Abstract. On 22 December 2018, a tsunami was generated from the Mount Anak Krakatau area that was caused by volcanic flank failures. The tsunami had severe impacts on the western coast of Banten and the southern coasts of Lampung in Indonesia. A series of surveys to measure the impacts of the tsunami was started 3 d after the tsunami and lasted for 10 d. Immediate investigations allowed the collection of relatively authentic images of the tsunami impacts before the clearing process started. This article investigates the impacts of the 2018 Sunda Strait tsunami on the affected areas and presents an analysis of the impacts of pure hydrodynamic tsunami forces on buildings. Impacts of the tsunami were expected to exhibit different characteristics than those found following the 2004 Indian Ocean tsunami in Aceh. Data were collected from 117 flow depths along the Banten and Lampung coasts. Furthermore, 98 buildings or houses were assessed for damage. Results of this study revealed that the flow depths were higher in Banten than in Lampung. Directions of the tsunami arrays created by the complex bathymetry around the strait caused these differences. Tsunami-induced damage to buildings was mostly the result of impact forces and drag forces. Damping forces could not be associated with the damage. The tsunami warning system in Indonesia should be extended to anticipate non-seismic tsunamis, such as landslides and volcanic processes driven by tsunamis. The lack of a tsunami warning during the first few minutes after the generation of the first wave led to a significant number of human casualties in both of the affected areas.

Abstract. This research aimed to assess the tsunami flow velocity and height reduction produced by a planned elevated road parallel to the coast of Banda Aceh, called the Banda Aceh Outer Ring Road (BORR). The road will transect several lagoons, settlements, and bare land around the coast of Banda Aceh. Beside its main function to reduce traffic congestion in the city, the BORR is also proposed to reduce the impacts of future tsunamis. The Cornell Multi-grid Coupled Tsunami Model (COMCOT) was used to simulate eight scenarios of the tsunami. One of them was based on the 2004 Indian Ocean tsunami. Two magnitudes of earthquake were used, that is, 8.5 and 9.15 Mw. Both the earthquakes were generated from the same source location as in the 2004 case, around the Andaman Sea. Land use data of the innermost layer of the simulation area were adopted based on the 2004 condition and the land use planning of the city for 2029. The results of this study reveal that the tsunami inundation area can be reduced by about 9 % by using the elevated road for the earthquake of magnitude 9.15 Mw and about 22 % for the earthquake of magnitude 8.5 Mw. Combined with the land use planning 2029, the elevated road could reduce the maximum flow velocities behind the road by about 72 %. Notably, the proposed land use for 2029 will not be sufficient to deliver any effects on the tsunami mitigation without the elevated road structures. We recommend the city to construct the elevated road as this could be part of the co-benefit structures for tsunami mitigation. The proposed BORR appears to deliver a significant reduction of impacts of the smaller intensity tsunamis compared to the 2004 Indian Ocean tsunami.

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Most of the coastal area in the Ulee Lheue Bay of Aceh Besar was affected by a tsunami wave during the 2004 Indian Ocean Tsunami. Such area has an inclined bed floor which varies in slope. Variations of slope can affect tsunami wave properties such as tsunami arrival time, wave height and velocity. With those variations, the degree of the tsunami effects is highly unpredictable. Therefore, it is important to conduct a research to understand the effects of coastal slopes on tsunami waves propagations and wave deformation. Google SketchUp was used for designing the coastal slopes’ 3 Dimensional models. For the tsunami waves, solitary waves were generated by using smoothed particle hydrodynamics numerical models through the DualSPHysics software. The computation was based on the meshless method. From the simulations, the waves’ properties were obtained and were analyzed how coastal slopes affect the arrival time of tsunami waves, also for their height and velocity. Results show that the steepest coastal slope has the highest velocity, but shortest wave height and longest arrival time. Conversely, the flattest coastal slope has the lowest velocity, but highest wave height and shortest arrival time. Longer tsunami arrival times will benefit people in the evacuation process during the hazard.

Open wall structures, such as those found in mosques, sustained large forces generated by a tsunami as in the case of the 2004 Indian Ocean tsunami. Although the surrounding buildings were flattened, there were a number of mosques in the tsunami affected area could still stand in the middle of the area. These motivated this study to look into more details the hydrodynamic forces generated around the open structures. This research was aimed at investigating the tsunami wave forces on open structures and at knowing relation between the tsunami waves velocity and the pressures on the pillars of the open structures. DualSPHysic was used to simulate the tsunami wave forces on the structures. The DualSPHysic is a smoothed particle hydrodynamic model with mesh-less method. We simulated 12 numerical simulations by constructing a-130 m wave flume equipped with dam-break at one end to generate the tsunami-like flows. A sloping bed was placed in front of an open wall structure. Four pillars were set to imitate a simplified model of open wall structure. Numerical observation points were placed at offshore part of the model, in front of the pillars (lee-side) and at the back of the pillars (wake-side). Simulations were performed for about 6 seconds started from releasing the dam gate and before the flow being reflected by the other end of the flume. This study proved that the impacts of the tsunami-like forces are more significant of the front row of the pillars. Meanwhile, tsunami wave forces at the back row of the pillars group are inconclusive to the wave velocity and wave heights.