Author(s): Hiroshi Nagashima; Ryosuke Takubo; Nozomu Yoneyama; Lisa Ito; Akihiro Tokai
Keywords: Tsunami; Chemical substance; Numerical analysis; Density current; Water supply
Abstract: In many cities around the world, river water is used for drinking and industrial water. Therefore, when a chemical substance flows into a river, the water supply is stopped while it stays near the water purification plant intake, which adversely affects the lives of citizens. This situation is expected to occur even during a large earthquake. It is conceivable that the chemical substances leaked from the facilities due to the great earthquake will flow into the river and will be transported by the tsunami running up the river, and the impact will be widespread. In Japan, a huge Nankai Trough earthquake is expected to occur in the near future. The Yodo River, which is located near the source, flows through urban areas, and there is concern that chemical substances leaked by the earthquake will flow into the river, be transported by the river run-up tsunami and reach the intake, which would affect the water supply system. In considering measures to minimize the effects of chemical substances flowing into rivers, it is important to quantitatively predict their behavior under various conditions. Since changes in fluid density affect flow, it is necessary to use a numerical analysis model that can consider the density current due to salinity and chemical substance in order to make predictions with high accuracy. In this study, we developed a 2DH-3D hybrid model that can analyze the propagation of a tsunami from a wave source in plane two dimensions and the local flow in three dimensions including the density difference. Using this model, we analyzed the behavior of chemical substances in the Yodo River at the time of the tsunami under different conditions of chemical substance density and river flow rate, resulting that the developed model can analyze the behavior of chemical substances in three dimensions under various conditions, and can quantitatively evaluate the effect on water intake.