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Figure 3.11. Map of New York Harbor complex and western Long Island Sound. The Battery is at the southern tip of Manhattan.

Figure 3.11. Map of New York Harbor complex and western Long Island Sound. The Battery is at the southern tip of Manhattan.

by sea level differences between different water bodies due to tidal and meteorological forcing. Weaker, but persistent two-layer flow is also driven by a salinity difference at the ends of the straits and by non-linear tidal dynamics.

the east river

Despite its name, the East River is not a river but rather a tidal strait, for it has no significant natural direct source of fresh water (in fact sewage outflows are the largest direct source of "fresh water" to the East River). Tidal currents in the East River are among the strongest in the region because of a remarkable difference in the amplitude and timing of the tide between Long Island Sound and New York Harbor. Tides in western Long Island are nearly 70 percent larger than those in the Harbor, and the time of high and low water occurs over

3 hours later in western Long Island Sound than in the Harbor (Fig. 3.12). This oscillating sea level slope drives 2 ms-1 tidal currents in the East River, and the notorious tidal currents at Hell Gate (at the junction of the East and Harlem Rivers) can exceed 3 ms-1.

Weaker but lower frequency flows in the East River are also driven by sea level slopes set up by a difference in the wind-driven response of the Harbor and Western Long Island Sound (Wilson, Wong, and Filadelfo, 1985). These flows fluctuate with winds thattypicallyvary ata2-5 daytime scale. While these flows are an order of magnitude weaker than the tidal currents, they are more persistent and may significantly contribute to the exchange between the Sound and the Harbor.

A mean salinity gradient exists along the East River with bottom waters in Western Long Island

Days

Figure 3.12. A) Upper panel, hourly sea level from Western Long Island Sound at Willets Point (thick line), The Battery (dashed line), Sandy Hook (dotted line) and the western Kill Van Kull atBayonne (thin line). B) Lower panel, Sea level difference between the Battery and Willets Point (thick line), Sandy Hook and the Battery (dashed-dotted line), and Bayonne and the Battery (thin line).

Days

Figure 3.12. A) Upper panel, hourly sea level from Western Long Island Sound at Willets Point (thick line), The Battery (dashed line), Sandy Hook (dotted line) and the western Kill Van Kull atBayonne (thin line). B) Lower panel, Sea level difference between the Battery and Willets Point (thick line), Sandy Hook and the Battery (dashed-dotted line), and Bayonne and the Battery (thin line).

Sound on average 4 psu more saline than those in the Harbor (Blumberg and Pritchard, 1997). Strong tidal currents in the lower East River maintains a well-mixed water column, while salinity stratification in the upper portions of the strait near Willets Point tends to be about 2 psu in the vertical dimension (Blumberg and Pritchard, 1997). Mixing is strong enough that the mean flow tends to be unidirectional throughout the water column. Yet there is debate on both the magnitude and even the direction of the mean flow. A number of investigators (Blumberg, Khan, and St. John, 1999;Blumberg and Pritchard, 1997; Jay and Bowman, 1975) estimate a mean flow of about 300 m3 s-1 from the Sound into the Harbor. However, Filadelfo, Wilson, and Gomez-Reyes (1991) report persistent flow in the opposite direction.

the kills, newark bay and raritan bay

Like the East River, the Kill Van Kull and Arthur Kill are tidal straits. Maximum tidal currents reach ms-1 in the narrowest reaches of these straits and attenuate to less than 0.5 m s-1 in Newark Bay. Tidal excursions in the Kill Van Kull are greater than the length of the channel, thus tidal motion is effective in mixing water between Newark Bay and New York Harbor, particularly during spring tides. In contrast, tidal excursions in the Arthur Kill are significantly shorter than the length of the tidal strait; thus, tides are an ineffective agent driving exchange between Newark Bay and Raritan Bay.

The Raritan River and Passaic River are the major direct sources of fresh water to Raritan and Newark Bays, respectively - both with mean annual discharges of 50 m3 s-1, with peak flows in the spring of 100-300 m3 s-1. This fresh water drives a two-layer exchange in the tidal straits and Newark Bay. Salinity stratification and two layer exchange is persistent in the southern reaches of the Arthur Kill.

Meteorological forcing drives flow through the Kills both by the direct action of the wind on the water's surface and by producing a difference in the water levels at the ends of the tidal straits. Similar to what occurred in the East River, these meteorologically forced flows tend to last for several days, and potentially are an effective means to exchange water fluid between Newark Bay and Raritan Bay (Blumberg et al., 1999; Chant, 2002).

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