this interaction often is not that significant. In the following, a short
discussion is provided on previous investigations on nearshore currents in the
laboratory and field pertinent to the present study. Several of the data sets
mentioned here enter in validation of NMLong-CW and will be discussed in
detail in other sections of this report. The data sets included are of two types,
waves propagating on an opposing current, and wave-generated longshore
current.
Sakai and Saeki (1984) investigated the transformation and breaking of
waves modified in encountering an opposing current on a sloping bottom in
the laboratory. They studied monochromatic waves and observed that the
wave height decay, after appropriate normalization, depended solely on the
bottom slope. Sakai, Hiyamizu, and Saeki (1986) continued the studies of
Sakai and Saeki (1984) employing random waves. Lai, Long, and Huang
(1989) conducted laboratory experiments to study the kinematics of waves on
an opposing current including wave blocking. Monochromatic waves of
different frequency were generated against the current, which flowed over a
false bottom in the flume to generate spatially varying conditions.
Measurements showed that the kinematic effect of the current on the waves
could be treated as a simple Doppler shift. Also, the blockage of the waves
by the current followed linear deepwater wave theory. Raichlen (1993)
investigated waves propagating on a 3-D jet in the laboratory that represented
the ebb-tide flow from a tidal inlet. Results of an exploratory nature
regarding wave-current interaction for this specific situation were presented.
Briggs and Liu (1993) carried out experiments in a basin to study the
interaction between monochromatic waves and an ebb current, and good
comparisons were found between the measurements and a model based on
the mild-slope equation including a current field (wave breaking was not
included). Briggs, Demirbilek, and Green (1996) conducted experiments in a
flume for monochromatic and random waves propagating on ebb (opposing)
and flood (following) currents. Only cases involving random waves and ebb
currents were discussed in the paper. Gentle or occasional wave breaking
was observed in the experiments. The paper mainly gave an overview of the
experiments and results from an initial analysis, but the long-term objective
was to develop a parameterization of the wave-breaking criterion in the
presence of a current. Smith, Resio, and Vincent (1997) and Smith et al.
(1998) performed detailed wave height measurements of waves shoaling and
breaking on an ebb current. Random waves were employed, and several
combinations of significant wave heights, peak spectral wave periods, and
ebb current speeds were used. The measurements were utilized to evaluate
and develop formulations of wave energy dissipation on a current.
In one of the most extensive laboratory studies to date regarding waves
on opposing currents, Chawla and Kirby (1998, 1999, 2002) investigated the
shoaling, breaking, and blocking both for monochromatic and random waves.
The conditions during the experiments were essentially deep water, although
some intermediate water depths were investigated. A spatially varying
current was obtained by inserting a false wall with a sloping side and for
several tests blocking occurred in this region. Chawla and Kirby (1998,
2000) observed that blocking took place for a larger current than predicted by
linear theory. However, by calculating the dispersion relation through third-
order Stokes wave theory, good agreement was obtained between
calculations and measurements, both regarding blocking and the wave height
decay due to breaking.
7
Chapter 2 Brief Literature Review
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