Application of Idealised Modelling and Data Analysis for Assessing the Compounding Effects of Sea Level Rise and Altered Riverine Inflows on Estuarine Tidal Dynamics

Estuaries worldwide are experiencing increasing threats from climate change, particularly from the compounding effects of sea level rise (SLR) and varying magnitude of river inflows. Understanding the tidal response of estuaries to these effects can guide future management and help assess ecological concerns. However, there is limited existing understanding on how estuarine tidal dynamics may respond to the compounding effects of SLR and altered riverine inflows in different estuaries. To partially address this knowledge gap, this study used data analysis and scrutinised idealised hydrodynamic models of different estuary shapes and boundary conditions to (i) identify broad effects of SLR on estuarine tidal dynamics under various river inflow conditions, (ii) determine how longitudinal cross-sections are impacted by these effects, and (iii) highlight some implications for environmental risk management. Results indicated that short- to moderate-length, high convergent estuaries experience the greatest and short- to moderate-length prismatic and low convergent estuaries experience the least variations in their overall tidal dynamics (i.e., tidal range, current velocity, and asymmetry). These variations were most evident in estuaries with large riverine inflows and macrotidal conditions. Compounding effects of SLR and altered riverine inflows induced spatially heterogenous changes to tidal range, current velocity, and asymmetry, with transects nearest to the estuary mouth/head and at a three-quarter estuary length (measured from estuary mouth) identified as the most and the least vulnerable zones, respectively. These findings provide an initial broad assessment of some effects of climate change in estuaries and may help to prioritise future investigations.