In this study, we investigated the sediment transport due to the 2004 Indian ocean tsunami along the natural coast at Hambantota, Sri-lanka. Bathymetry and topography surveys before and after the tsunami were conducted and the results showed significant erosion by the tsunami, especially around the places where shoreline discontinuations were observed. We conducted a numerical simulation of tsunami propagation as well as the bathymetry change induced by the tsunami. Furthermore, we also estimated the bathymetry change due to the usual sea waves at the coast. Our numerical results suggested that the tsunami has strong bottom shear stress at specific landform such as a river mouth and a cape. We also found that the sediment erosion and accumulation due to the tsunami had been mitigated by usual sea waves after the tsunami.
We analyzed the process decay of tsunami waveform based on the observed one due to the 2011 Tohoku-Oki earthquake. The observed waveforms at 31 stations along the Pacific coast of Japan were divided into four domains with periods and were evaluated respectively for each physical parameter such as the arrival time, the amplification time of tsunami of the later phase, the maximum tsunami amplitude of the later phase and the decay time. We found out that the decay time of the long period component is generally longer than the short period, but in some cases the time of short period component becomes longer than the others, which may be affected by radiation wave due to large scale bathymetric structure such as the Emperor seamount.
IntroductionIn order to develop a generalized numerical model for multi-layered tsunami wave system, a three-layer system was considered.Six governing equations, two for each layer were derived from Euler equations of motion and continuity for three layers, assuming long wave approximation, negligible friction and interfacial mixing.From derived equations, it is found that only top layer equations are independent of number of intermediate layers; equations for all other layers are dependent on number, extent and density of intermediate layer(s).Momentum and continuity equations for the top layer are exactly same as in the case of earlier developed governing equations for two-layered system.Continuity equation for the bottom layer is also exactly same as in the case of two-layered system.Momentum equation for the bottom layer is dependent on extent and density of top layer as well as all intermediate layers.Continuity equation for intermediate layer is affected by levels of immediate bottom layer.Momentum equation for the intermediate layer is affected by extent and density of upper layer(s).Developed governing equations were converted to a numerical model using staggered Leap-Frog scheme for the computations of water level and discharge in each layer in one-dimensional propagation.Developed numerical model results were compared with an earlier developed model for two layers, which was rigorously verified by analytical solution.It was found that this three-layer model produces same results when it is converted to two-layer through mathematical manipulation (i.e. by assuming a negligible/zero depth or similar density of adjacent layer for any layer).The details properties of three-layer model were discussed through numerical simulations for different scenarios.The developed model can be easily converted to a multi-layer (any number) model and can be applied confidently to simulate the basic features of different practical tsunami problems similar to that investigated in this study. BackgroundMulti-layered flow is related with many environmental phenomena.Thermally driven exchange flows through doorways to oceanic currents, salt water intrusion in estuaries, spillage of the oil on the sea surface, spreading of dense contaminated water, sediment laden discharges into lakes, generation of lee waves behind a mountain range and tidal www.intechopen.com
