Impact of the Danube River on the groundwater dynamics in the Kozloduy Lowland

Intense groundwater flow in the Kozloduy Lowland is related to the formed layered aquifer on the contemporary Danube River terrace. The main factors affecting the groundwater regime are fluctuations of the Danube River, water influx from the south and the recharge as a part of the rainfalls in the area. The drainage system in the central part of the lowland affects the water levels and creates a widespread depression. This forms a disturbed groundwater regime in the area. The impacts of the Danube River for a six-year period (from 2007 to 2012) have been estimated. The groundwater balance elements were analyzed, based on transient numerical model of the lowland. Fluctuations of the groundwater levels are the most significant close to the river at a distance of 300–400 m, reaching as much as 1000 m in the lowland. Oscillation’s amplitude of groundwater levels gradually decreases with distance from the river and as a result of the drainage system abstraction. There is relation between the water stages in the river and the intensity of the drainage flow.