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What to expect when your beach is nourished

August 10, 2011
Guest commentary by KEN & KATE GOODERHAM, Executive Directors of the American Shore & Beach Preservation Association , Island Reporter, Captiva Current, Sanibel-Captiva Islander

Reaction to a new beach nourishment project can be mixed, as residents and visitors welcome the new wide beach but are concerned about rapid changes of the newly placed sand.

Often, the perception is that the project has caused some undesired impact on the sandy shoreline, or that the beach is eroding too quickly and all that new sand will be lost. In a community where nourishment is a new approach to managing erosion, residents may ask themselves "Is it working? Have we spent our tax dollars wisely?" Every situation is different, but often the effects residents and visitors see are expected by project designers.

In Nags Head, N.C., a beach nourishment is currently under way with more than four million cubic yards of sand being pumped onto the beaches at a cost of $36 million. This project is being funded primarily by the town and has been the subject of heated debate by residents.

Recently, residents have commented on the development of "drop offs," also called scarps or escarpments. Scarps are a steep slope separating the high, dry beach berm and lower, wet sand. Typically, these are 1 to 3 feet high, but can be taller after severe storms. They are temporary and will smooth out as the sand dries and waves return to normal.

Tim Kana, principal of Coastal Science and Engineering that designed this project, said: "Wave action has cut back the nourishment 'berm' (the new sand placed on the beach) and left low escarpments at the edge of the surf. This sudden drop off of a few feet from the new dry beach to the wet beach is similar to what natural beaches experience after minor storm events, particularly during the first northeasters of the fall."

As Kana explained, erosion of the dry beach during storms is part of the natural beach cycle - the erosion of sand from the visible beach during storms, followed by the return of sand to the beach during fair weather periods. The condition of the beach people see therefore revolves around the beach cycle, tending to appear wider in the summer and narrow in the winter.

Some sand moves offshore when wave heights increase. The slope of the wet beach flattens so the higher wave energy can dissipate gradually across a wider surf zone (the dramatic waves breaking on the shoreline we typically identify with storms). The "lost" sand from the visible beach is pulled offshore by these waves and builds up a bar parallel to the coast. This bar then forms a natural barrier and helps break the incoming waves. The "drop offs" residents and visitors are seeing are not a direct result of the project, and can form during any mild storm event on both nourished and non-nourished sandy beaches.

In addition to scarp formation, erosion of the new beach sand often generates concern in residents. In nourishment projects such as Nags Head, the initial construction puts a majority of the sand on the visible beach for practical reasons of controlling the sand placement. Therefore, the initial beach width appears much wider than the final beach width will be.

A simple analogy is that of an iceberg. The visible beach is like the tip of the iceberg, but it is only stable if there is a large volume underwater supporting it. If most of the new sand is initially pumped onto the visible beach, it will be unstable; some of it will need to shift offshore and form the foundation for the new beach. As Kana pointed out: "It is helpful to have minor storms soon after nourishment so that waves quickly modify the profile to a natural shape. Storms do an efficient job of redistributing the nourishment sand -- for free."

After the initial adjustment, the new beach will undergo the same cycles of erosion in winter and buildup in the summer. Most important, the new beach even after adjustment will be wider than the pre-nourishment beach.

So the presence of scarps along beaches are a natural phenomenon - they indicate sand has moved offshore. Some of that sand will come back, but much of the new sand will remain offshore in shallow water creating the foundation for a wider beach over the next decade or more.

While residents and visitors new to beach nourishment may be apprehensive about changes on the beaches after sand is put on their beach, many times those changes are expected and not a cause for worry. It's just the beach design allowing nature to take its course to reshape the beach into a more sustainable shape - to make it into a beach residents and visitors can enjoy for years to come.

Founded in 1926, the ASBPA promotes the integration of science, policies and actions that maintain, protect and enhance the coasts of America. For more information on the ASBPA, visit www.asbpa.org, Facebook or www.twitter.com/asbpa.

 
 

 

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