Wetlands Provide Better Defense to Coastal Flooding

Photo: John Althouse, Scientific American

As the U.S. must contend with more flooding events in areas like Houston and Miami, there is increasing evidence that wetlands and marshes are far more effective at protecting homes and other structures from flooding than concrete barriers.  Most recently, according to Scientific American, researchers studying the impact of 2011’s Hurricane Irene on the North Carolina coast where the storm had a 10-foot surge that destroyed roads and more than 1100 homes on the Outer Banks, a popular vacation spot.  What the researchers found confirms what experts are increasingly seeing play out in more recent storms — that walls and structural barriers “reflect” wave energy instead of dispersing it and when storm surge overtops them they completely collapse, causing even more damage.  According to the researchers:

  • Along the hard-hit shorelines, three-quarters of the barriers (typically concrete walls about 6 feet high) were damaged.
  • By comparison, none of the natural marsh shorelines were impaired — they lost no sediment or elevation and a year later vegetation had bounced back and was as thick as ever in many cases.
  • The researchers surveyed 689 waterfront owners and found 37 percent of properties protected by bulkheads had suffered 93 percent of the damage.
  • And bulkhead owners routinely were four times more expensive to maintain as compared to residents who relied on natural barriers instead. Salt marshes bent but did not break.

Scientists are improving the techniques used to restore degraded wetlands, even creating custom configurations for individual shorelines.  Governments and disaster response planners are beginning to advocate for living shorelines, and funding for coastal wetlands restoration is rising.

Why This Matters:  Salt marshes are fluid and give and they don’t break down.  And they are much cheaper too.  A second study conducted in conjunction with insurers looked at storm damage along the Gulf Coast and compared the costs and benefits of natural solutions versus hardened shorelines and found, for example, that wetlands restoration could prevent $18.2 billion of losses and would cost just $2 billion. Similarly, oyster-reef restoration could prevent $9.7 billion in losses at a cost of only $1.3 billion. Barrier island restoration offered $5.9 billion of prevention for $1.2 billion. And “beach nourishment” (replenishing depleted beaches with sand dredged from the seafloor) in the eastern Gulf could save $9.3 billion for $5.5 billion. Cost matters — infrastructure funds are going to be precious — they must not be wasted on costly and ineffective measure.  We need to look beyond structures to protect our coasts.

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