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.
1. Rätsep, A., Liblik, V. Technogenic waterflows generated by oil shale mining: impact on Purtse catchment rivers // Oil Shale. 2000. Vol. 17, No. 2. P. 95–112.
2. Rätsep, A., Liblik, V. Impact of oil shale mining and mine closures on hydrological conditions of north-east Estonian rivers // Oil Shale. 2004. Vol.21, No. 2. P. 137–148.
3. Reinsalu, E., Valgma, I., Lind, H., Sokman, K. Technogenic water in closed oil shale mines // Oil Shale. 2006. Vol. 23, No. 1. P. 15–28
4. The Viru–Peipsi Catchment Area Management Plan. Assessment of the State of Surface Water Bodies and Groundwater / E. Andersmaa, P. Marksoo (Eds.). Tallinn: Estonian Environment Information Centre, 2004 [in Estonian, in English].
5. Reserve of Groundwater in USSR. Vol. 4. Baltic region, Estonia / M. Protaseva., T. Eipre (Eds.). Leningrad: Gidrometizdat, 1992 [in Russian].
6. Burnett, A. D., Watson, I. Hydrology an Environmental Approach. – New York, 1995.
7. Rätsep, A. Impact of oil shale mine closures on hydrological conditions of North–East Estonian rivers / V. Liblik, J-M. Punnng (Eds.). Publ. Inst. Ecol. Vol. 9. Tallinn, 2005. P. 53–63 [in Estonian, summary in English].
8. Järvekülg, A. Estonian Rivers. – Tartu, 2001 [in Estonian, summary in English].
9. Kattai, V., Saarde, T., Savitski, L. Estonian Oil Shale: Geology, Resources, Mining Conditions. – Tallinn: Geological Survey of Estonia, 2000 [in Estonian].
10. Arukaevu, A. Official Register of the Rivers, Streams and Ditches in Estonian SSR: verified 30.08.82. – Tallinn: Valgus, 1986 [in Estonian].
11. Rätsep, A., Liblik, V. The influence of polluted water flows on hydrological and hydrochemical conditions of Purtse catchment rivers, NE Estonia // Nordic Hydrology. 2001. Vol. 32, No. 3. P. 215–226.
12. Erg, K., Raukas, A., Kink, H. Groundwater state in oil shale region // Keskkonnatehnika (Environmental Technics). 2002. No. 4. P. 39–40 [in Estonian].
13. Savitski, L., Savva V. Prediction of the hydrogeological changes in the oil shale mining area // Annual of the Geological Survey of Estonia. 2001. P. 106–110 [in Estonian].
14. Yearbook of the Ida-Viru County / B. Uustal (Ed.). Ida-Viru County Government, Jõhvi, 1999 [in Estonian].
15. Jaagus, J. About precipitation regime of North-East Estonia // Natural Condition of Kurtna Lakes System and Its Evolution. I / M. Ilomets (comp.). Tallinn: Valgus, 1987. P. 68–71 [in Estonian].
16. Soovik, E.How the freshet deliquesces? How much water infiltrate to the soil? // Eesti Loodus (Estonian Nature). 2001. No. 4. P. 164–165 [in Estonian].
17. Reinsalu, E. Changes in mine dewatering after the closure of exhausted oil shale mines // Oil Shale. 2005. Vol. 22, No 3. P. 261–274.
18. Eesti Põlevkivi Ltd (2006). Personal contacts.
19. Jaagus, J. Climate Change Tendencies in Estonia in Relation with Changes in Atmospheric Circulation During the Second Half of the 20th Century // Studies on Climate of Estonia / J. Jaagus (Ed.). Tartu: Publicationes Instituti Geographici Universitatis Tartuensis. 93. Tartu, 2004. P. 62–79 [in Estonian, summary in English].