20091312 Ver 1_More Info Received_20091217

LETTER OF TRAN M 9'%WK
S I T T A L DICKSON
community Infrastructure consultants
720 Corporate Center Drive Raleigh, North Carolina 27607 919.782.0495 tel. [phone] fax
TO: 401 Permitting Review Unit DATE: 12-16-09
2321 Crabtree Blvd., Suite 250
Mail Service Center 1650 RE: Newland By-Pass Channel Project
Raleigh, NC 27699-1650 Design Development Plans
ATTENTION: Ian McMillan
We are sending via: ? Overnight ® Regular Mail ? Pick-up ? Hand Delivered
The following items: ? Correspondence ® Plans ? Specifications ? Other as listed below:
COPIES DATE NO. DESCRIPTION
2 Dec 15, 2009 Design Development Plans (Final Design) - (24"x36")
2 Dec 15, 2009 Design Development Plans (Final Design) - (11 "x17")
1 Dec 15, 2009 CD with TIFF Image of Plans

DEC 1 7 2009
DENR - wATFR QUALITy

THESE ARE TRANSMITTED as checked below:
® For Approval ? As Requested ? Approved as Submitted ? Returned for Corrections
? For Your Use ® For Review and Comment ? Approved as Noted ? Forward to Subcontractor
REMARKS:
Please let me know if you have any questions or need anything further. As you know we are under
a tight schedule and certainly would appreciate an assistance you could provide in keeping this
moving. Thanks for your help with our request.
H
COPY TO: 80499.00.RA SIGNED:
01-1,3i*,1-
WD[ ?_Z' I < S C,
community infrastructure consultants
December 16, 2009
Mr. Gray Hauser, PE
NCDENR - Division of Land Resources - Land Quality Section
1612 Mail Service Center
Raleigh, North Carolina 27699-1612
RE: Town of Newland Flood By-Pass Channel & Pineola Street Floodplain Improvements
Trout Buffer Variance Request
Dear Mr. Hauser:
WK Dickson requests review and comment on any possible issues that may emerge with respect to the trout
buffer requirements associated with the proposed Flood By-Pass Channel & Pineola Street Floodplain
Improvements project in Newland, North Carolina. The project is located along the North Toe River as
shown on the included set of design plans. The North Toe River is classified as trout (Tr) waters. As part of
the proposed project, land-disturbing activities will be performed within the 25-foot trout buffer zone. The
following is a description of the proposed project:
• Install a 60-foot wide, 536-foot long grass-lined earthen by-pass channel to divert flows around the
area currently constricting flood flows. This by-pass channel is located approximately 1,400 feet
downstream of Pineola Street (US Highway 194).
• Install a floodplain bench along the left and right overbank in the vicinity of Pineola Street. These
floodplain improvements also include a greenway trail in the right overbank which ties into the
existing parks that are located on either side of Pineola Street. The purpose of these floodplain
benches is to lower the tailwater elevation on the Pineola Street culverts to improve hydraulic
performance and also reduce upstream flood elevations.
• Install a new headwall with a beveled upstream face at the Pineola Street (Highway 194) box
culverts. Beveling the front face of the culvert requires securing a new concrete headwall that will
reduce energy losses through the culvert and reduce upstream water surface elevations.
• Install a 42-foot long pedestrian steel truss footbridge that ties in the existing upstream park with the
proposed greenway and existing downstream park.
• Improve local drainage at Old Cranberry Street. Currently, the road overtops approximately 20+
times per year.
• Install 387 linear feet of 12" diameter PVC closed drainage system to collect runoff from the
Newland Shopping Center. This new closed drainage system will outfall into the recently
constructed extended detention wetland.
• Install 274 linear feet of 8" diameter PVC closed drainage system to collect runoff from the
proposed greenway.
? t'xtlr„ r7€?i?E?

• Replace the existing undersized closed drainage system at Cranberry Street with 294 linear feet of
42" diameter RCP and 126 linear feet of 48" RCP. The existing closed drainage system does not
meet minimum NCDOT design standards for a local collector road.
