Wastewater disposal at safari lodges in the Okavango Delta, Botswana

Many safari lodges in the Okavango Delta obtain their water supply from boreholes in near-surface aquifers while disposing of their wastewater via soak-aways, creating a potential risk of contamination of their water supply. Most islands in the Delta contain sites where the groundwater has become salinised as a result of transpiration by island vegetation. This study of wastewater disposal at such a site on Chitabe Island, which involved surveying of the water table, measurement of groundwater salinity, field bacteriological screening and groundwater flow modelling has revealed that although water disposal has created a recharge mound, the depression in the water table induced by transpiration by island vegetation is such that pollutants will remain confined to the region of maximum groundwater depression. Although the soils are sandy, they exhibit significant filtration effects on bacteria. The field assay used in this study was unable to detect coliform and E. coli bacteria in groundwater within a distance of 20 m from the disposal point. Modelling of groundwater flows indicates that boreholes located on the outer fringes of the island are secure from contamination. The study suggests that disposal of wastewater into areas where the groundwater is salinised provides a sustainable solution to the problem of wastewater disposal in the Okavango Delta. Water SA Vol.30(1): 121-128