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Modelling Procedures
Published in Vanesa Magar, Sediment Transport and Morphodynamics Modelling for Coasts and Shallow Environments, 2020
The model developed by Roelvink et al. (2009), commonly known as XBeach, consists of a nonlinear shallow-water model (NLSW) coupled with a model of propagation for the short-wave envelope and sediment transport and bed update formulations. It was originally developed for modelling the impact of storms with timescales of the order of days, on sandy coasts in model domains with dimensions on the order of kilometres (Roelvink et al. 2015), but has also been used for other applications. In XBeach, the model is set up so that the x-coordinate is the cross-shore direction and the y-coordinate is the alongshore direction, as shown in Figure 3.7 XBeach reproduces short- and long-wave processes. The short-wave processes that are included are refraction, shoaling, and breaking. Note that diffraction is a not well resolved by any spectral wave model formulation and thus not well resolved by XBeach; however in the nonhydrostatic mode of XBeach, this is improved; this formulation was initially developed by Delft Technical University (Zijlema et al. 2011). The long (infragravity) wave processes include generation, propagation, and dissipation of infragravity waves; wave-induced set-up and unsteady currents; and overwash and inundation. Sediment transport formulations for bedload and suspended load are included. The beach morphodynamic processes include dune face avalanching, bed update, and breaching.
Study on the influence of infragravity waves on inundation characteristics at Minami-Ashiyahama in Osaka Bay induced by the 2018 Typhoon Jebi
Published in Coastal Engineering Journal, 2020
Naohiro Hattori, Yoshimitsu Tajima, Yusuke Yamanaka, Kenzou Kumagai
Infragravity waves are ocean waves with typical wave period of approximately 25–250 s. Since its discovery by Munk (1949), the generation mechanisms of infragravity waves have been investigated (e.g. Longuet-Higgins and Stewart 1962; Symonds, Huntley, and Bowen 1982; etc.). Infragravity waves have been studied more in the last decades (Bertin et al. 2018) and several researches indicate the influence of infragravity waves on damages to coasts in extreme storm events. In the disaster due to super typhoon Haiyan in 2013, for example, the east coast of Eastern Samar, Philippines, suffered severe inundation (Tajima et al. 2014, 2016a). Shimozono et al. (2015) points out that the combination of infragravity waves and sea swells played significant role to enlarge the run-up height. A video footage recorded at Hernani clearly captured tsunami-like bore induced by such infragravity waves (Roeber and Bricker 2015; Tajima 2017). Damages by infragravity waves have been reported also in Japan. In September 2007, Typhoon Fitow struck Seisho Coast, Kanagawa Prefecture, and destroyed Seisho Highway. Wave observation data and results of numerical simulation suggest that the long wave components with wave period of longer than 30 s were developed and were concentrated to particular places, which enlarged the damage to Seisho Coast (Tajima and Sato 2009). Sato et al. (1998) also reports the similar damage at nearly identical location and this feature may indicate that local bathymetric condition dominantly determines the local concentration of such coastal hazard. Although there are several cases indicating the influence of infragravity waves on the damage to coastal areas by storm events, the number of case studies are scarce, and the details remain elusive. Guza and Thornton (1982) point out the importance of infragravity waves for better understanding of complex nearshore hydrodynamics, which calls for more case studies.