The Swamp Stomp

Volume 19, Issue 8

After studying the effects of Hurricane Irene on the Outer Banks of NC, scientists faced some surprising data.  The surprising part was that so little information was available on the resilience of coastlines. Environmental Scientist at the University of North Carolina at Chapel Hill, Rachel Gittman, was quoted saying, “The more I researched, the more I realized that we just don’t know very much. So much policy and management are being made without the underlying science.” (1) Scientists understood the physics, but it was never put in a form the policymakers could easily understand. 

As Gittman was studying the shorelines, she noted that concrete walls were out weathered by the marshes. Irene damaged 76% of bulkheads surveyed, while no damage to other shoreline protection options was detected. However, in terms of habitat loss statistics, 30 to 50 percent of wetlands have already been lost, 19 percent of mangroves were lost from 1980–2005, and 75 percent of the world’s coral reefs are now rated as threatened. (3) 

Almost all money, historically, to protect the coastline has been spent on “gray infrastructure.” These include bulkheads, levees, seawalls, and rock revetments.  However, as research on “green” coastal protection is measured in the long term, this is beginning to change. It has become clear that living shorelines are a great defense against storms and surges.   

“Living shorelines” is a term used to define shoreline protection allowing for natural coastal processes to remain through the strategic placement of plants, stone, sand fill, and other structural and organic materials. (4) Yet the value of these ecosystems considered as “green infrastructure” is still not fully accepted or understood by policymakers, and these valuable ecosystems continue to be lost and degraded. Wetlands across the U.S. and the world continue to disappear at a rapid rate due to global warming, increased populations, and infrastructure. 

Storm responses suggest that marshes with and without sills are more durable than hard structures and may protect shorelines from erosion better than bulkheads in a Category 1 storm. Wetlands, i.e. marshes, coral reefs, and mangroves, prevented $625 million of damage during Irene from flooding although 60-90 percent of protective wetlands had been previously lost.  Coastal and marine ecosystems, particularly coral reefs and mangroves can reduce exposure to wind and waves, and they provide natural protection. Coral reefs are the most effective system for flood control. They form natural sea walls where nature intended and, thus, reduce wave energy up to 97%. Reviving reefs and mangrove ecosystems are also more cost-effective than artificial breakwater construction and maintenance.   

After Hurricane Irene, the vegetation in marshes was reduced, but the vegetation only took a year to replenish and become even thicker, and denser than prior to Irene.  However, scientists are now finding that a sill (a berm that is in front of the seaside edge) will bear the brunt of wave energy and will also trap sediment, so the grasses thrive. The marsh floor is sometimes built up as a result.  The sills are green protection and made of hard materials like rock, shells and stone or concrete.  

Along the San Francisco shoreline, restoration is taking on the most novel structure called horizontal levees.  Instead of a vertical wall, horizontal levees are mudflats, marshes, and grasslands that are broad and rise from the edge of the water sometimes hundreds of meters back onto land.  These types of levees are 40% of the cost of a traditional levee.   

NOAA has recently taken living shorelines to the center stage of its coastal resilience plan. 

Some of the recent legislation is: 

• San Francisco Bay Clean Water, Pollution Prevention and Habitat Restoration Measure passed  in 2016 which allocates $25 million a year for 20 years,  
• The Living Shorelines Act which designates $20 million in grants to living shoreline work,  
• North Carolina’s Coastal Resources Commission has approved an easier way to get a living shoreline permit, now comparable to the permit required for a bulkhead, and  
• Maryland has a strong law requiring property owners to prove the need for a bulkhead as opposed to a living shoreline.  

“Benefit-cost analysis” policy now favors investment in natural infrastructure and coastal restoration may be getting some well-deserved attention. This emphasis should result in federally funded projects in Florida, Puerto Rico and the Gulf Coast. The importance of coastal resilience and natural shorelines will guide development worldwide. “When this happens, it will mark a moment when society realizes nature is not a luxury. It is the future.” (1) 

Sources:

(1) Rowan Jacobsen, “Beyond Seawalls,” Scientific American, Vol. 320 Number 4, April 2019. 

(2) Gittman, Rachel K., “Marshes with and without Sills Protect Estuarine Shorelines from Erosion Better Than Bulkheads during a Category 1 Hurricane,” Ocean and Coastal Management, Vol. 102, Part A, Pages 94-102; December 2014. 

(3) Beck, M.W., Lange, G.M. “Managing Coasts with Natural Solutions: Guidelines for Measuring and Valuing the Coastal Protection Services of Mangroves and Coral Reefs,” World Bank, January 2016. 

(4) Living Shorelines Academy: www.livingshorelinesacademy.org