Preliminary Investigation on the Effects of Sea-Level Rise on the Wave Overtopping Performance and Armour Stability of an Existing Breakwater

Aquino, C.J.P. and De Leon, M.P., 2024. Preliminary investigation on the effects of sea-level rise on the wave overtopping performance and armour stability of an existing breakwater. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 210-214. Charlotte (North Carolina), ISSN 0749-0208. The Sixth Assessment Report (AR6) published by the Intergovernmental Panel on Climate Change (IPCC) presented a new set of sea-level rise projections. In the Philippines, the sea level trend ranges from 1.28 to 13.13 mm/year considering long-term observations of 19 years or beyond. Because of these alarming projections, the effects of sea level rise may exceed the initial design expectations of our coastal infrastructures. This study aims to determine the impact of sea level rise on the wave overtopping performance and armour stability of an existing breakwater located at the Manila South Harbor, Manila Bay, Philippines. The main parts of the methodology include extensive data collection from global and local credible sources, hydrodynamic (numerical) modelling using MIKE 21 Coupled Hydrodynamic and Spectral Wave model, application of sea level rise projections to the resulting water levels, and evaluation of the existing breakwater through empirical calculations. The results of the wave modelling revealed that a maximum storm surge level of 1.13m (referenced from MSL) is expected. This would result to a maximum design water level of 2.85m MLLW for SSP5-8.5(LC) sea level rise scenario. A maximum overtopping of roughly 1684.36 l/s/m was calculated. This excessive overtopping was primary due to the existing low crest level of +3.0m MLLW. For armour stability, only three breakwater sections (Sta 0+400, Sta0+600, and Sta0+630) were not able to satisfy the criteria. An increase of 50.70% rock armour weight is required to satisfy the design criteria under the most critical sea level scenario of SSP5-8.5 (LC).