Research

Instrumental water level and discharge measurements in Lower Austria for medium-sized and smaller rivers only date back a little over 100 years. Historical flood statistics are therefore limited in time, which seems insufficient, especially in times of climate change with predicted more frequent and larger extreme floods. For individual rivers, historical floods have been documented and analyzed on the basis of local chronicles and flood marks (see, for example, the work of Heinz Wiesbauer). However, it can be assumed that many documents on historical floods prior to instrumental measurements have not yet been collected and consistently evaluated. The aim of the project is to collect and process information on historical floods in Lower Austria prior to the start of instrumental hydrological recordings. The surveys focus on flood marks, but written sources and historical literature will also be collected and evaluated.

The grayling (Thymallus thymallus) and rainbow trout (Onchorhynchus mykiss), which are key species for the fishing industry, show strong population fluctuations and sometimes unsatisfactorily low stocks in large parts of the Ybbs. In particular, a decline in the grayling population in the middle reaches of the river documented in 2024 and the noticeable decline in rainbow trout raise questions about the causes responsible. The proposed project aims to explain population demographic developments using abiotic descriptors – specifically flow and water temperature. The focus here is on the critical phase of incubation and emergence, a period that has been shown to be of great relevance for the further population development of salmonids (Unfer et al., 2011, Pinter et al., 2025). An additional focus is on the development of cohorts (year classes), i.e. the survival of individual age stages from year to year. The data available for the Ybbs is ideal for these analyses, as in addition to continuous hydrological data, there is a complete seven-year data series (2019–2025) of fish stock data from a district upstream of Amstetten – a unique data basis in the hyporhithral zone that enables well-founded and detailed analyses of reproductive success and cohort development. As part of the interpretation, influencing factors such as water morphology and potential stressors such as predation pressure and interspecies competition should not be ignored. By considering seamless population development, a new basis for future fisheries management steps and considerations is created. This redefines the prerequisites for sustainable and forward-looking management and lays the foundation for further considerations on current problems in fisheries management (status of the huchen population, consequences of climate change, etc.). Such research results are of great importance for this key species in the grayling region, especially in view of the unstable stocks of grayling, which is classified as vulnerable (Wolfram & Mikschi, 2007).

Rivers are important sources of environmental health, economic prosperity and human well-being. For thousands of years, rivers have provided people with food, water for domestic and agricultural use, transport corridors and, more recently, power generation and industrial production. The RiverSpaces project analyses how river spaces are currently used, what uses they accommodate and how they can be designed in the future to maximise the benefits for society and nature. In 5 work packages, river spaces are first delineated and their characteristics described in terms of natural space and socio-economic uses. This data will be combined with socio-economic framework conditions in order to discuss with decision-makers in a case study how river basins should be designed in the future. At the end, the findings will be summarised in order to develop win-win solutions.