Non-linear interactions between sea-level rise, tides, and geomorphic change in the Tamar Estuary, Australia

Abstract

Forecasting the likely impacts of sea-level rise (SLR) within estuaries is especially complicated by the interacting effects of geomorphic change and tidal distortion. The 70 km long kanamaluka1/Tamar Estuary, Australia, provides the setting for a simplified approach to explore the effects of SLR on tidal regime together with evolving estuary morphology. Scenarios of SLR, estuary infill, nodal tide modulation at the mouth, and increased wind speed are applied within a hydrodynamic model. The potential for amplified tidal range with SLR versus the damping potential of significant but plausible levels of estuary infill are explored. For this estuary, the simulated infilling had a strong effect on tidal distortion, up to a 57% reduction in tidal range at the estuary head. However, this reduction translates to just a 16% effective reduction in mean high water due to the elevation of mean tide level. Comparatively, SLR had a contrasting effect on tidal distortion, reducing flood tide dominant asymmetry by up to 40% without driving a significant change to the tidal range. The same 57% reduction in tidal range at the estuary head would limit projected SLR by 2100 to current (2018) levels, suggesting potential for mitigating SLR with engineered solutions. The efficient and effective design of mitigation strategies depends on the improved availability and quality of observational data. Data-driven modelling approaches will be essential for managing future coastal flood risk with SLR and ensure long term resilience.