What you may not know about vertical seawalls

by Angela Herring

If you looked up and down the coast of Alabama’s Mobile Bay a half-​​century ago, you would have seen that roughly 90 per­cent of its shores were lined with fringing salt marshes and other nat­ural coastal habi­tats. But today, more than 70 per­cent of the res­i­den­tial shore­line has been rein­forced with ver­tical walls, erected by home­owners in indi­vidual attempts to stave off ero­sion or, in some cases, as a con­ve­nient place to dock one’s boat.

Nat­ural habi­tats are known to pro­vide a range of “ecosystem ser­vices” that ben­efit not only the marine species that live there, but also their human neigh­bors. For instance, oys­ters and other inter­tidal mol­lusks filter the water of organic waste runoff and also rep­re­sent a valu­able food source. Steven Scyphers, a post-​​doctoral research fellow in marine and envi­ron­mental sci­ences asso­ciate pro­fessor Jon Grabowski’s lab at Northeastern’s Marine Sci­ence Center, said that one of the major prob­lems with man-​​made shore­line struc­tures is that they often damage these nat­ural habi­tats and don’t pro­vide the same benefits.

Fur­ther­more, he said, they’re expen­sive. “People think ver­tical walls are less expen­sive than reg­ular main­te­nance of a nat­ural shore­line, but it’s actu­ally two times as costly,” he explained.

In a paper pub­lished Friday in the journal Con­ser­va­tion Let­ters, Scyphers and his col­leagues at the Uni­ver­sity of South Alabama and the Dauphin Island Sea Lab present research exam­ining the values and decision-​​making processes of water­front home­owners. The goal of the research, he said, is to iden­tify con­ser­va­tion strate­gies that are most likely to suc­ceed given the need for stake­holder buy-​​in.

Scyphers is inter­ested in how home­owners manage their shore­lines, because this is where indi­vidual changes are hap­pening quickly and con­sis­tently. “It’s not just one large-​​scale con­ser­va­tion project—it’s hun­dreds of thou­sands of little ones,” he said.

The researchers used a 40-​​question written survey devel­oped in con­junc­tion with coastal sci­en­tists, prac­ti­tioners, and water­front home­owners to develop a better under­standing of the per­cep­tions and expe­ri­ences of nearly 400 home­owners on Mobile Bay.

These are two views of shore­lines in Mobile Bay in Alabama. At left, a nat­ural shore­line is seen, and at right, a man-​​made ver­tical wall is seen. Photos taken by Steven Scyphers.

These are two views of shore­lines in Mobile Bay in Alabama. At left, a nat­ural shore­line is seen, and at right, a man-​​made ver­tical wall is seen. Photos taken by Steven Scyphers.

An analysis of the feed­back revealed two impor­tant dis­cov­eries: First, there was a lot of mis­in­for­ma­tion regarding the envi­ron­mental impacts and cost-​​effectiveness of var­ious shore­line solutions—not only ver­tical walls, but also things like rocks and simply leaving the nat­ural shore intact. Second, home­owners were much more likely to add a ver­tical wall to their own prop­erty as a response to damage done by a neighbor’s wall.

“The deci­sion of one neighbor to build a ver­tical wall can cas­cade down the shore­line,” Scyphers said. He noted that the most common form of shore­line intervention—vertical walls—is also the most dam­aging because for more than half a cen­tury, con­ser­va­tion poli­cies have favored this kind of infrastructure.

The study’s results give Scyphers and his team valu­able data for informing future policy mea­sures. The cas­cading phe­nom­enon, Scyphers said, sug­gests that per­haps the most impor­tant places to pro­tect are long, existing stretches of unde­vel­oped shore­line. Con­ser­va­tion efforts, he noted, should focus on restoring habi­tats in the most degraded areas as best as pos­sible, but policy should focus on pro­moting better deci­sions among home­owners. That latter effort will require working col­lab­o­ra­tively with home­owners to under­stand and develop the best solu­tions that ben­efit them and coastal ecosys­tems, according to Scyphers, whose research is also focused on living shorelines.

Solu­tions range from man-​​made oyster reefs to salt marshes, which reduce ero­sion by absorbing wave impacts without the neg­a­tive effects brought on by sea­walls. Fur­ther­more, these so-​​called “green” or “nature-​​based” approaches actu­ally pro­mote habitat for the local ecosys­tems rather than degrading it.

“The over­whelming majority of home­owners want what’s best for the Bay as long as it pro­tects their prop­erty and is cost effec­tive,” Scyphers said. The key to suc­ceeding on that front, he explained, is get­ting the home­owners accu­rate infor­ma­tion about their var­ious choices before they make their decisions.

Originally published in [email protected] on June 16, 2014

College of Science