Canalizing and Dams
The Rhine between Basel and Iffezheim is almost entirely canalized. On a stretch of 180 km, there are ten dams, provided with hydropower station and locks. Between Basel and Breisach, the old river bed carries hardly any water; almost all water is diverted through the Grand Canal d'Alsace on the French side, to ensure safe shipping and hydro power generation around the clock. Only when there is a large supply of water, then the old river bed will receive more water than the canal. France gained the right to do this in the 1919 Treaty of Versailles; the right applies to the segment between Basel and Neuburgweier/Lauterbourg, where the Rhine forms the border between France and Germany.
The straightening (1817-1876) and channeling (1928-1977) reduced the water table by up to 16 m and thus had a negative effect on flora and fauna. Gravel is also missing from the river, due to the dams. This has caused erosion below the dam at Iffezheim. To counter this, 173.000 cubic meters per year of a mixture of sand and gravel with an average grain diameter of 20 mm (corresponding to the local sediment transport capacity) has been dumped into the river, since 1978, using two motorized barges.
Read more about this topic: Upper Rhine