To appear: Shore & Beach, Vol 72, No. 1, 2004.
in some areas of the inlet. Other areas of the inlet system have been subjected
to excessive scour due to migration of tidal channels around areas of shoal
buildup.
Numerous barrier island breaches have occurred along the south shore of
Long Island due to major storms. Breaches are usually short-lived because they
tend to shoal and close or they are closed by mechanical operations. Moriches
and Shinnecock Inlets were originally opened by storms in 1931 and 1938.
Jetties now stabilize both of these inlets (Headland et al., 1999).
Sea level rise is known to increase the height of wave run-up onto
beaches and contribute to beach erosion. This increase in water depth alters the
equilibrium beach profile, leading to shoreline retreat and increasing the
possibility of coastal disasters. When integrated over the long term, sea-level
rise combined with episodic storm surge can have a severe effect on coastal
areas. The combined effects of eustatic (worldwide) sea-level rise and isostatic
adjustments in the Long Island area land elevations have resulted in a net
relative sea level rise of about 1 ft over the past 130 years. Tide gauge records
indicate that there has been an 0.36 ft per century eustatic rise in sea level (Dean
and Dalrymple, 2002; Gornitz et al., 1982).
The currents and tidal prism of Fire Island Inlet have had a remarkable
effect on the transport of longshore sediment since the 1950's. In the 1950's, the
average current speed in the inlet was about 5 ft/s and the mean tidal range was
approximately 4.1 ft at the entrance and 0.7 ft in Great South Bay (Gofseyeff,
1952). This yields a tidal prism of 1.1 x 108 cy for Fire Island Inlet (Kraus, et al.
2003). The net longshore sediment transport is directed to the east and has
been estimated to be in the range of 230,000 cy to 600,000 cy per year
depending on calculation methods and assumptions made to estimate the long-
term littoral sand budget (Rosati et al., 1999). The jetty directs this littoral drift
into the inlet area, resulting in rapid shoaling and extension of Democrat Point
(USACE, 2002).
Tidal inlets are often considered from an equilibrium point of view (Bruun,
1978; Escoffier, 1977). According to the Escoffier stability criteria, Fire Island
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