DELAWARE BAY BENTHIC AND SUB-BOTTOM MAPPING: IMPACTING COASTAL RESOURCE MANAGEMENT

Delaware Coastal Programs within the Department of Natural Resources and Environmental Control (DNREC), Delaware’s National Estuarine Research Reserve, and the Department of Geology at the University of Delaware have partnered in a five-year project to identify and map the benthic habitats and bottom and sub-bottom sediments of Delaware Bay. This project was initiated in order to document the Bay’s biodiversity and to examine human impact (e.g., beach replenishment, fishing activities) on the bay bottom and its living resources. This past summer a 60 km stretch of the Delaware Bay nearshore (as close to shore as 1 m mean low water out to distances of 2 km offshore) was mapped using three acoustic instruments: a RoxAnn® seabed classification system, a chirp sub-bottom profiler, and a multi-beam bathymetric mapping system. These techniques were integrated with bottom sediment grab samples, 7.62 cm diameter vibra-cores, and underwater video imaging. The information collected will greatly aid the State of Delaware which actively manages 7 beaches along Delaware Bay. This management includes periodic dredging of sand deposits offshore to replenish the beaches. Replenishment is necessary after coastal storms, for flood protection, and wildlife habitat preservation and formation. At present, there is limited information on the location, quality, and spatial extent of sand deposits in the nearshore zone of the Bay. There is also concern over the short and long-term effects of dredging on the local marine ecosystem. DNREC continues to develop and provide biodiversity information, this includes mapping oyster beds and worm “reefs” (Sabellaria vulgaris), artificial reef monitoring, monitoring critical areas for organisms such as horseshoe crabs, larval to juvenile fishes, and macro-invertebrates. There is regional concern about how the disturbance due to increased trawling by the conch fishery may affect the benthos and other important commercial and recreational stocks. Through identifying and mapping the benthic habitat and bottom and sub-bottom sediments of the Delaware Bay, and supplying this information in a public-friendly (i.e., GIS) format, decision makers and stakeholders will have access to critical data that will allow them to successfully manage and conserve Delaware’s nearshore coastal zone.