Sohlmorphologische Analyse Untere Salzach

The riverbed morphological development of the river Lower Salzach from the confluence of the river Saalach downstream over a distance of around 47 km is examined. In this section, the river forms the border between Germany and Austria. Starting with the regulatory works in the second half of the 19th century, the Salzach became ever deeper and disconnect from the riparian wetlands in the basin landscapes. From 1953 to 2023, the riverbed at the mouth of the river Saalach eroded by around 4 m. This was also due to a breakthrough in the tertiary, fine-grained valley fillings beneath the quaternary gravel during the nearly 100-year flood in 2002. In parallel to the bed erosion, the morphological structures and thus the morphodynamics decreased significantly, especially in the basins of Tittmoning and Freilassing. The riverbed survey carried out in spring 2023 showed a positive bedload balance over the entire river stretch for the first time. Between 2019 and spring 2023, the bedload storage of the riverbed increased by approx. 65,000 m³/year. Hydrologically, the years from 2019 to 2022 were somewhat drier than the long-term average, but in terms of bedload transport capacity, they corresponded to the average of the last 70 years. With the positive bedload balance, this leads to the conclusion that the bedload input from the catchment area has increased significantly. Together with the increased bedload supply, based on the Water Management Framework Study Salzach, implemented measures like a ramp in the basin of Freilassing, a loose riprap in the Laufener Enge and self-dynamic widening areas positively influence the bed development.