Wpływ zrzutów wód kopalnianych na odpływ rzek Górnośląskiego Zagłębia Węglowego

Abstract

Mining activity is an important fact or that modifies the outflow of surface water in the area of the Upper Silesian Coal Basin. At the peak period of coal mining in the USCB, there were 83 points of discharging mine water from hard coal mines to the surface hydrographic network. Currently, in this area there are 64 discharge points: 23 in the Polish and 8 in the Czech part of the Odra basin, and 33 in the Vistula basin. The following rivers are the major ‘receivers’ of the discharged mine water: the Odra, the Ruda with the Nacyna, the Bierawka, the Kłodnica with the Bytomka, the Czarna Przemsza, the Pogoria, the Brynica, the Biała Przemsza with the Bobrek, the Przemsza, the Mleczna, the Gostynia and the Vistula. In the period of 1967– 2013, on average 10.39 m3∙s–1 of the mine water coming from the drainage of the hard coal mines in the USCB was discharged to the rivers; 2.46 m3∙s–1 of which was discharged to the Odra, whereas 7.94 m3∙s–1 to the Vistula. The volume of the discharged mine water reached its maximum in the years of 1985–1988. The average volume of the discharged mine water at that time was 14.19 m3∙s–1; 11.03 m3∙s–1 of which was discharged to the Vistula basin, and – 3.16 m3∙s–1 to the Odra basin. The process of restructuring the mining industry initiated in 1989 resulted in a systematic reduction of the volume of the discharged mine water. The quantity of the discharged mine water decreased by 26% in relation to the peak period of the discharge in the years of 1977–1989. The catchment of the Bytomka is an exception, since there was an increase in the volume of the discharged mine water. The largest volume of the mine water was discharged into the Przemsza basin (6.66 m3∙s–1 on average). In the Odra basin, the greatest amount of the mine water was discharged to the Kłodnica. Its mean volume amounted to 1.05 m3∙s–1. The greatest portion of mine water in the flow was characteristic of the Brynica in Czeladź, where the average portion of mine water in SNQ was 61%, whereas in SSQ – 43%. Periodically, as much as 100% portion of mine water in the average annual low flow was recorded, i.e. in dry periods and during the maximum intake of water from ‘Kozłowa Góra’ reservoir, which is located above this section. The river flow consisted merely of mine water. A big portion of mine water is also characteristic of the Biała Przemsza, wherein mine water amounts to more than 50% of the average annual low flow, and accounts for 46% of the average annual flow. In the case of the Mleczna, the Gostynia, the Przemsza, the Pogoria, the Brynica (Szabelnia), the Bytomki and the Vistula (Pustynia), the volume of mine water in the average annual low and medium flows amounts to over 20%. The lowest portion of mine water, i.e. not exceeding 10% in SNQR and SQR, is characteristic of: the Vistula in Jawiszowice and Nowy Bieruń, the Czarna Przemsza in the cross section of the Radocha, and the Odra in the cross-sections of Krzyżanowice and Miedonia. The research into the impact of mine water on the runoff of the rivers carried out in the 1980s by, among others, A.T. Jankowski (1986, 1988), S. Czaja (1988, 1999), S. Czaja and A.T. Jankowski (1986, 1991b, 1992, 1993), J. Włodarczyk and L. Ośródka (1988), I. Hołda and L. Ośródka (1989), I. Hołda and M. Wojtylak (1991) revealed that the river flows increased as a result of the discharge of mine water into the local water system. In the flows of, among others, the Brynica, the Przemsza, the Gostynia, the Mleczna, the Bytomka, the Kłodnica and the Szotkówka generally growing trends were observed, especially in the 1970s. The process of stabilization took place in the next decade. The re-searchers observed that the impact of hydrometeorological factors on the runoff regime of these rivers was constantly decreasing while the portion of other waters in the outflow was increasing. What can illustrate the situation is the example of the Szotkówka, which was the largest receiver of other waters at that time – their portion in the runoff amounted to 66% (Włodarczyk, Ośródka, 1988; Hołda, Ośródka, 1989). The prognosis by A.T. Jankowski (1986) for an increase in the volume of mine water discharged to the Szotkówka turned out to be wrong, since as the result of the restructuring of the gas industry the volume of mine water decreased, and thus the flows of the Szotkówka ‘returned’ to the values from the period before their increase in the early 1970s. The prognosis from the 1980s also assumed an increase in the volume of mine water discharged into the catchments of the Brynica, the Czarna Przemsza and the Biała Przemsza by about 0.6 