Integrated Assessment of Vadose Zone Physical and Hydraulic Properties in Semiarid and Arid Mining Landscapes in Namibia

Mining deposits form anthropogenic vadose zones with physical, hydrological, and chemical characteristics that diverge strongly from natural soils. Observations show that these deposits rarely undergo spontaneous revegetation, although surrounding landscapes recover without intervention. The mechanisms controlling this failure remain poorly understood, quantitative datasets on these materials are scarce, and no framework currently links deposit genesis, material properties, hydrological functioning, and plant viability. This knowledge gap is critical in countries such as Namibia, where mining underpins the national economy but also causes severe ecological disturbance. As the driest nation in Sub-Saharan Africa, restoration of mine deposits in Namibia is not only constrained by toxicity and altered physical soil properties, but also water scarcity.

The WaMiSAR project aims to develop a toolbox for sustainable, climate-adapted water management within the mining sector of the Southern African Region by jointly addressing water scarcity and restoration of disturbed substrates. A combination of field monitoring, laboratory analyses, and process-based modeling is needed to identify the dominant factors limiting plant growth and to evaluate remediation strategies and irrigation effects in mine residue deposits. The central hypothesis is that plant-available water, rather than chemical contamination, constitutes the primary limiting factor for vegetation establishment on mine deposits in the region, particularly during early seedling stages.

To date, three field campaigns have quantified chemical, physical, and hydrological properties at two contrasting sites in Namibia: (i) Tsumeb, a decommissioned copper mine in the semi-arid north, and (ii) Rosh Pinah, an active zinc-lead mine in the arid south. Initial observations indicate that spontaneous vegetation occurs almost exclusively on sandy surface materials, whereas silt-rich layers, salt crusts, and gravelly substrates remain largely unvegetated. Where vegetation is present, roots extend several decimeters into the substrate. Elevated concentrations of copper, zinc, or lead do not appear to inhibit plant growth, whereas strong contrasts in texture and water-holding capacity are evident. Soil moisture sensors installed at multiple depths capture vadose zone dynamics. The usage of low-cost, humidity-based sensors enable the characterization of water retention in the ultra-dry range, overcoming limitations of conventional techniques.

The project generates a quantitative hydro-physical dataset for mining residues across the full moisture spectrum, identify key constraints on plant establishment, and improve hydraulic parameterizations for dry, anthropogenically altered substrates. These outcomes will support scientifically grounded remediation strategies and form the basis for an operational framework linking deposit origin, climate, substrate properties, and appropriate restoration interventions.