– highest:
August 15th, 2002 The main channel of the Danube was separated from its side channels by the flood control measures that were constructed around the year 1900. The outcome was a higher current velocity in the main channel, with a resulting deepening of the river bed, while in the side channels—which no longer had current flowing through them—sand and loam deposits were no longer removed by the current. In a natural
riparian ecosystem woody plants and deadwood have a strong impact on the natural flow dynamics, by stabilizing riverbanks, by reducing erosion, and by creating areas of reducing or increased flow rates, and thus affecting in which areas sediments are deposited or removed. Large tree trunks and accumulations of smaller flotsam cause the water to stagnate and the speed of the current to drop, leading to increased sedimentation. To counteract the effects of the flood control measures, beginning in 2002 individual side channels were tied in with the main channel again—at least at high water times—via Gewässervernetzungen ("water crossings"), which lower or remove the levees protecting those channels. In a 2006 pilot project created with the support of the
LIFE+ Program of the
European Union and the Austrian riverways agency
via donau, about three kilometers of the complete flood works were removed across the river from Hainburg, so that the river once again could spread into the floodplain areas. In a similar project near
Witzelsdorf, about one kilometer of the levees were removed. After the completion of the pilot projects in Hainburg and Witzelsdorf, future plans for this river engineering project are for removal of 50% of the levees and flood control works between Vienna and the eastern border of Austria. Aside from a revitalization of the
Au (
riparian zone), the project promises to mediate the effects of floods on the river and to stabilize the riverbed to the benefit of both river ecology and navigation. == Photo gallery ==