m3∙s–1. According to S. Czaja and A.T. Jankowski (1991), it was not to bring about an increase in the overall volume of other waters in the river water, due to the cessation of dewatering zinc and lead ore mines. The closure of mines and the reduction of coal mining resulted in the reduction of the volume of the discharged mine water. In the Vistula basin this decrease equalled 25%, whereas in the Odra basin it was 30% in comparison to the peak period of coal mining in the years of 1977–1989. A significant change in the flows, which can be associated with the reduction of the discharge of underground water, took place within the Pogoria catchment. The volume of the flow evidently decreased in 1989, i.e. at the very beginning of the restructuring period. At that time, the discharge of mine water was reduced by half. This resulted in the decrease of the annual NQR and SNQR in the years of 1990–2013. In turn, the drop of the annual average flows, which may be correlated with a further decrease in the volume of the discharged underground water, has been observed since the late 90s of the 20th century. In each of the analyzed catchments in the Odra basin, the annual low flows (NQR) decreased. In the Vistula basin, downward and statistically significant trends were detected in 10 catchments. Upward trends in the course of annual low flows occurred only in three water gauges: Gostynia – Bojszowy, Brynica – Namiarki and Czeladź. In four water gauges: Wisła – Skoczów, Mleczna – Bieruń Stary, Czarna Przemsza – Przeczyce, Biała Przemsza – Niwka, no statistically significant NQR trend developed. A decrease in the average annual low flow rates (SNQR) was also observed in 8 catchments in the Odra basin. A lack of trend was noticed in the case of the Odra (cross-sections: Chałupki, Krzyżanowice and Miedonia) and the Bierawka. In the Vistula basin, downward trends in the average annual low flows were detected in 10 catchments. An upward trend was noticed in the catchments of the Vistula (Jawiszowice), the Gostynia and the Brynica (Namiarki and Czeladź). The trend did not emerge in the catchments of the Mleczna and the Czarna Przemsza in Przeczyce. In the multi-year course of the average annual flows, no trends in the catchment areas of the Odra, the Piotrówka, the Bierawka, the Gostynia and the Vistula (Skoczów and Pustynia) developed. An increase of the average annual flow was observed in the case of the Brynica (Namiarki and Czeladź). In the analyzed period, the average annual flows in 17 catchments were characterized by a statistically significant downward trend. What is the major cause for the detected trends are anthropogenic factors, and among them – discharging mine water into the rivers. Paradoxically, the lack of trend in some water gauges may be the effect of anthropogenic factors as well. Such situations arose in the catchments wherein a decrease in precipitation and an increased intake of water were observed, and these were balanced by a greater inflow of other water, including mine water. What is a characteristic feature of the course of the runoff in the rivers that were the receivers of mine water, in the case of which downward trends were noticed, is an evident decline of the values of NQR, SNQR and SQR from the beginning of the 70s to the end of the 80s of the 20th century, whereas the values reached the maximum in the mid 80s. In the other catchments that were not affected by discharged mine water, the period of 1982–1992 was noticeable because of a conspicuous decrease of the flow values. The change point analysis indicated that the drop in the values of the flow is dominant in the studied catchments. An increase in the flows was recorded only in 7 cases. The observed increase of the flows is mainly conditioned by anthropogenic factors, such as: mine water discharge, industrial sewage discharge, or cessation of water intake. In turn, the declining values of the flow in the 1980s were conditioned by climatic factors, whereas in the 90s of the 20th century and at the beginning of the 21st century they were primarily caused by the reduction of the quantity of discharged industrial wastes, including mine water. The change points of the average annual runoff coefficient α identified in 1999 and 2000 in water gauges: the Przemsza – Jeleń and the Vistula – Pustynia, that is wherein the total volume of mine water in the Vistula basin is balanced, confirm the declining portion of mine water in the runoff. Addressing the question whether in the multi-year course of low, medium annual low and medium flows reflects merely the result of the discharge of mine water, it can be stated that only in the water gauge of Kłodnica – Kłodnica the increase in the runoff is