The New York Bight and the Coastal Current

In total, the Harbor system discharges annualmean flow amounting to over 700 m3 s-1 of fresh water to the New York Bight. Approximately 600 m3 s-1 of this is from the Hudson, Raritan, and Passaic Rivers, with an additional 100 m3 s-1 from sewage outflows. In addition, the estimated 300 m3 s-1 transported through the East River augments this flow and yields a mean volume transport leaving the Harbor complex through the Sandy Hook-Rockaway transect of approximately 1,000 m3 s-1 -nearly double the discharge of the Hudson.

The flow through the Sandy Hook-Rockaway transect, like the flow throughout much of the Harbor system is two layered, with the surface layer flowing seaward and the lower layer flowing landward. Thus, the transport of fluid in the upper layer must also compensate for the inflow in the lower layer. Based on salt conservation at the Sandy Hook-Rockaway transect, an annual mean outflow of approximately 3,500 m3 s-1 of estuar-ine water enters the New York Bight, with approximately 2,500 m3 s-1 of saline waters from the Bight entering into the Harbor. These transports significantly vary at weekly, monthly, seasonal, andinter-annual time scales.

Once past the Sandy Hook-Rockaway transect, the estuarine water from New York Harbor forms a coastal current that flows south along the New Jersey shore. The tendency for the current to head southward is due to the effect of the earth's rotation, or the "Coriolis effect," which turns the fluid to the right in the absence of other forces. Winds also play a major role in defining the structure and direction of the outflow. Southerly winds (winds from the south) spread the plume offshore causing it to thin and may arrest its southward flow. Northerly winds compress the plume against the coast and augment its flow to the south. As the plume is transported south along the New Jersey coast it continuously mixes with the more saline shelf waters in the coastal ocean. The mixing is primarily wind driven, while the weak tidal currents, that tend to be less than 15 cm/s along the New Jersey inner shelf, play a secondary role. The Hudson's coastal current has been observed along southern New Jersey near Cape May, more than 150 km south of the Battery (Yankovsky et al., 2002). Eventually, the signature of the Hudson's freshwater flowis lost south of Cape May, New Jersey, where its plume becomes obscured when it mixes with waters from Delaware Bay.

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