As you are aware, several of the listed items are proposed to take place within the 25-foot buffer as shown
on the attached plans. Efforts were made to minimize impacts within this trout buffer zone. The following
items document the efforts to minimize adverse impacts to water quality and improve trout habitat:
• Remove existing rip-rap banks: The project will be removing over 300-feet of rip-rap on the left and
right banks of the North Toe River. The seven (7) to twelve (12) foot high channel banks will be
reshaped and a floodplain bench installed at the bankfull flood elevation. The left bank will be
naturally vegetated and the right bank will include a 1 foot wide grass buffer located adjacent to the
greenway. Removing this rip-rap bank will reduce the quantity of rock exposed to sunlight and
should help reduce water temperatures after flood events.
• Create a floodplain bench: A floodplain bench is proposed approximately four (4) feet above the
existing channel invert. This will allow the more frequent flood events to access this floodplain
bench in efforts to reduce in town flooding.
• Install boulder toes: Boulder toes are proposed to replace the rip-rap banks. The footer rocks will be
set 18 inches below the channel bottom for stability purposes. This will provide some habitat
improvements over the existing rip-rap banks.
• Plant native vegetation on the south bank of the channel: As shown on the separately attached plans,
the project will provide some new plantings to enhance the shading of the North Toe River.
Additional plantings have been placed on either side of the proposed by-pass channel located 1400
feet downstream of Pineola Street.
Efforts were made to reduce the widths per your direction however this resulted in increased flood
elevations in the downtown business district. Therefore you will see the existing and proposed toes very
close to each other. We thank you in advance for your timely response and cooperation. Please feel free to
contact us with any questions that you may have concerning this project.
Sincerely,
W.K. Dickson & Co., Inc.
David Kiker, PE
Attachments (2)
1. 24" x 36" set of design plans
2. Financial Responsibility /Ownership Form
3. Erosion Control Narrative with By-Pass Channel Design Calcs
J,
FINANCIAL RESPONSIBILITY/OWNERSHIP FORM
SEDIMENTATION POLLUTION CONTROL ACT
EXPRESS PERMITTING OPTION 08012007
No person may initiate any land-disturbing activity on one or more acres as covered by the Act before this
form and an acceptable erosion and sedimentation control plan have been completed and approved by the
Land Ouality Section, N.C. Department of Environment and Natural Resources. (Please type or print and, if
the question is not applicable or the e-mail and/or fax information unavailable, place N/A in the blank)
Part A.
1. Project Name Town of Newland - Flood By-Pass Channel & Pinola Street FbW- plain Improvements
2. Location of land-disturbing activity: County Avery City or Township Newland
Highway/Street ?ineola St & Old Cranberry St Latitude 36° 05' 05.07° Longitude 81 ° 55' 54.58°
3. Approximate date land-disturbing activity will commence: March 2010
4. Purpose of development (residential, commercial, industrial, institutional, etc.): Public Flood Reduction
5. Total acreage disturbed or uncovered (including off-site borrow and waste areas): 4.73
6. Amount of fee enclosed: $ 1.575 The Express Permitting application fee is a dual charge.
The normal fee of $65.00 per acre is assessed without a ceiling amount. In addition, the Express
Permitting supplement is $250.00 per acre up to eight acres, after which the Express Permitting
supplemental fee is a faced $2,000.00 (Example: 9 acres total is $2,585). NOTE: Both fees are
rounded up to the next whole acre and need to be paid by separate checks to NCDENR.
7. Has an erosion and sediment control plan been filed? Yes No Enclosed X
8. Person to contact should erosion and sediment control issues arise during land-disturbing activity:
Name Keith Hoilman E-mail Address [e-mail]
Telephone [phone] Cell # Fax # [phone]
9. Landowner(s) of Record (attach accompanied page to list additional owners):
See plans and attached spreadsheet
Name Telephone Fax Number
Current Mailing Address
City State Zip
Current Street Address
city state Zip
10. Deed Book No. Page No. Provide a copy of the most current deed.
Part B.
