Design and functionality of sedimentation areas – Targeted lowering of floodplains to improve the habitat quality and flood safety by removing high loads of fine sediments

In many rivers of the Bohemian Massif in Northern Upper Austria, an increase in sediment loads can be observed, which has a negative impact on food safety and the habitat quality for aquatic organisms. To protect endangered species, measures must be taken to preserve natural aquatic habitats. Nature-based measures are well suited for improving the sediment balance of streams. Sediment deposition can be forced through the targeted lowering of a riparian plain. On these so-called sedimentation areas, sand and fine sediments in particular are removed from the watercourse. This locally improves the composition and morphology of the riverbed and restores important structures for aquatic organisms. The present work deals with the implementation of nine sedimentation areas and the verification of their functionality. The implementation of sedimentation areas requires technical requirements and the involvement of property owners, operators and authorities. To investigate the sediment budget, the removals from the sedimentation areas were documented. For the evaluation of the riverbed structure, surveys of the substrate composition and the morphology were carried out in several transects. The results show that even on small sedimentation areas significant amounts of sand and fine sediments are deposited. Furthermore sedimentation areas locally lead to an improvement of habitat conditions in the watercourse and can thus contribute to the conservation of endangered species. As the positive effects of sedimentation areas are locally limited, for far-reaching effects the implementation of several sedimentation areas in a watercourse section is required.