Flooding and erosion of coastal roads - exposure, mitigation and climate change impact

The coastal zone is a dynamic region where the sea meets land, making it highly influenced by environmental conditions such as storm surges, extreme weather events, and coastal erosion. Coastal areas are also characterized by high population densities, significant urban development, and important socio-economic functions such as transportation, trade, tourism and recreation. Consequently, they are particularly vulnerable to natural hazards and coastal processes, with risks such as flooding and erosion expected to increase due to climate change-driven global sea level rise.

This thesis focuses specifically on coastal roads, which are critical infrastructures typically situated at the frontline of exposure to flooding and erosion. Given their long design life, it is essential to assess how exposure will evolve under rising sea levels. A robust risk assessment requires high-quality data to estimate the probability of impacts and evaluate them against anticipated consequences. For coastal processes, such assessments rely on detailed data concerning wave dynamics and water level variations, which drive morphological changes. In this research, a detailed hindcast time series of decadal wave climate data for the southern Baltic Sea has been generated, validated, and analysed to enhance the understanding of variability in hydrodynamic forcing.

The aim of this thesis is to develop a methodology for assessing the exposure of coastal roads to the impacts of flooding, wave impact, and erosion. The proposed framework integrates numerical modelling, field observations, and case studies to evaluate exposure under both current climate conditions and future scenarios, accounting for sea level rise and long-term coastal development. Its application is demonstrated through a case study assessing the exposure of the main road along Sweden's southern coast. Results indicate that present-day exposure to flooding and erosion is limited to a few hotspots during extreme events. In future scenarios, the exposure will increase, and coastal erosion will pose the greatest threat to the road, highlighting the need for future coastal protection strategies.

To explore potential adaptation measures, a second case study was conducted along the east coast of Denmark. The study evaluated a hybrid coastal protection solution, combining rock revetments with small-scale beach nourishment, as a solution to mitigate the impact of coastal processes on the road. The morphological evolution of the nourishment was analysed under varying hydrodynamic conditions to better understand and optimize its design. Collectively, the findings of this thesis contribute to improved methodologies for risk assessment, enhanced datasets for wave climate analysis, and insights into the design of effective coastal protection measures to support infrastructure planning and resilience.