Effects of temperature fluctuations on tidally-influenced coastal unconfined aquifers

Abstract

Temperature has been found to play an important role in controlling groundwater flow and salinity distribution in coastal aquifers. However, previous studies focused on the effects of fixed temperature. In nature, both land surface temperature and seawater temperature fluctuate seasonally. The yearly fluctuation ranges of land surface and seawater temperatures can commonly reach 30°C. These surface temperature signals could propagate into coastal aquifers and change the temperature distribution in coastal aquifers. This may further induce seasonal variations in groundwater flow and solute transport processes. This research aims to investigate the effects of seasonal fluctuation in land surface and seawater temperatures on salinity distribution and water exchange in coastal unconfined aquifers subject to semi-diurnal tide. A numerical model, SUTRA-MS, is used to simulate the variably saturated and density-dependent groundwater flow coupled with salt and heat transport. Salt mass stored in the aquifer and water fluxes across the aquifer-ocean interface are used to evaluate the effects. Sensitivity analyses of fluctuation amplitude of temperature and tidal amplitude are also conducted. Finally, we discuss the implications of these results for nearshore biogeochemical processes and for accurate assessment of submarine groundwater discharge.