1. Person(s) or firm(s) who are financially responsible for the land-disturbing activity (Provide a
comprehensive list of all responsible parties on an attached sheet):
Brenda Pittman brenda at7newlandgov com
Name E-mail Address
301 Cranberry Street 01 Cranberry t
Current Mailing Address Current Street Address
Newland NC 28657 1 Newland NC 28657
City state zip I City state Zip
Telephone [phone] Fax Number 828-733-2069
2. (a) If the Financially Responsible Party is not a resident of North Carolina, give name and street address
of the designated North Carolina Agent:
Name
Current Mailing Address
E-mail Address
Current Street Address
City State . Zip
Telephone
City State Zip
Fax Number
(b) If the Financially Responsible Party is a Partnership or other person engaging in business under an
assumed name, attach a COPY Of the Cerdficabs of Assumed Name. If the Financially Responsible
Party is a Corporation, give name and street address of the Registered Agent:
Name of Registered Agent
Current Mailing Address
E-mail Address
Current Street Address
city state zip city State Zip
Telephone Fax Number
(c) In order to facilitate Express Permitting, it is necessary to be able to contact the Engineer or other
consultant who can assist in providing any necessary information regarding the plan and its preparation:
WK Dickson and Co.. Inc. dikikerOwkdickson.com
Engineering Firm or other consultant E-mail Address
Dave Kiker 919-782-0495 919-782-9672
Individual contact person (type or print) Telephone Fax Number
The above information is true and correct to the best of my knowledge and belief and was provided by me
under oath (This form must be signed by the Financially Responsible Person if an individual or his attomey-in-
fact, or if not an individual, by an officer, director, partner, or registered agent with the authority to execute
instruments for the Financially Responsible Person). I agree to provide corrected information should there be
any change in the information provided herein.
Brenda Pittman Town of Newland Manager
Type or print name Tide or Authority
Signature Date
1, LY1 a Notary Public of the Countyof Ave-viq
State of North Carolina, reby certify that brP11 O&2- Vt Thq-j1 Ln appeared personally
before me this-day-and being duly sworn acknowledged that the above form was executed by him.
Witnese\- lhand and nWoal seal, this _-_LL _day of &-ZMbVY. 20_Cft
Notary
My commission expires V tai
SEDIMENT/EROSION CONTROL
PERMIT APPLICATION
FOR
FLOOD BY-PASS CHANNEL & PINEOLA STREET FLOODPLAIN
IMPROVEMENTS PROJECT
NEWLAND, NORTH CAROLINA
PREPARED FOR
NCDENR DIVISION OF WATER RESOURCES
PREPARED BY
W.K. DICKSON & CO., INC.
720 CORPORATE CENTER DRIVE
RALEIGH, NC 27607
DECEMBER 9, 2009 DAVID J. KIKER, PE
INTRODUCTION
Table of Contents
Page
Introduction ....................................................................................................................... 1
Project Need ................................................................................................................. 2
Existing Conditions ....................................................................................................... 2
Erosion Control Plan .......................................................................................................... 3
Overview and Construction Sequencing ......................................................................... 3
Erosion Control Measures .............................................................................................. 4
Channel Stability Analysis .............................................................................................. 5
List of Tables
Table No.
Page
1 Permissible Shear Stresses for Boulder Toe ......................................................... 5
2 Permissible Velocities for Greenway and Floodplain Bench ................................ 5
3 Outlet Protection at Culverts and Ditch Outfall .................................................. 6
4 Channel Liner Summary .................................................................................... 7
5 Hydraulic Summary at Proposed Footbridge ....................................................... 7
6 By-Pass Channel Design Summary ..................................................................... 8
List of Appendices
Appendix A Project Overview Map and USGS Quad Map
Appendix B Vicinity Map
Appendix C Limits of Disturbance Overview Map and Notification of affected property owners
Appendix D NRCS Soil Survey Map and Geotech Report
Appendix E Sediment Trap Sizing Calculations
Appendix F Rip-Rap Pad Calculations
Appendix G Channel Liner Calculations
Appendix H HEC-RAS Output
Appendix I Erosion and Sedimentation Control Plan Preliminary Review Checklist, technical
specifications
Appendix I Technical Specifications
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
INTRODUCTION
This narrative supports the request for a sediment and erosion control permit for the proposed Flood By-
Pass Channel & Pineola Street Floodplain Improvements project in Newland, North Carolina. WK
Dickson is submitting this request on behalf of the Town of Newland and the North Carolina
Department of Environmental and Natural Resources - Division of Water Resources (NCDENR-DWQ).
