Combined electrical resistivity tomography and magnetic resonance sounding investigation of the surface-water/groundwater interaction in the Urema Graben, Mozambique

Chirindja, F. J.; Dahlin, T.; Perttu, N.; Steinbruch, F.; Owen, R.

Combined electrical resistivity tomography and magnetic resonance sounding investigation of the surface-water/groundwater interaction in the Urema Graben, Mozambique | Investigation sur les interactions eau de surface/eau souterraine par tomographie électrique et sondage de résonnance magnétique dans le Graben Urema, Mozambique Investigación de la combinación de tomografías de resistividad eléctrica y sondeos de resonancia magnética en la interacción del agua superficial/agua subterránea en el Urema Graben, Mozambique 采用电阻率成像法结合磁共振法调查莫桑比克Urema地堑地下水/地表水相互作用 Combinação de tomografia de resistividade elétrica e sonda de ressonância magnética para investigação da interação água superficial/água subterrânea no Graben de Urema, Moçambique

2016

Chirindja, F. J. | Dahlin, T. | Perttu, N. | Steinbruch, F. | Owen, R.

This study focusses on the hydrogeology of Urema Graben, especially possible interactions between surface water and groundwater around Lake Urema, in Gorongosa National Park (GNP). Lake Urema is the only permanent water source for wildlife inside GNP, and there are concerns that it will disappear due to interferences in surface-water/groundwater interactions as a result of changes in the hydraulic environment. As the lake is the only permanent water source, this would be a disaster for the ecosystem of the park. The sub-surface geology in Urema Graben was investigated by 20 km of electrical resistivity tomography (ERT) and three magnetic resonance sounding (MRS) surveys. The average depth penetration was 60 and 100 m, respectively. The location of the ERT lines was decided based on general rift morphology and therefore orientated perpendicular to Urema Graben, from the transitional areas of the margins of the Barue platform in the west to the Cheringoma plateau escarpments in the east. ERT and MRS both indicate a second aquifer, where Urema Lake is a window of the first upper semi-confined aquifer, while the lower aquifer is confined by a clay layer 30–40 m thick. The location and depth of this aquifer suggest that it is probably linked to the Pungwe River which could be a main source of recharge during the dry season. If a dam or any other infra-structure is constructed in Pungwe River upstream of GNP, the groundwater level will decrease which could lead to drying out of Urema Lake.

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