Simulating the effects of lake wind waves on water and solute exchange across the lakeshore using hydrus-2D

Abstract

Wind waves, which frequently occur on large surface water bodies such as lakes, may temporarily alter flow patterns in a subsurface zone and the corresponding water and nutrient interactions between surface waters and shallow groundwaters. To better understand these processes, soil flume experiments were carried out to investigate wind wave-driven water and chloride interactions across the lake–groundwater interface, and the Hydrus-2D model was used to analyze and evaluate the observed experimental results. Two interaction cases between the lake and groundwater systems were considered: groundwater discharging into a lake (the GDL case), and lake water recharging groundwater (the LRG case). For comparison, no-wave conditions for both the GDL and LRG cases were also analyzed. The results revealed that, similarly to no-wave conditions, water and chloride exchange fluxes between the lake and groundwater systems under wave conditions occurred mainly within narrow bands near the intersection of the water level in the lake and the interface in both the GDL and LRG cases, and then exponentially decreased along the interface. Most water and chloride that infiltrated into the subsurface zone through the upper part of the interface during a wave crest returned to the lake through the lower part during a wave trough in both the GDL and LRG cases, creating local recirculation zones in the subsurface near the interface. Such recirculation produced a more frequent exchange of water and solute across the interface compared with those under no-wave conditions. During a one-day period after wind waves started, the total exchange fluxes of water and chloride to the lake decreased by 36.2% and 71.9%, respectively, compared to the no-wave conditions in the GDL case. In the LRG case, the total exchange water fluxes to the subsurface increased by 89.7%, while the total exchange chloride fluxes increased only slightly (4.5%) compared to the no-wave conditions due to the difference in chloride concentrations between the upper and lower parts of the interface. The sensitivity analysis revealed that the hydraulic conductivity of the lakeshore zone and the characteristics of the waves were important factors influencing water and chloride exchange between the lake and groundwater systems. The simulated results helped us to better understand water and solute interactions in the lake–groundwater system during windy periods.