Efficacy of Nature-Based versus Man-Made Tsunami Wave Run-up Mitigation Strategies

Abstract

Following significant physical and economic damage associated with large tsunami disasters, this research assessed the efficacy of both nature-based and man-made tsunami mitigation measures. With an expected increase of the population living in tsunami-prone areas, it is critical to develop a better understanding of tsunami engineering.

To achieve this, a series of large-scale tsunami modelling experiments was carried out at HR Wallingford. The experiments utilized the Tsunami Simulator and involved generating a set of 20 trough- and crest-led waves with periods ranging from 20 to 240 seconds in a divided flume with a length of 100 meters.

The effectiveness of nature-based mitigation techniques was assessed through the implementation of land cover roughness onto a sloping bathymetry. The man-made measures included the in-situ construction of a scaled-down offshore breakwater similar to the Kamaishi breakwater. The study involved a comprehensive assessment of multiple factors, including run-up height, delay of inundation, pressures exerted on the breakwater, and a stability analysis of the breakwater.

In addition to determining the effect of roughness on tsunami-like wave run-up, the results were compared to available predictor equations. The empirical relation defined by McGovern et al. (2018) is found to be suitable for the prediction of waves with a period of 50 seconds or less. On the other hand, the predictive equation proposed by Wronna et al. (2021) displayed a similar trend but significantly overestimated the dimensionless run-up parameter.

The results demonstrate that nature-based run-up mitigation strategies are most effective for waves with laboratory periods less than 60 seconds. However, nature-based mitigation measures provide more promising results in terms of inundation delay. The offshore breakwater was found to be the most effective measure against tsunami run-up, significantly reducing the dimensionless run-up parameter.

Man-made mitigation measures are found to be the most effective solution for tsunami mitigation. However, not all coastal communities possess the financial resources to construct an offshore breakwater. In such cases, a combination of nature-based and man-made measures with robust early warning systems and evacuation strategies should be considered. This balanced approach maximizes coastal resilience given financial constraints and geographical circumstances.