Trends bei Wasserständen und mittleren Abflüssen in der Donau östlich von Wien und donaunahen Grundwasserständen: Starke Effekte durch Sohlerosion und Klimawandel

In the free-flowing reach of the Danube River east of Vienna, downstream of the hydropower plant Freudenau, there is a bedload deficit, which is compensated only in part by artificial gravel supply, thus the river reach is still incising. Incision rates for the period 1996/2021 are quantified by hydrographic data and by means of trend analysis (Mann-Kendall-test). In addition, mean annual groundwater levels of monitoring wells close to the river are investigated. Also these data indicate declining tendencies (mostly between −2 and −3 cm/yr). There is also a significant hydrological trend, which is obviously a consequence of climate change. For the annual average discharges and the period 1996/2023 a significant (α = 10%, two-tailed test) declining trend of −10.9 (m³/s)/a can be detected. This hydrological factor alone is associated with a decline of water levels of about −1.4 cm/a, and this effect overlays and further increases the morphological based incision rates. Both processes entail serious environmental problems for the floodplain landscape, and also the use of groundwater resources is affected. In context of bed degradation, which could be easily prevented (by a complete bed load management), it seems that public interest (according to the Austrian Water Act) is affected.