Evaluation of Tide Embankment and Protection Forest Width on Tsunami Disaster Using Tsunami Simulator

Abstract

The tsunami that occurred after the Tohoku Earthquake of March 11, 2011, devastated the infrastructure in Tohoku, including roads and water channels. This study reports the results of a tsunami simulation experiment using an open channel for evaluation of tide embankments and protection forest in controlling the force of tsunami waves and flow of sand carried by tsunami. Coastal areas in Minami Soma City, Fukushima Prefecture, that were devastated by the Tohoku Earthquake were assumed as the experimental location. A 0.3 m-wide, 12 m-long open channel was used for the tsunami experiment. To simulate a tsunami, a removable barrier was set near the upstream end of the channel to retain water. The barrier was lifted to generate a bore. The scale for the model was 1/100. A model protection forest and a tide embankment made of acrylic were placed at the longitudinal midpoint of the channel. To examine the sand control effect of the tide embankment and protection forest at the time of tsunami, Toyoura silica sand was laid in the channel bottom upstream of the tide embankment and protection forest. The sand left behind after the tsunami simulation was measured for dry weight. The speed of the wave beyond the protection forest tended to decrease with increases in forest width. The amount of sand carried by the tsunami was found to decrease with increases in forest width. The results, however, are from a simplified model channel experiment. It is necessary to perform experiments that more closely reproduce the original sites in terms of topography and vegetation.