The estimation of tsunami height and arrival time is very important to design the coastal tsunami prevention and port protection facilities. The numerical simulation can be performed using not only simple topography conditions, but also complex topography. However, the numerical results in relatively complex areas may have errors in the calculation. Coastal dunes may exist at the front of the important structures like tidal walls. This paper discusses on the variation of tsunami force acting the tidal wall located behind the dune employing physical experiments.
Japanese coastal areas have high tsunami risk and the risk has been increasing year by year mainly due to the concentration of population and social property to urban areas usually located near coasts. Therefore, the prediction of future tsunami intensity and implementation of tsunami prevention technique are very important. The prediction with high accuracy needs the consideration with correct information of coastal geometry bordering sea. Natural coastal sand dunes may be effective to reduce the tsunami energy (Matuyama et al., 2012). Meanwhile the tsunami wave pressures acting on a vertical tide wall is estimated in Asakura formula (Asakura et al., 2000). Few papers concerns the tsunami pressures behind a relatively large sand dune. Figure 1 shows an example of coastal zone cross section. In the photograph, the wave incident direction is the right side and the center part becomes steep valley and the surface is scoured by wave action. The cross–section figures demonstrate that the coast has a hilly mound and the face is scoured by wave action. The scouring on the coastal hilly mound (dune) was generated in the 2011 Great East Japan Earthquake Tsunami (ex., Hiraishi et al., 2011). When a gigantic tsunami attacks, the tsunami wave may overflow the sand dune and reach to the coastal structures behind it. The tsunami wave pressure on the coastal dike located behind the dune may be varied by the existence of the dune compared with the case of no sand dune. The main purpose of this experiment is the prediction of the effect of the sand dune to reduce the tsunami wave pressure acting on the tidal wall. The effect of tsunami is very important to reserve the dune geometry in the target urban area. The experiment was carried out in the Tsunami Reproduction Basin in Kyoto University (Hiraishi el al.,2015).
