Although longshore currents generated by breaking waves is a classical
topic that has been studied for several decades, relatively few detailed, high-
quality measurements exist from either the laboratory or the field. The
experiments by Visser (1982) were a pioneering effort in the laboratory to
measure the cross-shore variation in the wave-generated longshore current.
Considerable effort was made to eliminate the influence of the basin and
obtain a current representative of the conditions at an infinite, straight beach.
Monochromatic waves were generated for a range of heights, periods, and
incident wave angles, and two different bottom roughnesses were used.
Recently, similar high-quality laboratory experiments were carried out by
Hamilton and Ebersole (2001), but at a larger scale. In these experiments,
both monochromatic and random waves were run.
Kraus and Sasaki (1979) performed the first field measurement of the
cross-shore distribution of the longshore current. They recorded the current
profile along seven transects on a sandy beach facing the Japan Sea, where
the beach profile had a step-type shape. The current was measured by timing
the movement of almost neutrally buoyant floats at middepth. Kuriyama
and Ozaki (1993) performed similar measurements at the Hazaki
Oceanographical Research Facility (HORF) on the Japan Pacific coast. The
beach profile at the HORF typically has several bars, which were also present
during the time of the measurements. A marked peak in the measured current
distribution was observed in the trough. In a later field campaign (Kuriyama
and Nakatsukasa 1999) the longshore current speed was measured using
electromagnetic current meters at three cross-shore locations. Kuriyama and
Nakatsukasa (1999) also developed a numerical model to simulate the cross-
shore distribution of the longshore current using the conservation of wave
energy flux and describing the energy dissipation due to breaking waves by a
bore model. An energy equation that included the surface roller was added to
the governing set of equations.
A few detailed field experiments have also been carried out along the
United States Coast. Thornton and Guza (1986) (see also Seymour 1989)
collected data on the longshore current during an experiment conducted at
Leadbetter Beach, Santa Barbara, CA. At this site the bottom contours are
relatively straight and parallel with no appreciable bars and troughs. The
measurements by Thornton and Guza differ somewhat from other data sets in
that the peak in the cross-shore longshore current distribution is located
seaward of the maximum energy dissipation (i.e., mean break point).
Typically, the peak in the longshore current lies shoreward of the break point,
attributable to the action of momentum transport in the breaking wave or
roller, as previously discussed.
Several dedicated field campaigns on nearshore currents have been
carried out at the U.S. Army Engineer Field Research Facility of the U.S.
Army Engineer Research, and Development Center, located in Duck, NC. A
field data-collection project called DELILAH was conducted in October 1990
with the objectives of measuring the wave- and wind-forced 3-D nearshore
dynamics and to monitor the bathymetric response to the operating hydro-
dynamic processes (Smith, Larson, and Kraus 1993). Pressure gauges and
current meters were placed at nine cross-shore locations and measurements
were performed during a period of almost 20 days. Smith, Larson, and Kraus
(1993) numerically simulated the cross-shore distributions of waves and
longshore current for eight measurement cases from 14 October. A marked
longshore bar was present during the measurements and the peak in the
current distribution was located in the trough, shoreward of where the
8
Chapter 2 Brief Literature Review
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