Study of sediment transport by tsunami waves：Ⅳ：Local scour around structures

Tsunami scour around a coastal structure is one of the primary causes of structure damages. However, the mechanisms of tsunami-induced scour and beach erosion are less understood compared to that of tsunami run-up and tsunami inundation. A series of two-dimensional laboratory experiments of tsunami scour is conducted in accordance with coastal road conditions situated on a sandy beach. The initial 1/10—1/20 composite beach slope is respectively exposed to the N-waves. Measurements are made for the free surface elevations, the wave uprush and backwash processes, run-down jump, and the change of cross-shore beach profiles. The experimental result shows that there exists not only a profile change in the beach due to the impact of back sheet flows, but also the scour around the coastal road resulting from the helical flow. The location of roadway is a key factor affecting the scour depth along the coastal road. The incident wave height is also a contributing factor, but the depth of road embedment has little effect on the scour depth as shown in the experiments. The experiments reveal that coastal roads are vulnerable to tsunami damages due to serious scouring. The information reported in this study is useful for local authorities to better plan for tsunami disaster relief.