Groundwater in Sudan: an improved understanding of wadi-directed recharge

Like many dryland regions around the world, the Butana Region of Sudan is almost entirely dependent on groundwater, and its main source of recharge comes from the highly variable 150–200 mm/yr rain that arrives mostly during a three-month rainy season. These rains cause ephemeral wadis to flow and flood, and provide a critical component of shallow aquifer replenishment. This study uses water table fluctuations along a 20 km wadi reach and chemical and stable isotopic tracers in 27 shallow (<40 m) and 6 deep (70–170 m) wells to show differences between mean recharge in the alluvial aquifer, estimated as 38–105 mm/yr, and the basal Nubian sandstone aquifer unit at 13–36 mm/yr. This study suggests while groundwater from the Nubian sandstone is predominantly palaeowater of −8 to −6‰ δ18O formed during a wetter, early-Holocene climate, modern recharge does reach the Nubian sandstone aquifer unit in areas