case. Along much of the rest of the surf zone, an accretional fillet is evident,
with the fillet at the bar location being the most pronounced. This location
corresponds to the peak in the distribution of the LST rate. The presence of a
pervasive accretion fillet also was observed for the spilling wave case. Near the
shoreline, an erosion perturbation is evident, not an accretion fillet. This is
different from the spilling-wave case. Its occurrence is attributed to the more
active swash zone associated with the longer-period waves and the stronger
interaction of wave uprush associated with the bricks used to construct the
downdrift profile template.
Alongshore Uniformity of Processes
Beach profile shape
For both the spilling- and plunging-breaker cases, reasonably straight and
parallel contours were maintained in the region of beach between alongshore
coordinates of 15 and 30 m. This is the same region that had the greatest degree
of alongshore uniformity, in terms of waves and mean currents, for the fixed-bed
concrete-beach experiments. A slight bar feature formed in the vicinity of the
incipient breaker line, in the region between cross-shore coordinates of 13 and 16
m in for the spilling-breaker case. A pronounced break-point bar formed in
nearly the same location for the plunging-breaker case. Both cases had a similar
incident wave height, but peak periods differed substantially. Throughout most
of the mid- and innersurf zones, beach profile shapes were quite similar. The
foreshore beach slope was slightly greater for the plunging wave case.
Figures 83 and 84 illustrate the alongshore variability in beach profile shape
for the spilling and plunging-wave cases, respectively. The beach profiles
depicted in these figures were measured after the beach had reached an
equilibrium condition (or very nearly so) and the proper mean longhore currents
were being pumped. The upper panel in each figure shows beach profiles, at 1-m
intervals, between the alongshore coordinates of 15 and 30 m. Note that the still
water level is at an elevation of 0.9 m. The lower panel shows the mean profile
shape computed from all profiles in this section of the beach, along with
envelopes representing +/- one standard deviation of elevation difference
between the various profiles and the mean profile. The degree of alongshore
uniformity is high, particularly for the spilling-breaker case. Uniformity for the
plunging wave case is also good, but there is more alongshore variability in the
vicinity of the bar. This is also evident in Figure 82, which shows the beach
contours for this case.
Waves and currents
Figures 85 and 86 illustrate the degree of alongshore uniformity in significant
wave height, and Figures 87 and 88 illustrate uniformity in mean longshore
current, for the spilling and plunging wave cases, respectively. The proper
longshore current was being pumped in both cases. Wave and current parameters
displayed in the figures were computed for a 10-min sampling record. The
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Chapter 10
Longshore Sediment Transport Experiments
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