Numerical simulations of the 2004 Indian Ocean tsunami deposits' thicknesses and emplacements

Erosion processes and its effects were quite profound and severe along most of Aceh's west coast. Severe erosion associated with the 2004 tsunami actually created a new island. Tsunami waves transported large volumes of sediment of several hundred meters at certain locations, resulting in a large-scale coastline recession. Large shear stresses generated by the long waves overpowered the critical shear stress of bedload materials throughout the coastal zone. Numerical simulations were performed using the Cornell Multi-grid Coupled Tsunami (COMCOT) model and Delft3D to reproduce tsunami-induced sediment deposits, i.e., their locations and thicknesses. The study area was Lhoong, in the Aceh Besar District, located approximately 60 km southwest of Banda Aceh. Field data collected in 2015 and 2016 validated the forward modeling techniques adopted in this study. However, agreements between numerical simulations and field observations were more robust using data collected in 2005, i.e., just months after the tsunami. Four sediment transport formulae were used in the simulations, namely van Rijn 1993, Engelund–Hansen 1967, Meyer-Peter–Mueller (MPM) 1948, and Soulsby 1997. The resulting numerical simulations are useful when estimating the locations and the thicknesses of the tsunami deposits. The agreement between the field data and the numerical simulations is reasonable despite a trend that overestimates the field observations. The study aims to couple two hydrodynamic numerical models in order to reproduce the spatiality of the 2004 tsunami sediment deposits, i.e., their locations and thicknesses. The study also analyzed the possible sources of large shear stresses produced by the tsunami which transported sediment grains of various sizes. Several studies observed that backwash processes, associated with tsunami waves, deposited large volumes of sediments offshore. Sediment properties, such as grain size, correlate poorly with the thicknesses of tsunami sediment deposits. Another poorly characterized physical process related to the tsunami is the location and extent of inland sediment deposition, which differs from the extent of tsunami inundation. The study estimates the energy required to transport sediments via a tsunami wave. The trajectory of the 2004 Indian Ocean tsunami was numerically simulated using the Cornell Multi-grid Coupled Tsunami (COMCOT) model, from its rupture area to the shoreline, and Delft3D-FLOW was applied to simulate sediment transport processes by inland flooding in the study area. The combination of these two models provides an ideal framework for understanding the physical processes involved during the transport of sediment.