Alluvial aquifer

This work is part of the AUVERWATCH project (AUVERgne WATer CHemistry), which aims to better characterise some Auvergne water bodies, specifically the alluvial hydrosystem of Allier River (France). Alluvial aquifers constitute worldwide a productive water resource, superficial and easily exploitable. In France, 45% of the groundwater use comes from these aquifers. The study site is a wellfield that withdraws 8.5 million m3 of water annually from an alluvial aquifer to produce domestic water for 80% of the local population.

he Danakil Depression of the Afar Rift forms part of the north/south-trending Ethiopia-Eritrean arm of the East African Rift System, whereas the western margin of the depression forms part of an active plate boundary between the western Nubian and eastern Danakil tectonic blocks. Dallol (within the Danakil Depression) currently holds the record for the highest average temperature for an inhabited place on Earth, with annual average temperatures of ~35-36°C.

The Omaruru River Basin encompasses an area of approximately 19 625 km2 in central west Namibia. The headwaters extend to the area north of the Etjo Mountains, ephemeral surface runoff and groundwater flow is generally directed south-westward until they reach the Atlantic Ocean. Annual rainfall decreases steadily from 380 mm at the headwaters to <50 mm at the river mouth implying that majority of runoff is generated in the upper headwaters.

Three dimensional numerical flow modelling has become one of the best tools to optimise and management wellfields across the world. This paper presents a case study of simulating an existing wellfield in an alluvial aquifer directly recharged by a major perennial river with fluctuating head stages. The wellfield was originally commissioned in 2010 to provide a supply of water to a nearby Mine. Ten large diameter boreholes capable of abstracting ±2 000 m3 /hour were initially installed in the wellfield.