Supplementary Material

Abstract of the study: 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 environemental 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 0.115 m³/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 0.0874 m³/s during winter for achieving quasii-natural flow regime conditions. The approaches enable long-term low-flow analyses and environmental flow assessments in mining impacted catchments

Supplementary Material: Figure S1: Study site. (a) Catchment boundaries and streamflow network. b) Relief. (c) Geology. (d) Soils. Figure S2: Daily Qmean rates at all investigated gauges ((a), (c)-(h)) and (b) Qmean rates at the gauge Frankleben for four different time periods with different intensities of anthropogenic impacts. Table S1: Overview of the used PCD, each theoretical approach, and the results for each investigated catchment. Following PCD groups were used: Land use and vegetation, mean discharge data, meteorological parameters, soil and geology, form indices, relief derivations, and recession parameters. Table S2: EMC of the FDCS method at the gauge Frankleben, respective management conditions, and applied percentages of natural annual Qmean. Table S3: Estimated monthly baseflow rates and BFI values at all seven investigated gauges. Figure S3: (a) Monthly Qmean, (b) calculated monthly QB rates, and (c) calculated monthly BFI at all investigated gauges. Table S4: Measured Qmean rates [m³/s], regionalized QBmean rates [m³/s], and regionalized BFI values at the gauge Frankleben for individual time periods with different intensities of anthropogenic impacts. Table S5: Monthly EFR of the time period from Jul 1993 to Dec 2017 (post mining era) at the gauge Frankleben calculated with (a) regionalized low-flow index approach; (b) 7Q10 method; (c) TM method; (d) FDCS method. Table S6: Flow duration curve data for six different EMC calculated with the FDCS method at the gauge Frankleben. Figure S3: EFR calculated with the FDCS method for three quasi-natural gauges in Central Germany (Stedten, Unterrißdorf, and Zappendorf) and the respective flow duration curves. Percentages of annual Qmean: gauge Stedten: scenario A = 85.9 %, scenario B = 76.0 %, scenario C = 68.3 %, scenario D = 62.1 %, scenario E = 56.8 %, scenario F = 52.2 %; gauge Unterrißdorf: scenario A = 72.9 %, scenario B = 55.9 %, scenario C = 43.6 %, scenario D = 34.1 %, scenario E = 26.4 %, scenario F = 20.2 %; gauge Zappendorf: scenario A = 85.1 %, scenario B = 74.4 %, scenario C
= 65.9 %, scenario D = 59.0 %, scenario E = 53.2 %, scenario F = 48.5
%. Table S7: Monthly EFR and flow duration curve data for six different EMC calculated with FDCS method for three quasi-natural catchments in Central Germany (Stedten, Unterrißdorf, and Zappendorf)