180
P. Wang et al. / Coastal Engineering 46 (2002) 175211
Fig. 2. Cross-shore distribution of significant wave height and breaker index defined as Hmo/h.
plunging cases is 1.5 s (0.67 Hz) and 3.0 s (0.33 Hz),
before the survey of the initial beach to smooth out the
respectively, with various amounts of low frequency
tractor-tire tracks from construction. This wave action
energy (Fig. 3). The period of the low-frequency peak
caused the slight deviation from the segmented planar
varied somewhat across the surf zone but remained
beach in the offshore region from 9 to 13 m (Fig. 4).
mostly between 11 s (0.09 Hz) and 21 s (0.05 Hz). Its
The spilling case, which lasted a total of 33 h, was
relative energy density increased substantially toward
conducted with the power-function profile of Eq. (6)
shore, becoming the dominant peak at the two land-
as the initial condition. The spilling-breaker experi-
wardmost gages, 1.1 and 2.7 m from the shoreline,
ment was conducted in eighteen 15- to 200-min seg-
respectively. Low-frequency motion was found to
ments (Wang et al., 2002). The beach profile was
have significant influence on sediment transport in
surveyed at the end of each segment. The modest
the swash zone and immediately seaward (e.g., Puelo
change of beach-profile shape (Fig. 4) occurred during
et al., 2000).
the first 22 h. The beach profile reached quasi-equi-
librium, or stable shape, after 22 h of the spilling-
3.2. Beach conditions
wave action. The spilling profile shown in Fig. 4
represents the average of 16 profiles in the middle
The test beach was initially constructed based on
section of the test beach surveyed between 22 and 33
the equilibrium profile shape described by Bruun
h. Boundary effects in the middle 16 m of the test
beach were negligible. Modest erosion was measured
in the inner surf zone between 0.5 and 5.0 m from
2
h Ax3
6
shoreline, while modest accumulation was measured
in the vicinity of the breaker line from 9.5 to 14.5 m.
Little net change in bed elevation was measured in the
where h is still-water depth, x is horizontal distance
mid-surf zone between 5.0 and 9.5 m. The hydro-
from the shoreline, A is a dimensional-scaling param-
eter determined by sediment grain size to be 0.07 m1/3
dynamic and sediment concentration data presented
here are those collected after equilibrium between 22
based on the Dean (1991) method. The beach profile
and 33 h.
calculated using Eq. (6) was approximated with three
The plunging-breaker case, which lasted a total of
planar segments for convenience of construction.
10.5 h, was conducted after the spilling case, using the
Approximately 20 min of wave action was imposed
Previous Page
