A study by University of South Alabama researchers, released in June 2014, found that the man-made seawalls lining much of the residential shoreline of Mobile Bay could be costly to maintain and damaging to the natural habitat they replaced.
The findings challenged a widespread assumption among waterfront property owners that a hardened vertical wall was the surest way to protect land from erosion.
A transformed shoreline
Fifty years earlier, more than 90 percent of Mobile Bay’s shores were lined with salt marshes and other natural habitats, according to the report. To guard against erosion and make it easier to build boat docks, more than 70 percent of surveyed homeowners had since installed vertical walls along the water, dramatically reshaping the bay’s edge.
Researchers found that those seawalls damaged natural habitats and the species that depended on them, including oysters and other mollusks that filter water and serve as a valuable food source. The upkeep of the walls, the report added, cost roughly twice as much as maintaining a natural shoreline.
A cycle of construction
The study also pointed to a chain-reaction effect along the bay. A survey of 400 homeowners showed that residents were more likely to build a seawall in response to damage caused by a neighbor’s wall, as the hardened structures deflected wave energy onto adjacent, unprotected properties.
The survey further revealed significant misinformation about the relative benefits of natural habitat compared with seawalls. Many homeowners, the researchers found, underestimated how effectively marshes and reefs could shield their land.
Alternatives to hardened walls
Rather than simply cataloging the problem, the report offered potential solutions. Salt marshes, the researchers noted, reduce erosion by absorbing wave energy without harming the surrounding ecosystem. Man-made oyster reefs offered another option, dampening waves while restoring habitat for the very shellfish that help keep bay waters clean.
Such approaches, often grouped under the heading of living shorelines, aimed to protect property and habitat at the same time, a contrast to the walls that had come to define so much of the bay’s residential frontage. Where a seawall reflects wave energy and can scour the bottom in front of it, a marsh or reef absorbs that energy, trapping sediment and building rather than losing ground over time.
Costs that add up over time
The report’s emphasis on cost carried particular weight for waterfront owners weighing their options. A seawall is not a one-time expense; it must be repaired and eventually replaced as waves, storms and settling take their toll. By finding that natural shorelines cost about half as much to maintain, the researchers suggested that the cheaper long-term choice was often the one that also did the least harm to the bay.
The study underscored how individual property decisions, repeated hundreds of times around the bay, had reshaped an entire ecosystem. Each homeowner who added a wall in response to a neighbor’s could, without intending to, accelerate erosion next door and chip away at the marshes and oyster beds that once buffered the whole shoreline.
For a region whose identity is bound up with Mobile Bay, the study served as a reminder that decisions made lot by lot along the water could add up to broad consequences for habitat, water quality and the long-term cost of living on the shoreline.