water flow of 373 m³/s (mean summer discharge 700 m³/s) it is the largest waterfall in Europe in terms of potential energy. The High Rhine is characterized by numerous dams. On the few remaining natural sections, there are still several rapids. Near Koblenz in the canton of Aargau, the Aare joins the Rhine. With an average discharge of 557 m³/s, the Aare is more voluminous than the Rhine, which has an average discharge of 439 m³/s. Nevertheless, the Alpine Rhine is considered the main branch, because it is longer. Upper Rhine In the center of Basel, the first major city in the course of the stream, is located the "Rhine knee"; this is a major bend, where the overall direction of the Rhine changes from west to north. Here the High Rhine ends. Legally, the Central Bridge is the boundary between High and Upper Rhine. The river now flows north as Upper Rhine through the Upper Rhine Plain, which is about 300 km long and up to 40 km wide. The most important tributaries in this area are the Ill below of Strasbourg, the Neckar in Mannheim and the Main across from Mainz. In Mainz, the Rhine leaves the Upper Rhine Valley and flows through the Mainz Basin. The southern half of the Upper Rhine forms the border between France (Alsace) and Germany (Baden-Württemberg). The northern part forms the border between the German states of Rhineland-Palatinate in the west on the one hand, and Baden-Württemberg and Hesse on the other hand, in the east and north. A curiosity of this border line is that the parts of the city of Mainz on the right bank of the Rhine were given to Hesse by the occupying forces in 1945. The Upper Rhine was a significant cultural landscape in Central Europe already in antiquity and during the Middle Ages. Today, the Upper Rhine area hosts many important manufacturing and service industries, particularly in the centers Basel, Strasbourg and Mannheim-Ludwigshafen. Strasbourg is the seat of the European Parliament, and so one of the three European capitals is located on the Upper Rhine. The Upper Rhine region was changed significantly by a Rhine straightening program in the 19th century. The rate of flow was increased and the ground water level fell significantly. Dead branches were removed by construction workers and the area around the river was made more habitable for humans on flood plains