Advances in understanding the challenges and opportunities of hybrid sea defence approaches for coastal resilience

• For the first time, existing knowledge on the coastal protection performance of hybrid coastal sea defences is examined. • Key terminology and definitions of the hybrid sea defence approach are not consistent across the literature. • Hybrid sea defence approaches have huge potential in enhancing the robustness and resilience of coastal areas. • Data and evidence supporting the wave attenuation benefits of hybrid sea defence approaches are limited. The intensification of global climate change and rising sea levels continue to exacerbate risks of coastal erosion and flooding, presenting significant challenges for coastal regions' sustainable development and management. Climate change also adversely affects coastal ecosystems, which struggle to adapt to evolving environmental conditions. In recent years, there has been a growing emphasis on climate adaptation measures for coastal habitats, particularly implementing sustainable methods to mitigate coastal hazards and protect ecosystems. In this context, hybrid sea defence approaches, combining conventional and natural solutions, offer innovative and versatile strategies to enhance resilience and reduce the vulnerability of coastal areas. While previous studies have predominantly focussed on the ecological benefits of nature-based and hybrid-engineering solutions, there remains a scarcity of data and evidence regarding wave-structure interactions at these sea defences. This study comprehensively discusses the main functions, limitations and research methods of hybrid sea defences and technical and social barriers to effectively implementing these innovative approaches by systematically reviewing 95 papers and suggesting potential solutions and future research interests to overcome the problems of incorporating these approaches effectively. Hybrid sea defences offer greater robustness than nature-based solutions while performing more environmentally friendly than hard sea defences in many cases. However, the population of hybrid sea defences is questionable because of the lack of accurate and clearly quantitative evidence. This paper aims to provide coastal managers, engineers, researchers, and policymakers with a better understanding of the applications and performance of hybrid engineering in creating sustainable coastal cities in the face of climate change and extreme climatic events.