Abstract
This study is conducted for clarifying the energy dissipation effects of coastal lagoon for more than Level-1 tsunami that can overtop the sea embankment and propagate inland. The numerical model is validated for reproducing the 2011 Great East Japan tsunami at Torinoumi Lagoon. The time series and maximum values of inundation depth, current velocity, fluid force at three selected locations were calculated with/without lagoon. Moreover, the storage capacity effect was analyzed with different tsunami conditions. Lagoon can reduce the velocity and fluid force especially at cross-stream direction because of the low velocity of the overflow current from the lagoon which mixes with the inundated tsunami from seaward, thus reducing the percentage of washout houses. The effect is greatly changed with the rate of tsunami inundation flux to lagoon and storage capacity of the lagoon.
