DELAWARE BAY BENTHIC MAPPING PROJECT: SUB-BOTTOM IMAGING CONSTRAINING SAND RESOURCES AND ESTABLISHING RECENT GEOLOGIC FRAMEWORK

The Coastal Management Program of the Delaware Department of Natural Resources and Environmental Control is engaged in a bottom and sub-bottom imaging project to identify and map the benthic habitat and sub-bottom sediments of the Delaware Bay. The project, now in the third of its five year implementation, integrates the use of three types of acoustical systems: RoxAnn seabed classification, chirp sub-bottom profiling, and multi-beam bathymetric mapping. Verification of the acoustic data with bottom and sub-bottom sediments is performed through the collection of grab and core samples and underwater video images. All this information is being compiled into a GIS database to enable coastal decision makers to effectively manage this estuarine resource.

Sub-bottom profiles, collected using an Edgetech X-STAR chirp sonar system, are being used to map potential, and past, offshore sand borrow sites that can be/have been used for beach replenishment and to study the deposition and/or erosion of sediments and the evolution of the Delaware Estuary over the past 10,000 years. In locations along Delaware Bay where beach replenishment is necessary, the chirp data has been integrated with additional information from sediment cores to develop maps of suitable sand deposits based upon location, thickness, overburden, and grain size. The sub-bottom data has been used to map the Holocene/Pre-Holocene boundary and to constrain the paleo-environmental setting of the recent transgressive sea-level sequence in the estuary.

The morphology of the bay bottom is being mapped in selected areas using a Reson 8124 multibeam bathymetric system. The system has thus far been used to map selected high-interest areas of the bay including natural and artificial reefs, oyster beds, and critical fish habitat. The downstream reaches of several rivers that drain into the middle portion of estuary have also been mapped to assess the bathymetry and changes in channel morphology.