associated with the increased volume of the discharged mine water. However, only in the Pogoria the decrease in the runoff may be clearly related to the reduction in its volume. In the catchments that are the major mine water receivers, the specific runoff reaches the values that are observed in the catchments of mountain rivers. The runoff is clearly disturbed and shaped mainly by anthropogenic factors. This is confirmed by the high values of the runoff coefficient (α), which in the catchments of the Bytomka, the Kłodnica (Gliwice), the Bierawka, the Szotkówka and the Pogoria reaches over 60%. This is the evidence of a large portion of ‘other water’, including mine water, in their runoff. To analyze the changes in the annual hydrological cycle, also the concentration ratio GMO was used. Research into the variability of the regime of rivers (GZW) at the end of the 20th century was carried out, among others, by S. Czaja (1999), who observed that in many rivers the portion of other water stabilized at the level significantly exceeding 50% of the runoff of the rivers, which led to strengthening the changes of their regime. In the Katowice conurbation, a new type of the river regime was established, (the regime was outstandingly equalized, and had an anthropogenic-rainwater- snow supply). It was characterized by high and balanced low and medium flows and a predominance of the supply of water of anthropogenic origin, including mine water (Czaja, 1999). This has been also confirmed by the research carried out by me. The lowest average values of GMO, often reaching its lower limit, occurred in the catchments that are the major receivers of mine water: the Pogoria, the Biała Przemsza, the Przemsza, the Bytomka, the Brynica (Szabelnia), the Bobrek and the Nacyna. This indicates that the monthly average flows of these rivers are very balanced. In the other catchments that are also the receivers of mine water, the values of GMO indicate that these catchments are characterized by a more concentrated runoff in the annual cycle, and that an increase of the runoff in the spring period is more conspicuous.They are significantly overloaded with mine water discharges, nevertheless, the decisive role in shaping their regime is performed by climatic factors, which can be attested. The largest rivers with a low portion of mine water in the course of the monthly average flow are characterised by a conspicuous two-part period of an increased runoff and low runoffs in autumn. Mine water does not induce the change in the regime of these rivers, or in the balance of the runoff during the year. The study showed that the decreasing portion of mine water and other sewage re-increases the runoff variation during the year. This situation is developing rather slowly. It may be observed for the time being in small catchments of, e.g. the Pogoria or the Biała. It may be anticipated that the further limitation of the mine water discharge, resulting from the planned restructuring activities in the coal industry, will bring about an increasingly greater variability of the runoff of the rivers. In the following decades, a complete cessation of dewatering of hard coal mines will result in a less balanced outflow, whereas its variability in the hydrological cycle will be once again influenced in a greater and greater degree by climatic factors. Other effects of coal mining that manifest in the form of changes in the river network, the course of watersheds, changes in water reservoirs, and which were indicated, among others, by A.T. Jankowski (1986) and S. Czaja (1999), have a long-lasting and partly irreversible character. These changes will continue to occur especially in the areas where coal extraction is done with the method of mine collapse. Once this problem was acknowledged, more and more renaturization projects in the river valleys have been launched, which may be illustrated by an example of the Szarlejka river valley, where coal mining over many centuries resulted in a complete transformation of the river valley. In 2012 renaturization works were made at the most dramatically transformed section of the river (Absalon, Matysik, 2009; Matysik, Absalon, 2012). The results obtained in this work and the observed regularity may be also utilized in the case of starting new hard coal mines or mines producing other mineral resources the extraction of which involves dewatering mine workings and discharging mine water to a hydrographic network. While making assessments of the impact of these projects on the environment, the observed influence, related to mine water discharge, on water circulation in the catchment may be taken into consideration for the purpose of the rational water management.