Process-based modeling of tsunami inundation and sediment transport

Abstract

[1] The infrequent and unpredictable nature of tsunamis precludes the use of field experiments to measure the hydrodynamic and sediment transport processes that occur. Instead, these processes are often approximated from laboratory, numerical, and theoretical studies or inferred from observations of the resultant sediment deposits. Here Delft3D, a three-dimensional numerical model, is used to simulate the inundation and sediment transport of a tsunami similar in magnitude to the 26 December 2004 Indian Ocean tsunami over one measured and three idealized morphologies. The model is first shown to match well the observations taken at Kuala Meurisi, Sumatra, and then used to examine in detail the processes that occur during the tsunami. The model predicts that at a given cross-shore location the onshore flow accelerates rapidly to a maximum as the wavefront passes, and then gradually decelerates before reversing direction and flowing offshore. The onshore flow does not tend to zero everywhere at maximum inundation, but instead flow reversal occurs near the shoreline even as the wavefront continues to inundate landward. While some sediment is eroded by the passing wavefront, the suspension of sandy sediment is dominated by the long-duration, high-velocity backwash that occurs along the beach face and offshore of the shoreline. Some of the sediment suspended during backwash is advected shoreward by the subsequent wave, creating large spatial gradients in the suspended sediment concentrations, which may not be in equilibrium with the local hydrodynamics. The inundation and transport of sediment during a tsunami can be affected by complexities in the morphological profile and interactions between multiple waves, and many of the hydrodynamic and sediment transport processes predicted here are similar to analogous processes previously observed in the swash zone.Citation: Apotsos, A., G. Gelfenbaum, and B. Jaffe (2011), Process-based modeling of tsunami inundation and sediment transport,

Tsunami-induced coastal change: scenario studies for Painan, West Sumatra, Indonesia

“…Our simulation shows that the modified settling velocity does not cause noticeable changes in the deposit thickness or the scour depth; our results are consistent with those of Apotsos et al (2011), who considered the combined effects of hindered settling and stratification. However, for 3D models, Apotsos et al (2011) found the significant influence of hindered settling velocity on the deposit thickness if the mixing of sediment into water was not reduced by the density stratification due to the high concentration of suspended sediment. 4.3 Hydrodynamics and sediment transport for scenario S3 We examine scenario S3 in Table 4, which has a negative leading wave.…”

“…This phenomena is consistent with the bathymetric surveys conducted at Kuala Meurisi (a site about 100 km south of Banda Aceh) following the 2004 tsunami in which a large offshore bar was observed (Gelfenbaum et al, 2007). Apotsos et al (2011) attributed the formation of large offshore bars to collisions of the backwash flows and the up-rushing waves. A thin layer (about 5-30 cm thick) of sediment could be deposited in the city area, and a maximum scour depth of nearly 5 m might occur on the seaward side of the road, which is caused by the abrupt change of the erodible and non-erodible beach materials.…”

“…The formula proposed by van Rijn (1993) is used to calculate the equilibrium sediment concentration; The expressions for C eq and T s are given in Appendix. Since XBeach is a numerical 2DH model, the effects of density stratification and hindered settling (Apotsos et al, 2011) can only be considered indirectly through the adaptation time T s and the equilibrium sediment concentration C eq . The change of bottom elevation is updated by the following continuity equation:…”

Numerical experiment and a case study of sediment transport simulation of the 2004 Indian Ocean tsunami in Lhok Nga, Banda Aceh, Indonesia

“…wave heights, wave lengths). Though some investigations (Kobayashi and Lawrence, 2004;Apotsos et al, 2011) claimed that the leading depression wave would cause little erosion during retreating stage of first wave. Meanwhile, smaller runup and weaker backwash flow would cause less sediment movement.…”

Simulation of tsunami generation, propagation and coastal inundation in the Eastern Mediterranean

“…The sequence of a tsunami hitting the coast comprises a series of processes: from the tsunami generation and propagation, to coastal-zone hydrodynamics (including surf and swash zone dynamics), coastal inundation and wave-structure interactions with the built environment. Regarding the modeling part -and focusing on coastal inundation -exemplary reference can be made to the work of Borrero et al (2006), who used the MOST model (Titov and González, 1997) for tsunami generation and inundation in western Sumatra; Gayer et al (2010), who used the MIKE21 Flow Model FM to simulate inundation based on roughness maps for Indonesia; Omira et al (2010), who applied a modified version of the COMCOT model (Liu et al, 1998) to selected cases in Casablanca, Morocco; Apotsos et al (2011), who used the Delft3D model to study inundation and sediment transport by the 2004 SE Asia tsunami in measured and idealized morphologies; and Løvholt et al (2012), who used models based on the Boussinesq equations for tsunami propagation and nonlinear shallow-water wave equations for coastal inundation to simulate the 2011 Tohoku tsunami. Extending to coastal planning, vulnerability assessment and tsunami hazard mitigation, one may refer to the work of Bernard (2005), González et al (2009), Post et al (2009, Kumar et al (2010), Sørensen et al (2012) and González-Riancho et al (2014).…”