20230797 Ver 1_More Info Received_20240509

4700 Falls of Neuse Rd.
Ste. 300
Raleigh, NC 27609
moffatt & nichol [phone]
www.moffattnichol.com
May 8, 2024
Division of Water Resources
NC Department of Environmental Quality
512 North Salisbury Street
Raleigh, NC 27699
Attn: Stephanie Goss (via email at stephanie.goss(cD.deg.nc.gov)
Subject: Modeling Plan — Water Exchange/Flushing Analysis
241 Morada Bay Drive, Newport, NC
Western Carteret County Boat Launch Facility, DWR#20230797
Dear Ms. Goss:
Moffatt & Nichol (M&N) has provided the following responses to Item 1 of your February 16, 2024,
Request for Additional Information (RAI). Item 1 consisted of several comments and clarifications related
to the submitted Flushing Analysis for the Western Carteret Boat Launch Project submitted by M&N in
support of the Coastal Area Management Act (CAMA) permit application in August 2023.
A primary concern of the Division of Water Resources (DWR) was the use of the MIKE21 modeling
platform, which DWR considers a proprietary model that is not in the public domain since there is a licensing
fee associated with using the platform. Although MIKE21 has been widely used in academic, government,
and private sectors since the 1980's, and has been refined to improve its capabilities, M&N will utilize the
Environmental Fluid Dynamics Code (EFDC) model to evaluate water exchange and flushing for the inland
boat launch basin. The EFDC model is a U.S. Environmental Protection Agency (USEPA) distributed legacy
model that is no longer supported (V1.01, Released 2007) but has been used in the past to evaluate water
exchange and water quality in estuarine environments.
A modeling plan has been developed that aligns with the previous approach, as well as with the DWR
guidance document for planning of inland marina basins. The modeling plan has been updated to
incorporate DWR comments related to coverage of dye concentration (now set to full coverage of basin),
and detailed description of model calibration and boundary conditions.
This approach to evaluate inland basin flushing and water quality is consistent with industry guidance from
US Army Corps of Engineers, The Association of For Waterborne Transport Infrastructure (PIANC), and
the USEPA, dating back to the original reference criteria from Alton Boozer (Boozer, 1979) and the work of
Van de Kreeke (Van de Kreeke, 1983).
We look forward to discussing the hydrodynamic and water quality assessment aspects of the modeling
plan at your earliest convenience, as we hope to proceed with implementation of this model as quickly as
possible.
Sincerely,
f%
Doug Huggett
Environmental Permit Specialist
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