The impacts on groundwater development on shallow aquifers in the lower Okavango Delta, northwestern Botswana

The Okavango Delta is a large alluvial fan complex in the northwest corner of Botswana. Both surface and groundwater in this area are important to wildlife, flora, and human settlements. A groundwater exploration study covering an area of over 14,000 km(2) was undertaken to assess the potential of groundwater to supply a major town and associated settlements. The primary control on groundwater development potential is water quality, with much of the area characterised by brackish/ saline aquifers. This largely reflects the high rate of potential evapotranspiration. As a consequence, freshwater aquifers are strongly dependent on recharge from surface water during annual flooding. In the absence of river flow, water quality in the fresh aquifers begins to deteriorate and the thickness of the fresh water lens reduces through upward migration from underlying saline aquifers. Lateral inflow from surrounding saline aquifers does not appear to be a significant. The impacts of evapotranspiration indicate the importance of regular surface water recharge to sustainable development of groundwater resources. Groundwater development strategies are changing as a result of the understanding of salinification processes in these aquifers.