western quadrant, producing longshore current and sediment transport directed toward
the east for the central and eastern portions of Long Island. For the study sites, fetch
length for waves originating from the west is considerably larger than the fetch length
from the east. Fetch length for the study area is approximately 50 miles from the
northwest and 20 miles from the northeast (New York District 1969). Larger fetch length
will yield comparatively larger wave heights from the west under similar conditions,
further augmenting the dominant direction of sediment transport.
A wave analysis performed by New York District (1999)1 calculated significant
wave heights and wave periods for various long-term return periods for waves
approaching Mattituck Inlet (Table 2-3). The calculated wave heights listed are for
extreme weather events. Calculated wave directions were from 260 to 280 deg at 10-deg
intervals. Wave height and period for the 10- through 200-year storms have a limited
spread because of the restricted fetch of Long Island Sound.
Calculated Significant Wave Height and Period (New York
Return Period (year)
Significant Wave Height (ft)
. During flood tide, water enters Long Island
Ocean. Current strength is greatest during this time and greatest at The Race, with a
consistent westward decrease in velocity. Circulation within Long Island Sound is
counterclockwise, with flood current entering to the north and preceding west, and ebb
current running from west to east along the north shore of Long Island (U.S.
Environmental Protection Agency (USEPA) and USACE (2001)). The tidal current has
been observed to decrease consistently with water depth throughout the sound. Current
speed for Long Island Sound is asymmetric. Western and Central Long Island Sound are
flood-dominant, where flood-tide speeds are about 1-3 cm/sec greater than ebb speeds.
In eastern Long Island Sound, ebb tide speeds were found to be about 1-5 cm/sec greater
than flood speeds. Table 2-4 summarizes mean and maximum currents from the study by
the USEPA and USACE (2001). Mean current velocities were calculated by averaging
the mean velocities of a number of current meters that were deployed throughout the
U.S. Army Engineer District, New York. (1999). "Mattituck Inlet, New York," unpublished memorandum.
Chapter 2 Study Area and Physical Setting