Groundwater Resources Mapping in Mozambique

The project assesses the use of hydrogeophysics as a tool for groundwater studies. The aim is to improve the knowledge about the groundwater occurrence in areas with little background information. Therefore some geophysical methods are tested for their applicability in areas with real hydrogeological problems. The geophysical methods measure the different physical property of geological material. The implemented methods are electrical resistivity tomography (ERT), magnetic resonance sounding (MRS), induced polarization (IP) and geophysical borehole logging (BL).

The ERT and MRS combination is tested to study possible interaction between surface and groundwater in the Urema floodplain in a part of Gorongosa National Park. The aquifer layers detected by ERT were also detected by MRS, due to high free water content compared with clay layers with low water content and low resistivity. There is a possible connection between the Pungue River and the upper aquifer, which appears to be feeding the lake during the dry season, but the processes and fluxes are not well understood. Pungue River is an international river that crosses Zambia and Zimbabwe before it enters Mozambique. If a dam is constructed upstream of the Gorongosa Park, there is a risk of reducing the recharge to the national park, or increasing the groundwater discharge from it, and the Urema lake can dry. The consequence would be catastrophic because the lake is the main source of water for wild life during the dry season.

The Mozambican government has invested heavily in borehole projects throughout the country to satisfy the population´s needs, aiming to achieve one of the Millennium Development Goals (more than 50% of population should have access to safe drinking water by 2015). But detecting the groundwater in consolidated rock areas has been challenging. Consequently the drilling failure rate is high. ERT and IP are tested in an attempt to explain the failures in order to be able to suggest more efficient well siting methodologies.