Modelling combined wave and water-level hazards at a nature-based infrastructure site in British Columbia, Canada

Climate change is continuing to affect coastal regions through rising global sea levels and evolving storm conditions, while land subsidence further amplifies relative sea-level rise in many low-lying areas. Coastal hazards arising from the combined effects of waves and high water levels are increasingly exposing areas to erosion and flooding. In this study, a low-lying region along the coast of Boundary Bay in British Columbia (BC), which is exposed to waves and storm surges, is studied. Communities and critical infrastructure in this region are protected from flooding by an existing 100-year-old dyke, which was not designed to account for sea-level rise. The “Living Dyke” is a pilot study implemented by the City of Surrey, BC, to assess and demonstrate the viability of nature-based infrastructure solutions to enhance coastal flood protection in the region. The project involves placing sediment and planting native salt marsh vegetation to test four stabilization techniques including brushwood dams, a sand berm, rock berm, and oyster-shell bags within the intertidal zone to attenuate waves and reduce wave overtopping of the dyke. In collaboration with biologists and ecologists, adaptive management, monitoring, replanting, and brushwood dam repair has occurred since construction in 2023. A series of in-situ pressure sensors have been deployed to monitor wave and water-level conditions at the field site. Using the observations, a high-resolution numerical model (XBeach) is calibrated, validated and applied to simulate storm events and flooding scenarios at the Living Dyke. Modelling of major wave events and sea-level rise scenarios is conducted to evaluate the performance of the different stabilization techniques. The results provide insight to the potential benefits of the Living Dyke as a nature-based technique to mitigate coastal squeeze and reduce the combined impacts of waves, storm surges, and sea-level rise. Ultimately, the interdisciplinary results integrate to provide the City of Surrey with guidance on the implementation of a field-scale nature-based infrastructure solution along the dyke.