Investigators:

• Dr. Jonas Schaper, Eberhard Karls University Tuebingen
• Manuel Dörrich, Eberhard Karls University Tuebingen

In terms of quantity, wastewater from urban water management infrastructure is the main pathway for organic trace substances such as pharmaceuticals and pathogenic germs such as Cryptosporidium parvum to enter watercourses. In addition to treated wastewater from municipal sewage treatment plants, so-called mixed water overflows, i.e. a mixture of untreated wastewater and rainwater, carry considerable loads of these substances into watercourses during heavy rainfall events and thus lead to a deterioration in the hygienic and chemical water quality. To counteract this, rainwater can be temporarily stored in decentralised, blue-green infrastructures such as rainwater retention basins and mixed water in rainwater overflow basins (RÜB) before it enters watercourses directly or indirectly via a sewage treatment plant. However, often neither the temporal dynamics of the water volumes that enter watercourses via different input paths during a heavy rainfall event nor the substance concentrations are known. The aim of this project is therefore i) to develop a method that makes it possible to allocate the water volumes and pollutant loads in urban watercourses to their various input paths with high temporal resolution and ii) to investigate the influence of decentralised blue-green infrastructure, RÜB and the fourth purification stage on the loads of germs and trace substances in the Tübingen Ammer. With the use of measured time series of sum parameters such as turbidity and electrical conductivity and continuous flow measurements at RÜB, which will be available nationwide in the future as part of the ‘Measuring at RÜB’ decree, a process-based transport model is to be developed that calculates bathing water quality and trace substance concentrations as a continuous function of time. At the same time, trace substances contained in the river water are to be allocated to their various urban sources using a ‘chemical fingerprint’ method. It is expected that the combination of both methods will significantly reduce the uncertainty of source and load estimation and allow practical questions to be answered, also with regard to expected climatic changes. In the longer term, the modelling approach should enable continuous prediction of hygienic water quality in urban rivers and thus promote biodiversity, human well-being and sustainable management of urban watercourses.

The project is funded by the Baden-Württemberg Stiftung.