During inundation, tsunami-induced scour is a major threat to the stability of onshore coastal structures. Nevertheless, the majority of current experimental research concentrate on single structures orientated perpendicular to the flow propagation, while in the real environment, coastal structures often arranged in sheltered and rotated configurations against the incident waves. This study delineates large-scale experimental research analysing tsunami-induced scour around onshore rectangular and square structures under two different setups: (i) two structures positioned in a sheltered arrangement, and (ii) single structures orientated at a 45°angle to the incoming flow. Three representative long waves with periods of 20 s, 49 s, and 147 s are generated in the HR Wallingford Fast Flow Facility using a pneumatic tsunami generator. Overhead video observations and GoPro camera are employed to analyse the maximum scour depth, spatial development of scour, and flow-structure interaction. The results show that the upstream structure modifies the flow and sediment transport processes around the downstream structure, generally reducing scour development at the rear structure through wake sheltering. The magnitude of this reduction depends on tsunami-wave period, inundation duration, and structural geometry. In contrast, structural rotation changes the flow–structure interaction by directing the incoming flow towards an exposed corner and along the adjacent faces, promoting localised scour near the corners and enhancing lateral base vortex activity. Rotated structures generally produced greater scour than the corresponding non-rotated cases, although the degree of increase varied with wave period and geometry. These findings demonstrate that structural arrangement and orientation can significantly influence the magnitude, location, and temporal development of tsunami-induced scour. The study provides new experimental evidence for improving tsunami scour hazard assessment, resilient coastal layout design, and numerical model validation for non-isolated and obliquely aligned coastal structures. ... Read more

More than 20 years have passed since the tragic 2004 Indian Ocean earthquake and tsunami, which killed over 227 000 people and devastated the coastlines of 14 countries surrounding the Indian Ocean. This tragic event kickstarted a worldwide effort in advancing knowledge towards mitigating the catastrophic effects of future tsunami. The ensuing research has greatly enhanced our understanding of tsunami, informing better infrastructure design and risk mitigation practices. ... Read more

Coastal boulder deposits hold the potential to aid in the reconstruction of past extreme wave events. However, commonly used hydrodynamic equations for calculating wave heights from transported boulders can be inaccurate. New and alternative methods need to be explored in an interdisciplinary way to ensure a more complete picture of the phenomenon of boulder transport is achieved. Through the use of a physical experiment, this study aims to investigate the influence of different tsunami wave types, wave parameters and boulder shapes on boulder transport distance. The experimental results also allow for a novel application of dimensional analysis to enable comparisons with other experiments as well as a field case study. In the experiment an elongate irregularly shaped boulder showed transport distances up to 1 m farther than a cuboid shaped boulder under the influence of the same waves. The irregularly shaped boulder had a predominant transport mode of rolling, whereas the cuboid shaped boulder predominantly underwent sliding transport. Tsunami wave type also influenced boulder transport distances, with N-waves frequently showing greater transport than E-waves of a comparable wave steepness. Key offshore wave and boulder parameters were then compared through dimensional analysis using Buckingham's Pi Theorem, enabling comparisons to other datasets to be made. Data from another published experimental study and a field study in Settai, Japan, showed reasonable agreement, particularly for the shorter period field data. These findings emphasize the importance of incorporating boulder shape, wave type, and dimensional analysis into future studies, providing a foundation for more accurate reconstructions of past tsunami events. ... Read more

In a time of climate emergency due to global warming, nature-based coastal defence systems are attractive solutions for flood mitigation and adaptation. Coastal forests such as mangroves have received a growing interest for their disaster mitigation effectiveness such as water flow energy dissipation, hence helping communities to become more resilient (Iimura & Tanaka, 2012). The role of coastal forests as a defence measure was highlighted in the aftermath of the 2004 Indian Ocean Tsunami, which claimed the lives of more than 200,000 people and displaced millions more across fourteen countries. Post-disaster damage observations indicated that forests, particularly mangroves, reduced the impact of the tsunami wave in some locations. As a result, significant international relief and reconstruction efforts focused on extensive forest replantation of coastlines (Satake, 2014).

The role of coastal vegetation in reducing the severity of tsunami waves has been studied since. Several studies using physical modelling and computational approaches have provided insights into the wave attenuation provided by coastal vegetation, in terms of relationships between incident hydrodynamic conditions, forest configurations and wave height decay. However, there are still many gaps in knowledge, particularly in quantifying the efficacy of coastal forests in reducing inland hydrodynamic conditions (Tomiczek et al., 2020). It is therefore essential to improve the understanding on how wave heights, velocities and runup are influenced by the characteristics of the “obstacles”, e.g. the forest density, as well as the incident hydrodynamic conditions, e.g. the wave period. This study aims to address these questions conducting physical experiments using the novel pneumatic Tsunami Simulator (TS) developed by HR Wallingford together with UCL (Rossetto et al., 2011). ... Read more

Tsunami events are traditionally represented in the geological record by a sequence of fine-grained sediments, but increasingly coastal boulder deposits are being used as indicators of past tsunami events. The emplacement mechanism of many boulder deposits, however, is heavily debated and determining whether the inundation event was a tsunami or storm remains an unresolved challenge (Cox et al., 2020). Using physical experiments, we aim to achieve a better understanding of how tsunamis move coastal boulders. This knowledge will aid field geomorphologists in the identification of the emplacement mechanism for coastal boulder deposits and allow for the determination of wave parameters. In January 2023, physical experiments using the HR Wallingford Tsunami Simulator were completed as part of the MAKEWAVES collaboration. These experiments investigated the movement of a cuboid and irregular shaped boulder model when impacted by different tsunami waveforms on a plane beach. We propose new empirical formulae to describe relationships between transport distance and different tsunami waves. ... Read more