INLAND FRESHWATER LENS OCCURRENCE AND LONGEVITY IN RESPONSE TO RECHARGE RATE IN DRYLAND ENVIRONMENTS USING A PHYSICAL LABORATORY MODEL

Variable density groundwater systems are common in coastal areas; however, inland accumulations of freshwater floating atop regional saline groundwater, referred to as inland freshwater lenses (IFLs), have been identified in the Arabian Peninsula and other drylands with similar climatic, geomorphic, and hydrogeologic settings. IFLs are the only source of renewable freshwater in northern Kuwait, but the general characteristics and freshwater volume of verified IFLs remain unclear. Improved understanding of the topic is requisite for the accurate estimation of the freshwater volume contained in the IFLs of Kuwait, but also to support a growing consensus that dryland IFLs are more numerous than previously thought and could potentially provide freshwater to remote, desert communities if verified. This study utilized a physical hydrologic model to examine differences in geometry (i.e. thickness, length) between coastal freshwater lenses and IFLs, as well as investigate the effect of recharge rate on IFL dynamics (i.e. geometry, formation, degradation). Simulated IFLs formed directly beneath the recharge area, migrated in the direction of the regional gradient and appeared to stretch, or degrade through time. Results demonstrated that recharge rate had a significant effect on both analytically derived coastal and inland lenses; however, recharge rate was positively correlated only with IFL length as coastal lens length was restricted by island diameter. Recharge rate was positively correlated with the ratio of IFL thickness to length [R²=0.92, n=8, p=5.373 x 10^-05], and IFLs formed more quickly but took longer to degrade in step with increased recharge rate [R²=0.90, n=8, p=0.0003] and [R²=0.88, n=8, p=0.0006] respectively. Physical laboratory simulations provide qualitative insights into IFL formation and sustainability as a function of recharge rate. Results from the study motivate the refinement of analytical and numerical solutions for IFLs in order to accurately estimate IFL position and volume through time in response to recharge rate, but also help to explain variable density groundwater recharge mechanisms in drylands in analogous environments.