OBSERVATIONS OF BOTTOM CURRENTS AND ESTIMATES OF RESUSPENDED SEDIMENTTRANSPORT AT THE NEW-YORK-BIGHT 12-MILE DUMPSITE

To document storm events that may induce a redistribution of sediment in the vicinity of the New York Bight 12-mile sewage sludge dumpsite, current meter moorings were deployed in water depths from 20 m (near t he mouth of New York Harbor) to 53 m (within the Hudson Shelf Valley) from July 1986 through June 1989. Ten usable instrument records rangin g from one month to one year in duration were obtained; eight of them near-bottom records. Seasonal and geographic variability of wind-induc ed flow were examined. The wind is most efficient in driving the subti dal currents in the 2-10 day frequency band during winter when the wat er column is well mixed and when the eastward component of the wind of ten induces and sustains an up-valley (northward) bottom flow. Maximum efficiency occurs for wind from 300-degrees (WNW) and at sites locate d within the Hudson Shelf Valley. A continental shelf bottom boundary layer model (Glenn and Grant, 1987) was used to estimate resuspended s ediment transport. Model inputs include bottom currents (observed), or bital wave velocities (estimated), and sediment grain size (from the l iterature). Model output indicates that sediment resuspension at the c urrent meter sites occurs approximately 5% of the time, primarily duri ng winter months. The difference in along-valley flux between two moor ings provides a rough estimate (6-month time series) of deposition and erosion. The net deposition (+.02 mm) was no greater than the deposit ion and erosion resulting from individual storms. A three-dimensional circulation model (You et al., 1991) is applied to increase the spatia l resolution of the near-bottom current field (4 km grid) for a storm event in May of 1987. Given these velocities that vary in space and ti me, the redistribution of sediment was modeled for different surface w ave conditions. Areas of deposition aligned with the Hudson Shelf Vall ey due to less wave-induced resuspension in deeper waters. Given all t he uncertainties in the input variables (grain size, surface waves) an d the simplistic assumptions made in modeling the deposition and erosi on, it is still uncertain how much sludge is permanently removed from the area, but episodic redistribution of surficial sediment evidently occurs throughout the Inner New York Bight.