TSUNAMI WAVE BREAKING BEHAVIOR ON A REEF WITH A ...

4. Results
Since the wave breaking geometry was determined manually using a grid that was of a low resolution,
the measurements could only be made to within 0.25m, giving a maximum error of ±0.125m. Since the
scale of this experiment was on the order of tens of meters, the possible maximum error was not
considered significant. Because a normal digital camera was used, the video only captured the
movement at 30 fps. This could cause a small source of error since the wave breaking point could have
occurred between frames. If the breaking point was between two frames, the difference in the point of
breaking between the frames was no more than 0.125m, again making the error insignificant.
All relationships and graphics were made using Ho’ as the independent variable except for those
relationships being compared to the previous literature. Following the standard method to describe
hydraulic experiments, all variables were turned into ratios.
While the original intent was to use all of the trials in every different experimental setup, it was difficult
to determine the breaking point when the waves were very small (Ho’= 0.05 or 0.1). After calculating
the slope parameter So (Eqn 2), the reason for difficulty was found. Waves with Ho’ ≤0.15 were
considered surging instead of plunging (Table 1), indicating that these waves did not have a defined
breaking point. Consequently, surging waves were not considered in this study. Out of the eight
bedform configurations, three were left out of data analysis due to time constraints. Blank surface trials
were also omitted as they were run after this paper was written. While data from all water levels was
analyzed, only data from water level 20cm is shown in the majority of this report.
4.1 Roughness
The roughness altered the breaking behavior of the waves. The bedforms slowed the waves, causing
them to lose energy and consequently affecting the breaking parameters (Hb, hb, db, dc). The flat reef
bedforms had minimal affect on the breaking parameters however since they were placed beyond the
zone where the waves usually broke. The wave height at breaking (Hb) was significantly lower when the
bedforms were on the slope (Figure 7) and the waves also broke and crashed sooner than when the
roughness was on the reef flat (Figures 8 and 9). Of the different bedform configurations on the slope,
BS2 had the lowest roughness coefficient and therefore was considered the roughest (Table 2). As seen
in Figures 8 and 9, the waves that propagated over BS2 had the smallest breaking and crashing
distances, indicating that the energy had dissipated the most. The difference in roughness in BS1 and
BS3 was very similar, and therefore they behaved almost identically. Since the reef roughness didn’t
affect the breaking behavior significantly, BR3 and BR4 also behaved similarly. The blank trials would
have been a useful addition to this analysis as they would have given insight into exactly how the
bedforms affected the waves.
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