As a result of the severe flooding experienced in this area, the State of North Carolina through Senate
Bill 7 developed a series of projects intended to alleviate future flooding. One of these projects is the
Newland Flood By-Pass Channel & Pineola Street Floodplain Improvements project. The proposed
project will reduce 100-year flood elevations by approximately 1.5 feet by constructing a by-pass
channel and creating a floodplain bench for floodwaters to access. As shown on the separately attached
set of design plans, the project is composed of the following:
• Install a 60-foot wide, 536-foot long grass-lined earthen by-pass channel to divert flows around
the area currently constricting flood flows. This by-pass channel is located approximately 1,400
feet downstream of Pineola Street (US Highway 194).
• Install a floodplain bench along the left and right overbank in the vicinity of Pineola Street.
These floodplain improvements also include 810 linear feet of greenway trail in the right
overbank which ties together two existing parks that are located on either side of Pineola Street.
The purpose of these floodplain benches is to lower the tailwater elevation on the Pineola Street
culverts to improve hydraulic performance and also reduce upstream flood elevations.
• Retrofit the existing headwall with a beveled upstream face at the Pineola Street (Highway 194)
box culverts. Retrofitting a beveled front face to the concrete headwall will reduce energy
losses through the culvert and will reduce upstream water surface elevations.
• Install a 43-feet long pedestrian steel truss footbridge that ties in the existing upstream park with
the proposed greenway and existing downstream park.
• Plant trout-habitat-friendly trees on the south bank of the channel to provide shade for trout.
• Install boulder toe protection on the right channel bank to provide additional protection for the
proposed footbridge abutment.
• Install 387 linear feet of 12" diameter PVC closed drainage system to collect runoff from the
Newland Shopping Center. This new closed drainage system will outfall into the recently
constructed extended detention wetland designed to treat water quality.
• Install 274 linear feet of 8" diameter PVC closed drainage system to collect runoff from the
proposed greenway.
• Replace the existing undersized closed drainage system at Old Cranberry Street with 294 linear
feet of 42" diameter RCP and 126 linear feet of 48" RCP. The existing closed drainage system
does not meet minimum NCDOT design standards for a local collector road. Currently the road
overtops approximately 20 times per year and does not meet minimum NCDOT design
standards.
Although the main purpose of the project is to reduce flooding, measures have been taken to design a
project that is stable long term and requires minimal maintenance. Some of those design measures
include:
Set the slope of the grass lined by-pass channel to 0.4 feet/feet to minimize the 10- and 100-year
channel velocities. The 10- and 100-year velocities are 4.3 and 5.9 feet/second.
Oversize the boulder toes along the proposed floodplain bench and greenway trail to minimize
potential for bank erosion. These boulders will be approximately 3'x3'x2' in size and will
include a footer boulder that will be set 18-inches below the channel bottom. The boulders
have been oversized to exceed the permissible shear stress that would be experienced in the
channel during a 100-year flood event.
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
INTRODUCTION
Project Need
In September 2004, remnants of Tropical Storm Frances and Hurricane Ivan caused severe flooding in
western North Carolina. One area that experienced some of the worst flooding was the Town of
Newland. As many as thirty-five (35) businesses and six (6) residential structures experienced flooding.
Additionally, numerous roads in the downtown area overtopped. Flooding in the downtown area is
exacerbated by the following three downstream floodplain conditions:
High channel banks that approach 12 to 15 feet
in height for the first 300 feet downstream of
Pineola Street (State Highway 194). The banks
are this high due to fill placed to raise the rear
of the commercial lots adjacent to the channel.
Natural bank heights approach 4 to 5 feet for
the area immediately downstream of Town.
Pineola Street (State Highway 194) roadway
crossing with four 11-foot by 8-foot reinforced
concrete box culverts (RCBCs).
A natural floodplain constriction located
approximately 1500 feet downstream of Pineola Street
from Hurricane Ivan
Pineola Street (State Highway 194). This v
floodplain constriction is vulnerable to debris
accumulation and also causes upstream flood elevations to be higher than would be expected.
Debris accumulation on the right floodplain approached 6 feet in height after remnants of
Hurricane Ivan passed through.
The attached plans reflect the erosion control plan that was developed for the recommended alternative
developed to reduce flooding in the Town of Newland.
