A key measure to achieve these goals is granulometric riverbed stabilisation, a method intended to prevent the further deepening of the riverbed. A new generation of groynes shall help increase the water level in the fairway.
As a project also backed by EU funding, the IRRP involves a number of ecological enhancement measures revitalising the riverbanks and linking waterbodies with each other. Since the IRRP contains a number of novel elements, via donau decided to gather some practical experience for its large-scale project in a heavily rock-lined river section not exposed to the river flow.
The perfect setting was eventually found near Eckartsau, between the 1,893.4 and 1,891.7 river kilometre marks. Next to the stone riprap lining the riverbank to control erosion, one lengthwise and eight transverse dykes had been squeezed into this stretch barely 2 km in length.
Started in 2007 and inching to completion, the “Witzelsdorf” pilot project consisted in removing rock armour and riprap (800 m: complete removal, 200 m: up to low flow level, 500 m: up to low flow level + 0.3), lowering the river training structures to 0.5 m above low flow level, and replacing the old transverse groynes by four new ones with novel geometry.
These new groynes are tilted in flow direction, with their heads flattened to reduce the formation of kolks. The roots of the groynes are lower in level to ensure they are submerged in water even during low-flow conditions. This reduces sediment accrual in the groyne fields and enhances streambank erosion and cavings, thus allowing young fish to migrate between the groyne fields.
Construction activities were carried out under ecological expert supervision. In addition to the Witzelsdorf pilot project, researchers from the Vienna University of Technology developed yet another indoor hydroengineering model, with 15 m x 50 m in size the largest of its kind in Austria.
Built to the scale of 1:33 1/3, it typically reflects the river bend east of Vienna and thus provides additional details of use for the project.