Hydrological Processes and Water Management in Urban Areas (Proceedings of the Duisberg Symposium, April 1988). IAHS Publ. no. 198, 1990.

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1 Hydrological Processes and Water Management in Urban Areas (Proceedings of the Duisberg Symposium, April 1988). IAHS Publ. no. 198, SURFACE AND GROUNDWATER USE IN THE URBAN AREA OF ZAGREB S. Tedeschi Civil Engineering Faculty, Zagreb, Yugoslavia ABSTRACT Water supply of the city of Zagreb uses groundwater, which is renewed from the surface and through infiltration of the Sava River water. Gradual growth of the urban area reduces the pumping well protection zones and periodically results in pollution of pumping wells. Sava River water quality deteriorates due to untreated waste water discharges. Further use of surface and groundwater calls for extensive remedial measures. INTRODUCTION The city of Zagreb, with a population of , lies on the alluvium of the Sava River. Groundwater from the aquifer which is recharged by good quality Sava water, began to be used in 1876, when construction of a water supply system commenced. This system is still developing simultaneously with the urbanization process. Water quality control in the water supply system was carried out (according to Bradjic-Sabo, 1978) from 1879 in its physical and chemical aspects, and from 1888 in its bacteriological aspect. Although first written traces about the construction of a sewage may be found in the rulings of the City authorities in 1653, construction of today's sewage system commenced, (according to Svilicie, 1981), in The sewage system of Zagreb carries storm and waste water and discharges it into the Sava River. At the beginning of this century, the Sava was a clean river and was suitable for water sports, bathing and fishing in the whole of Zagreb. IMPACT OF URBANIZATION ON SURFACE AND GROUND WATER USE Aquifers of the Zagreb area are found along both the left and the right bank of the Sava River. Thickness of the water-bearing sand and gravel stratum, according to Roudnicky (1978), is from several to a hundred metres. Above it, a surface layer (mud, loam, clay), 1 to 8 m thick, is found. The aquifer is recharged to a small extent by vertical percolation through the soil, but predominantly by horizontal infiltration from The Sava. The pumping well protection zone was established, according to Roudnicky (1978), when the first pumping well began to be constructed in In the sanitary protection zone, a strict sanitary regime was described and development as well as pit excavation was prohibited. The first pumping well was at a large distance from the city, which at that time had inhabitants. With the gradual growth of the city, and particularly after the First World War, The city's development areas widened also, thus constricting the sanitary zones of pumping wells. As 95

2 S. Tedeschi an illustration, Roudnicky (1978) states that in 1907 the construction of an electric power station for the city of Zagreb was authorized on the protection zone of the pumping well. When coal was substituted with petroleum in the power station, an oil storage facility was constructed only 80 to 100 m from the pumping well in The city development caused the deterioration of the groundwater quality in a variety of ways, of which only a few are mentioned: deep foundations of tall buildings are located in the aquifer, perforating the protective surface layer, most of the city's sewer system lies under the covering layer. The system carries storm, domestic and industrial waste water, so damaging waste matter infiltrates into the aquifer, in the development of the city, sand and gravel from aquifers was used. Abandoned, unkept gravel pits were often used for the deposition of waste matter, and are sources of pollutants in the soil. Urban development unfavorably affected the Sava River water quality. The Sava River water is already of poor quality when entering the Zagreb area as a consequence of untreated waste water discharge in communities and industries up-river. It should be mentioned that, according to Kopia (1986), the city authorities in 1911 protested to a competent Ministry against pollution of the Sava water by waste water from coal mines (Trbovlje). After a series of repeated protests, regulations were issued in 1923 ordering coal mine waste water treatment, regulations which have not yet been implemented. In the Zagreb area, untreated waste water from industries and suburban communities, as well as storm water, flow into the Sava River up-river from the pumping wells. Sava River water in the Zagreb area, according to Tedeschi (1978), has a high load of suspended organic and inorganic matter, and a low oxygen content, 50-60% saturation. Consequent to such water management, the water supply of the city has been seriously disturbed. In 1984, Siktar and Vuckoviâ (1985) report that of 13 constructed pumping wells, only 8 were in operation because of pollution. This lead to a water deficit of 18% in the water supply system of the urban area. Groundwater pollution sources were industrial facilities in the vicinity of the pumping wells. Siktar and Vuckoviâ (1985) cite that the concentrations of trichlorineethylene and tetrachlorineethylene in groundwater exceed the allowed concentrations in the WHO recommendations. Due to a significant self-purification process in the aquifer, the impact of the untreated Sava water is much less. Changes in the water quality are observed at locations near The Sava River, while, according to investigations of Kubelka and others (1985), the effect of polluted Sava water was not found in pumping wells 600 metres from the Sava River. However, urbanization processes also affected the hydrological regime of the Sava River. Namely, due to anti-erosion works up-river, the Sava River in the Zagreb area is unsaturated with deposit so it erodes its own bed. Consequent to intensified water pumping from unpolluted wells, the groundwater level has dropped, resulting in a reduced low water level and, thus, more intense bed erosion. In the Zagreb area, according to Bonacci and Trninie (1986), the bottom of the Sava River, on a section 44 km long, has declined by 0.5 to 1 m in the last ten years. This water level drop in the Sava and in the water table 96