Existing Conditions
The project site is composed of two sub-project areas that flank the North Toe River (see Appendix A).
A vicinity map has been included in Appendix B. The first project area is located in the highly
developed downtown area of Newland and is referred to as the Pineola Street Floodplain Improvements
project. This area is bordered by existing businesses at Pineola Street, including the Ugly Mugg Coffee
Shop, Advanced Auto and the Newland Shopping. The existing channel banks downstream of Pineola
Street are currently covered with Class I rip-rap. The second project area is in a very rural area of Town
located approximately 1300 feet downstream of Pineola Street and is referred to as the proposed Flood
By-Pass Channel project. The area of the proposed by-pass channel is currently undeveloped with
landuse of woods and grass. The total limit of disturbance for these two areas is 4.73 acres (see
Appendix Q.
A review of the NRCS soils mapping shows that the soil is widely varied at the site, with the
predominant soils groups consisting of Nikwasi (loam) and Porters (gravelly loam). Porters is a well
draining soils with a Hydrology Soil Group classification of "B" and Nikwasi is a poorly draining soil
with a Hydrology Soil Group classification of "B/D" for use in NRCS hydrologic calculations. An NRCS
soil survey map has been included along with soil boring results in Appendix D.
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
2
EROSION CONTROL PLAN
Overview and Construction Sequencing
The separately attached plans and this narrative outline the erosion control measures that will be
implemented to meet NCDENR erosion control requirements for the project. A detailed description of
the erosion control measures and construction sequencing has been provided in the separately attached
plans. It should be noted that due to the extensive grading associated with the proposed by-pass
channel area, this erosion control for this project area will be handled in a two phased plan. The
erosion control improvements in the downtown area will be constructed in a single-phased approach.
The following sections provide additional clarification of how the erosion control measures will be
phased into the construction of the different project areas. A more detailed description of the
construction sequencing is provided in the Erosion Control Plan section of the separately attached
plans.
By-Pass Channel Erosion Control
The By-Pass Channel Erosion Control will be broken into two phases to control erosion during the
initial clearing and grubbing of the site, with additional measures installed following completion of the
grading until the site is stabilized. Phase 1 erosion control measures will include silt fencing to keep
runoff onsite, and a series of diversion ditches that outlet to three temporary sediment traps to treat
runoff from exposed surfaces. The Phase 1 erosion control measures will remain in place until
construction is complete and site is stabilized.
The Phase 2 erosion control measures will be installed after rough grading is complete and will remain
in place until the site is stabilized. Initial grading will include a 3 foot high berm that will separate the
downstream by-pass channel from the upstream floodplain of the North Toe River. The purpose of this
berm is to reduce the potential the by-pass channel will be activated prior to the temporary and
permanent seeding being in place. The Phase 2 erosion control measures incorporate several additional
diversion ditches and rip rap lined channels. Upon completion of the removal of this 3 foot high berm
this area will be seeded and mulch
At the downstream end of the bypass channel a concrete level spreader dissipates energy and treats
runoff before it enters the North Toe River. This BMP needs to be installed after the site has been
stabilized. Upon completion of the level spreader all temporary diversion ditches shall be removed or
replaced with permanent ditches and corresponding liners.
Pineola Street Grading Erosion Control
Erosion control for the grading associated with the Pineola Street floodplain improvements will be
installed as work proceeds. The proposed plans call for the contractor to create a bench to work off and
all construction equipment to remain out of the channel. As the drainage basin is larger than 9 square
miles, a pump around will not be required. In lieu of this, an innovative construction sequence will
prevent fines from leaving the project area:
• Set boulder toe and chink (offset) boulders from an upstream to downstream direction.
• Install 8 oz geotextile filter fabric on back side of boulders to prevent fines from leaving site.
• All work done behind the boulder toe should not result in fines leaving the banks and entering the
channel.
• Since drainage area is larger than 5 square mile a pump around is not required.
• Contractor shall be required to take additional measures if the originally proposed measures do not
adequately stabilize site.
Hood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
EROSION CONTROL PLAN
As work progresses along the River, subsequent boulder toes will be added with filter fabric to keep
disturbed sediment from leaving the work area. Along with this in-stream stabilization, inlet protection
and riprap culvert protection will be used for the closed drainage system adjacent to the asphalt path on
the North side of the North Toe River. See below for a discussion of each erosion control measure
used.
