Most beachgoers don’t think anything of the brown line of seaweed and other organic material that marks beach tide lines. This natural material that washes onto the beach – called wrack – includes algae, sea grasses and some invertebrates such as sponges and soft corals. Despite its unassumingness, wrack may be essential to helping dunes in protecting coastal shorelines from damaging weather such as hurricanes and tropical storms.
Researchers at the U.S. Army Engineer Research and Development Center (ERDC), along with partners at the U.S. Army Corps of Engineers (USACE) Mobile District and The University of Southern Mississippi (USM), are studying beach wrack to see if it is key to a more resilient dune system.
USACE Regional Sediment Management researchers are currently studying the placement of wrack that has washed up on beach coastlines, collected and then strategically placed on existing dunes to measure the stability of the dunes and how resilient they are to turbulent weather.
Dunes are standard features along sandy coastlines around the world, except for the Arctic and Antarctic that lack extensive coastal dunes.
A line of dunes can protect from flooding due to high water levels and wave overtopping. Dunes can also reduce wave damage in developed landward areas by causing waves to break as they propagate over the dunes.
“Many coastal communities rake their beaches because they view wrack as smelly and unsightly,” Leigh Provost, an ERDC research coastal engineer with ERDC Environmental Laboratory, said. “However, wrack material placed on the dunes can trap sand and assist with initiating natural dune-building processes, and through this method of wrack management, which is known as wrack-cycling, coastal communities are actually building protection for themselves while dealing with what they see as an economic problem.”
Unlike previous methods to construct man-made dunes, where dunes are built to an elevation and then planted with vegetation, researchers are evaluating how a man-made dune responds when biological material is incorporated into the dune incrementally, mimicking the natural growth cycle of dunes.
By making these dunes more resilient, USACE is also helping to reduce the need for future dune restoration construction projects and possibly even reducing the need for future beach nourishment.
For this ongoing study on the Mississippi Coast, Provost and her USACE and USM collaborators collect wrack and place it to test the effect on the resilience and stability of the dunes.
Placing the wrack by hand is time-consuming, but it has produced positive results despite large weather events that have pounded the coastline.
“We recently came under the Engineering With Nature® (EWN) program at the beginning of FY23, and I am very excited to continue to test in the Mobile District, which is an EWN Proving Ground,” Provost said. “The Mobile District and the Harrison County Sand Beach Authority have been very open to trying new theories to research, and it will be interesting to see where this allows us to take our research.”
After Tropical Storm Cristobal, Hurricane Zeta and other hurricanes, the team was able to observe that the dunes in the study area lost volume but had a noted visible benefit of wrack placement along the treated dunes shared Eve Eisemann, previously a research physical scientist with ERDC’s Coastal and Hydraulics Laboratory.
Continuing to assist the program under the EWN umbrella, USM’s Gulf Coast Geospatial Center provides high-quality surveys of the area using the most precise equipment available, leveraging state-of-the-art survey-grade equipment and a team of experienced staff, faculty and students.
The different instrumentation used for the precise measurements includes a variety of land-based and aerial, drone-based lidar devices used over a multi-day survey.
That experience of both the geospatial science and knowledge of the Mississippi coastline has made USM’s Gulf Coast Geospatial Center a key partner in the research.
In the United States, approximately 127 million people live in coastal counties, according to the National Oceanic and Atmospheric Administration. That’s as much as the entire population of Japan.
“With so many people living along the coastlines, the impact of a storm can be billions of dollars,” Provost said. “That’s why research such as wrackcycling is so important to USACE and the United States. It’s imperative that we find solutions quickly to protect these communities.”