Reading the sedimentary archives in the Danube floodplain downstream of Vienna (Austria)

Many human interventions in river systems, e.g., river channelization, hydropower dams, or restoration measures, affect geomorphological and sedimentological settings. Anthropogenic impact can lead to alterations in stream dynamics and sedimentary imbalances, as recorded in the sediments of large riverplains.

In the project “From Romans to the Anthropocene, from Carnuntum to Vienna: An Urban Anthropocene Field Lab” (WWTF ESR20-027) we explore long-term urban and geomorphological transformations within the Danube floodplain between Vienna (Austria) and Bratislava (Slovakia). Combining historical and sedimentological methods, our research focuses on the development of a very old settlement area within the transition zone between eastern and Central Europe.

Extensive river engineering, starting in the 19^th century, was a precondition for Vienna’s development as a residence and metropolis. This includes extensive river training and the construction of flood control structures. After a long period of river engineering and the construction of many hydro-power dams along the upper Danube, around 2000 the local removal of river bank fortifications started and also the restoration of fluvial dynamics primarily within our study area downstream of Vienna, in the free-flowing river section of the Donau-Auen National Park.

Fine overbank deposits record river dynamics through climatic and anthropogenic drivers. Reading the sequence of alluvial deposits allows us to understand the human impact on floodplain morphology. The great advantage of analyzing sedimentary archives is the temporal depth they offer: we can evaluate the conditions prior to river training (~200 years ago), the effects of engineering measures (e.g. river channelization, construction of hydropower stations), and recent restoration measures as well.

The characterization of sediment archives, including sediment dating (radioactive isotopes, OSL, dendrochronology), provides information on major flooding events, changes in the flow regime, and the dynamics of sedimentation. For investigations into sedimentary processes and river morphology downstream of Vienna, it is also necessary to have a look not only at the present state of a trained river but also at the former, near-natural situation of the riverscape. Therefore, comparisons of changing river morphologies before, during, and after the erection of dams and weirs are a requirement.