Freshwater Lens Dynamics in Semi-Arid Aquifers

In semi-arid regions, freshwater lenses develop where episodic recharge from rainfall, rivers or oases creates a buoyant layer of low-salinity groundwater overlying denser saline water within coastal or inland aquifers. The shape and persistence of these lenses are governed by the interplay between recharge magnitude, density-driven dispersion at the freshwater–saltwater interface and lateral or vertical mixing. Key controls include aquifer geometry, hydraulic conductivity contrasts, evapotranspiration demand and regional saltwater heads. Freshwater lenses are vital for sustaining drinking supplies in remote communities and for maintaining riparian and wetland ecosystems in drylands. Recent advances in high-resolution hydrochemical profiling, ground-penetrating radar surveys and coupled numerical–physical experiments have deepened understanding of lens formation, transient evolution and vulnerability to over-abstraction. Insights from global case studies—ranging from coastal plains in Western Australia to inland basins across the Arabian Peninsula—are informing adaptive management strategies such as controlled pumping schedules, artificial recharge schemes and ecological flow allocations to preserve lens integrity under changing climate and land-use pressures.

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Freshwater Lens Dynamics in Semi-Arid Aquifers publication trend

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Technical terms

Freshwater lens: A buoyant body of fresh groundwater overlying denser saline groundwater within an aquifer, typically recharged by precipitation or river inflow.

Semi-arid aquifer: A subsurface water-bearing formation in climates with low and highly variable precipitation, where recharge is episodic and evapotranspiration rates are high.

Riparian lens: A freshwater lens formed adjacent to a gaining river in a saline aquifer, maintained by density contrasts and river discharge.

Dupuit–Forchheimer approximation: A simplification of groundwater flow equations assuming mainly horizontal flow and hydrostatic pressure distribution, used to model sharp interfaces between fluids of differing density.

References

1. Effects of River Partial Penetration on the Occurrence of Riparian Freshwater Lenses: Experimental Investigation. Water Resources Research (2021).
2. The Interface Between Fresh and Salt Groundwater in Horizontal Aquifers: The Dupuit–Forchheimer Approximation Revisited. Transport in Porous Media (2017).
3. Transient Evolution of Inland Freshwater Lenses: Comparison of Numerical and Physical Experiments. Water (2020).