| 研究実績の概要 |
We have completed our study on destructive tsunami-like bores. The destructive tsunami-like bore that was observed during Typhoon resulted from infra-gravity waves locally generated over a patch of fringing reefs. Extremely large and steep typhoon waves approached the reef near Hernani, Philippines, and broke abruptly at the reef edge. The breaking process dissipated a portion of the gravity wave energy but did not affect the infra-gravity band. This resulted in a pronounced surf beat, which shoaled (steepened) near the shoreline and formed a bore-like wave front similar to a dambreak or tsunami.
In contrast to the tropical environment in the Philippines, gentle slopes characterize the Tohoku coast with sandy beaches in the South and steep cliffs with short or no beaches in the North. Typhoon waves are approaching the southern Tohoku coast on a regular basis during summer/fall; however, the waves are usually of lower amplitude and shorter period. Nevertheless, energetic surf beat can develop in the nearshore zone. Though, the infra-gravity component does not grow to extreme levels like over fringing reefs, the gravity waves carry energy throughout the entire surf zone due to gradual -in contrast to - abrupt dissipation. This causes superposition of short waves on top of the surf beat. The resulting runup can reach high flow speeds, baring the potential for strong dune and foreshore erosion as well as for damage to coastal infrastructure.
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