DANUBE RIVER PETRE GÂŞTESCU1 Key words: Danube basin, discharge regime, hystory, management The Danube is the second largest (805, 300 sqkm) and longest river (2,860 km) in Europe after the Volga. Its source area lies in the central-western part of Europe, in the Schwartwald, where two of its tributaries – the Breg and the Brigach – spring from, bringing their waters together at Donaueschingen. Thence, the Danube crosses central Europe up to Budapest, the Pannonian Depression down to the junction with the Drava, to finally pierce the Carpathian range at the Iron Gate and form a defile. It represents the southern border between the Romanian Plain and the Prebalkan Tableland. From Călăraşi (Romania) and Silistra (Bulgaria) to the Black Sea, the Danube rounds up the Dobrogea Plateau and its mountains, forming a Delta. Drainage basin The Danube covers 8% of the continent of Europe, its waters flowing on the territory of seventeen states (Germany, Switzerland, Italy, Austria, Czechia, Slovakia, Hungary, Slovenia, Poland, Croaţia, Bosnia-Hertzegovina, Albania, Yugoslavia, Romania, Bulgaria, the Republic of Moldavia, and the Ukraine). The formation process of the riverbed and valley of the Danube ended in the Late Pliocene and the Early Quaternary as the result of the successive drainage, in time, of some huge lakes from the Vienna, Pannonian and Pontic basins, themeselves separated from the vast Sarmatian Sea by the uplifting of the Alps, the Carpathians, and the Stara Planina mountains. The points of epigenetic or catchment penetrations show up today in the well-known gates or defiles (Devin, Iron Gate), dividing the river course into three distinct sectors: upper or Alpine, middle or Panonian and lower or Pontic (Walachian or Romanian). Upper course, long of 1,060 km, extends from the source area down to the Devin Gate. Right after the Brig joins the Brigach at Donaueschingen, the Danube loses in the Jurassic limestones of the Swabo-Franconian Jura Mts. Some 5 cu m/sec which run through the underground karst down to Tuttligen, in the Neckar drainage basin, a tributary of the Rhine (fig. 1). The Danube flows on between the Hercynian Swabo-Franconian Jura range, on the left, and the Prealpine heights, on the right, into the Münnich Basin at Ulm, wherefrom its channel becomes navigable. The major righthand tributaries (the Riss, Iller, Günz, Mindel, Lech, Isar, Traun and the Enns) spring from the northern slopes of the Alps, accounting for the alpine discharge regime of this sector. Most of these tributaries drain a lot of lakes situated in glacial, moraine-barred valleys (the Forggen, Ammer, Starnberger, Walchen, Tegern, Chiem, Atter, Mond, Hallstätter, and the Traun). Some of the important lefthand tributaries are the Altmühl, the Naab and the Regen, the Danube joining the last one at Regensburg. The Ludwigs Canal, built on the Altmühl and the Main (a tributary of the Rhine), connects the Danube to the Rhine and the Black Sea with the North Sea. The highest discharge rate in this sector has the Inn (810 cu m/sec), which is more than the Danube’s there (660 cu m/sec). As the riverbed slope varies from 0.6 – 0.9%, streamflow speeds by 1-3.5 m/sec. A landscape of gorges or defiles occurs wherever the Danube crosses some mountain summits or runs through hard rock, e.g. at Neuburg, Kalheim, Wachau, Bisamberg – Kahlenberg, the cataracts of Ardagger – Persenbeug, Strudel and Wirbel. The Grein-Ybbs Defile downstream the junction with the Enns, near the town of Linz, is particulary picturesque. Defiles and cracks in slopes increase the hydropower station at Iochenstein (140 MW), Aschach (258 MW), Ottensheim, Linz etc.). 1 “Valahia” University, Târgoviste Petre Gâştescu In Vienna, the Danube out into three streams: Donau Kanal, Alte Donau which is abandoned but still enjoyed by holiday-makers, and the Danube proper, used for navigation. Before passing through the Devin Gate, the Danube receives a lefthand tributary – the Czeck Moravia – (average discharge 62 cu m/sec), representing about 100 km – long border between Austria and Slovakia. Middle course from the Devin Gate to Baziaş (Romania) along 725 km. The portion which narrows down at Devin represents the river passage from the Vienna to the Pannonian basins, and is imposed by the smaller Carpathian range (Male Karpati). A few kilometers away, downstream the Devin Gate and the point where the Danube enters Slovakian territory, lies Bratislava, Slovakia’s capital. Between Bratislava and Komarno (Komaron on the Hungarian side), the river stretches out two arms – the Danube itself on the right, forming the border between Slovakia and Hungary, and the smaller Danube (Mali Dunaj) on the left, closing in a 90 km – long island called inland delta by the Slovaks. It is in this sector that the two countries had built a hydropower station at Gabcikova, subsequently contested