Presenter/s: Bernd Cyffka
Symposium Session: 2024 - 09 Different Dam Problems with Different Dam Solutions
Topics covered: adaptive management and monitoring, modeling, and outside PNW
ABSTRACT
In Europe, the Water Framework Directive (WFD) is a legally binding instrument to restore water bodies to good status. One aspect of the WFD is that all transverse structures, small or large, must be passable for migratory species. This has often led to purely technical measures, such as fish ladders. In some cases, however, where space and money were available, longer bypass watercourses were also built. This presentation deals with the restoration measure called “Dynamisation of the Danube floodplains between Neuburg and Ingolstadt/Bavaria”. The centrepiece of this measure is an approximately 5-mile-long watercourse that bypasses the Bergheim hydropower station through a riparian forest of about 4.6 sq. mi. and thus makes it possible for species to migrate upstream.
However, this bypass, which today is existing for more than twelve years and has thus developed accordingly, not only serves the migration of species, of course mainly fish. It has meanwhile developed into a habitat where adult fish spawn, young fish grow up and certain species live permanently. This success story has become known and recognised beyond the region. But is it that simple, do you just have to let the water flow?
At the beginning, there were fears that the water body in the predominant alluvial clay would very quickly colmate and develop into a clayey-sandy habitat. This would not do justice to the overall habitat conditions, because the restoration area lies in front of the Alps and the creatures in the water bodies depend on clean, fast-flowing water that flows over a generally gravelly streambed. There were two measures that prevented this: a) the creation of gravel depots during the construction of the watercourse and b) so-called controlled floodings, which provides hydrological dynamics about twice a year with five times more water than usual and continually changes the streambed and the river banks through erosion and aggradation. This has led to the fact that even in formerly clayey sections of the river, gravel banks can now be found inhabited by Red List species.
This presentation shows selected examples of changes in the riverbed over the years and describes monitoring measures such as profile surveying, laser scanning and photogrammetry.