During 1939-1941, a jetty was constructed on the east side of Fire Island Inlet to stabilize the
entrance, but by the mid-1950's it had become impounded, with finger shoals encroaching into
the navigation channel. In 1959, an 800-m long sand training dike was constructed to force the
ebb current away from Oak Beach. Storage of sand in the shoals has reduced bypassing
capacity, contributing to chronic erosion along Gilgo Beach, located 5 km to the west of the
entrance. Gilgo Beach may be in a nodal region of longshore transport created by the shadow of
the combined masses of Democrat Point and the Fire Island Inlet ebb shoal and bypassing bar.
Concern remains about the erosive ebb current running along Oak Beach and condition of the
training dike, which is maintained by local government. Some back passing of dredged sediment
is also performed to Atlantic-fronting beaches east of Democrat Point; backpassed sand is
eventually transported west and re-enters the inlet.
The question can be raised why not relocate the inlet back to its early 19th century position
and construct dual jetties to eliminate or greatly reduce problems associated with the present inlet
configuration in a regional sediment management approach? What direct and indirect
consequences, positive and negative, would emerge as a result of the relocation? This paper
examines, at scoping level, functional designs and regional sediment management considerations
of hypothetical relocation of Fire Island Inlet.
HYPOTHETICAL FUNCTIONAL DESIGN OF RELOCATED (NEW) INLET
Numerous physical processes, as well as political and socio-economic issues, must be
addressed in considering inlet relocation in an urban area. If Fire Island Inlet were to be
relocated 8 km to the east (and the old entrance closed or allowed to close), the existing ebb
shoal having an estimated volume of about 30 million m3 would migrate shoreward to the
western beaches.
Under an estimated annual-average net westerly transport rate of
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300,000 m /year, Cedar Beach, Gilgo Beach, and beaches to the west would be supplied with
sand for close to a century. The existing jetty might be shortened gradually to hold the beach
along the terminus of Fire Island (Democrat Point), minimizing formation of a cape to the west.
Such considerations of various regional sediment and physical processes are discussed here.
As a hypothetical regional sediment management alternative, the inlet is relocated 8 km to
the east, back to its position in 1827, with the east jetty of the relocated inlet placed 150 m west
of the lighthouse. The jetties are constructed 330 (1,000 ft) apart and extend to the 6-m (20-ft)
contour (mean sea level, MSL). Approximately 500 m of barrier island is dredged to create the
inlet. Assuming an average barrier island elevation of 4 m above MSL, the total volume
removed to create the relocated inlet is about 1.6 x 106 m3. This material could be (1) placed
offshore to form a nascent ebb shoal and promote natural sand bypassing, (2) pumped west to
plug the old inlet, or (3) stockpiled for various uses such as for wetland creation, and for beach
nourishment and breach filling during a storm. Inlet dimensions were chosen to approximate the
natural cross-sectional area of the existing inlet and provide reliable navigation. The 6-m depth
MSL is almost equivalent to the authorized depth of 4.27 m mean lower low water (MLLW).
The dual jetties of the hypothetical relocated inlet are aligned 11 deg to shore-normal and at a
NE-SW orientation to shelter vessels from larger waves out of the SE and to direct the flood tidal
plume away from Sexton Island and the two small "Fire Islands" in Great South Bay (see Fig. 2).
The flood current of the relocated inlet might tend to erode these islands, which are
environmental resources. The relocated inlet will create both an ebb shoal and a flood shoal.
Other processes and possible consequences are discussed below.
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