Dr. Will Mayes, University of Hull, United Kingdom
Prof. Ülo Mander, University of Tartu
Dr. Julien Tournebize, National Research Institute of Science and Technology for Environment and Agriculture (IRSTEA), Antony, France
Mining activity can change both the runoff regimes and drainage areas of river systems when new mines are opened or closed. Mine water discharge can affect river run-off seasonally or can influence river hydrological regime annually. Current analyses show that the annual mine water discharged to the River Purtse catchment area does not affect its long-term annual as it regime shift appears to be driven primarily by precipitation. Although, the percentage of extra groundwater in the mine water is much higher and effect on the River Pühajõgi is greater.
However, mine water discharge can affect the River Purtse baseflow minima, thus increasing the amount of the run-off during summer months and changes in high water period. During phases of intense mining, summer baseflow is between 53-72% higher than long-term average baseflow in the Purtse catchment, and between 66-92% higher in the smaller Pühajõgi catchment, where the volumetric significance of mine discharges is greater. Also mine water influences high water period behaviour, where the average before-peak period is four days shorter, with a smaller run-off rate, but is usually longer with much higher run-off after the peak period. The reference catchment of the River Keila does not show any significant change in summer baseflow during the study period, suggesting that the changes in the Pühajõgi and Purtse are not controlled by climatic drivers.
The strategic placement of mine water discharge points in positions that minimise flow path changes and minimise the volumetric significance of change in flow in receiving water courses would limit the extent of any impacts. Thus, results of this study can be used for the planning and sustainable management of mining-influenced river catchments.