EVALUATION OF A LITTORAL SOURCE OFFSHORE OF FIRE ISLAND
Several researchers have postulated that the inner shelf, and/or shoals offshore of central
Fire Island may provide a source of littoral material for the beaches west of this location.
The foundation for their reasoning is based on several observations:
The relative stability of central Fire Island over the past 1200 years, as compared to the
remainder of the barrier island (Kana 1995, Schwab 1999).
The presence of shoreface-attached sand ridges and the availability of littoral sediments
offshore of central Fire Island (Williams and Morgan 1993, Schwab 1999).
The net LST rate at Fire Island Inlet as calculated by previous sediment budgets which
ranges from 240,000 (RPI 1983) to 360,000 m3/yr (Kana 1995) as compared to an
accepted net LST rate east of Fire Island Inlet up to 460,000 m3/yr (Taney 1961a).
The impact of including an offshore source of littoral sediment was evaluated as a part
of this study by adding a source along Fire Island from Stations 14.8 (Point of Woods) to
28.0 km (west of Watch Hill). The onshore source of littoral material was assumed to
increase the net LST rate within the region west of the source. An offshore source equal
to 75,000 m3/yr results in net LST rate estimates which agree with the maximum estimate
for growth of Democrat Point (238,000 m3/yr) and agreeing with Taney' (1961a,b)
estimates. A source of 160,000 m3/yr results in net LST rates that exceed the spit analysis
standard deviation value, but agrees with Taney' "best" estimate (344,000 m3/yr). The
highest value exceeds the Democrat Point analysis, but is lower than Taney' highest
estimate. Thus, the source of offshore sediment to Fire Island beaches appears to be a
possible contributing factor to the nearshore sediment budget, although the regional
sediment budget presented herein indicates that it is not required.
Rosati et al.