20160672 Ver 1_RE Bridge 126 WBS No 17BP 7 R 69_20160707 (2)

Carpenter,Kristi
From:
Sent:
To:
Thomson, Nicole J
Thursday, July 07, 2016 11:13 AM
Wilson, Travis W.; [e-mail]; Wrenn, Brian L;
[e-mail]
Cc: Carpenter,Kristi; Parker, Jerry A; Powers, Tim
Subject: RE: Bridge 126 on SR 1526 (Gray Rd) over Lick Creek, Orange Co. WBS No.
17BP.7.R.69
Attachments:
Follow Up Flag:
Flag Status:
Bridge to Culvert Justifaction 670126 01-21-2016.docx
Follow up
Completed
Just in case I made a goof (which is entirely possible! This is me we are talking about), please see the attached.
And my apologies if this didn't come through in the first round of emails. (see what happens when I think I can fit it all in
2 emails instead of 7???)
Nik
From: Wilson, Travis W.
Sent: Thursday, July 07, 2016 9:37 AM
To: Thomson, Nicole J; [e-mail]; Wrenn, Brian L; [e-mail]
Cc: Carpenter,Kristi; Parker, Jerry A; Powers, Tim
Subject: RE: Bridge 126 on SR 1526 (Gray Rd) over Lick Creek, Orange Co. WBS No. 17BP.7.R.69
Although Dwarf wedge mussel was not found at this location. We have records of multiple mussel species at this site
including state list species: Creeper (Strophitus undulatus: state T) and Eastern lampmussel (Lampsilis radiata: state
T). Lick Creek in this area is also designated as a significant natural heritage area. We have worked with NCDOT in the
past on several bridge to culvert projects; in areas with degraded habitat this type of project can be accomplished
without further impacting aquatic species populations. This would not be the case for this project. What is the
justification for replacing this bridge with a culvert?
Travis W. Wilson
Eastern Region Highway Project Coordinator
Habitat Conservation Program
NC Wildlife Resources Commission
1718 Hwy 56 West
Creedmoor, NC 27522
Phone: [phone]
Fax: [phone]
Travis.Wilson(cDncwildlife.ora
ncwildlife.ora
� � �

From: Thomson, Nicole J
Sent: Wednesday, July 06, 2016 5:55 PM
To: [e-mail]; Wrenn, Brian L<brian.wrenn@ncdenr.�ov>; Gary Jordan@FWS.�ov; Wilson,
Travis W. <[e-mail]�>
Cc: Carpenter,Kristi <kristilynn.carpenter@ncdenr.�ov>; Parker, Jerry A<Iparker@ncdot.�ov>; Powers, Tim
<tpowers@ ncdot.�ov>
Subject: Bridge 126 on SR 1526 (Gray Rd) over Lick Creek, Orange Co. WBS No. 17BP.7.R.69
Good afternoon!
Please find the attached permit application for the above proposed bridge-to-culvert replacement with supplemental
information. Dave B. —your hard copy is in the mail.
Due to file sizes, I'll have to split this up into multiple emails (I'm sorry).
Please don't hesitate to call me with any questions or concerns!
Thanks!
Nikki
Nicole J. Thomson
Division Environmental Supervisor Assistant
Division Environmental Office
919-754-7806 Mobile
Nithomson2(a�ncdot.qov
PO Box 14996
Greensboro, NC 27415-4996
�M � +� � � �
Email correspondence to and from this address is subject to the
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Email correspondence to and from this sender is subject to the N.C. Public Records Law and may be disclosed to third parties.

Orange County
Br# 670126
Replace Bridge # 126 on SR 1526 (Gray Road) over Lick Creek
The project consists of replacing Bridge #126 in Orange County. This bridge is a 3 span (2 @ 25'; 1@ 26'
—Total length=76') structure with timber abutments and deck on I-beams with timber interior
piers/bents on concrete footers. One interior timber bent is located in the creek. The bridge is
Structurally Deficient and has a Sufficiency Rating of 37. The current structure was constructed in 1964.
Timber structures typically have a life span of 50 years and this structure is 52 years old and has reached
the end of its life cycle.
The proposed structure is a 34'-11" wide x 10'-4" tall aluminum 4-sided box culvert. Inlet and outlet low
flow sills and a baffle mid-length are proposed in the box. The low flow width is set to best fit and
maintain the existing low flow stream width. This structure meets the hydrological requirements of the
drainage area without significantly altering the FEMA Flood study backwater. The use of the aluminum
box culvert will reduce the construction time from 120 days to 90 days as compared to that of a bridge.
Aluminum box culverts have lower construction and maintenance cost over the life cycle of the
structure as compared to a bridge. Current budget constraints require us to take the most economical
option that meets environmental and safety concerns.
At this location a preliminary proposed bridge length of 100 ft was estimated. If a single span bridge
was used it is estimated the grade would need to be raised an additional 1 ft above proposed due to
structure type required.
Typically the length of a bridge will be much longer than that of a culvert. Increasing the bridge length
creates several issues that must be overcome. If a bridge is utilized there must be at least four feet of
clearance under the bridge to allow access for maintenance workers at the abutment. In areas where
culverts are recommended this requires us to raise the roadway grade which also increases the impacts
due to the increased fill slopes. Raising the roadway grade also affects the FEMA Flood Plain Mapping.
In turn we cannot meet the requirements of the Memorandum of Agreement (MOA) with FEMA. If the
new bridge cannot be sized to meet the requirements of an MOA then map revisions need to be
performed for FEMA. First through a CLOMR (Conditional Letter of Map Revision) then a LOMR (Letter
Of Map Revision). NCDOT works very hard to make sure the replacement structure meets the
requirements of the MOA. Smaller streams in the Piedmont area are often best suited for culverts to
minimize raising the roadway grade.
The culvert has met NC Floodplain Mapping/FEMA MOA requirements.
Justification for bridge to culvert:
• The basin drainage area (3.5 sq miles) and estimated discharges are compatible with a culvert
structure. And as mentioned, typically prefer culverts due to longer service life and reduced
maintenance vs a bridge.

• The proposed 34' wide culvert and 75' long bridge (with vertical timber abutments) have similar
hydraulic type openings and properties considering the existing skew of the bridge relative to
floodplain flow. Hydraulic function including backwater, outlet and internal structure velocities,
etc will remain similar.
• The existing stream banks just up and downstream of the bridge are nominally stable to
unstable. Stream bank armoring is proposed up and downstream of the proposed culvert along
with low flow benches matching sill dimensions at culvert inlet and outlet. Bank armoring will
improve bank stability at these locations.