TSUNAMI ATTENUATION PROCESS BY COASTAL DUNES AND TREES IN THE SHINMAIKO BEACH AREA, IWAKI CITY, JAPAN

Abstract

 In the Shinmaiko beach area of Iwaki City, Fukushima Prefecture, expectations for coastal forests went beyond academic findings, as tsunami attenuation was visually recognizable during the 2011 off the Pacific coast of Tohoku earthquake tsunami. However, it is highly likely that the attenuation process included considerable topographical characteristics such as sand dunes. Although several academic studies have already been conducted on the relationship between tsunami and coastal forests in this area, the tsunami attenuation process has not been summarized. In this study, numerical simulations were conducted to clarify the tsunami attenuation process in the Shinmaiko beach area, especially the effect of different tsunami periods. The main result is that the apparent attenuation of the dunes is large due to the drop of the water level after the coughing event, but the actual attenuation is about 25%. The attenuation due to coastal forests was about 10%, which was attributed to the attenuation effect and the capping effect by micro-elevation.