The "surfability" of waves has been the subject of scientific investigation (e.g.,
Walker 1974; Dally 1989, 1990, 2001). Most such studies have concerned surfing
environments on the open coast, away from structures. In the case of Threes, several
factors control the breaking of waves inside Shinnecock Inlet, including the incident
wave field properties, presence of reflecting structures, and the stage of the tidal cycle.
The most limiting factor is the incident wave angle, because breaking of Threes can only
occur in a narrow directional window. Shinnecock Inlet jetties are approximately
oriented from north to south, with the eastern barrier offset to the south. Incident waves
approaching from the southeast are blocked from entering the inlet by the orientation of
the channel and offset of the barrier islands. Similarly, much of the energy associated
with waves approaching from the southwest is dissipated on the extensive ebb shoal.
Waves that approach the inlet from the south-southeast to the south-southwest appear to
propagate into the throat and could initiate the breaking of Threes. However, if the
waves travel along the axis of the channel without reflecting off the eastern jetty, they
will not make their way to the western bay side shoal. These waves then propagate into
the bay where they are gradually dissipated on the flood shoal or in Shinnecock Bay.
Both the tidal current velocity and water elevation alter the incident waves and exert
control on the location of wave breaking. Threes was surfable 12 days between July and
August 2003, and conditions were reported best from an hour or two on either side of
slack low tide (Mr. Joe Alber, personal communication). During this portion of the tidal
cycle, the ebb current is weak and less likely to block waves. However, a weak ebb
current is expected to block or filter out the shorter period waves, resulting in waves that
are longer in period, cleaner, and more surfable (Figures 1 and 5). For all of these events,
the wave heights ranged between 1.5 and 2.5 m. If the incident wave height is too large,
the wave will break on the ebb shoal, dissipating much of its energy before reaching the
inlet. During high water, larger waves can propagate over the ebb-shoal without breaking
and then through the inlet unimpeded by the ebb current. However, during high water the
bay side shoal where Threes is found is also too deep to initiate wave breaking. The
incident wave height needs to be small enough to pass over the outer shoals without
breaking during an ebbing tide, but with long enough period to propagate against an ebb
tidal current without being blocked. There is some variability in the system, and the size
of the waves that will activate Threes depends on the lunar stage of the tidal cycle, as
well as other external variables such as storm surge, wind direction, and wind-driven
circulation.
The quality and size of the waves at Threes has also been influenced by engineering
activities. The most noticeable changes occur from dredging of the main channel and
deposition basin, and rehabilitation of the jetties. Dredging of the inlet allows larger
waves to propagate into the throat without breaking, increasing the "source" of wave
energy for Threes. Rehabilitation of the east and west jetties between 1992 and 1994,
and again in 2003 has maintained or increased the reflecting potential of the structures
and the amount of wave energy transmitted to the third wave (Threes). For the 2003 jetty
rehabilitation, the U.S. Army Corps of Engineers, New York District, adapted
construction as much as practicable to meet recommendations of the local surfing
community. Thus, Threes lives on.
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