3 Surface and groundwater use has lead to a water loss in the aquifer of 50x lu iri 00., n m m the period. Due to periodical pollution of particular pumping wells and lower groundwater level in times of unfavourable hydrological conditions, there exists in the Zagreb water supply system a water deficit of approximately 20%, causing troublesome crises, particularly in the higher parts of the city. POSSIBLE REMEDIAL MEASURES Water supply problems in Zagreb, lately becoming a limiting factor for development, are being carefully studied. According to Svel (1982), the existence of sufficient groundwater in the Zagreb area has been evaluated, and these reserves may be increased by the construction of impoundments on the Sava River, permanently raising the Sava water level and increasing the infiltration into the underground. As the Sava River changes from a mountain to a lowland river in the Zagreb area, a planned impoundment lake might be used for electric energy production and for recreational purposes. One of the essential prerequisites for the construction of multipurpose impoundments however is suitable water quality in the Sava. The construction of water steps on the Sava River will cause changes in the habitat of the existing ecosystem due to morphological changes and changes of the flow regime. The existing river flow velocity, m/s, would fall to m/s, leading to the sedimentation of organic and inorganic matter in the impoundments. The present Sava River water quality would, in conjunction with the intense build-up of sediment organic matter, lead to a further decrease of dissolved oxygen, increase of nutrients, change in ph value, increase of complexing matter capacity, and remobilization of heavy metals ions which are adsorbed on the solid particles in the river bed. Without previous improvement of the Sava water quality, the construction of the impoundments cannot be recommended. The control of waste matter discharged into the Sava is not only necessary in the Zagreb area, but also in the up-river regions. Application of the facilities for communal and industrial waste water treatment before discharge into the Sava and its tributaries is, according to Tedeschi (1982), necessary but inadequate. Other measures are also necessary, namely pollution control at source and the inhibition of solid waste disposal on the river, streams banks and flood plains. Groundwater quality improvement in the Zagreb area calls for the regulation of abandoned gravel pits, which are now lakes with water areas of several tens of hectares. Bottoms and banks of these artificial lakes should be free of deposits sludge and solid waste. Neither untreated waste water, nor storm water which washes off traffic areas in the vicinity of the lakes (parking lots, roads), should be discharged into these lakes. Regulated and controlled lakes may be used for water sports (motorboats excluded) and recreation. The artificial lake Jarun, with a water area of 8 x 10 m, was made into a sports and recreation centre for water sports of the recently organized student games "Universiade 87". Pumping wells, whose protection zone has been significantly reduced by the industrial and 97

