FRESH GROUNDWATER LENS DEVELOPMENT IN SMALL ISLANDS UNDER A CHANGING CLIMATE
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Groundwater is stored in surficial coastal aquifers in small islands in the form of freshwater lens floating on the seawater due to density difference. In many small islands, groundwater lenses are important freshwater supplies to island inhabitants due to the lack of sufficient surface water reservoirs. The shape and volume of a groundwater lens is sensitive to changing environmental and climate conditions, including recharge from precipitation, sea-level rise, and anthropogenic activities such as groundwater withdrawal. This thesis research implements a systematic research plan to investigate the dynamic spatiotemporal behavior of a groundwater lens under a changing climate and anthropogenic activities. A series of analytical solutions and numerical models have been developed to describe the transient change of the freshwater-seawater interface profile that delineates the geometry of a groundwater lens in a small strip island. Laboratory visualization experiments were also designed and conducted to validate the solutions, models and scientific findings. Fundamental scientific questions addressed include (1) how the lens interface changes in response to spatially and temporally variable recharge rates in a changing climate; (2) how high the groundwater withdrawal rate can be for a sustainable groundwater management in small islands with the prevention of saltwater upconing; and (3) how short-term and long-term sea level changes will impact the shape and volume of a groundwater lens. The developed modeling tools and findings have the potential to render significant social and economic impact for groundwater resources management in small islands.