Contribution of the time domain electromagnetic method to the study of the Kalahari transboundary multilayered aquifer systems in Southern AngolaContribution de la méthode électromagnétique transitoire à l’étude du système aquifère multicouche transfrontalier du Kalahari dans le sud de l’AngolaContribución del método electromagnético en el dominio tiempo al estudio de los sistemas acuíferos multicapa transfronterizos del Kalahari en el sur de Angola时域电磁法对南安哥拉喀拉哈里跨界多层含水层系统研究的贡献Contribuição do método eletromagnético no domínio do tempo para o estudo dos sistemas aquíferos multicamada transfronteiriços do Kalahari no sul de Angola

The Cunene Province (Southern Angola) is facing recurrent and pluriannual droughts. Surface water supply could be reinforced using the groundwater resources of the multilayered aquifer systems (MAS) hosted in the siliciclastic sediments of the Kalahari Group. The MAS were first identified in the early 2000s in Northern Namibia and recently in the Cunene Province, by studies of the PLANAGEO project based on modern processing and reinterpretation of legacy data from the 1960s and 1970s (electrical resistivity data and deep boreholes). This article presents the results of a time domain electromagnetic (TDEM) survey conducted in the Cunene Province to: (i) contribute to the design of the hydrogeological conceptual model of the transboundary MAS, namely their geometry and extension; (ii) validate the reprocessing of the legacy data; and (iii) guide the future location of boreholes. Results depict the geometry of the sedimentary basin and the characterization of the MAS, with particular emphasis on the intermediate and deep aquifers. The borehole siting, based on the interpretation of the new TDEM data and the legacy data (clay markers in borehole logs), was successful, with a good agreement between estimated and observed horizons of the deep aquifers. However, the presence of clayey layers, a clay-rich matrix in the detrital deposits and saline/brackish groundwater led to uncertainties in the interpretation of the electrical transects. As such, recommendations are made to improve future data collection and mapping of the MAS.