Geology and dynamics of underground waters in Cerna Valley/Băile Herculane (Romania)

Abstract

A resort near the border with Serbia in southwestern Romania has been associated with thermal springs for over 2,000 years. The thermal springs are a result of a geothermal anomaly developed in the Băile Herculane area, along a narrow and deep graben. In late 1970s, the Romanian government began the construction of the Cerna-Motru-Tismana hydropower system. Dams were built on these rivers, including their main tributaries, forming Cerna Lake and Motru Lake. Waters from the resulting impoundment, Cerna Lake, were directed through tunnels to Motru Lake and then to the power station at Tismana Lake. Due to this anthropogenic impact, the volume of water available to recharge the thermal water reservoir was substantially diminished. A study was requested by the government, to determine the effect of water withdrawal from the Cerna River on the thermal water reservoir and to evaluate potential hydrogeologic connections between the Cerna River, its tributaries, and the thermal water reservoirs. In 1988, an additional dam was built on the Cerna River, 5 km north of Băile Herculane (forming Prisaca Lake) to supply power, water, and recharge the thermal water reservoirs. Selected results of this study, with emphasis on the geology, hydrogeology, and recharge areas of the main springs of Mehedinţi Mountains south of Arsasca Valley, are presented in this paper. Several sinking streams were identified in the northern part of the study area, near the boundary between non karstifiable rocks and limestones. Monitoring of selected springs during dye studies performed in July 2010 is still ongoing. At the time of publication, no dye had been detected in the monitored springs. The long residence times reflects the complexity of the geology in the area. The sinking stream and the springs being monitored are in limestone units separated by 300 m of low primary permeability flysch deposits.