALEIGH, NORTH CAROLINA
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Title: Soils Map (Wake County GIS, 2003)
Project:
_ Stormwater Analysis
Elm F1 Plantation Point
Kimley-Horn and Associates, Inc, Raleigh, North Carolina
Date: Scale: Project No. Appendix:
• 08/04 012298001
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Plantation Point Kimley-Horn and Associates, Inc.
Raleigh, North Carolina Date: 8/30/2004
Soil Classifications Prepared by: JCA
Checked by: JNG
Solis present in the watershed, based on Wake County GIS, 2003
Symbol Name Description Slope Group
ApB2 Appling sandy loam 2-6% eroded B
ApC2 Appling sandy loam 6-10% eroded B
ApD Appling sandy loam 10-15% B
CeB2 Cecil sandy loam 2-6% eroded B
< CeC2 Cecil sandy loam 6-10% eroded B
CeD Cecil sandy loam 10-15% B
Cn Colfax sandy loam - C
LoC Louisburg loamy sand 6-10% B
LoD Louisburg loamy sand 10-15% B
ME Wake Soils - 10-25% D
Wy Worsham sandy loam - D
Soil Group B will be used in the analysis contained herein.
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1• Kimley-Horn
Czrl and Associates, Inc.
Stormwater Wetland Design Summary
Per NCDENR's
Stormwater BMP Manual
Project Information
Project Name: Plantation Point
KHA Project #: 012298001
Designed by: JCA Date: 10125/2004
Revised by: JCA .Date: 6/6/2005
Checked by: JJW Date: 6/6/2005
Site Information
Drainage Area (DA): 55.01 Acres (Includes Post-1, Offsite Old Wake Forest, and Offsite Capital)
Impervious Area (IA): 43.89 Acres (see Watershed and CN Summary)
Percent Impervious (1): 79.79
Required Surface Area at Permanent Pool
Depth Range = 0-1.5 feet Avg. Depth= 0.75 feet
TSS Removal= 85 %
SA/DA = 3.35 % (from Table 1.1 in BMP Manual)
SA = 80,274 SF = 1.8 Ac
Provided Surface Area
SA= 81,968 SF = 1.9 Ac
Required Treatment Volume: (Simple Method - prefered)
Design Storm = 1 inches
Determine Rv Value= 0.05 +.009. (1) = 0.77 in/in
Volume Required= 153,373 CF
Volume = Design Rainfall*Rv*DA (Drawn over a period of 2-5 days)
Req'd Depth of Temp. Pool: ** = 1.91 ft above permanent pool
= 3.41 ft above pond bottom
Permanent Pool Volume: = 60,205 cf (assuming avg. depth = 0.75')
Required Forebay Volume: = 16,257 cf (15% of Permanent Pool)
" Additional storage (detention) volume provided for Water Quantity
" This depth is approximate; final depth to be calculated based on average end area of wetland contours
Surface Area Breakdown
Surface Area Required = 80,274 SF
Surface Area Provided = 81,968 SF
Description Area
Forebays 16,257
Micropools 12,373
Marsh 66,542
Total 95,172
Marsh Area Breakdown Area
Uplands 4,267
High Marsh (0-0.75' Deep) 32,085
Low Marsh (0.75-1.5' Deep) 25,465
Deep Pools (>1.5' Deep) 4,725
Total 66,542
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Cl , and Associates,
Z and Associates, inc.
Orifice Sizing (2-5 Day Bleed Dow
Q2day=
Q5day=
Orifice Diameter =
Average Head=
Stormwater Wetland Design Summary
Per NCDENR's
Stormwater SMP Manual
i Orifice)
0.89 cfs (Flowrate req. for 2 day drawdown)
0.36 cfs (Flowrate req. for 5 day drawdown)
5 in => Area=
0.85 ft Q= CdA(2gh)^0.5=
Drawdown Time =
Anti-Floatation Calculations
Strucure 1 (to 1-540 60" RCP) `
Area: 85.5 sf (Water Displaced)
Volume: 512.9 cf (Water Displaced)
Factor of Safety: 1.3
Weight: 32,007 Ibs (Water Displaced)
Wt. Req'd of Anti-Floatation Device: 41,610 Ibs
Weight of Structure: 46,800 Ibs
Therefore no addi tional antifloa tation is required.
Strucure 2 (to 1-540 72" RCP) '
Area: 20.0 sf (Water Displaced)
Volume: 154.0 cf (Water Displaced)
Factor of Safety: 1.3
Weight: 9,610 Ibs(W ater Displaced)
Wt. Req'd of Anti-Floatation Device: 12,492 Ibs
Weight of Structure: 24,640 Ibs
Therefore no add itional antifloatation is required.
' See Detail for all dimensions
0.14 sf
0.61 cfs
70.34 hrs
2.93 days

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Job Subject "r'? ??? D ?? ?G S• Job No.
Designed by Date Checked by Date