Groundwater in Bulgaria an overview

The structural-tectonic conditions are of primary importance for the occurrence of groundwater. This overview reflects a large variety of hydrogeo-logical settings. They have influence on the groundwater regime, and on its vulnerability to climate variability. In the territory of Bulgaria three main hydrogeological units are distinguished (Antonov & Danchev 1980).

Low-Danubian artesian region

This region covers the north part of Bulgaria, from the Balkan mountains up to the Danube River. It is a typical platform structure, stratified, with very well defined aquifers separated by aquitards. The groundwater is accumulated in Neogene sands and friable sandstones, Palaeogene limestone and Mesozoic carbonate formations. In the southern part of the artesian basin at the foot of the Balkan range, local karst basins are widely distributed due to folding and fault processes. Alluvial aquifers are formed along the rivers and are superimposed over earlier formations.

Intermediate hydrogeological region

The higher parts of the Balkan and the areas south of it up to the Rila-Rhodopes massif are included within this region. It is characterized by a complicated block structure. Different rocks (magmatic, sedimentary and volcanic-sedimentary) bear fissured groundwater (including thermal waters) that is related to weathering zones and large tectonic dislocations. In local outcrops of carbonate rocks, detached karst basins are formed. Typical of this region is the presence of considerable depressions, filled in with unconsolidated Neogene and Quaternary deposits in which porous ground-water with large resource is accumulated.

Rila-Rhodopes massif region

This region coincides with the Rila-Rhodopes mountain massif. Here in the western part, mag-matic rocks of different ages are presented, as well as Precambrian highly metamorphosed rocks with important weathering zones. Thus, fissured water is widespread in this region. In the zone with a large occurrence of Proterozoic marbles, important karst basins are formed, having typical mountainous character. In the eastern part of the region the predominant distribution has Cenozoic volcanic-sedimentary groundwater with fissured, layered water bodies and partly Precambrian meta-morphic rocks bearing fissured groundwater.

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