Numerical Investigations of Tsunami Run-Up and Flow Structure on Coastal Vegetated Beaches

Abstract

Tsunami waves become hazardous when they reach the coast. In South and Southeast Asian countries, coastal forest is widely utilized as a natural approach to mitigate tsunami damage. In this study, a depth-integrated numerical model was established to simulate wave propagation in a coastal region with and without forest cover. This numerical model was based on a finite volume Roe-type scheme, and was developed to solve the governing equations with the option of treating either a wet or dry wave front boundary. The governing equations were modified by adding a drag force term caused by vegetation. First, the model was validated for the case of solitary wave (breaking and non-breaking) run-up and run-down on a sloping beach, and long periodic wave propagation was investigated on a partially vegetated beach. The simulated results agree well with the measured data. Further, tsunami wave propagation on an actual-scale slope covered by coastal forest Pandanus odoratissimus (P. odoratissimus) and Casuarina equisetifolia (C. equisetifolia) was simulated to elucidate the influence of vegetation on tsunami mitigation with a different forest open gap. The numerical results revealed that coastal vegetation on sloping beach has significant potential to mitigate the impacts from tsunami waves by acting as a buffer zone. Coastal vegetation with open gaps causes the peak flow velocity at the exit of the gap to increase, and reduces the peak flow velocity behind the forest. Compared to a forest with open gaps in a linear arrangement, specific arrangements of gaps in the forest can increase the energy attenuation from tsunami wave. The results also showed that different cost-effective natural strategies in varying forest parameters including vegetation collocations, densities, and growth stages had significant impacts in reducing the severity of tsunami damage.

Holocene vegetation dynamics in response to climate change and hydrological processes in the Bohai region

“…Many previous studies of northern and northeastern China have used the Quercus pollen percentage to infer regional temperature variation (Ren and Zhang, 1998;Yi et al, 2003;Li et al, 2004;Xu et al, 2014;Zhang et al, 2019). The Quercus pollen percentage from CJ06-435 core is consistent with previous studies, which also provide a regional air temperature reference.…”

“…A high-resolution 1000-year pollen record from the Sanjiaowan Marr Lake in northeastern China revealed that Quercus is an effective indicator for temperature reconstructions. Several notable cold periods, with lower Quercus frequencies, occurred at approximately 1200 CE, 1410 CE, 1580 CE, 1770 CE and 1870 CE (Zhang et al, 2019). Another 5350-year pollen record from an annually laminated maar lake in northeastern China revealed a decrease of Quercus and increases of the Pinus component; this indicates a cooling trend during the past 5350 years (Xu et al, 2014).…”

“…Previous studies have revealed that Pinus and Quercus were the most common components of the forests in northeast China (including the land areas surrounding the BS) during the Holocene. The variation of Pinus and Quercus contents were closely related to the change of temperature (Ren and Zhang, 1998;Yi et al, 2003;Li et al, 2004;Xu et al, 2014;Zhang et al, 2019). Ren and Zhang (1998) investigated pollen data from northeastern China and found that Quercus and Ulmus were the dominant components of the forests between 10 000 and 5000 BP, while Pinus were much sparser, indicating warmer and drier summers in northeastern China for the Early to Middle Holocene.…”

Ocean Exchange and Circulation

“…One paper in this Special Issue represents an example of numerical modelling application, displayed by Zhang et al [2], where the authors study the interaction of the ocean with the coastal area: in fact, coastal areas are the most densely populated and urbanized, but they are also complex and delicate environments. In coastal areas, waves have a strong impact that can be devastating and produce great damage as well as the loss of human lives.…”

Holocene vegetation dynamics in response to climate change and hydrological processes in the Bohai region

“…Because they are located between marine ecosystems and terrestrial ecosystems, coastal area are prone to many natural hazards such as flooding, storms and tsunamis (Hou and Hou, 2020). Coastal vegetation, which acts as a natural barrier, is widely distributed in coastal areas and could effectively mitigate the damage of marine disasters to the economy and environment of coastal areas (Zhang et al, 2018). Moreover, despite their relatively small global extent (between 0.5 and 1×10 6 km 2 ), coastal vegetation ecosystems, tidal marshes, mangroves, and seagrasses play an important role in the global carbon cycle (Serrano et al, 2019;Spivak et al, 2019).…”