Cost analysis of nature-based solutions for bank protection compared to rock armor revetments un-der consideration of embodied CO2 emissions

Although numerous scientific studies claim ecological and functional advantages of near-natural shoreline or bank protection over hard bank protection, responsible authorities often still prefer hard construction methods, assuming them to be more cost-effective. While there is anecdotal support for this assumption, there has been no rigorous evaluation in terms of a comprehensive cost comparison based on real-world data. In this study a complete cost comparison between nature-based solutions for bank protection and hard bank protection is presented using cost data from bank protection measures carried out in German estuarine waterways with the aim of supporting evidence-based decision-making. A sensitivity analysis highlights the most important boundary conditions such as maintenance intervals influencing total costs. The study highlights different cost structures, maintenance intervals and total costs for the investigated measures. Embodied carbon emissions of rock armor revetments were calculated and amounts monetized to investigate influence on total costs. Results show that nature-based solutions for bank protection typically require lower initial investment but incur higher maintenance costs. Monetized values of embodied carbon emissions do not significantly influence the overall costs. Nevertheless, nature-based solutions are shown to be cost-competitive with hard-engineered structures if maintenance intervals are low.