Beach Equilibrium

Beaches in equilibrium have four things:

1) Dunes are a mix of sand and vegetation and lack steep slopes. Dunes allow wave overwash.
2) No steep slopes, bluffs. Bluffs are often sandy but steep. No wave can overwash
3) Extensive development that prevents beach migration.
4) Interruption of Longshore transport. Longshore transport always exists, so it is only when it is interrupted by barriers or a natural deep channel that is a problem for downshore beaches.

Beaches lacking dunes, having abrupt slopes changes, barriers or development preventing longshore transport or wave overwash are not in equilibrium.

Below are two galleries. The first is a series of examples. Followed by the beaches you have to analyze for the assignment.

Gallery I: Examples of beach in or not in equilibrium

Gallery II: Answer YES or NO if the following beaches are in equilibrium?


Beach renourishment

With sea levels rising, renourishment of beaches has become a billion dollar per year industry.  What is this process and when is it a good investment?

Beach erosion is replaced by dredging sand typically from offshore to renourish the beach.  The process is costly several million dollars per mile on the typical shorefront.  With sea level rising at 3.2 mm/year this puts more and more pressure on beaches; which means more beaches need renourishing and the new sand may not endure.  Thirty years ago there was one renourished beach, Miami Beach.  Today on the east coast there are not many major beaches that have not been renourished.  A list with costs is provided by Western Carolina University. Below are some visual examples or renourished beaches.  The key to determining if it is a good investment is:

  • What is the duration of the repaired beach?
  • Does it prevent damage?
  • Value of real estate it protects?