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The sediments of the artificial Urft reservoir preserve a century of environmental information due to undisturbed sedimentation conditions. The Urft reservoir is located in the Eifel Mountains in western Germany and was built between 1900 and 1905. At the time of its construction, the Urft reservoir was the largest reservoir (45.51 million m³) and drove, with 12 MW, the most powerful water storage power plant in Europe. During construction works in November 2020, the reservoir was nearly completely drained. This offered the unique possibility to analyse the sediment volume and the composition deposited during the last 115 years.We used high resolution maps with a scale of 1:1,000 from 1898 which were compiled to calculate the original storage volume of the reservoir. To assess the present-day surface, the entire lake area was photogrammetrically surveyed using an Unmanned Aerial Vehicle (UAV). Additionally, 10 drill cores were retrieved in 2020 to quantify the anthropogenic influence on the sediments in the form of mining-induced sediment-bound pollutants (e.g., heavy metals) and to relate this to the history of use in the catchment area. Furthermore, microplastics were studied in the sediments. To derive the sediment ages, a detailed Cs-137 chronology was created for one of the cores.In summer 2021, the northern Eifel Mountains were impacted by a catastrophic flooding event, resulting in massive destructions in the catchment of the Urft and strong relocation of sediments in the floodplain. To assess these geomorphologic changes in the Urft reservoir, the water level was lowered again in December 2021. Consequently, an additional digital elevation model was produced by UAV surveying. Furthermore, additional sediment cores were taken to get information on changes in the sediment composition due to the flood event. In the upper part of the reservoir, up to 30 cm of sediments were deposited in summer 2021 while channels below the water surface experienced strong modifications.

Extreme precipitation and discharge between July 13th and 16th 2021 caused serious flooding with bank erosion, including damages to infrastructure and buildings nearby the Eifel mountain region. Especially the small town of Stolberg and Eschweiler in the Inde River catchment were heavily affected. On-site investigation along the Inde River and its tributary, the Vichtbach creek, after the flood event show that mainly coarse sediments were remobilized and accumulated in the upper and middle reaches. The water masses mobilized not only sediments including gravel but also large objects like broken down trees and cars. In contrast, silty sediments were deposited in the lower reaches.The Stolberg region is a former mining area with related industries resulting in contaminated soils and tailings close to the floodplains (Esser et al. 2020). Therefore, our investigations also focus on pollution by sediment-bound heavy metals and their distribution in the floodplains before and after this event. Flood sediment samples were taken immediately after the extreme flood event. Based on the results of flood-related pollution monitoring, conducted between 2016 and 2019 (Esser, 2020), the impact of the extreme event in July can be evaluated. During the July flood event, an exceptional amount of pollutants was remobilized. In addition to an increase in pollutants on the modern floodplain, wider areas of older and higher floodplains (Altauen) were also affected.Esser, V. (2020): Untersuchungen zur fluvialen Morphodynamik und zur rezenten Schadstoffausbreitung in Flusssystemen - Beispiele aus der Grenzregion Belgien, Niederlande und Deutschland. PhD-Thesis, RWTH Aachen University.Esser, V., Buchty-Lemke, M., Schulte, P., Podzun, L.S., Lehmkuhl, F. (2020): Signatures of recent pollution profiles in comparable Central European rivers - Examples from the International River Basin District Meuse. Catena 193: 104646. https://doi.org/10.1016/j.catena.2020.104646