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

Figure 9: Roughness on the slope (BS1, BS2, BS3) consistently caused the waves to crash sooner as seen by the lower values
of crashing distance (dc).
4.2 Reef Geometry
The bottom bathymetry of the wave flume was modeled after a reef and had a significant effect on the
experiment. The steep slope of 1:12 followed by a flat reef produced results that showed a higher
breaking index and lower breaking water depth compared to studies done on a mild slope with no reef
crest (Grilli et al. 1997).
A breaking index of Hb/hb=0.80 for solitary waves is commonly used (Smith, 2002), however it has been
found to be inaccurate for reef bathymetry. A more improved, yet still empirical, relationship was found
by Grilli (1997) as Hb/hb=0.841exp(6.421So). Using this formula, the values of Hb/hb for this experiment
should have ranged from 0.94 to 1.01. However this study shows a significantly higher breaking index
(Figure 10). The mean index was Hb/hb= 2.878 with a standard deviation of ±0.560. These results are
most likely due to the geometry of the reef with the steep slope followed by flat surface.
By comparing the data from this experiment to an empirically derived formula for the breaking water
depth for solitary plunging breakers hb/ho= 0.149/(So/Ho’)^0.523 (Grilli et al 1997) , the breaking depth
was found to be consistently lower (Figure 11). The steep slope and reef flat were the cause of this
behavior.
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