20070721 Ver 2_More Info Received_20211214

Moore, Andrew W
From: Greg Jennings <[e-mail]>
Sent: Tuesday, December 14, 2021 8:03 AM
To: Leslie, Andrea J
Cc: Tyson Kurtz; Zan Price; Moore, Andrew W; Brown, David W SAW; Hamstead, Byron A;
Goudreau, Chris J.
Subject: Re: FW: [External] N. Fork Dredging NWP 3 Application
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Andrea, Thank your for these comments.
We will update the permit drawings and operations sequence to address the turbidity question.
Regarding the analysis of sediment release de minimus conditions, we have analyzed 20 water years and produced the
same conclusion regarding the estimated minimum baseflow of 10 cfs during normal rainfall years. This analysis will be
included in the final report.
Regarding the proposed sediment release operations, we have updated the management plan as follows:
1. Management Plan for Sediment Release from the North Fork Reservoir
The sediment release management plan will be implemented to discharge bottom cold water and sediment from the
lower outlet pipe while achieving de minimis sediment impacts downstream. The following remote -controlled
instrumentation will be installed at the dam to send data to the water plant and facilitate remote sediment release
operations:
• Rain gauge with continuous recording of rainfall depth;
• Flow measurement and valve control at the bottom -release discharge pipe.
1.1. Continuous Bottom Release During Baseflow Conditions:
• During baseflow, keep the outlet pipe gate valve open at least 5.2 inches to discharge at least 8 cfs in
compliance with the required minimum downstream flow rate condition.
• Increase the bottom gate valve opening to match watershed inflow to the reservoir while maintaining
full reservoir pool conditions.
1.2. Storm Event Flushing Releases:
• During rainfall events of greater than one-half inch during a running 24-hour period, open the outlet
pipe gate valve fully to maximize the discharge of bottom water and sediment.
• After the storm event when flow over the dam weir ceases, partially close the gate valve to maintain full
reservoir pool conditions while continuing to release at least 8 cfs.
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1.3. Monitoring Plan for Downstream Impacts of Sediment Release
• Following storm events of greater than one inch, visually inspect the outlet pipe to ensure no blockage
and inspect the stream bed within 1,000 ft downstream of the dam to observe any sediment accumulation
conditions.
• Establish six permanent monumented stream cross -sections at the locations of three riffles and three
pools downstream of the dam for repeated topographic surveys.
• Survey the cross -sections before initiation of the sediment release program to establish baseline
morphology.
• Repeat the cross-section surveys quarterly for at least three years and compare data in order to
determine changes over time.
• Photograph cross -sections during surveys.
• Report monitoring results including graphs, tables, and photographs, to regulatory agencies to
determine if any changes are needed in the sediment release plan.
The question about using dam overflow to trigger remote valve opening instead of rainfall is a good one. I
believe that remote rainfall data will be more reliable considering the weir condition at the dam. We have
reduced the storm event "trigger" rainfall depth to 1/2 inch over a running 24-hour period. Keep in mind that
during "continuous" discharge operations, the valve will be opened to match watershed flows so that sediment
discharge is optimized during wet periods even when there is no rain storm event.
Please feel free to comment and/or schedule a meeting to discuss other concerns.
Thank you, Greg
Greg Jennings, PhD, PE
Jennings Environmental PLLC
919-600-4790
[e-mail]
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On Fri, Dec 10, 2021 at 2:26 PM Leslie, Andrea J <[e-mail]> wrote:
Hi Tyson and Greg -
We've reviewed the North Fork Dredging application. We appreciate the thoughtful design and sequencing
of the project. It is clear that you all have taken our concerns into consideration. We have a few questions
and recommendations at this stage in review -
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Turbidity
• How will the 8 cfs release be maintained during dredging? Through the gate valve or siphon?
• We recommend that turbidity of the release be monitored daily and a contingency plan be developed
in case of high turbidity originating from project activities. This monitoring and contingency plan
should be developed with input from NCDWR and NCWRC.
Sediment release plan (please direct discussion to both me and Chris Goudreau for this)
Hydrology/Sediment Analysis
• Why was only 10 years of flow data (WY 2010-2019) from Mills River gage used to determine flow
statistics? Usually, the dataset should be at least 20 years. Is there a reason you didn't use 20 years?
• Would the results have differed significantly using WY 2000-2019?
Sediment Management Protocols
• The plan calls for opening the gate fully when rainfall events are >1 inch, but little detail is provided.
o Where will the rain gauge be located - at the dam or elsewhere?
o If at the dam, will the rain gauge be automated and send data to the water plant?
o Will you use PLC software and remotely operated gate controls to implement the plan?
• It is unclear if the 1" event is over 24 hours, a calendar day, or total for the rain event.
o This matters because a 1.5" event that occurs equally over two calendar days (0.75"/day) would
not trigger a gate opening.
o If over a 24-hour period, then you need software to know when the event started. The same
holds true rain events exceed 24 hours.
o We recommend that the period be a running 24 hours; if different, please explain your logic.
• We think a better trigger is to use flow instead of rain, which is what you suggest on page 6 of
Appendix B.
o When flow is >31 cfs, the gate would be fully open, regardless of any rain event. This would
maximize the time that the gate is passing sediment; not just during rain events. During
typical winter and spring months they could be passing sediment continuously.
o Of course, this means you would have to install a gauge to measure flow, but that could be
done with a gauge that measures height over the spillway as a surrogate. Such systems are
regularly used by small hydro operators.
o Please explain why using the storm event approach is preferable to using a flow trigger.
Thank you,
Andrea
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Andrea Leslie
Mountain Habitat Conservation Coordinator
NC Wildlife Resources Commission
645 Fish Hatchery Rd., Building B
Marion, NC 28752
828-400-4223 (cell)
www.ncwildlife.org
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From: Tyson Kurtz <[e-mail]>
Sent: Monday, November 15, 2021 10:19 AM
To: Yankura, Kaylie <[e-mail]>; Leslie, Andrea J <[e-mail]>; Hamstead, Byron A
<byron [e-mail]>
Cc: Brown, David W CIV USARMY CESAW (USA) <[e-mail]>
Subject: [External] N. Fork Dredging NWP 3 Application
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All,
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Please see the attached Nationwide Permit 3 application for the N. Fork Reservoir dredging project, on behalf of the
City of Hendersonville.
The attached application was submitted through the NC DEQ project portal this morning.
Feel free to let me know if you have any questions about the project or application materials,
Thanks,
Tyson Kurtz
Biologist
CLearWaLe r
An E'PY Fence C.4713anylg
145 7th Avenue West, Suite B
Hendersonville, NC 28792
Office: 828-698-9800 ext. 302
Mobile: [phone]
tysoncwenv.com WWW.CWENV.COM
WWW.EnviroSciencel nc.COM
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