4 S. Tedeschi housing development, and which have been periodically out of use due to groundwater pollution during the last years, will probably have to be abandoned. The most common groundwater pollution cause in these sites was the infiltration of waste water from the sewer system. Sewer network repair, consisting of the construction of permanently safe, impermeable ducts, is not only expensive but also insufficiently safe, so these pumping wells may be used in the future as sources of industrial water and excluded from the public water supply system of the city. The loss of existing pumping wells may be compensated in two ways: by the construction of impoundments on the Sava and by opening new pumping wells in more protected parts of the Sava alluvium. According to suppositions to date, Svel (1982) quotes that, by the construction of impoundments on the Sava, the infiltration of river water into the underground would increase, increasing pumping well capacities by approximately 10%. Meanwhile research work is been carried out with the aim of opening new pumping wells on the remaining area of the aquifer not yet endangered by urbanization. First results show satisfactory extent and good water quality. However, it should be noted that this last zone is not completely protected from urbanization effects. Namely, in the wider area, the city's refuse dump, the relief highway, railway lines and the airport are located. In the case of further groundwater quality deterioration, there are two solutions for the water supply of the city: the construction of very efficient treatment facilities and the construction of the regional water supply system, which could convey water from other watersheds several tens of kilometers away. CONCLUSION The city of Zagreb is a typical example of mismanagement of water resources quality. A city actually "standing" on groundwater, with aquifer capacity sufficient for a much larger consumer, might be brought into a situation where water should be conveyed from distant areas. For decades, the protection zones of pumping wells have been reduced by the development of new urban areas, with an ever present false dilemma: "The city or water". Of course, all the possibilities are not yet lost. Plans for remedial measures exist, the realization of which would ensure a harmonious development of the city and a steady water supply, a necessary condition for the life of the present and the future city. These measures, however, call for significant financial means, much larger than those that would have necessary had the city been taking account of water for its survival. REFERENCES Bonnaci O. Trninie D Promjene hidroloskog re ima Save u okolici Zagreba (The Sava Hydrological Changes in the Zagreb Area), Zagreba ka vodoprivreda, 17, Brajdi -Sabo V Kvaliteta vode iz vodovoda kroz 100 godina (Water Quality in the Water Supply system During a 100 Years), In: Vodovod grada Zagreba 98

5 Surface and groundwater use , D. Magdiô (éd.), Tehni kaknjiga. Zagreb, pp Kopic J Peticija protiv Trbovljanskih ugljenokopa (The Petition Against the Trbovlje Coal Mines), Zagreba ka vodoprivreda, 18, Kubelka V. Branica M. Bis an J Program istra nih radova potrebnih za utvrdjivanje radioloskog stanja i kontrolu padzemne vode i vode rijeke Save (1979/80, Sava I), Istra ivanje utjecaja NE Krsko na radioaktivno zagadjenje podzemnih voda i vode rijeke Save (1981/83, Sava II), (Programme of Research Work Necessary for the Determination of the Radiological State and Groundwater and the Sava Water Control (...), Investigation of the NE Krsko Impact on the Pollution of Groundwater and the Sava River Water), Institut "Rudjer Boskovic", Zagreb, 75 pp. Roudnicky M Zastitna podru ja i briga o zastiti crpilista (Protection Areas and Care for Pumping Sites Protection), In: Vodovod grada Zagreba , D. Magdia (éd.), Tehni ka knjiga, Zagreb, pp Roudnicky M Istrazni radovi (Research Works), In: Vodovod grada Zagreba , D. Magdiô (éd.), Tehni ka knjiga, Zagreb, pp Svili iô M Prikaz kanalskog sistema grada Zagreba, Zbornik savjetovanja: Akumuliranje, tretman. transport i evakuacija voda (A Review of the City of Zagreb Sewer System, Proceedings of the Symposium Accumulation, Treatment, Transportation and Evacuation of Water), 28-30, October 1981, Subotica, pp Siktar S. Vu Koviâ B. Zagadjivanje podzemnih voda Zagreba i problemi zastite (Groundwater Pollution in Zagreb and Protection Problems), Vodoprivreda, 17, Svel B Vodoopskrba grada Zagreba (The City of Zagreb Water Supply), Gradjevinar,34, Tedeschi S Zastita voda na podru ju grada Zagreba (Water Protection in the City of Zagreb Area), Gradjevinar, 34, Tedeschi S Utjecaj vodnih stepenica u podru ju Zagreba na kvalitet vode rijeke Save, Zbornik savjetovanja; Rijeka Sava - zastita i koristenje voda ("The influence of Water Impoundments in the Zagreb Area on the Sava River Water Quality", Proceedings of the Symposium "The Sava River - Water Protection and Use"), November 10-12, 1987, Zagreb. 99

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