PERIODIC SHORELINE MORPHOLOGY, FIRE ISLAND, NEW YORK
Mark B. Gravens1, AM. ASCE
Abstract: The presence of shoreline undulations along the Atlantic coast of
Fire Island, NY requires careful consideration in developing erosion control
and hurricane protection plans and design alternatives for the protection of the
Fire Island barrier and the Long Island mainland. An analysis and geometric
characterization of these morphologic shoreline features revealed that the
magnitude of the shoreline undulations approximates typical protective berm
design widths and exceeds typical advance nourishment beach widths. Because
shoreline undulations are natural morphologic features of the Fire Island
shoreline their presence after project construction must be anticipated.
Conclusions drawn from the analysis of the Fire Island shoreline undulations
indicate that the design berm width could be compromised well before
scheduled renourishment if explicit consideration of shoreline undulations is not
included in the development of the design cross-section.
Fire Island is one of several barrier islands that lie along the southern edge of Long
Island, New York. The Fire Island barrier is approximately 50 km in length and is
bounded on the east by Moriches Inlet and on the west by Fire Island Inlet. North of the
island lies Great South Bay and to the south is the Atlantic Ocean (Fig.1). The average
net longshore sand transport rate on Fire Island is from east to west, and its magnitude
is estimated at approximately 200,000 m3/year with representative values for west- and
east-directed transports of 350,000 and 150,000 m3/year, respectively (Rosati et al. 1999).
The Atlantic shoreline of Fire Island is consistently characterized by undulating shoreline
features that are locally referred to as longshore sand waves or erosion waves. The
shoreline features discussed in this paper are distinguished from commonly observed beach
cusps in that the shoreline undulations found on Fire Island appear to be more random
1) Research Hydraulic Engineer, U.S. Army Engineer Waterways Experiment Station, Coastal
and Hydraulics Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199 USA.