The Danube (German Donau, Hungarian Duna, Serbo-Croatian Dunav, Slovak Dunaj, Romanian Dunărea) is the second-longest river in Europe (the Volga being the longest).
It is the only major European river to flow from west to east. It rises in Germany in the Black Forest as two smaller rivers called Brigach and Breg, which join in Donaueschingen and are called Donau henceforth, flowing south-east for a distance of about 2850 km (1770 miles), to the Black Sea in Romania where the Danube Delta is.
The Danube is an important international waterway. It flows through ten countries (Austria, Bulgaria, Croatia, Germany, Hungary, Moldova, Slovakia, Romania, Ukraine, Serbia and Montenegro) and has tributary rivers in seven other countries. It flows through the following large cities:
After the construction of the German Rhine-Main-Danube Canal in 1992, the river is part of a trans-european waterway from Rotterdam on the North Sea to Sulina on the Black Sea (3500 km). The amount of goods transported on the Danube raised to about 100 million tons in 1987. In 1999, transport on the river was made difficult by the NATO bombing of 3 bridges in Serbia. The clearance of the debris was finished in 2002.The Danube is mentioned in the title of a famous waltz by Austrian composer Johann Strauss, An der schönen, blauen Donau (On the Beautiful Blue Danube).
Although the headwaters of the Danube are relatively small today, geologically, the Danube is much older than the Rhine, with which its catchment area competes in today's southern Germany. This has a few interesting geological complications. Since the Rhine as the only river rising in the Alps mountains flows north towards the North Sea, an invisible line divides large parts of southern Germany, which is sometimes referred to as the European Watershed.
However, before the last Ice Age in the Pleistocene, the Rhine started at the southwestern tip of the Black Forest, while the waters from the Alps that today feed the Rhine were carried east by the so-called Urdonau (original Danube).
Parts of this ancient river's bed, which was much larger than today's Danube, can still be seen in (now waterless) canyons in today's landshape of the Swabian Alb.
After the Upper Rhine Valley had descended, most waters from the Alps changed their direction and began feeding the Rhine.
Today's upper Danube is but a meak reflection of the ancient one.
Since the Swabian Alb is largely shaped of porous limestone, and since the Rhine's level is much lower compared to the Danube, today, subsurface rivers carry much water from the Danube to the Rhine. On many days in the summer, when the Danube carries little water, it completely oozes away noisily into these underground channels at two locations in the Swabian Alp, which are referred to as the Donauversickerung (Danube Sink). Most of this water resurfaces only 12 km south at the Aachtopf, Germany's most yielding wellspring with an average production of 8,000 liters per second, north of Lake Constance -- thus feeding the Rhine. The European Water Divide thus in fact only for those waters that pass beyond this point, and only during the days of the year where the Danube carries enough water in the first place.
Since this enormous amount of underground water erodes much of its surrounding limestone, it is estimated that the Danube upper course will one day disappear entirely in favor of the Rhine.
Geology
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