The role of wave and current forcing in the process of barrier island overwash

With the rapid growth and development of barrier islands, understanding the long-termstability of these islands is an integral part of future coastal planning. The overwash process isthe largest influence on the long-term stability of these islands and thus a correspondingunderstanding is of major importance. A laboratory experiment was undertaken to physicallymodel the wave and current forcing as they pertain to the overwash process. The physical modelwas subjected to various storm conditions common to the occurrence of the overwash.Combinations of wave height, wave period, and overwash depth were tested in an attempt toisolate the significant parameters. Water surface gradients were also applied to observe theirinfluence on the overwash process. Wave height, current, and bed profile measurements weretaken at different locations throughout the tank. In addition, wave height transformationmodeling and mean current prediction were performed and compared to the laboratory results inan attempt to model the overwash process through computer simulations.The experimental results demonstrate that the water surface gradient is the mechanismfor transporting large quantities of sand on to and over barrier islands. In addition, two otherconclusions were drawn about the overwash process: 1) the overwash depth plays an importantrole in determining the overwash velocity and hence the amount of sand deposited on the barrierisland. 2) There seems to exist a correlation between the strength of the return flow and barformation.It was also determined that modeling the wave height transformation during the overwashprocess is possible if the model is expressly written for the overwash process and not for nonoverwashingcases. The method utilized to predict the mean currents during overwash was notable to predict their strength but was able to substantiate the correlation between return flow andbar formation. As a result of overwash, the increased shoreward mass transport and reducedreturn flow in the water column are able to initiate and sustain a shoreward sediment transport.Finally, it was concluded that in all likelihood only "significant" overwash events affect the longtermstability of the barrier islands.

Bibliographic Details

Main Author:	Pirrello, Mark A.
Format:	thesis biblioteca
Language:	English
Published:	University of Florida, Coastal and Oceanographic Engineering Department 1992
Subjects:	Oceanography, Engineering, Earth Sciences, barrier islands, overwash, modeling, beach erosion, ocean waves,
Online Access:	http://hdl.handle.net/1834/18396
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