NUMERICAL EXPERIMENT ON WATER LEVEL CHANGE IN RIVER WITH DIFFERENT MAGNITUDE OF TSUNAMIS

Abstract

 In this study, a numerical experiment on water level change in river induced by tsunamis were conducted to discuss the mechanism of longer duration of high water level in rivers than the period of tsunami, which was observed in 2011 tsunami event. Wave conditions which has 5~100 % of wave heights of 2011 tsunami were made based on the simulated wave form of 2011 tsunami, and the characteristics of water level change with the different magnitude of tsunamis were tested through numerical simulation in Kitakami River. It is found that increase of tsunami height induce larger discharge across the river mouth for both of incoming and outgoing flow, while the increase rate is larger for incoming flow. And that results in the transition of the condition to keep higher water level in longer period with higher waves. This characteristics were observed for many simulated historical tsunami events. And tsunami period does not have significant effect to cause the difference on characteristics of the flow across the river mouth.