Reports
Assessment of sediment releases from dike breaches at the Poplar Island Environmental Restoration Project due to Hurricane Isabel
2005, Halka, J.P.
File Reports, Coastal and Estuarine Geology, File Report 2005-02
Introduction
Although it had been downgraded from a full Hurricane to a Tropical Storm by the time it passed through the Chesapeake Bay region, the storm induced tidal surge combined with significant waves associated with Isabel caused damage to portions of the dikes at the Poplar Island Environmental Restoration Project (PIERP). Concern was raised that the damage may have resulted in the movement of either dike sand or finer grained dredged sediments from within the project area to the shallow platform surrounding the dike. The sand sized grains, if present in a thick deposit, may have had the potential to migrate into adjacent areas where oysters occur. Finer grained sediments, due to their ability to remain in suspension during turbulent wave events would be transported greater distances from the dike. The potential for sand sized sediments to be located in thick deposits or to cover adjacent oyster shells could be evaluated, in part, by examining pre-Isabel and post-Isabel conditions on the shallow platform adjacent to the dike breaches. Side-scan sonar surveys of the area had been made during the dike construction and post-construction phases of the project and could provide a basis for comparison to post-Isabel conditions. The potential for finer grained sediment movement could not be as effectively examined using the technique, because thin deposits of fine sediments are generally not observable using side-scan sonar. This report presents results from the various side-scan sonar surveys conducted in the vicinity of the dike damage, and interprets these for the potential of identifying sand deposits that may have been associated with the dike breaches.
