Development of Rigid Landslide Tsunami Physical Modelling: A Simplified Model for The Palu Bay, Indonesia

The Palu Bay Tsunami on September 28, 2018 still left some unresolved hydraulic phenomena. One of them was the arrival time of the tsunami to certain locations as the event mechanisms are still not fully known. This research was aimed at estimating tsunami arrival times due to landslide tsunami in the Palu Bay through a physical modelling. A simplified shape of the Palu Bay was constructed at Tsunami- Wave Flume facility at Tsunami and Disaster Mitigation Research Center (TDMRC). The simplified model was 9.5 m long, 2.5 m wide and 1.0 m deep. The slopes of the bay were made 42° for the east side of the modelled bay and 54° at the west side of the bay following average slopes of both sides of the bay. It has one open boundary at the north direction, while Palu city was hypothetically located at the closed boundary at the south part of the bay. The physical model was made in distorted scales of 1:3,200 for horizontal and 1:550 for vertical. The landslide material was made as a half-spherical shape to approach the volume of submarine landslide at Buluri of Palu at the west bay side as published by Pakoksung et al. (2019). In the experiment, the location was marked as S5 which is the largest landslide volume during the 2018 Palu Bay tsunami. A series of wave gauges were installed at some observation points, namely at Pantoloan Port, North Taipa, Tondo-Tadulako, Lere of West Palu, Tipo, Watusampu of West Palu, Banawa of Donggala, and Donggala Port. No capillary wave effects were detected during the experiments proving that the surface tension effects could be excluded. The experiments results showed that there is no significant difference of tsunami arrival times in related to the position of the rigid landslide material relative to the water surface. A significant trend of influence was observed in terms of tsunami heights monitored at the wave gauges. The results will be beneficial for further development model of landslide tsunamis for the Palu Bay