Posted on January 30, 2023
Due to recurring scour and maintenance concerns at the NC 24 Causeway between Swansboro and Cedar Point, the North Carolina Department of Transportation (NCDOT) partnered with the North Carolina Coastal Federation to begin a year-long Living Shorelines Project in November 2022.
Fast-moving waters in the White Oak River cause soil erosion surrounding the NC 24 Causeway foundation, which leaves behind scour holes. Together, the NCDOT Hydraulics Unit and NC Coastal Federation agreed to build various living shorelines on the White Oak River side of the bridge.
“While investigating solutions, NCDOT Hydraulics worked with the Federation to come up with the current living shoreline plan,” explains Daniel Waugh and Brian Lipscomb of the NCDOT Hydraulics Unit. “It is part of the Federation’s commitment to increase the use of living shorelines instead of bulkheads and seawalls coastwide.”
NCDOT contracted T.A. Loving Construction Company to begin construction on roughly 900 linear feet of rock sills, 800 linear feet of Sandbar Oyster Company’s Oyster Catcher, 0.024 acres of wetland plantings and a third 500 feet living shoreline.
Besides living shoreline construction, T.A. Loving will also add 1,300 tons of rock to the existing embankment, re-grade the site, repair the bridge sidewalk, and install sod between the re-built embankment and repaired sidewalk.
The NCDOT expects to begin construction on their third living shoreline at the end of 2023, after their final construction permit is approved this year.
Until then, construction of the first living shoreline will begin by installing 3,000 tons of granite stone to span 900 linear ft of rock sills. The rock sills will sit in the water more or less than 100 ft from the shore to serve as a harder shoreline structure.
Waugh and Lipscomb explain, “The sills will function as a wave break to provide a protected wetland area.”
Along the outer edge of the rock sills, workers will install an added 800 linear feet of Sandbar Oyster Community’s Oyster Catcher to further decrease wave action at the shoreline.
Living shorelines will create a barrier to protect and restore salt marsh and oyster reef habitats in the White Oak River. The workers will fill and grade remaining waters landward of the sills to create an environment suitable for planting salt marsh grass in the White Oak River.
“The entire system will help reduce wave energy and ultimately reduce forces reaching the roadway embankment,” said Waugh and Lipscomb. “The living shorelines will naturally stabilize, protect and maintain the shorelines along the state highway while restoring fisheries habitat,” added the NC Coastal Federation Living Shoreline Program Director, Dr. Lexia Weaver.
Total design and construction costs for the living shoreline project and bridge repairs totals approximately $3.6 million. The National Fish and Wildlife Foundation awarded a $1.7 million grant to the NC Coastal Federation, which will fund part of the project under the coastal resilience plan that followed hurricane Florence in 2018.
The NC General Assembly through Session Law 2019-251 funds the remaining cost of the project, along with NCDOT Bridge Maintenance Funding.
Dr. Weaver, Waugh, and Lipscomb mentioned additional benefits, “A living shoreline can be more economical due to lower installation and maintenance costs, while adding a natural wetland component to the finished product,” and said, “living shorelines have been shown to be more resilient and have less failure due to scour.”
This is not the first living shoreline to pop up along the Crystal Coast—it is only the first one constructed directly by NCDOT. The NC Coastal Federation helped construct similar living shorelines at Carteret Community College in Morehead City and at Ward Shore Park in Swansboro.
NCDOT plans for construction of the third living shoreline to end before 2024, but final salt marsh grass plantings will not be complete until some time in the spring of 2024.
