To appear: Shore & Beach, Vol 72, No. 1, 2004.
erosion of the main or secondary flood shoal versus the amount of filling or
deposition that has taken place (Figure 12, 13). This may be explained by the
lack of dredging of the flood shoals for beach fill and sand bypassing.
volume of the secondary flood shoal, calculated from a base elevation of -37.7 ft
NGVD, was estimated to contain about 15.2 million cy of sand in 1996.
The combined volume of the main and secondary flood shoals is
approximately 36.5 million cy, versus 32.1 million cy for the ebb shoal. A factor
that might have contributed to the relatively slow growth of the ebb shoal over the
past 50 years is the persistent dredging and bypassing of sand from the
navigational channels, which might otherwise feed the growth of the Fire Island
Inlet shoals. In addition to channel dredging and sand bypassing directly from
the ebb shoal, the capture of sand in the main and secondary flood shoal is
another factor slowing the growth of the ebb shoal over the last 50 years.
The stability and morphology of an inlet are dependent upon a balance
among currents that carry sediment into the inlet channel, tidal flows within the
channel that scour the banks and channels, and wave-driven currents that
provide littoral sediment supply and sand bypassing. Engineering structures and
sand management practices interact with natural processes to define the
morphologic condition of an inlet.
In the case of Fire Island Inlet, a strong
westward-directed net littoral sand transport past the Democrat Point Jetty is a
dominant process for the evolution of the inlet and surrounding barrier segments.
The Escoffier (1977) closure curve identifies Fire Island Inlet as being marginally
stable. The excessive length of the inlet channel through the barrier overlap area
makes Fire Island Inlet hydraulically inefficient.
Without continued dredging
operations, Fire Island Inlet would likely close and, in fact, seemed to be near
closure in 1940 and again in 1950 due to excessive shoaling.
The addition of a jetty on Fire Island's western tip in 1941 impounded
littoral sand and halted the westward extension of the barrier island, but may