POST-SUPERSTORM SANDY (2012-2018) RECOVERY OF A BACKDUNE OVERTOP CORRIDOR, ISLAND BEACH, NEW JERSEY: FIELD MONITORING AND GRAY-SCALE IMAGE ANALYSIS

Superstorm Sandy (October 2012) produced several breaches and localized overwash along the U.S. Mid-Atlantic coast, however most of the geological impact involved limited landward penetration, which resulted in massive overtopping and aggradation of coastal barriers. An overtop site on Island Beach State Park, New Jersey, located just north of the landfall has been monitored on the annual basis to provide a time-series of post-storm morphological and sedimentological trends. Changes to the storm-surge channel site as of April 2018 include: 1) establishment of a foredune ridge; 2) formation of a gravel lag (shells, anthropogenic debris) and heavy-mineral concentrations (HMC) through deflation of storm-surge interdune deposit, and 3) re-establishment of vegetation within the landward segment of the overtop fan and at adjacent sites. Persistent features are represented by: 1) gross topography of the surge corridor, and 2) landward-leaning trees and trunk-wrapping dune grass. Analysis of a series of satellite images (November 2012 through October 2017) reveals sedimentological anomalies immediately following the storm (upper beach HMC) and progressive re-vegetation of the site. The latter is quantified using comparative gray-scale analysis (linear scale: 0.36 m/pixel), with ~35% value reduction (darkening) within the storm-surge corridor and at least 92% of the profile length. Whereas inter-image lighting can be normalized using fixed feature identification, darkening due to HMC vs. vegetation may require site-specific intra-image calibration. Establishment of high-contrast image benchmarks allows rapid and accurate reproducibility of gray-scale values by multiple operators. Our study demonstrates how original post-storm investigations (trenching, georadar imaging, magnetic susceptibility measurements) can be complemented with field-based and remotely sensed datasets to catalog the transformation of a storm-surge site.