The hydraulic engineering measures implemented in the course of the Pilot Project Witzelsdorf (2007-2009) resulted in the desired widening of the fairway cross-section and had the anticipated positive ecological effect. At the same time, the new structures caused significant sedimentation in this river section, which necessitated the dredging of more than 200.000m³ gravel between 2009 and 2015. Apart from considerable additional maintenance efforts, navigation was affected due to reduced fairway depths. Furthermore, dredging works always entail impairments of the ecosystem.
It is also noteworthy that prior to the modifications conducted in 2007 no maintenance dredging of the fairway was necessary in this area and that the original aim of the pilot project 2007-2009 was to establish a situation neutral for navigation.
The objective of this optimisation project was to moderately adapt the new hydraulic structures in order to revive bedload transport in the fairway. The adaptations were planned in such a way as to decelerate sedimentation while preserving the positive ecological project outputs. The existing longitudinal training works and four groynes were heightened and one groyne was extended.
- Elaboration of the project structure (December 2014)
- Permits acquired under the Water Act and the respective legal frameworks in the areas of conservation, navigation, etc. (March 2015)
- Implementation of construction works 14.09.2015 – 02.10.2015 by STRABAG Bau GmbH
- Post-monitoring to observe the effectiveness of the measures is done regularly in the course of waterway inspection tours and riverbed surveying
The project is already concluded. At the moment, a monitoring program is in progress in order to assess the project impacts. The lessons learned are incorporated in the development of further measures for the whole sections.
The project makes a substantial contribution to the implementation of measure 02. Clear nautical bottlenecks in an environmentally friendly way of the Action Programme for the Danube 2022.