0.30
T3g
0.25
T3g_case1
T3g_case2
0.20
0.15
0.10
0.05
0.00
0
5
10
15
20
Cross-shore location (m)
Figure 74. Measurements of significant wave height for successive wave runs at
the same cross-shore transect for the plunging-breaker case
Figures 75 and 76 show results for the mean longshore current. Results
suggest repeatability was good for the spilling-breaker case, considering the fact
that small irregularities in the beach exist for each case (the beach does not have
exactly straight and parallel contours). Also, small changes in topography might
occur between runs as a result of the evolution toward equilibrium or due to
beach perturbations that are created during the remolding process, which only
can be performed to a certain level of accuracy and resolution. Results for the
plunging-breaker case are not as good. This is attributed to the nonuniformities
that developed in the region of the break-point bar. The beach was remolded
after case T3g to a condition in which the bottom contours were straight and
parallel in the bar region. Upon exposure to waves and currents, perturbations
began to develop in the bar region and changed with time, i.e., from case to case.
Figure 77 illustrates the repeatability in sediment concentration
measurements for the spilling-breaker case. The top panel shows measurements
made in the incipient breaker zone, and the lower panel shows measurements
from the midsurf zone. Concentrations are mean values, averaged over a 10-min
sampling interval. Repeatability is reasonable and is, in general, better for higher
concentrations that are measured closer to the bottom than for low concentration
values measured higher in the water column. At elevations within 5 cm of the
bed, where most of the longshore sediment flux occurs, mean concentrations are
repeatable to within about +/- 25 percent.
130
Chapter 10
Longshore Sediment Transport Experiments
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