Hydrogeological characterisation of regional faults and dolerite dykes in the Precambrian Basement and Karoo Supergroup (Tete Province, Mozambique)

Abstract

Abstract Faults and dolerite dykes within Basement- and Karoo-aquifers in northern Mozambique may increase groundwater occurrence but may also be barriers to groundwater flow. Should observation boreholes drilled into regional and local faults as well as dykes show a response to aquifer testing, it would be deduced that these hydrogeological discontinuities are not barriers to groundwater flow. The approach adopted for this study included a sequential process involving data acquisition through a hydrogeological fieldwork programme consisting of geophysical surveys, borehole drilling, aquifer testing, and groundwater level monitoring. The Zambezi Border and geological contact faults were characterised by high variability in hydraulic properties. Aquifer testing resulted in drawdown in observation boreholes as well as a reduction in piezometric surface in the installed vibrating wire piezometers located in different aquifer units, indicating the Zambezi Border- and geological contact-faults were not barriers to groundwater flow. Not all the northwest-southeast trending dykes acted as barriers to groundwater flow, as there were discreet intervals with relatively high permeability present.