conditions during eight different months of the year and spanning a period of nearly 18
years provided the input to the analyses conducted in this study. Four of the HWL data
sets were interpreted from rectified aerial photography (December 1979, April 1983,
March 1988, and April 1995). Leatherman and Allen (1985) compiled the December
1979 shoreline position data set from aerial photography as part of their geomorphic
analysis of the south shore of Long Island. The April 1983, March 1988, and April 1995
HWL data sets were interpreted from digitally rectified aerial photography by the Coastal
and Hydraulics Laboratory at WES as part of the FIMP Coastal Processes studies. The
remaining seven HWL shoreline position data sets were obtained using a kinematic GPS
survey system mounted on an ATV and traversing the high water line between Fire Island
Inlet and Moriches Inlet (Allen and LaBash 1996). These GPS survey data sets of the Fire
Island HWL shoreline were provided by Dr. James R. Allen, U.S. Geological Survey, who
also directed the survey program with partial funding provided by the Corps of Engineers,
New York District. The GPS shoreline position surveys were conducted in: (1) August
1993, (2) September 1994, (3) August 1995, (4) November 1996, (5) January 1997, (6)
May 1997, (7) September 1997. The original interpreted and surveyed HWL data sets
were comprised of Northing and Easting coordinate pairs referenced horizontally to the
North American Datum of 1983 (NAD83), in New York Long Island Zone 3104 State
Plane coordinates, in units of meters. The HWL data sets were subsequently interpolated
at 25-meter intervals relative to an arbitrary baseline oriented along the general trend of
the Fire Island barrier. The result of this step was co-located shoreline position data sets
(station and offset from baseline) that could be analyzed to determine for example, rates
of shoreline change between various time intervals. The Fire Island baseline has a 71-
degree azimuth orientation, is 50 km long, and its origin is centrally located in Fire Island
Inlet.
ANALYSES
Shoreline Change
The influence shoreline undulations have on typical engineering calculations at Fire
Island is readily illustrated by examining the rate of shoreline change over various time
intervals. For example, the rates of shoreline change over a representative 10-km reach
in central Fire Island (approximately from Fire Island Pines to Watch Hill) for the intervals
December 1979 to April 1983, April 1983 to March 1988, and March 1988 to April 1995
are plotted in Fig. 2. Fig. 2 shows that the local rate of shoreline change can be relatively
large, ranging from about "10 m/year over an approximate 3-year interval to around
"5 m/year over a 7-year interval. As can be seen in the figure, the rate of shoreline change
is highly variable both spatially and temporally with high rates of accretion followed by
high rates of erosion at the same location depending on the interval of time examined.
Because of this high degree of variability, the historical rate of shoreline change may be
relatively small (on the order of 1 m/year erosion) but have a large standard deviation (on
the order of 5 m/year). Fig. 3 illustrates the wide fluctuations in shoreline position that
result in the large rates of shoreline change and high degree of spatial variability in the
rates plotted in Fig. 2. Note the comparatively wide berm width present on the right-hand
side of both images and the very eroded condition (narrow berm width) in the central
portion of the top image that subsequently
Gravens
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