Thermal modulation of nearshore groundwater flow and solute transport in a tidally influenced coastal aquifer bounded by a mild-slope beach

Coupled groundwater flow with solute and heat transport in coastal aquifers affects water, solute and energy exchanges between freshwater and saltwater systems. Of particular interest, but significantly understudied, is the effect of temperature differences between groundwater and seawater on saltwater intrusion and nutrient cycling in coastal aquifers. In this study, we use a physics-based multi-components numerical model to systematically explore how such temperature variations influence groundwater flow dynamics, and salt and heat distributions in mildly sloped beach aquifers exposed to tidal fluctuations. The results show that the temperature contrast between groundwater and seawater leads to a reduction in the period of the unstable flow cycle compared to the isothermal scenario. With increasing seawater temperature, both the mixing intensity and exchange flux increase due to more pronounced effects of temperature on hydraulic properties of the aquifer. Rising seawater temperature also influences the patterns and number of salt fingers, resulting in variable shapes of the salinity distribution as temperature increases. These findings highlight the necessity of a more comprehensive framework with temperature effects included for evaluating nearshore flow and mass transport processes within coastal aquifers.