INTERACTIONS OF SEDIMENT SUPPLY AND COASTAL TOPOGRAPHY AT SANDY HOOK, NEW JERSEY. (GATEWAY NATIONAL RECREATION AREA)

Relationships between sediment supply, sediment budget, and coastal topography are examined over a variety of time scales at Sandy Hook, NJ, utilizing 15 years of topographical data. Intermittent large scale replenishment projects updrift of the park produce irregular pulses of sediment entering the system that require the combination of analyses at a variety of temporal resolutions to adequately describe the long term topographical evolution. The data viewed from five year trend perspectives display the pulses as large accumulations corresponding with the period of time following the updrift beach fill projects. Finer temporal segregations ranging from one to five years reveal small alongshore segments of the system interacting dynamically, with localized cells of erosion providing source sediment for downdrift accumulation.

For the 15 year period, Sandy Hook accumulated ~300,000 m³ of sediment, providing the summation of coupled sediment supply and storage regimes occurring within that time. Until the late 1990s, the typical vector of net shoreline position change had been landward, and especially so in the middle third of the park’s length where studies indicated the greatest magnitude of alongshore sediment transport, with localized erosion of over 100,000 m³/y. After this time, large scale replenishment projects in communities updrift of Sandy Hook altered the magnitude of sediment input, and the budget was accordingly shifted towards a neutral to positive balance for all segments of the spit.

Between 2000 and 2005, DEMs created from LiDAR datasets show ~600,000 m³ of accumulation within the park, mostly in the northern and southern zones. The 2005-2010 period saw a return to an erosive condition in the middle third of the park shoreline, with losses of ~50,000 m³. The last five years can be characterized by pre-Sandy accumulation, losses resulting from the storm, and the post-storm recovery including the influence of replenishment. As the topography evolves based on the mid to long term sediment budget parameters, short term alongshore shifts in the transport cells may be occurring and bi-annual GPS survey data–including the reoccupation of beach/dune profiles and the recollection of the entire Sandy Hook shoreline position–provides the temporal resolution to evaluate these developments.