For the plunging-breaker case, total LST rates varied from 6,500 to
7,700 m3/yr, with a mean of about 7,200 m3/yr. Variability was similar, 7 to 10
percent. Repeatability for the total LST rate is considered to be good.
Figures 95 and 96 show cross-shore distributions of corrected LST rates for
both the spilling and plunging wave cases, respectively. In both figures, wave
runs that should produce nearly the same transport rate distributions are shown.
The general shape of the distribution was reproduced in all cases. The degree of
repeatability in the distribution of LST also is considered to be good, but not
quite as good as the total LST rate. At most locations, local estimates of LST
generally vary by 10 to 25 percent about a mean value for all the wave runs.
More variability is evident near the incipient breaker zone and in the zone closest
to the shoreline.
600
adjusted T1h_case 1&2
T1h_case 3
500
adjusted T1h_case 4
adjusted T1h_case 5
400
adjusted T1h_case 8
adjusted T1h_case 9
300
200
100
0
-5
0
5
10
15
Distance from Shoreline (m)
Figure 95. Cross-shore distribution of the LST rate for the spilling-breaker case
The variability of LST estimates in the nearshore zone is worth commenting
on. Estimates in this region are considered to have the greatest degree of error
and the lowest degree of repeatability, for a number of reasons. The foreshore
zone is characterized by a relatively steep beach and is rather energetic as a result
of the presence of the wave uprush and downrush. An adjustable brick template
is used to hold the sand beach in place across the entire profile. Ceramic
"pavers" having different thickness (1.4- and 2.8-cm) and standard construction
bricks (5.6-cm thickness) are used to construct the template. The thinner pavers
are used along most of the profile to provide better resolution for matching the
natural beach elevations. In the energetic swash zone, the template is constructed
mostly of standard-sized bricks so that they will not move when impacted by up-
rush bores. For both the spilling- and plunging-breaker cases, the pavers were
not stable on the foreshore slope. Consequently the brick template is a rather
crude approximation of the steep slope, and most importantly, edges of bricks are
151
Chapter 10
Longshore Sediment Transport Experiments
Previous Page
