Waves at tidal inlets refract, diffract, and shoal as they travel from deeper
water, over the ebb shoal, and into the navigation channel toward the bay. How
waves transform as they change direction and height is of interest to navigation
because the knowledge will assist in understanding sediment transport in the
inlet, especially near the navigation channel, and anticipating wave-related
processes inside the inlet, such as shoreline erosion and accretion. In particular,
waves diffract where they encounter a jetty, breakwater, or other discontinuity.
Diffraction at a jetty can cast a wave shadow either inside the inlet or on the
adjacent beach, depending on the incident wave direction. Controlled
measurements of wave diffraction on a sloping beach are lacking, yet this
combined transformation process is ubiquitous at all coastal inlets.
The purpose of these laboratory experiments was to measure wave height and
and refraction. At many locations, coastal structures are built to reduce wave
height and minimize sedimentation of the navigation channel. In this study, a
shore-parallel breakwater and a dogleg jetty were examined in the seaward side
of the inlet. Measurements were also made on the bay side of the inlet for a
jettied and nonjettied condition.
Figure 1 illustrates diffraction and refraction on the bay side of Shinnecock
Inlet, Long Island, New York. Coastal inlet entrance channels are typically
incised in relatively shallow depths and are thus susceptible to movement of
sediment into the channel by coastal currents of tidal and wind wave-generated
origin. The entrance channel may be flanked by jetties and/or breakwaters to
reduce sediment influx to the channel and to provide protection for navigation.
In order to understand the mechanisms of sediment movement into the channel,
the simulation of the wind-wave field is a central component of any modeling
study of techniques to minimize channel shoaling. Historically, for coastal
problems at sites with complex bathymetry and protective structures such as
jetties, breakwaters, and groins, studies were conducted in physical models.
Chapter 1 Introduction