2023-05-02 Response Letter to NC WRC

May 2, 2023

Andrea Leslie
North Carolina Wildlife Resources Commission
645 Fish Hatchery Rd., Building B
Marion, NC 28752
Subject: Response to April 4, 2023 Letter of Recommendations
Reservoir Drain and Geotechnical Subsurface Investigation,
Lake Lure Dam (RUTHE-003), Rutherford County, North Carolina
Dear Ms. Leslie:

SCHNABEL ENGINEERING SOUTH, P.C. is pleased to present responses to the recommendations
included in your April 4, 2023 letter to Ms. Brandee Boggs with the USACE regarding the proposed
Reservoir Drain Project and geotechnical subsurface investigation at Lake Lure Dam. Listed below are
the recommendations from your letter dated April 4, 2023, followed by our response. These responses
have been prepared in coordination with the Town of Lake Lure and Mr. Gerald Pottern of Mogensen
Mitigation Inc (MMI), our environmental subconsultant and the submitting applicant for the electronic Pre-
Construction Notification for a Nationwide Permit 3 and Preliminary Jurisdictional Determination Request
package (PCN-PJD Package) dated February 6, 2023.

1. The USGS gauge below the dam is no longer in use; we recommend that the gauge be restored
to collect flow data and fitted with temperature and dissolved oxygen probes. These data should
be accessible through USGS’ on-line data portal.

The stream gauge below the dam is owned by the Town of Lake Lure (Town) and historically the
Town has made the data available to the USGS. The Town will evaluate options to restore this
gauge. Restoration of this gauge prior to reservoir drain construction is likely not feasible.

2. We strongly recommend using the new gate valve or a smaller accessory valve to provide a
portion of downstream flows to moderate high stream temperatures during the summer months.

The intent of the reservoir drain is to provide a means to lower the lake level in the event of a dam
safety emergency. The reservoir drain is not intended to be operated regularly, and we do not
recommend that it be used to moderate stream temperatures during the summer months. Once
planning and design of the future replacement dam begins, the Town will discuss options with
NCWRC to incorporate a feature(s) into the replacement dam to potentially allow moderation of
high stream temperatures during the summer months.

Response to Request for Additional Information on Permit Application
Lake Lure Dam (RUTHE-003) – Reservoir Drain and Geotechnical Subsurface Investigation

Project 18C21024 / May 2, 2023 Page 2 Schnabel Engineering South, P.C.
3. Sediment at risk of being lost through the new gate valve should be dredged out of the lake
before use of the gate valve.

A survey of the dam and surrounding area was performed in 2019, and the results of that survey
are shown on the reservoir drain construction drawings which are included with this letter as
Attachment 1. The upstream face of the dam and the lake area immediately upstream of the dam
were surveyed using multi-beam sonar scanning equipment. The data from the scan indicates
that the sediment at the center of the arch at Bay 5 is at an elevation of approximately 898 feet,
12 feet below the invert of the reservoir drain opening. Additionally, the reservoir drain
penetration and pipe are oriented perpendicular to the upstream face of the dam to further limit
the potential for any accumulated sediment to be discharged downstream over the service life of
the drain system. Furthermore, portions of the reservoir drain work on the upstream side of the
dam will be performed by divers. Any minor sediment accumulation on the concrete arches in the
area of the reservoir drain will be removed by divers prior to making the penetration through the
dam.

4. The gate valve would be tested annually; we ask that this be done during the cold season so that
the aquatic community is not shocked by extreme temperature swings. We ask that the Town of
Lake Lure coordinate with NCWRC on when and how this valve is tested.

The Town is agreeable to performing the annual testing of the valves during the cold season and
will coordinate with NCWRC regarding the timing and details of this annual exercise.

5. Currently, there is no warning siren that is used before power generation, when flows can rise
quickly and become dangerous. We recommend using an audible warning system to announce
power generation and the use of the jet gate valve.

The Town will consider the addition of a warning siren.

6. We request that the Town involve NCWRC and NCDWR staff early in dam replacement design
discussions so that the design can incorporate elements that will allow for a more natural flow
regime and temperature in the Broad River.

The Town and their consultants will involve NCWRC and NCDWR early and throughout the dam
replacement design process.

7. In-channel work should be accomplished as quickly as possible and vigilance used in sediment
and erosion control during site preparation, construction, and clean up. Disturbed areas should be
seeded, mulched and/or matted as soon as possible.

In-channel work, which is expected to be limited to installation and removal of the temporary
stream crossing, will be accomplished as quickly as possible. Ground disturbance in the area of
the stream crossing will be minimized, with the majority of the stream crossing being founded on
bedrock. The stream crossing will be constructed of clean, non-erodible materials (washed riprap
and stone) placed over geotextile to minimize impacts to water quality, etc. during construction,
operation/use, and removal. Best management practices (e.g., silt fence, turbidity curtain) will be
Response to Request for Additional Information on Permit Application
Lake Lure Dam (RUTHE-003) – Reservoir Drain and Geotechnical Subsurface Investigation

Project 18C21024 / May 2, 2023 Page 3 Schnabel Engineering South, P.C.
utilized as necessary in accordance with the North Carolina Erosion and Sediment Control
Planning and Design Manual. Upon removal of the access road, vegetation will be re-established
along any disturbed areas of the river banks, though disturbance is expected to be minimal as
indicated above.

8. Any erosion control matting used should be free of nylon or plastic mesh, as this type of mesh
netting frequently entangles wildlife and is slow to degrade, resulting in a hazard that may last for
years.

The need for erosion control matting for the reservoir drain construction project is not anticipated
since ground disturbance is expected to be minimal and much of the exposed surfaces within the
limits of disturbance are bedrock. However, if needed, erosion control matting will consist of
heavy twisted jute mesh. No matting containing plastics or other similar materials will be
permitted.

Please contact the undersigned if clarification is needed for any aspect of this letter.

Sincerely,

SCHNABEL ENGINEERING SOUTH, P.C.

Jonathan M. Pittman, PE
Project Manager / Principal

BFS:JMP

Attachment 1: Reservoir Drain Construction Drawings

cc: Gerald Pottern, MMI
Michael Dydula, Dean Lindsey, and Hank Perkins, Town of Lake Lure
Brandee Boggs, US Army Corps of Engineers
Joey Winston, NCDEQ Division of Water Resources
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