To appear: Shore & Beach, Vol 72, No. 1, 2004.
According to the analysis of the photographic record, the sand trapping
capacity of the jetty was reached by 1948. The sand then swept around the
edge of the jetty and accumulated as spits and shoals within the channel as
Gilgo Beach and Oak Beach eroded from the lack of sediment supply. By 1956,
the spit extended about one mile northwest of the jetty and constricted the inlet
width to 1,200 ft. In 1959, to reduce the extensive erosion around Oak Beach, a
one-half mile perpendicular dike (known locally as "The Sore Thumb") was
created from approximately 1.1 million cy of material dredged from the ebb shoal
(Figure 5). The dike was to some extent advantageous in preserving channel
location and preventing erosion on the downdrift end of the inlet. However, the
channel still requires almost yearly maintenance dredging to maintain
navigational channel depths (USACE 2002).
The total volume of material that has been dredged from Fire Island Inlet
channel since 1946 is approximately 19 million cy (Table 1). The cost has been
about million per year to dredge the inlet and bypass the sand to downdrift
locations. This cost is equivalent to the combined annual dredging operations
performed on the other five tidal inlets on the south shore of Long Island (Kraus
et al., 2003).
Inlets evolve toward dynamic equilibrium, and thus continuously respond
to waves, littoral drift, and engineering activities.
The stability of an inlet is
dependent upon a balance between currents that carry sediment into the inlet
channel from the wave-dominated littoral system, and the strong tidal flows that
scour the channel (Headland et al. 1999). Inlets can abruptly shoal due to rapid
deposition of littoral sand during storm events. Over time, the main channel of an
inlet can split into multiple channels by natural or anthropogenic causes, be
impacted by changes in the lagoon/bay area surrounding the inlet, or experience
lengthening of the inlet conveyance channel (Bruun, 1978).
lengthened over the past 70 years, is the main reason for the excessive shoaling