The Pühajõgi River runoff components (infiltration, interflow, groundwater recharge) and human impact (discharge of mine water and municipal wastewater) have been studied during three periods (1945–1963; 1978–1990; 2000–2003). This study characterises different hydrological periods: natural state of the river, influence of intensive mining and closing down of mines. The basic balance schemes based on available data have been worked out by linear regression calculations. The collected data is annual and gives a general overview.
The study shows that mine water exerts a significant impact on the river runoff and also confirms that human impact has considerably changed the average runoff of the Pühajõgi River after the 1960’s. It was established that the average runoff from the river catchment area enlarged by almost 24%, compared with the average natural surface runoff. During the period when oil shale mines were being closed, the average surface runoff of the Pühajõgi River decreased by more than 38% compared to that of the oil shale mining period. However, the annual amount of precipitation has continued to increase within all observed periods.
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