Water table oscillation due to hydroelectric dam reservoir impoundment in Sao Paulo state, Brazil

Hydrogeological studies have been carried out to evaluate the impacts, prior to the reservoir impoundment, of water table elevation on phreatic aquifers in influence areas surrounding hydroeletric dam reservoirs, to determine preventive, mitigative and corrective actions. These studies started out in the beginning of the eighties, from the detection of environmental problems associated with land use and occupation (soil saturation, well walls collapse, settlings of structures, flooding of depression areas) in influencial areas of reservoirs installed in the sixties and the seventies. A brief history, the origin and the objectives of the studies are described, as well as the hydrogeological impacts concerning monitored reservoirs, taking as an example, the Brazilian case of Tres Irmaos dam, due to its special characteristics.