Long-term baseflow estimation and environmental flow assessment in a mining-impacted catchment in Central Germany

Abstract

Wenzel, J. L., Schmidt, G., Usman, M., Conrad, C., Volk, M.: Long-term baseflow estimation and environmental flow assessment in a mining-impacted catchment in Central Germany. - Hercynia N. F. 54/2 (2021): 103 – 143.

The local water regime of the small-scale Geisel catchment in Central Germany is vastly impacted by strong lignite-mining activities. Missing knowledge about hydrological regimes and low-flow discharges in this impacted region prevented integrated environmental flow assessments. As a consequence, targeted environmental flows of the lower Geisel usually cannot be achieved. To close this knowledge gap, we present a novel approach for an integrated environmental flow assessment in non-natural catchments using long-term baseflow rates, seen as an approach to environmental flows, and simple hydrological methods. Since baseflow rates cannot be estimated accurately in non-natural catchments, we combine 14 different hydrograph separation methods, statistical regionalization, and numerical catchment descriptors. The long-term baseflow equals 0.28 m³/s from 1981 to 2017 (75.4% of total discharge), and in the post-mining era since 2011, the mean baseflow equals 0.115m³/s (77.2% of total discharge). The combination of hydrograph separation with hydrological regionalization and numerical catchment descriptors reveals new opportunities for describing discharge components in non-natural catchments. Determined environmental flows are similar as achieved by other hydrological methods and can be linked to different intensities of anthropogenic impacts. The environmental flow assessment reveals required additional water amounts of 0.0608 m³/s during summer and 0.0874m³/s during winter for achieving quasi-natural flow regime conditions. The approaches enable long-term low-flow analyses and environmental flow assessments in mining impacted catchments.