Response of Salt, Circulation and Sediment Transport to Variations in Tidal Forcing and River Discharge in the Passaic River

Robert J. Chant (1), David Fugate (2)

(1)Rutgers University, 71 Dudley Road, 732-932-6555 x 544, 732-932-8578 chant@marine.rutgers.edu, marine.rutgers.edu/cool

(2)Department of Marine and Ecological Sciences, Florida Gulf Coast University, 10501 FGCU Blvd. South, Fort Myers, FL 33965, 239-590-7136, 239-590-7200, dfugate@fgcu.edu

A series of moored and shipboard hydrodynamic surveys of the lower Passaic River have characterized critical aspects of the response of the salt field, circulation and sediment transport to changes in River discharge and tidal forcing. Observations show that during moderate to high river flows the salinity distribution is characterized by a salt wedge with a well defined turbidity maximum near the head of the wedge. During high (~100 m³/s) river flow events the salt front is transported out of the river during the ebb. In contrast, during low flow the river is characterized by a partially mixed estuary with a nearly linear salinity gradient that extends nearly 20km up river. This seasonally variability in the salt field has significant implications on the transport of suspended sediment.  Estimates of suspended sediment transport were made with acoustic backscatter calibrated against total suspended sediment measurements.  The temporal nature of the tidally averaged net sediment transport is weakly up river during base flow conditions and large episodic down stream transports (towards Newark Bay) during high flow events. Estimates of sediment budgets suggest that the net transport over a year is dominated by the high flow events and results in a net transport towards Newark Bay.  The net sediment transport is of the same order of estimates of sediment loadings to the Passaic River and suggests that the rapid accretion that has occurred over the last 50 years has slowed significantly.