Experimental investigations on protection effects of vegetation on coastal bridges against extreme waves

Abstract Coastal bridges play a vital role in supporting transportation and economic activities in coastal regions but are increasingly vulnerable to extreme wave events, exacerbated by climate change and rising sea levels. Traditional engineering solutions, such as seawalls and breakwaters, offer protection but are often expensive and environmentally disruptive. Vegetated coastlines, such as mangroves and salt marshes, have emerged as a sustainable alternative, capable of attenuating wave energy and providing natural protection. However, the mechanisms through which vegetation reduces wave impacts and its practical application to protect coastal bridges remain inadequately understood. This study addresses these gaps through laboratory experiments that investigate the attenuation effects of vegetation on extreme waves under varying initial wave states and vegetation densities. The experimental data are used to perform stochastic analyses to quantify bridge vulnerability under extreme wave scenarios, with and without vegetation protection. The paper presents the experimental design, methods for estimating wave-induced loads on bridge superstructures, and a probabilistic vulnerability model to assess bridge performance. Comparative results highlight the effectiveness of vegetation in mitigating wave loads and reducing bridge vulnerability. Findings from this study could contribute to advancing sustainable coastal protection strategies and provide critical insights for integrating vegetation-based solutions into coastal bridge design and management practices.