Predicting Coastal Sand Dune Growth Rates at the Wildwood's Convention and Civic Center, Wildwood, NJ

Abstract

Sand dunes can provide an effective barrier to coastal flooding and wave damage. High, continuous dunes protect against flooding. Dunes containing large volumes of sand protect against wave damage by contributing their sand to the littoral stream during periods of high water and large waves. The level of protection is thus related to the height and volume of the dune. Coastal dunes evolve naturally as vegetation grows and flourishes on the backbeach. Dune growth is also induced by the erection of sand fencing. When the level of protection is reduced by coastal storms, the backbeach area becomes vulnerable to damage by subsequent storms until the dune is rebuilt, either naturally or by man's intervention. Thus there is a need to be able to predict rates of dune growth in order to estimate their recovery following a storm. The rate of sand dune growth at the Wildwood Convention and Civic Center (WCCC) was predicted using historical wind data (wind rose) and the median sand diameter. The predicted values were judged to be too high and were subsequently adjusted downward based on a comparison of the beach sand size distributions with the dune sand distribution and on dune growth rates observed elsewhere. A dune monitoring program was established to measure growth rates as well as the evolution of plants growing on the dunes. Measured dune growth rates during the first 1½ years following dune planting and sand fence erection were close to the predicted rates for each of three dune reaches. In the following years, dune growth slowed, presumably since much of the sand fence was buried. Later, dune volume was augmented by sand excavated from the construction site. An improved model using hourly offshore wind data was subsequently used. This model gave a good prediction of the rate of dune growth rate as well as an estimate of the dune sand size distribution.