FloodRisk: Earthquakes, uplift, and long-term liabilities – risk minimisation during mine flooding

Due to the cessation of coal mining in Germany, mine water management in the former coal districts is subject to change and of environmental and economic significance. Since there is no technical need to drain the abandoned coal mines, mine water levels rise. As a result, subsurface rock pore pressures rise changing the subsurface effective stress regime. This may induce local ground movements and activate mining-related and natural fault zones. In order to develop a better understanding of the processes and their interaction, FloodRisk applies an interdisciplinary approach involving geological, geomechanical, geodetic, and geophysical methods. For this purpose, former German coal districts in the Saarland, Ruhr area, and Ibbenbüren serve as suitable study areas. Based on a geological 3D subsurface model complemented by petrophysical (porosity and permeability) and structural data (fracture network characterization), geomechanical properties such as slip and dilation tendencies of faults were calculated. These data give insights into the expected fault behaviour under assumed stress conditions and provide a basis for the localisation of suitable areas for soil gas measurements (222Rn, 220Rn, CO2, O2, H2, S, CH4) using recently developed economic sensors. Simultaneously, seismic events and ground movements are continuously monitored using seismic network, GNSS, Nivellement, and InSAR data and subsequently compared with the evolution of mine water levels. These multidisciplinary observations will be combined in a conceptual model on flood-induced ground movements and seismicity. This enables the deduction of operations for future mine flooding and the establishment of an optimised reservoir management.