Seawalls: Ecological Effects Of Coastal Armoring In Soft Sediment Environments

2017-07-26T15:38:28+00:00 July 26, 2017|

For nearly a century, the O’Shaughnessy seawall has held back the sand and seas of San Francisco’s Ocean Beach. At work even longer: the Galveston seawall, built after America’s deadliest hurricane in 1900 killed thousands in Texas.

(From ScienceDaily / by Julie Cohen) — These are just two examples of how America’s coasts — particularly those with large urban populations — have been armored with humanmade structures.

These structures essentially draw a line in the sand that constrains the ability of the shoreline to respond to changes in sea level and other dynamic coastal processes. While the resulting ecological effects have been studied more in recent years, the research largely has been conducted in specific settings, making it difficult to generalize these effects across ecosystems and structure types.

A new study by a team of UC Santa Barbara marine scientists and colleagues from three coastal sites in the National Science Foundation’s Long-Term Ecological Research (LTER) network provides a key first step toward generalizing ecological responses to armoring across the wide diversity of coastal settings where these structures are used. The team’s findings appear online and will be published this fall in a special issue of the journal Estuaries and Coasts, “Impacts of Coastal Land Use and Shoreline Armoring on Estuarine Ecosystems.”

Comparing Notes

The type of armoring structure varies widely with the environmental setting, ranging from massive seawalls and revetments along the wave-exposed open coast to smaller bulkheads and humanmade oyster reefs in tidal marshes and estuaries. “The size and shape of these humanmade structures often result in the loss of intertidal habitats,” said lead author Jenifer Dugan, a research biologist at UCSB’s Marine Science Institute. “The extent of that loss is a function of environmental setting, structure type and how far seaward and along the shore the structure extends.”

Scientists from three very different LTER programs were already working on the ecological impact of coastal armoring at their respective sites. At the Santa Barbara Coastal LTER, studies of the effects of seawalls on open coast beaches had revealed significant ecological impacts extending up to birds. The Georgia Coastal Ecosystems (GCE) project conducted studies of the effects of small-scale armoring in salt marshes. Studies at the Virginia Coast Reserve LTER focused on the use of constructed oyster reefs and living shorelines as coastal protection strategies.

“What was novel about this cross-site collaboration was putting these site-specific studies into perspective by making comparisons across a broad range of habitats,” said co-author Merryl Alber, a marine science professor at the University of Georgia and principal investigator of the GCE LTER project.

The collaborative study synthesizes the findings of existing literature examining different types of armoring across a variety of soft sediment ecosystems. The scientists used that data to evaluate a new conceptual model they created during two LTER cross-site workshops.

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