20171099 Ver 1_More Info Received_20180117

Moore, Andrew W
From: Greg Jennings <[e-mail]>
Sent: Wednesday, January 17, 2018 4:00 PM
To: Moore, Andrew W; Swartley, Bill; Coats, William A; Leslie, Andrea J; Amanda Fuemmeler;
Price, Zan (George)
Subject: [External] Re: Request for Additional Information, Linville River Restoration, Avery
County (DWR Project # 20171099)
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Thank you Andrew for your evaluation of this project. After re -visiting the site during high flow conditions and evaluating
several options for achieving water quality and habitat restoration goals, the design team is ready to proceed with revising
design plans to reduce impacts to the healthy riparian buffer and stream channel in the downstream section of the project. As
we discussed in the field, we think we can remove 3 of the proposed log j -hook vanes in the downstream section and maintain
a healthy stream system. In the upstream section of the project where the channel splits at the former low-water crossing,
the right channel is clearly not of sufficient width to support a functional meandering riffle -pool stream with natural energy
dissipation along the reach. During near-bankfull flow conditions in December, I observed 200 -mm -diameter cobble bedload
being transported with scour depths of at least 3 feet. The reason for this high -velocity, high -shear stress flow condition is
the ineffective hydraulic status of the left split channel caused by downstream debris blockage. In other words, most of the
flood flow proceeds down the straight right channel carrying much higher energy than observed in the equilibrium reference
reach upstream. This observation indicates that local applied bankfull shear stress in that narrow section of channel is about
twice the reference condition observed upstream of the high bridge. The long-term impact of this high shear stress condition
in theis expected to produce an incised straight plane -bed channel cut down to bedrock with potentially undercut right bank
and unstable vegetation. It is my strong opinion that the most appropriate plan for the upstream reach is to implement the
proposed meandering single -thread channel with width -to -depth ratio matching upstream reference conditions. The existing
mid -channel bar will be shifted to the edges of the meandering channel to form a functional bankfull floodplain. Log j -hook
vanes will serve as habitat structures as well as supporting grade control and bank protection functions for several years as
the new stream alignment matures. Please let me know if you have objections to this approach before we finalize our revised
plan and re -submit for review.
Regarding Condition 11.9. of Water Quality General Certification 4087, we propose that all in -stream work will be done during
low -flow, base flow conditions with stream flow diverted about the active construction area using cobble "push-up" dams and
diversions. At the end of each work day, all disturbed in -stream work areas will be stabilized to protect from overnight erosive
flow conditions.
Thank you, Greg
Greg Jennings, PhD, PE
Jennings Environmental
Professor Emeritus, NC State University
919-600-4790
On Oct 19, 2017, at 10:45 AM, Moore, Andrew W <[e-mail]> wrote:
Bill and Alan,

Thanks for driving down last week and meeting me and Andrea to discuss the subject project. As we
discussed on-site, there is some additional information I will need to process the 401 Water Quality
Certification. The Division will place the project on hold until the following items are addressed:
Condition 11.9. of Water Quality General Certification 4087 requires that all work in streams be
conducted so that the flowing stream does not come in contact with the disturbed area. Please
explain how you plan to meet this condition. If this condition cannot be met, please describe the
construction techniques and sequencing that will be used to minimize turbidity and
sedimentation during in -stream construction activities.
During the site visit, several design changes were discussed and agreed upon. Please re -submit
the design drawings showing the revisions or provide a narrative description of the design
changes including station location.
Pursuant to Title 15A NCAC 02H .0502(c), the applicant shall furnish all of the above requested
information for the proper consideration of the application.
Feel free to contact me if you have any questions.
Thanks,
Andrew W. Moore, P.G.
Environmental Specialist — Asheville Regional Office
Water Quality Regional Operations Section
NCDEQ — Division of Water Resources
828 296 4684 office
email: [e-mail]
2090 U.S. Hwy. 70
Swannanoa, N.C. 28778
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