The 2011 Tohoku Tsunami caused severe damage to many coastal defenses along the Japanese coastline, including areas where two adjacent upright sea dikes of different heights met. There are many places along the coastline where structures of different heights and shapes meet due to the various design codes. In this study, the authors aim to examine the tsunami flow around such dikes by conducting three-dimensional hydraulic experiments in a tsunami wave basin and numerical simulations using the fluid dynamics model OpenFOAM. Twelve experimental cases were tested by changing the waveforms, and also by keeping the height of one side of the dike model constant while adjusting the dimensions of the other side. The results show that the difference in height between the structures significantly influences the volume of overtopping over the relatively lower dike and the inundation depth and velocity behind the dikes. Furthermore, different characteristics of inundation patterns are observed between the inundation depth and velocity. Hence, this study illustrates the necessity to re-assess the effectiveness of such structures against tsunami events.
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