Hydraulic experiment on spatial distribution and formation process of tsunami deposits in a flat ground with a cliff topography

Tsunami deposits are known as evidence of past tsunami inundation. Due to the spatial distribution of tsunami deposits, it is possible to estimate the approximate inundation range of the tsunami. In fact, it is also known from the field survey that there is a difference between the distribution of tsunami deposits and the tsunami inundation limit. For the formation of tsunami deposits, it will be influenced by tsunami condition, particle size condition, topography condition, etc., so that the final sediment distribution will be formed. If the relation between the formation process of tsunami deposit and the tsunami flow characteristics is clarified, the tsunami flow conditions may be clarified form the tsunami deposit. However, it is difficult to measure the formation process of tsunami deposits in the field. In addition, local tsunami deposits are affected by complicated irregularities of the topography. It is difficult to clarify the characteristics of the tsunami that comes from the tsunami deposits at the limited investigation points.

In this study, tsunami deposit formation was reproduced by waterway experiment adjusted experimental conditions, and the hydraulic characteristics of the tsunami and the spatial distribution of the tsunami deposits were measured. Hydraulic experiment was conducted with two-dimensional water channel. Tsunami was inputted as a bore wave flow. The moving floor section was installed as a 1/20 slope. The fixed floor section as a flat ground was connected with the moving floor section. Three cases were set as the position of the cliff topography, and the cliff was installed on the flat floor with different positions. The water level and the flow velocity were measured at some points. The spatial distribution of tsunami deposits on flat ground was measured with sand catcher in each 20x20cm cells on weight of sand. The distribution of tsunami sediments was measured to change greatly depending on the position of the cliff even for the same incident tsunami conditions. However, regardless of the location of the cliffs, the total amount of tsunami deposits was consistent with the conditions of the incident tsunami.