Old Cranberry Street Closed-System Erosion Control
Erosion control for the Old Cranberry Street closed-system will consist of temporary block and gravel
inlet protection around the proposed drop inlets, culvert inlet protection at the upstream end of the
system, and culvert outlet protection in the form of a rip rap pad. Because the channel invert is being
lowered 6 inches at the upstream face of the system, inlet protection is being proposed. Design for this
culvert inlet and outlet protection is included with this report as Appendix F.
Erosion Control Measures
The following erosion control devices will be used to stabilize the site and minimize onsite sediment
loss.
Sediment Traps
Three sediment traps have been proposed onsite. These traps were design for the following criteria as
taken from the North Carolina Erosion and Sediment Control Planning and Design Manual, revised
March 2009:
• Maximum drainage area - 5.0 acres
• Basin shape - Length to width ration greater than 2.0
• Minimum depth - 3.5 feet, 1.5 feet excavated below grade
• Maximum weir height - 3.5 feet above adjacent grade
• Minimum volume - 3600 cubic feet/acre disturbed
• Discharge and treatment capacity for the 10-year, 24-hour storm event
Appendix E shows the in-house spreadsheets and calculations used to size the sediment traps for this
project.
Silt Fence
Silt fence (NCDENR E&SC Std. 6.62.1) shall be placed in several areas onsite as shown on the Erosion
and Sediment Control plan sheets. In all locations of proposed silt fence, the drainage area is less than
'/4-acre per 100 linear feet of fencing.
Temporary Gravel Construction Entrance/Exit
Several temporary construction entrances (NCDENR E&SC Std. 6.06.1) will be provided at various
locations throughout the project as shown on the Erosion and Sediment Control plan sheets. The
construction entrances will provide a buffer area where vehicles can drop their mud and sediment to
avoid transporting it onto public roads, to control erosion from surface runoff and to help control dust.
Block and Gravel Inlet Protection (Temporary)
Block and gravel inlet protection (NCDENR E&SC Std. 6.52.1) will be provided at all inlets as shown on
the Erosion and Sediment Control plan sheets. The inlet protection will help prevent sediment from
entering storm drains before stabilizing the contributing watershed. This practice allows early use of the
storm drain system.
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
4
EROSION CONTROL PLAN
Channel Stability Analysis
A detailed hydraulic evaluation was completed to determine what stabilization measures would be
required for the proposed by-pass channel, outlet protection at culverts, abutment protection at the
pedestrian footbridge, and greenway and floodplain improvements. The following is a summary of this
evaluation.
Proposed Greenway and Floodplain Bench Design
The proposed greenway and floodplain bench were designed to reduce flood levels along the North
Toe River. To construct the greenway and floodplain bench, two walls are proposed along the toe of
the channel and at an elevation just above the bankfull flood elevation. The lower wall is composed of
geogrid lifts, an underdrain system and a boulder fagade. Large boulders with an approximate size of 3
feet by 3 feet by 2 feet are proposed for this fagade. The following table summarizes the shear stresses
the channel and floodplain bench will experience along with the shear stress the proposed boulder toe
can withstand:
Table 1 -Permissible Shear Stresses for Boulder Toe
Flood Event Maximum Shear Stress at Maximum Shear Stress at Permissible Shear
Wall along Toe of Channel Wall along Floodplain Stress (lb/sq ft)
(lb/sq ft) Bench (lb/sq ft)
10-Year Flood 2.5 0.75 >10
100-Year Flood 3.2 1.0 >10
Class II rip-rap can withstand a shear stress of 4.5 pounds per square foot based on specifications
provided in the North Carolina Department of Environment and Natural Resources (NCDENR) Erosion
and Sediment Control Planning and Design Manual. The maximum weight of a Class II boulder is
approximately 250 pounds. The boulders proposed for the construction of the main channel wall will
each weigh approximately 2250 pounds. A permissible shear stress for the boulders used in this project
was not calculated but it is anticipated that these boulders may exceed a shear stress of 10 pounds per
square foot. As shown in Table 1, the proposed wall can withstand the shear stresses imposed by the
100-year flood. Shear stresses for flood events larger than the 100-year flood will not significantly
increase relative to the 100-year flood because it will access the floodplain at these higher elevations. It
can therefore be concluded that the proposed walls have been designed to hold up in larger flood
events.
