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Dune Preparation

In general, it is best to avoid mechanical manipulation (bulldozing sand up beach) or at least only do as a last resort, since the sand that creates the slope lower on beach reduces the energy of the waves and thus that sand is already protecting the beach where it is.  Moving it higher on the beach doesn't increase overall protection, and may even make things worse in the long term.  If you have the time, use of sand fences, trees and planting dune grasses to allow dunes to accrete naturally, will result in dunes that are more stable and thus better able to protect the communities behind them from flooding in future storms.

Clearly, though, sometimes you don't have time to wait for Mother Nature to do her "thing".   If you have the necessary permits, you can hurry things along by piling sand from the beach onto dunes and planting that, but the resulting dune won't be as strong as dune that establishes by natural processes. Mechanically placed sand tends to be looser than naturally formed dunes which have been worked by the environment (wind, rain, etc) Obviously, once the plants develop their root systems, that will help stabilize and bind the sand in the dune.  Also, if your dune is just a pile of fresh sand, it will have even less organic materials in it to hold onto and provide water to plant roots than a naturally accumulated dune.  This lack of water and nutrients in the sand may mean the difference between success and failure of your plants.  If you are planted into freshly bulldozed sand piles, please see our section on  planting amendments for things you can do to help promote the success of your plantings.

Another important idea to consider as you develop your dune system, is the directionality of any dune access paths. When access paths are perpendicular to the shore, the ocean tends to force its way through them as if through a funnel, gaining power and eroding the dunes significantly.  After Sandy, less flooding was seen behind dunes where paths passed through the dune at about a 45 degree angle, rather than perpendicular to the shore.

It is important to realize that all dunes erode, and if we've learned anything from Hurricane Sandy, it is that it is the volume of sand in the dune is what's really important. Tall skinny dunes would keep you dry if the water simply came up and went down with no waves.  But when you add in the waves, they chop away at the base of the dune causing it to collapse resulting in a vertical cliff or scarp. Eventually, if there is not enough sand in the dune, it will breach. How much sand is required to prevent this depends on the size of the storm. FEMA suggests 540 ft3 per linear foot (in the frontal dune reservoir) based on studies of hurricanes impacting dunes in North Carolina.  However, experts suggest that this should actually be a bit higher here in New Jersey, because the nor'easters here can beat on the dunes for days at a time.

 

Content of these pages was contributed by Chris Miller, Jon Miller, Michael Peek, Ray Bukowski, and Louise Wootton.  Edited by Louise Wootton.