20231102-NorthForkReservoir-401404RevisionRequest

CITY COUNCIL:
BARBARA G. VOLK
Mayor
LYNDSEY SIMPSON
Mayor Pro Tempore
1ERRY A. SMITH, JR.,J.D.
DR. )ENNIFER HENSLEY
DEBBIE O'NEAL-ROUNDTREE
November 2, 2023
CITY OF HENDERSONVILLE
The City of Four Seasons
eH'ndersonville
Water ei Sewer
WATER AND SEWER DEPARTMENT
Adam Steurer, PE, Utilities Director
Andrew Moore, P.G.
NCDEQ— Division of Water Quality
Via email: [e-mail]
Brooke Davis
USACE Wilmington District —Asheville Regulatory Field Office
Via email: [e-mail]
Subject: Request for Approved Plan Revision 401/404 Water Quality Certification
North Fork Reservoir
DWR # 07-0721 V2
USACE Action ID 2020-01908
Mr. Moore and Ms. Davis,
OFFICERS:
JOHN F. CONNET
City Manager
ANGELA S. BEEKER
City Attorney
JILL MURRAY
City Clerk
On February 7, 2022, the Division of Water Resources (DWR) issued the City of Hendersonville (City) an approval of a 401
Water Quality Certification under Water Quality General Certification 4132 (GC 4132) for the subject project. Condition
11.1. of GC 4132 states, "When written authorization is required, the plans and specifications for the project are
incorporated into the authorization by reference and are an enforceable part of the Certification. Any modifications to the
project require notification to DWR and may require an application submittal to DWR with the appropriate fee."
On March 7, 2022, the US Army Corps of Engineers (USACE) issued a NWP 3 with special condition 2 stating, "The long-
term release of sediment from the reservoir through the dam outlet system is to be conducted as outlined in Section 2 of
the Sediment Release Program of the North Fork Reservoir. IF future release of sediment from the reservoir differ than the
procedures outlined in this document, then the permittee shall consult with the regulatory agencies to determine potential
changes to the Sediment Release Program."
The City is requesting an approved plan revision of the 401 Water Quality Certification and 404 General NWP 3 as follows:
305 Williams St. [e-mail] Phone: [phone]
Hendersonville, NC 28792-4461 www.hendersonvillenc.gov Fax: [phone]

1. The approved plans call for remote instrumentation, including a rain gauge, flow measurement, and valve control
at the bottom -release discharge pipe. Due to the remote nature of the reservoir, installation and long-term
operation of such equipment is difficult to implement and would cause excessive maintenance burdens on City
staff. Instead, the City proposes to manually adjust the bottom release valve.
The attached Standard Operating Procedure (SOP) describes the City's procedures for manually operating the
valve to comply with permit conditions for minimum flow through the bottom valve opening. This valve is
calibrated using the orifice equation as documented in the Sediment Release Plan such that the baseline discharge
of 8 cubic feet per second (cfs) occurs with the valve opened 5.2 inches (15 % turns). The SOP documents the
procedures to be followed during drought conditions when discharge at the USGS Mills River gauge drops below
55 cfs. That will trigger decreasing the bottom discharge on North Fork Reservoir to match upstream flow into the
reservoir to maintain normal pool elevation at or near the top of the dam.
2. The approved Sediment Release Plan calls for quarterly cross-section surveys for three years through 2026. The
City requests approval of revisions to sections 2.0 and 2.3 outlined in the attached Sediment Release Plan dated
October 13, 2023 to manually operate the bottom -release discharge valve and to implement a monitoring plan
that allows for quarterly visual observations and annual cross-section surveys. This is justified based on the
expectation that most of the sediment likely to flush out the bottom valve will be sands and finer grains which are
easily observed if accumulating on the rocky stream bottom downstream. In the case that substantial sand
accumulation of more than two inches is observed at a cross-section location during any quarter, a cross-section
survey will be performed to document exactly what has changed from previous measurements.
Thank you for your attention to this matter. If you have any questions or require additional information, please contact
me at [phone].
Sincerely,
a4a_ A Jtzz�
Adam A. Steurer, PE
Utilities Director
City of Hendersonville
Attachments: North Fork Reservoir Bottom Release Valve — Standard Operating Procedure
North Fork Reservoir Sediment Management Plan dated October 13, 2023