A check was made to determine if the proposed cover for the floodplain bench and greenway trail
could withstand the velocities from a 10-year flood. Table 2 summarizes the flood velocities
experienced on the grass-lined left floodplain bench and asphalt covered right greenway trail.
Table 2 - Permissible Velocities for Greenway and Floodplain Bench
Cross Section
(Stream Station) Left Overbank Velocity
(ft/sec) Right Overbank Velocity
(ft/sec)
374223 3.71 7.13
374295 3.21 7.13
374382 3.31 7.31
374436 2.65 5.89
Pineola Street (State Highway 194)
374508 N/A 1.15
374558 N/A 6.64
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
EROSION CONTROL PLAN
The permissible velocity for grass with the flat floodplain bench and silty soils is 4.5 foot per second
(NCDENR Erosion and Sediment Control Planning and Design Manual). The permissible velocity for an
asphalt covered trail is well in excess of 7.1 foot per second. As shown in Tablet, the velocities on the
floodplain bench and greenway trail are well below the permissible velocities that will cause erosion.
Rip-Rap Pad Design
The rip-rap outlet protection, shown on the plans and details, was designed using the New York
Department of Transportation (NYDOT) method along with Figures 8.06c and 8.06d found in the
NCDENR Erosion and Sediment Control Planning and Design Manual. Based on a culvert diameter and
flow velocity, the figures can be used to calculate a rip-rap pad length; width and stone size (see
Appendix F). The following table summarizes the outlet protection of culverts outfalls for this project:
Table 3 - Outlet Protection at Culverts and Ditch Outfall
Location Culvert
Size
(in) 10-Year
Peak Flow
(cfs) Pad
Length (ft) Pad Width
(ft) Pad Depth
(in) NCDOT
Rip-Rap
Size Rip-Rap
Weight
(tons)
PAD #1 24 20 12 7 24 Class II 10.5
PAD #2 48 112 24 14 24 Class II 35.5
PAD #3 12 4 10 6 18 Class II 5.5
PAD #4 12 4 10 6 18 Class B 5.5
PAD #5 8 2 10 6 18 Class B 5.5
PAD #6 42 80 21 12 24 Class 1 33.5
Because the outlet of the PAD #2 is located in an existing pool, the outlet protection will be buried and
treated like a buried riffle grade control structure. By burying the structure at the bottom of the pool,
the energy leaving the 48-inch diameter RCP will be dissipated both within the pool and by using the
buried riffle grade control structure, as needed. Pools are very shallow along this run of the North Toe
River therefore at this location; the buried riffle grade control structure will be buried just below the
bottom of the existing pool. This particular application is used to minimize the adverse impacts to the
existing pools along the North Toe River which are important to the trout habitat.
A new, open ditch is proposed in the left overbank near cross section 373275. This ditch will collect
runoff from the hillside slope drains, Railroad Street and the contributing drainage area. It is proposed
that the last 15 feet of this ditch be lined with Class B rip-rap to help drop the invert of the ditch to the
invert of the North Toe River.
Channel Liner for Open Ditches
Ditches with velocities over 4.5 ft per second have been lined with a permanent vegetative lining or a
rip-rap liner. An in-house spreadsheet (Appendix G) along with Dodsons's Hydrocalc Hydraulics
computer model was used to determine a liner that could be used to handle all ditches that exceeded
the permissible velocity and shear stress. The plans call for the immediate stabilization of the ditch to
prevent sediment from entering the downstream receiving systems.
All ditches consist of 4:1
Ditch slopes range from
project:
side slopes, which helps to reduce the shear stresses that would cause erosion.
