Long-Term Sand Cap Stability: New York Dredged Material Disposal Site

Abstract : A comprehensive physical oceanographic field study was conducted in November 1986 to determine the bathymetry of the New York Mud Dump site and assess the long-term stability of an experimental sand cap, or mud damp (EMD), located in the southeast quadrant of the site. Results of a precision bathymetric survey were compared with results from surveys conducted in 1980 and 1981. A REMOTS sediment-profile survey was conducted over the entire site, and a subbottom profiling survey was conducted at the EMD. A significant accumulation of sediment was found at the dredged material disposal point in the northeast quadrant, and decreases in depth to the south and east of this point indicated accumulation of dredged material beyond the eastern boundary of the site. Significant erosion of the sand cap was not detected, and clean sand representing the final cap material was found to persist in a continuous layer in the center of the EMD. A few patches of finer-grained material, possibly dredged material transported from the north, were found to exist over the sand. The effects of bioturbation on the sand cap appeared to be negligible. It was suggested that monitoring should occur during and following disposal operations to ensure adequate management control and later to assess the stability and environmental impacts of disposal mounds.