Old drainage tunnels – new, innovative water reservoirs? Hydrogeological investigations and modeling for a potential analysis

Mineral resources and water have been uniquely interwoven in the Harz Mountains region. For centuries, the waters of the Harz powered mine drainage systems and were channeled through an ingenious network of drainage tunnels. Today, the Harz region has great importance for supra-regional drinking water supply. With climate change, extreme hydro-meteorological events are putting increasing pressure on existing water infrastructures. The Ernst-August-Stollen (EAS), a 40 km long drainage tunnel in the Upper Harz, offers potential for underground storage and other water management uses. In the EAGruMo project (Ernst-August-Grubenwassermonitoring) we aim to assess this potential by understanding the hydrogeological system of the EAS, estimating water residence times in the Paleozoic fractured aquifers, and quantifying water flow rates. Methodologically, we employ stable water isotopes, conduct tracer tests, and perform hydrological investigations (field studies, modeling) to gain a deeper process understanding of water dynamics. These hydrogeological investigations are complemented by the continuous monitoring of water quality and quantity, in order to evaluate the suitability of the tunnel system for water management uses, taking into account local geological and hydraulic conditions. The insights will not only benefit the Harz region but can serve as a model for other post-mining regions facing similar water management challenges under changing climatic conditions.