11 % to 17%. The following table shows the proposed liners called out for this
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
EROSION CONTROL PLAN
Table 4 - Channel Liner Summary
Ditch Location Channel Slope
(ft/ft) 10-Year Channel
Velocity (ft/s) 10-Year Shear
Stress (lb/sq ft) Liner
RR Channel #1 0.136 3.59 1.87 Class B
RR Channel #2 0.124 2.64 1.16 Class B
RR Channel #3 0.170 3.31 1.16 Class B
RR Channel #4 0.172 3.41 1.82 Class B
RR Channel #5 0.112 4.45 2.52 Class
Hydraulic Evaluation at Pedestrian Footbridge
A field walk and hydraulic evaluation of the channel was performed for the proposed pedestrian
footbridge to determine if mitigative measures are needed to prevent excessive scour at the abutments.
Due to the following factors it was concluded that the channel is not subject to significant vertical
change and that the potential for scour at this crossing is minimal:
The proposed footbridge is located approximately 130 feet upstream of Pineola Street and 145
feet downstream of Ash Street. The proximity of the two road crossings limits the potential for a
significant change in grade due to headcut or downcut along the channel.
A field walk of the channel revealed very shallow pools along the thalweg of the channel for
several hundred feet in either direction of the proposed footbridge.
The Pineola Street culverts at are causing flood waters to back up behind the road. As a result
channel velocities and shear stresses are relatively low for the 10- through 100-year flood
events. The energy grade is extremely flat upstream of Pineola Street which is resulting in low
shear stresses at the proposed location of the footbridge. These low shear stresses and channel
velocities indicate that the potential for significant scour are low.
The following is a summary of the hydraulics taken from the proposed conditions HEC-RAS model (see
Appendix H) for the channel area at the location of the proposed footbridge:
Table 5 - Hydraulic Summary at Proposed Footbridge
10-Year Channel
Velocity (ft/sec) 100-Year Channel
Velocity (ft/sec) 10-Year Shear Stress
(lb/sq ft) 100-Year Shear Stress
(lb/sq ft)
2.3 1.7 0.23 0.10
As summarized in the Table 5, velocities and shear stresses are extremely low for all significant flood
events. The low channel velocities and shear stresses are causing the cobbles and gravels to fall out at
the large point bar located at the confluence of the North Toe River and Kentucky Creek. This indicates
that the channel is not subject to degrading and the abutments are not vulnerable to significant vertical
change. A large depositional point bar does indicate that there is potential for lateral movement.
Lateral movement is not occurring at this time however the significant bank protection in the form of
roots from trees has prevented the channel from moving significantly. At this time the toe of the
channel is unstable and mitigative measures in the form of a boulder toe is proposed to reduce lateral
movement in the right overbank.
By-Pass Channel Design
The design of the grass-lined, earthen by-pass channel was based on limiting the velocity in the 10-year
flood event to 4.5 feet per second and the shear stresses to 0.70 pounds per square foot. As shown in
Appendix I, the silty soils, flat slope and grass coverage allow for a permissible shear stress of 0.70
pounds per square foot. Per the NCDENR Erosion and Sediment Control Planning and Design Manual,
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson
EROSION CONTROL PLAN
the allowable velocity for Kentucky Bluegrass on silty soils with a flat slope is 4.5 feet per second. As
shown in the following table, the 10-year velocities and the shear stresses in the by-pass channel are
less than the maximum permissible limits:
Table 6 - By-Pass Channel Design Summary

Storm Event Maximum
Velocity (ft/sec) Permissible
Velocity (ft/sec) Maximum Shear
Stress (lb/sq ft)) Permissible Shear
Stress (lb/sq ft)
10-Year Flood 4.3 4.5 0.55 0.70
100-Year Flood 5.9 4.5 0.95 0.70
A check was made on the 100-year velocity to confirm the velocities would not be excessively high and
cause severe erosion in the grass-lined by-pass channel. As shown in Table 6, the 100-year flood event
is slightly above the acceptable limits for a stable channel. Two grade control structures have been
proposed along the by-pass channel to minimize the channel's susceptibility to erosion in a 100-year
flood. At the downstream end, a concrete level spreader is proposed to create diffuse flow from the
runoff of Old Cranberry Street. This structure will also act as a grade control structure for the proposed
by-pass channel. In addition, a buried log floodplain sill will be installed approximately 185 feet
upstream of the concrete level spreader. This buried log floodplain sill will act as a second grade
control structure for to minimize erosion in a 100-year flood.
Flood By-Pass Channel & Pineola Street Floodplain Improvements Project
WK Dickson

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