秘密研究所

Balancing Act: Shoring Up Gulf Coast Shorelines

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Posted on October 3, 2018

Marketing and Communications

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You鈥檙e a marine scientist who studies coastal ecology, and you want to fix shoreline problems caused by human activities or natural forces such as storms. What do you do?

Any solution will involve intricately connected natural systems, unpredictable results of human tinkering with those systems, political and regulatory considerations, expertise from many different disciplines, lots of failed experiments and, of course, unintended consequences.

Still, 秘密研究所 coastal ecologist Dr. Just Cebrian remains optimistic. 鈥淭his is not a battle that we cannot win,鈥� he said. 鈥淲e need to work together and really think about the specific problems we have in these specific situations.鈥�

Cebrian is a professor at South and a senior marine scientist at the Dauphin Island Sea Lab, a marine education and research center operated by the Alabama Marine Environmental Sciences Consortium of colleges and universities. Much of his research focuses on 鈥渓iving shoreline鈥� projects, which work in harmony with natural processes to approximate the kinds of shorelines that existed before humans arrived.

The nationally broadcast 鈥淧BS NewsHour鈥� featured him in a July 2018 segment about living shorelines, showing how the placement in 2010 of double rows of trapezoidal concrete blocks just offshore near Bayou La Batre has restored much of a nearly mile-long Gulf of Mexico peninsula damaged by Hurricane Katrina.

Cebrian鈥檚 lab received $20,000 in state-distributed National Oceanic and Atmospheric Administration funding to monitor the success of the $8 million project.

At the same time this summer, a new living shoreline project spearheaded by South graduate student Jamie Amato, one of Cebrian鈥檚 students, received media attention in coastal Mississippi. The experiment involves bolting fabric-lined metal cages filled with sand and marine plants to bulkheads at Bennett Bayou in Moss Point, Miss. The yearlong project will test whether those miniature artificial marshes can restore fish habitat, filter the water and protect the bulkheads from storm damage.

So what are living shorelines, and why do they present such a difficult puzzle for researchers? Well, let鈥檚 say you want to stop your waterfront land from eroding, and you also want to provide habitat for some delicious seafood 鈥� for example, blue crabs.

You could put a row of structures in the water parallel to the shore to knock down waves. That prevents them from eating away the land and also restores eroded land by causing the waves to drop the sand and other sediment they鈥檙e carrying.

Any such structures 鈥� and there are many designs, each with advantages and drawbacks 鈥� have to be close to the shoreline, because that鈥檚 where you want the sediment to fall. And the structures have to stick out above the water much of the time, depending on the tide. 鈥淏ut if you do that, you know that blue crabs won鈥檛 come,鈥� Cebrian said.

Blue crabs live in the water, not above it. Their habitat needs to be submerged, out in deeper water. 鈥淭hat could be 50 yards seaward, that could be 100 yards, that could be 150 yards,鈥� Cebrian said, 鈥渄epending upon the topography of the bottom.鈥� And that鈥檚 too far out and too far underwater to have much effect on waves.

It seems, then, that you have two choices: build close to shore for erosion control but not blue crab habitat, or build offshore for crab habitat but not erosion control.

鈥淚deally, what we, a bunch of researchers, are trying to do now is to find a design that does it all,鈥� Cebrian said. 鈥淎nd there is some evidence to suggest that it is possible. Difficult but possible. For example, you can have subtidal reefs that are long enough, tall enough and wide enough to truly reduce wave energy even though they are somewhat away from the shoreline.鈥�

鈥淚deally, what we, a bunch of researchers, are trying to do now is to find a design that does it all. And there is some evidence to suggest that it is possible.鈥�

鈥淪ubtidal鈥� means underwater even at low tide, which pleases the crabs. But there鈥檚 a catch: 鈥淭o do that, you really need to know how the sediment and the water move in the area,鈥� Cebrian said. So there鈥檚 no off-the-shelf solution. Instead, you have to research each individual stretch of shoreline and custom design a solution based on that data.

That鈥檚 where Dr. Bret Webb comes in. He鈥檚 a professor of coastal engineering at South. He uses two University facilities, a wave basin (20 feet wide by 30 feet long) and a wave-current flume (5 feet wide by 85 feet long), to test Cebrian鈥檚 ideas, using scale models of the structures they want to try.

鈥淥ne of the reasons why Dr. Cebrian and I get along so well together,鈥� Webb said, 鈥渋s because I respect what he does as an ecologist and he respects what I do as an engineer. And neither one of us pretends to know what the other one does. So for the past seven or eight years, Cebrian and I have been trying to stress the importance of integrating engineering and ecology to have a better chance of success in these projects.鈥�

Shorelines are complex ecosystems. They vary from rock cliffs to marshes, from mangrove forests thicketed with tangles of arching roots to wide sand beaches blanketed with gaggles of sunbathing tourists. Waves may pound or merely lap. The sea bottom may slope steeply or gently. Crosscurrents may carry sediment, or not. Damming of rivers may reduce sediment flows to the sea. Boat wakes may exacerbate erosion. The land may be sinking.

And, everywhere, the sea level is rising. According to a 2014 comprehensive U.S. government report, the global sea level will rise, depending on the model you favor, by anywhere from 8 inches to 6.6 feet by the end of this century.

Trying to account for all those factors and complexities has to be incredibly frustrating, right?

鈥淣o,鈥� said Webb. 鈥淚t鈥檚 not frustrating for me because as a coastal engineer, I鈥檓 used to dealing with large amounts of uncertainty. That鈥檚 inherent in the practice of engineering.鈥� So you try something. If it works, great. If not, also great 鈥� because at least you learn things that will increase the chance of success on the next try.

Counterintuitively, Webb said, large projects are easier than small ones. 鈥淭he lessons that we鈥檝e learned in the coastal engineering community for the large-scale projects don鈥檛 always translate to the small-scale projects that are being done now on a homeowner-by-homeowner basis,鈥� he said. 鈥淣ature likes longer, bigger things to deal with. If you have a very short project, Mother Nature is going to try and immediately smooth that out to be consistent with what鈥檚 going on around it.鈥�

Sometimes even successes look like failures, at least at first. 鈥淚f you are doing a constructed tidal marsh as a part of your living shoreline, when you first put that out, it looks disgusting,鈥� Webb said. 鈥淭iny little plants. Mud everywhere. It鈥檚 dirty. It鈥檚 nasty. Doesn鈥檛 look healthy at all. In the first wintertime, a lot of that vegetation dies back, and people think, oh, great, my living shoreline is dead. It was a waste of money.鈥�

Actually, diebacks are natural and good. Healthy marshes use dead organic material to increase their land mass, fortifying them against sea level rise. 鈥淲e have to set a clear expectation of what the project is going to look like, how it鈥檚 going to perform, what to expect long term and short term,鈥� Webb said. 鈥淭hese aren鈥檛 maintenance-free commitments. It鈥檚 not a one-size-fits-all process.鈥�

Still, researchers have found coastal property owners willing to make those commitments. 鈥淚f you tell them the right thing, if you make them feel connected, then they have a stake and they realize it鈥檚 in their best benefit and interest to keep shorelines healthy,鈥� Cebrian said. 

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