most severe cases of erosion in the Balkans. As a result of this, the river brings large amounts of materials to the Great Morava, filling and elevating its river bed, which exacerbates the huge floods of its daughter river. Tributaries The South Morava has 157 tributaries. The most important left tributaries are: Jablanica, Veternica, Pusta reka and Toplica. Right tributaries are: Vrla, Vlasina, Nišava (the longest) and Sokobanjska Moravica. Economy The South Morava has a significant potential for electricity production, and a huge hydroelectrical system (Vlasina- Vrla I-IV power stations) has been constructed in its drainage basin. To a certain extent, its waters are used for irrigation. The river valley's most important role is as a channel for transportation. It is the natural route for both railway and highway between Belgrade–Skopje–Thessaloniki. It is part of the Pan-European corridor X, and the route of the E75 Highway. Historical name Till early 20th century and beyond it has been also known as Bulgarian Morava (, Balgarska Morava; , Bugarska Morava). This historical name derives from the Ottoman times when it was considered that as a whole the river was a natural border between Bulgarians from the east side, and Serbs and Albanians from the west one. A detailed ethnographic map of the then mixed (Albanian, Serbian and Bulgarian) population of the western bank of Bulgarian Morava Valley was made by Hahn and Zach in 1861. See also Pčinja River Notes and references Notes General Mala Prosvetina Enciklopedija, Third edition (1985); Prosveta; Jovan Đ. Marković (1990): "Enciklopedijski geografski leksikon Jugoslavije"; Svjetlost-Sarajevo; External links PIM "Ivan Milutinović", Belgrade, Serbia Morava - Vardar (Axios) Navigation Route (About 1,200 km shorter route (three days shorter time of navigation) from Belgrade to Port of Thessaloniki than across Danube, Black Sea and Aegean Sea. Electric power production, improvement of water quality and regulation of flooding wave.) Morava - Vardar (Axios) Navigation Route map (Concepts of regulation of rivers Great Morava and South Morava for navigation and hydropower production.) Macedonia's way to the Danube Rivers of Serbia Rivers of Kosovo Rivers of North Macedonia Geography of Gjilan District