ABSTRACT
The West Stara Planina Mountains are situated across two countries – Serbia and Bulgaria. The karstification is developed mainly in two carbonate complexes: Triassic and Upper-Jurassic, while in the western extension, i.e. in Vidlicˇ Mountain, karstified carbonate rocks of Cretaceous age prevail. This is a typical mountain karst with wide distribution of classical karstic landforms: dolines, small poljes, and blind valleys. There are also hundreds of caves in both countries, many of them well explored. Due to high infiltration of rainfall, abundant groundwater reserves are formed. The drainage takes place over numerous large karst springs. There are overflow sources while other sources are from upwelling water, draining the deeper saturated zones. Their discharge regime varies from relatively constant to highly changeable. Some are tapped and used for potable water supply, as in the case of Pirot, Dimitrovgrad (Serbia) or Svoge (Bulgaria). Most of the karst springs have relatively clearly defined inner catchment areas and are not subject to transboundary discharge. The water budget analysis at the bordering territories of Serbia and Bulgaria requires more hydrological, hydrogeological and climatic data, field survey and water tracings.
