Effect of Waves on Groundwater Flows and Contaminant Fluxes in Coastal Aquifers - Recent Advances and Perspectives

Abstract:

Oceanic forcing impacts groundwater flows and contaminant fluxes in coastal aquifers. While numerous studies have quantified the influence of tides on coastal groundwater processes, wave effects are less understood. This is in part due to the difficultly in quantifying wave effects due to the temporal complexity of the forcing, i.e., irregular and higher frequency. This presentation provides an overview of recent advances in our understanding of the impact of waves on groundwater flows and contaminant fluxes along permeable shorelines. Although initial numerical efforts demonstrated the influence of steady wave conditions (i.e., constant wave height) on groundwater flows, salt-freshwater mixing and the fate of reactive constituents (nutrients) in the nearshore aquifer, waves are highly unsteady. More recent simulations and field data show that unsteady wave forcing, in particular episodic wave events, highly perturb nearshore groundwater flow patterns, salt-freshwater mixing conditions and contaminant residence times. Further, episodic wave events impact the salt-freshwater mixing zone and geochemical conditions in the nearshore aquifer for much longer periods than the time over which the higher waves occurred. While consideration of the phase-averaged effect of waves only (i.e., wave set up) has been shown to be adequate for evaluating the impact of waves on dissolved contaminants in coastal aquifers, recent data analysis suggests that phase-resolved instantaneous wave effects may strongly regulate the behaviour of particulate and colloidal constituents (i.e., particulate organic matter, microbial contaminants) close to the sediment-water interface.