Modeling of coastal erosion and sediment deposition during the 2004 Indian Ocean tsunami in Lhok Nga, Sumatra, Indonesia

This study presents the results of numerical simulations of the 2004 Indian Ocean earthquake and tsunami in the Bay of Lhok Nga (northwestern coast of Sumatra, Indonesia) integrating sediment erosion and deposition. We investigate the transport of sediment both by suspension and by bedload under different scenarii of long breaking dispersive waves through a series of numerical experiments. The earthquake source model used by Koshimura et al. (Coast Eng J 51:243–273, 2008) with a 25-m dislocation better reproduces the wave travel time, flow depth and inundation area than the other models tested. The model reproduces realistically the pronounced coastal retreat in the northern part of Lhok Nga Bay (retreat ranging between 50 and 150 m), where Paris et al. (Geomorphology 104:59–72, 2009) estimated a mean retreat of 80 m. There is also a good agreement between the simulated area of coastal retreat (195,400 m2) and the field observations (203,200 m2). The simulation may underestimate the volume of tsunami deposits (611,700 m3 vs. 500,000–1,000,000 m3 estimated by Paris et al. (2009). The model fully reproduces the observed thickness of tsunami deposits when considering both bedload and suspension, even if bedload transport dominates. Limitations are due to micro-scale topographic, anthropic features (which are not always represented by the DEM) and the amount of debris which may influence flow dynamics and sediment transport.