EVALUATION OF SAND RESOURCES OFFSHORE NEW JERSEY: A MARINE SEISMIC SURVEY TO LOCATE AND QUANTIFY USABLE SAND DEPOSITS FOR BEACH REPLENISHMENT

The New Jersey Geological and Water Survey (NJGWS) conducts high-resolution marine seismic data acquisition and analysis to identify and quantify sand deposits off the coast of New Jersey for use in beach replenishment projects conducted by the US Army Corp of Engineers. The most recent seismic data collection occurred during the summer of 2013. 326 nautical miles of seismic data were surveyed between Barnegat and Manasquan Inlets up to 11 km offshore Ocean County, NJ. We employed an adaptive sampling framework wherein systematic half-mile spaced transects were surveyed initially. In areas with known targets a higher density sampling was conducted to gain a more detailed analysis of these potential resources. Data were collected on the R/V Northstar 4 using a Geopulse^TM boomer with a peak output frequency of ~1.0kHz and an 8-element single channel hydrophone streamer. This equipment was towed 25 meters behind the vessel at 3-4 knots. The data yielded a vertical resolution of ~.85m with useable data down to 20 m depending on seafloor multiple. During the 2013 Ocean County inventory, data was viewed in real time and stored using SonarWiz^TM5 (Chesapeake Technologies, Inc). Initial processing and review of the 2013 seismic data is being conducted jointly by NJGWS and Rutgers University.

Previously, Octopus and DrGeo^TMsoftware were used for data acquisition offshore Monmouth County. These data from previous years were subsequently digitized and reformatted to be compatible with SonarWiz. This allowed several data generations to be examined simultaneously, enabling a more complete, and economical analysis of potential offshore sand resources. The sub bottom profile data is ground-truthed with lithologic data from 6-meter vibracores, locations determined from review of the seismic data. NJGWS is then able to match sediment type and grain size information to observed acoustic impedance differences seen in the seismic profiles. In 2014 NJGWS plans to drill vibracores for ground-truth of the seismic profiles collected in 2013.

NJGWS is currently performing a volumetric analysis of the reformatted data for the area offshore Monmouth County. In this way, NJGWS is able to estimate sand volumes for any offshore sand deposits where the data exists, in a manner that can be compared accurately with other sections of the NJ coast.