INVESTIGATING THE EFFECTS OF PRECIPITATION DYNAMICS ON INLAND FRESHWATER LENS FORMATION USING A PHYSICAL MODEL

Inland freshwater lenses occur in unique climatic, topographic, and hydrologic conditions. Previous studies have revealed that inland lenses exist beneath topographic depressions throughout the Arabian Peninsula and are recharged by modern meteoric water. This study aims to investigate the effects of precipitation dynamics on inland freshwater lens formation and degradation over time. We hypothesized that following extreme rainfall events, inland freshwater lenses form as rainwater accumulates in topographic depressions and infiltrates into the subsurface, leading to the formation of a stable lens underlain by a gently graded saline groundwater layer. Moreover, once recharge stops, freshwater lens degradation occurs over time due to diffusion. We tested our hypotheses by constructing a laboratory scaled, physical model (2m x 0.75m x 0.15m) of northern Kuwait’s Raudhatain depression. We simulated the area’s hydrostratigraphy from scaled characteristics of the depression using unconsolidated coarse and medium sand with infiltration rates of 9 m/day, saline groundwater (ρ = 1025kg m^-3), and a regional gradient (2 km/m). Lens formation and degradation were modeled by pumping simulated, colored freshwater recharge (ρ = 1000kg m^-3) from four dripper tubes directly above the depression. We measured the effects of precipitation volume, intensity, and duration on lens thickness and length. Lens geometry results were correlated with a set of 2D analytical expressions to validate our model. Observed lens formation aligns with suggestions from previous studies and analytical models, where a lens develops after high-intensity freshwater bursts but not from low-volume, long duration applications. Furthermore, lens degradation occurs once recharge terminates for a prolonged period or decreases below a minimum threshold. These results advance our understanding of the relationship between the hydrologic cycle and inland lenses, encouraging the exploration of new inland lenses in the Arabian Peninsula and worldwide.