0.50
Test 2
0.45
Test 6C
0.40
Test 6D
Test 6E
0.35
Test 6G
0.30
Test 6J
0.25
Test 6N
0.20
0.15
0.10
0.05
0.00
0
2
4
6
8
10 12 14
16
18
20
Cross-shore Location (m)
Figure 57. Progression of pump settings for regular wave experiments
Results from Test 6D, an under-pumped case that was the fifth experiment in
the series, are shown in Figure 58. The peak longshore current measured at each
of the three transects was much higher than the peak current pumped through the
lateral boundaries. Offshore recirculation was diminished substantially in both
extent and magnitude compared to the no-pumping case; however, recirculation
remained rather strong at Y27. The longshore current distribution at Y35 showed
a region of flow reversal near the shoreline (negative values). This phenomenon
was observed during the 15 experiments and was limited within a region
extending from the upstream boundary to Y=34 m and 2 m offshore from the
still-water shoreline. This region of flow reversal decreased significantly in
magnitude and spatial extent as the proper distribution was approached with
subsequent pump settings, but it was never completely eliminated.
It appeared that the proper longshore current distribution was being
approached at the peak and shoreward of the peak during the tenth experiment
(Test 6I). However, there was concern that the offshore tail of the distribution
was over-pumped. To investigate the ramifications and signs of over-pumping,
Test 6J was performed. Figure 57 shows the longshore current distribution that
was recirculated in Test 6J, relative to other tests, and Figure 59 shows longshore
current results from the test. In the surf zone, the measured current distribution
matched the pump settings quite well. In this region, it would be difficult to
discern whether or not the lateral boundaries were over-pumped. However, the
over-pumped case (Test 6J) produced substantially more recirculation in the
offshore region, relative to Test 6I. The results from this experiment indicated
that there are signs of over pumping, but the results are subtle and not obvious
over much of the longshore current distribution, except in the offshore tail.
106
Chapter 9
Establishing Uniform Longshore Currents
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