Sand, salt and water in the Stampriet Basin, Namibia: Calculating unsaturated zone (Kalahari dunefield) recharge using the chloride mass balance approach

Abstract

Estimating groundwater recharge rates in the Stampriet Basin is important for assessing the sustainability of the ground water resource both within south-east Namibia, and across the borders of this transboundary resource into Botswana and South Africa. The 65 000 km 2 basin contains a multi-layered aquifer system, of up to 9 superimposed aquifers, with a major upper unconfined and 2 major artesian levels. The majority of water abstraction (66%) is from the unconfined Kalahari Aquifer. This research investigates the direct recharge pathway through the dune-sand cover of the southern Kalahari dunefield which overlies ~80% of the basin. This is undertaken using established chloride mass balance methods within 4 unsaturated zone profiles (9 m to 11.5 m depth) from 2 regions of the basin. The results indicate that recent recharge rates are between 7 mm·y-1 to 46 mm·y-1, with profiles representing between 10 years and 30 years of rainfall infiltration.

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