P. Wang et al. / Coastal Engineering 46 (2002) 175211
179
Table 2
influence on the determination of Hmo at the two
Summary of the wave and surf-zone conditions
landwardmost wave gages within 3 m from the still-
Spilling
Plunging
water shoreline, where low frequency motions were
breaker case
breaker case
substantial. Its influences at other cross-shore loca-
Conditions at the wave
tions were minimal.
generator (designed)
Water depth (m)
0.9
0.9
Significant wave height (m)
0.25
0.23
3. Wave and beach conditions
Peak wave period (s)
1.5
3.0
Wavelength (m)
3.4
8.7
Wave celerity (m/s)
2.2
2.9
3.1. The input wave conditions
Wave angle (j)
10
10
Two unidirectional, long-crested irregular wave
Deep-water wave conditions
conditions, each characterized by a relatively broad
(calculated)
spectral shape, were generated based on the TMA
Significant wave height (m)
0.27
0.24
Peak wave period (s)
1.5
3.0
spectra (Bouws et al., 1985) with the spectral width
Wavelength (m)
3.5
14.0
parameter of 3.3. Wave condition 1 with greater
Wave celerity (m/s)
2.3
4.7
steepness resulted in predominantly spilling breakers,
Wave angle (j)
10.4
16.3
while wave condition 2 with relatively low steepness
Wave steepness
0.077
0.017
resulted in predominantly plunging breakers. Deep-
Breaking wave conditions
water wave parameters were calculated from the
(measured)
conditions at the wave generator based on linear wave
Significant breaker height (m)
0.26
0.27
theory. Wave conditions, including both measured and
Main breaker angle (j)
6.5
6.4
calculated ones, are summarized in Table 2. The main
Breaking water depth (m)
0.46
0.28
breaker angle was estimated visually using the angle-
Breaker index (Hmo/h)
0.57
0.96
measuring device in an electronic total survey station.
Surf zone conditions
The breaker angles listed represent the averages of
(measured)
over 40 measurements.
Surf zone widtha (m)
14.0
13.0
The main breaker line was located at about 13.1 m
Surf zone slopeb
1:28 (0.035)
1:43 (0.023)
from the shoreline (gage 9, second from offshore) for
a
The surf zone width also includes the uprush zone above the
the spilling case (Fig. 2). For the plunging case, the
still-water shoreline.
b
main breaker line was located at 11.6 m (gage 8, third
The overall surf zone slope is calculated as the plane slope
from the breaker point to the still-water shoreline.
from offshore). Determination of the main breaker line
for irregular waves, and therefore the breaker height,
followed by a sharp decline to slightly less than 0.6. A
was somewhat subjective. In the present study, the
trend of landward increase of the Hmo/h ratio, from
main breaker line was determined to be at the location
slightly below 0.6 to nearly 0.8, was measured across
landward of which a significantly increased gradient
most of the surf zone for both the plunging and the
of wave-height decay was noticed (Fig. 2). This
spilling cases, indicating that the rate of wave-height
criterion was based on the comprehension that a
decay was slower than the rate of water-depth
drastic wave-energy loss, and therefore wave-height
decrease in the surf zone. Similar trend was reported
decrease, should follow major wave breaking. Visual
by Johnson and Kobayashi (2000). Across the mid-
observations of ``white water'' during the wave runs
surf zone, which was dominated by surf bores, the
supported the above measure. Similar breaker heights
magnitudes and trends of significant wave heights and
of 0.26 and 0.27 m were measured for the spilling and
the Hmo/h ratio were similar for both the plunging and
the plunging cases, respectively. The accuracy of the
the spilling cases, while conditions in the vicinities of
wave gages was F 2 mm (Hamilton et al., 2001).
the breaker line and shoreline were different (Fig. 2).
The ratio of significant wave height to water depth
The spectral density of the free surface fluctuations
ranged mostly from 0.6 to 0.8 (Fig. 2). A greater value
shows that peak wave period for the spilling and the
of nearly 1 was measured at the plunging breaker line,
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