Author(s): Maarten Schoemaker; Matthijs Bos; Michael Van De Watering; Joost Buurman; Matthijs Kok; Sebastiaan N. Jonkman

Linked Author(s):

Keywords: Flood protection; Flood defence; Flood risk; Adaptation pathways; Hydraulic infrastructure; Climate change; Robustness; Robust decision making; Increments; Discount rates

Abstract: Singapore is currently conducting feasibility studies for large-scale and long-term coastal protection to address rising sea levels. According to the third national climate change study by the Centre for Climate Research Singapore (CCRS, 2024), projections indicate that Singapore’s mean sea levels could rise by up to 1.15m by 2100 and about 2m in 2150 due to relative Sea Level Rise (rSLR) with the SSP5-8.5 low confidence climate change scenario, which would lead to an increased risk of flooding. In planning and designing protection measures against coastal flooding, the question arises: what pathways to 2.0m rSLR are cost-optimal (lowest Present Value of the investment costs) and are also robust for the uncertainty in future scenarios (e. g. a different climate change scenario or a different social discount rate). Should the infrastructure be constructed in one increment to 2.0m rSLR (ultimate build), or should infrastructure be constructed in several smaller adaptation steps called “increments”? The objective of this study is to find this out for six archetypes of coastal protection in Singapore: a coastal revetment, a setback embankment, a quay wall, a singular flood wall, a closure dam and a storm surge barrier. For each of these archetypes, possible pathways to 2.0m rSLR were explored. This includes all possible combinations of pathways with designs that work for 0.7m rSLR (increment 1), 1.15m rSLR (increment 2) and 2.0m rSLR (increment 3). Conceptual designs were made for each increment in the pathway, and costs were derived. This resulted in the costs per pathway, which allows for identifying a cost-optimal pathway. Using a sensitivity analysis, the influence of other future scenarios was assessed (e. g. a different climate change scenario and a different social discount rate). This has led to specific recommendations for all six archetypes on cost-optimal pathways that are also robust for other developments of future scenarios. This paper includes these recommendations for all six archetypes: a coastal revetment, setback embankment, quay wall, singular flood wall, closure dam (soil solution and structural solution) and a storm surge barrier. The paper includes two worked-out stylized archetypes: the setback embankment and quay wall. In general, one can conclude that for the archetypes that can be overlayed with an additional layer and are therefore expandable (such as the coastal revetment and setback embankment), pathways with incremental build are preferred. For the archetypes that consist of hard (often concrete) structures that would need to be replaced if protection level is insufficient (such as quay walls or storm surge barriers), an ultimate build design with 2.0m rSLR is preferred. Extending the technical lifetime of these structures beyond the 100-years that is prescribed in design codes to around 150-200 years is in likely beneficial as well, but requires further research and substantiation.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1621-cd

Year: 2025