by Hungary, when the Slovaks commissionned part of it. From the Smaller Carpathians (Devin Gate) and the Mid-Hungarian Mountains (Visegrad Defile), the Danube passes through the Kiss Alföld (Smaller Plain), in the South, and the Slovak Plain, in the North. Some of the main lefthand tributaries, originating from the Tatra Mts., are the Váh and the Nitra (discharge rate 139 cu m/sec), the Hron (82 cu m/sec) and the Ipoly, which forms a border between Hungary and Slovakia long of ca 150 km. An important righthand tributary is the Raaba (96 cu m/sec). After leaving the Visegrad Defile, the Danube takes a N-S direction, flowing along 275 km right through the middle of Hungary. Budapest, its capital, lies on either side of the Danube (Buda, on the right hills by the same name, and Pesta on the left, in a somehow higher floodplain). The two sides of the city are connected by numerous older and newer bridges. The place where Budapestans go for recreation and agreement is the Margareta Island. On the southern periphery of Budapest the Danube stretches out two arms: the river proper on the right, and Soroksari-Duna on the left with the Csepel Island lying in between. Farther on, the riverbed slope getting smaller (0.05%) the Danube meanders through the Pannonian Plain, leaving behind many abandoned arms, which we call ‘morotva’ (oxbow), on both sides. From the southern section of the plain, the Danube receives its biggest tributaries, substantially increasing its water volume. First comes the Drava (670 cu m/sec), next the Tisza (814 cu m/sec) and the Sava (1,460 cu m/sec), the last one running into the Danube in Beograde, the capital of the Federative Republic of Yugoslavia. From its junction with the Sava down to Bazias, wherefrom its lower course begins, the Danube receives three major lefthand tributaries, all coming from Romanian territory: the Tamis (Timiş), close to Beograde, the Karas (Caraş) and the Nera (right on the frontier-line between Romania and Yugoslavia). There is only one righthand tributary, the Serbian Morava, with remarkable discharge values (210 cu m/sec). Lower course, 1,075 km, stands for Romania’s natural border with Yugoslavia, Bulgaria, the Republic of Moldavia and the Ukraine. This sector boasts the longest and most beautiful defile, viz. the Iron Gate (144 km) and the most striking asymmetry (Drobeta Turnu Severin – Călăraşi, 566 km). It is a large floodplain, with the river braiding out and closing in successively two islands (Ialomita and Braila, 195 km). This is the sector of maritime navigation and of the Danube Delta (Braila – Sulina, 170 km). The Iron Gate Defile stretches out between Bazias and Gura Văii, narrowing down in some sections and getting larger in others, where small basins are formed. The first narrowed section is at Coronini, where big floods (e.g. in 1897) engendered a temporary upstream lake, suggestively called Mare Album, extending beyond Beograde. Similar conditions led to the formation of the Moldova Veche islet. The tectonic limestone zone at Coronini, called the Babacain Rock, constitutes an obstacle for navigation, likewise Cozia, Doica, Islazi, Tahtalia, Vrani, Vlas, Iuţi and Pregrada. A first Iron Gate dam was built at Pregrada and Iuţi Rocks. 30 Danube River The Iron Gate hydropower station, shared jointly by Romania and Yugoslavia, was commissioned in 1971, having been operated at full capacity (2,100 MW) ever since. The construction of a the dam at Gura Văii and the formation of a storage lake flooded the Ada- kaleh Island and some Roman vestiges. A second hydropower station (Iron Gate II), downstream the Iron Gate, was also built jointly with Yugoslavia. In this sector, the largest Danube tributaries lie on the leftside, in Romanian territory (the Jiu, the Olt and the Argeş); although rightside afluents from Yugoslavia and Bulgaria are more numerous, they are much smaller (the Timoc, Ogosta, Iskar, Vit, Osam, Iantra and the Lom). In 1954, a road and rail bridge was built between Giurgiu (Romania) and Ruse (Bulgaria). Between Călăraşi to Brăila, the Danube unbraids and its many arms encompass the floodplain itself which, rich in lakes and backwaters and frequently flooded, has been suggestively named Balta Ialomiţei (Borcei) and Balta Brăilei (‘balta’ stands for floodplain). Both were dyked and the land used for farming. An impressive bridge for rail traffic, the longest in Europe, was built between 1890 and 1895 by engineer Anghel Saligny. It was a remarkable performance for that time, spanning the river form Feteşti to Cernavodă. A second bridge for road and rail traffic was commissioned in 1987. Not far away, downstream, where waters gather into a single channel, there stands another bridge for the road traffic (totalling 1,450 m, of which 750 m are suspended over the Danube). This bridge, the longest over the Danube, was opened to traffic in 1970.