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[AHW21-05] Numerical analysis of freshwater lens in a narrow island considering evaporation from a central lake
In many small islands, freshwater lenses are the only source of drinking water, and the only source of recharge for the lenses is precipitation. The volume of freshwater lenses is influenced by freshwater/seawater interaction, including dynamic flow processes in the mixing zone and human activities, plus the recharge rate and the hydraulic conductivity of aquifer.
The increase of surface water bodies on an island can increase the total evaporation, which can lead to a reduction in the shape and volume of freshwater lens. Also, high evaporation rates from lake would affect subsurface flow patterns and salinity distribution in the system.
Therefore, the purposes of this study are to understand the changes of freshwater lenses under different precipitation and evaporation conditions to search for critical conditions that would lead to significant change in the structure of freshwater lenses beneath the island.
We selected a series of islands with various precipitation and evaporation rates, and used 30 years of monthly average precipitation data. The annual and monthly average groundwater recharge rates were calculated considering the evaporation rate from the lake and the evapotranspiration rate from the land surface. We used HydroGeoSphere to develop several hypothetical symmetrical cross-sectional island models. The models simulated coupled surface-subsurface flow and solute transport processes with the density-driven effect. The models were used to evaluate the salinity distribution under various precipitation and evaporation conditions to discuss the effect of the existence of surface water bodies on the subsurface freshwater resources.
The increase of surface water bodies on an island can increase the total evaporation, which can lead to a reduction in the shape and volume of freshwater lens. Also, high evaporation rates from lake would affect subsurface flow patterns and salinity distribution in the system.
Therefore, the purposes of this study are to understand the changes of freshwater lenses under different precipitation and evaporation conditions to search for critical conditions that would lead to significant change in the structure of freshwater lenses beneath the island.
We selected a series of islands with various precipitation and evaporation rates, and used 30 years of monthly average precipitation data. The annual and monthly average groundwater recharge rates were calculated considering the evaporation rate from the lake and the evapotranspiration rate from the land surface. We used HydroGeoSphere to develop several hypothetical symmetrical cross-sectional island models. The models simulated coupled surface-subsurface flow and solute transport processes with the density-driven effect. The models were used to evaluate the salinity distribution under various precipitation and evaporation conditions to discuss the effect of the existence of surface water bodies on the subsurface freshwater resources.