volume of 4.6 x 106 m3, 50% and 90% inlet natural bypassing would occur in 60 and 200 years,
respectively, for a gross input longshore sand transport rate of 300,000 m3/year, which assumes
that little sand comes from the west. Mechanical bypassing during channel dredging would
augment natural bypassing. The maintenance-dredging requirement is expected to be similar to
that of the other south shore inlets, yielding the savings justification to construct the jetties in a
long-term regional sediment management plan.
Storm Surge, Water Level, and Circulation. The much smaller hydraulic length of the
relocated inlet (~ 1 km) as compared to the existing inlet (~ 6.5 km) will improve water
exchange between the ocean and Great South Bay. Preliminary calculations show an increase in
tide range of 5 to 6 cm. The increased efficiency will improve circulation in the vicinity of the
relocated inlet. Slow-moving storms will fill the bay about equally for the existing and relocated
inlet, but fast-moving storms will fill the bay faster for the relocated inlet. On the other hand,
bay filling by heavy precipitation will be more rapidly discharged to the ocean through the
relocated inlet. Such processes can be reliably calculated with tidal circulation and wave
propagation numerical models as part of a feasibility study. Great South Bay involves a multiple
inlet system, and examination of a major inlet modification should include all the inlets.
CONCLUDING DISCUSSION
This paper has explored regional sediment management considerations through a thought-
experiment case study of hypothetical eastward relocation of Fire Island Inlet, Long Island, New
York. Emphasis was on the physical processes and sediment redistribution and handling.
Simple calculation of the cost of relocation indicates the new inlet would begin yielding cost
savings in about 20 years while providing greatly improved shore protection to adjacent
(downdrift, updrift, back bay) beaches for on the order of a century or more.
Some negative consequences, both certain and probable, were identified. The new flood
shoal at the relocated inlet would cover existing bay bottom and remove sand from the littoral
system. Slightly increased tidal range may be a concern for wetland health under normal
weather conditions, but most likely would be offset by improved circulation in the bay. Bay
filling during fast moving tropical storms is a real concern that must and can be evaluated.
Environmental, socio-economic, and political issues were not considered. Numerous stake-
holders and interested parties would have to come together at the regional sediment management
table to identify issues that need addressing to assure that a system-wide approach anticipated all
direct and indirect consequences of inlet relocation. The authors believe that the knowledge and
technology exist to make reliable decisions and arrive at a properly performing design.
ACKNOWLEDGEMENTS
We appreciate the assistance of Dr. Andrew Morang for locating and digitizing the Beach
Erosion Board photographs and of Ms. Lynn Bocamazo for locating photographs at the U.S.
Army Corps of Engineers, New York District. This paper, developed as an activity of the
Coastal Morphology Modeling Work Unit of the Regional Sediment Management Research
Program, benefited from review by Ms. Julie Dean Rosati. Permission was granted by
Headquarters, U.S. Army Corps of Engineers, to publish this information. This paper concerned
a hypothetical alternative studied to examine concepts in regional sediment management; results
and conclusions should not be construed as a position on any action by the U.S. Army Corps of
Engineers for maintenance and operation of the federal navigation project at Fire Island Inlet.
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