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In response to increasing concerns about the potential toxicological impacts of (extreme) flood events, scientists from several disciplines have joined to form the interdisciplinary research project named FLOODSEARCH. FLOODSEARCH is one of the recent Pathfinder Projects supported by the German Excellence Initiative via the Exploratory Research Space at RWTH Aachen (ERS). FLOODSEARCH aims to combine methodologies of hydraulic engineering and ecotoxicology in a new interdisciplinary approach to assess the risks associated with the re-mobilisation of particulate bound contaminants often observed after severe flood events. Impacts of extreme flood events and aspects of re-mobilisation of sediment-bound toxic compounds will be characterised and evaluated in controlled experiments fusing flood simulation technologies with biological effects assessment. The overall goal is to establish a novel and more realistic approach towards flood event testing that can be applied to a number of different questions and species. Specifically, model aquatic species such as rainbow trout (Onchorhynchus mykiss) will be exposed to particle-bound contaminants in flood-like conditions in a specifically designed annular flume that permits monitoring of both physical/chemical and biological parameter. Ultimately, this approach will assist to further our understanding of the potential biological risks associated with increasingly frequent extreme flood events, e.g., as a consequence of climate change, by bridging the gap between the physical (re-)mobilisation of contaminants and resulting toxicological impacts on aquatic organisms. Thus, it is the objective of the project to derive relationships between the hydrodynamic parameters such as velocities and turbulences, the parameters associated to sediment transport such as sediment concentration and grain sizes and the biological parameters. [ABSTRACT FROM AUTHOR]

Mass bedload movement is thought to play a key role in initiating stream invertebrate drift during extreme flood events. However, little is known of the importance of the shear of invertebrates from stone surfaces relative to their entrainment along with bed material at different discharges. In particular, it is unclear whether so-called ‘catastrophic drift’ only occurs once mass bedload movement, and hence entrainment of invertebrates, occurs. We investigated the relationship between the mobilisation and transport of bed sediments and the entry ofBaetismayflies into the water column in a laboratory flume. Experiments quantified the percentage ofBaetisdrifting at a range of discharges that mobilised between 0 and 95% of the flume-bed sediments. Control experiments quantified drift losses from sediment fixed to the bed of the flume, such that sediments were immobile even at the highest discharges. Drift losses increased with increasing discharge and velocity in the flume. Sediment mobility contributed significantly to drift (ANCOVA,p<0.001), with consistently greater drift losses in mobile sediment experiments than in those with fixed sediment. The discharge which resulted in a loss of 100% ofBaetisfrom the mobile sediment bed (discharge 30 l s-1) resulted in a loss of approximately 50% of individuals from the fixed bed. Results indicate that once bed sediments are mobilised, entry ofBaetisinto the drift is greater than expected from the shear of animals from stone surfaces alone. Thus, entrainment of animals along with sediment contributes significantly to drift at high flows. This implies that differences in bed stability between sites or streams, or temporal changes in sediment characteristics within a site, could influence patterns of drift. [ABSTRACT FROM AUTHOR]