Water Quality State in the Hydro – System * Danube – Tisza – Danube Dragana Milijašević, Jovana Brankov,Ana Milanović, Geographical institute ”Jovan Cvijić“, Serbian Academy of Sciences and Arts, Belgrade, Serbia Apstract Hydro – system Danube – Tisa – Danube is a unique system of channels for drainage, irrigation, fishing, transport, tourism, water supply of settlements and industry. Channel system runs on about 12 700 km2 between the rivers Danube and Tisa in the north of Serbia (Vojvodina). Total length of channel is 929 km. Water quality examines the Republic Hydrometeorological Service of Serbia. The problem of pollution and protection of surface water must be specially treated, since it is one of the most valuable water resources in the area. The aim of this paper is to analyze existing state of water quality in the Danube – Tisa – Danube hydro–system and suggest measures of protection. Key words:hydro – sistem, Danube – Tisza – Danube, canal, water quality Introduction Small amount of rivers were formed in Vojvodina, because of its plain-like terrain, high air temperature, higher water evaporation, low quantity of rainfall (annually about 600mm) and the length that rainfall passes to the nearest water flows. This deficit is compensated with the abundance of transit waters, which are significantly more present in Vojvodina than in other parts of Serbia. This knowledge should be taken into consideration in the assessment of waterpower importance of rivers in Vojvodina, planning of their protection and the policy of economic development (Bjeljac, Kovačević, Milanović, 2003). Vojvodina, situated in southern part of Pannonian plain, has big water resources in the surface waters of the rivers: the Danube, the Sava and the Tisza, as well as in the developed canal system Danube- Tisza- Danube. The system of canals stretches over about 12 700 km2 between the Danube River and the Tisza River, in the regions of Vojvodina –Bačka and Banat in north Serbia. Disastrous floods and even more frequent droughts in this region have endangered the existence of population for ages. Hydro-land-reclamation measures started in the sixth and the seventh century, but even after 13-14 centuries they have not given the wanting results. In the period from 1958-1976. the reconstruction was made, as well as new canals in the existing system of canals which were made even during the time of Austria-Hungary. Eighty-four bridges were built then- 62 carriageway bridges, 19 railway and 3 pedestrian ones. A dam was raised at Novi Bečej on the Tisza River, as one of the most important constructions. The total length of the canal is 929 km, including new and old canals and tributaries which were partly, or as a whole, integrated into the system of canals. In the canal network there are 51 objects (24 gates, 16 locks, 5 safety gates, 6 pump stations and 180 bridges). The Danube-Tisza-Danube hydro-system enables drainage of 760000 ha in Vojvodina. The greatest success in drainage of Banat was achieved by cutting the watershed between the Tamiš River and the Karaš at Potporanj, by which excess water turned from marshes of Vrsac and ran off into the Danube. The most important drainage canal in Banat are Kikinda`s canal, and Novi Bečej-Botoš-Banatska Palanka, and in Bačka: Bački Petrovac-Karavukovo and Jegrička. (Bjeljac, Radovanović, Milanović, 2004). The canals of the system DTD enable irrigation of 510000 ha. The degree of their use is very small and it is 10%. The reasons for this are: the lack of modern equipment for irrigation, the lack of experts for exploitation of hydro-system, insufficient intensity of agricultural production etc (Stojšic, Bugarski, 1997). Inland navigation is possible on the length of 603,7 km, and in the system of canals there are 14 ports for loading-unloading of the freight (Dukić, 1967). * Paper is a part of the research within the project 146011, supported financially by Ministry of Science and Technological Development of the Republic of Serbia BALWOIS 2010 - Ohrid, Republic of Macedonia - 25, 29 May 2010 1 The most important rivers and the canals of the DTD drainage basin The biggest and the most important river on this area is the Danube which flows through Serbia on the length of 588 km. According to its natural characteristics its flow can be divided into 3 different sectors: Pannonian, Djerdap and Pontic (Gavrilović, Dukić, 2002). The Danube in the Pannonian sector has average fall of the river canal for 0,05 m/ km, the average velocity of the water is 3-4 km/h, and the average discharge is about 3500 m3/s. (Bjeljac, Kovačević, Milanović, 2003). The Tisza River is the largest tributary of the Danube and it flows through Serbia on the length of 164 km (Gavrilović, Dukić, 2002). The Tisza River has very small fall on the middle and the lower part of the basin, in average 4,57 cm/km, which causes increased intensity of lateral erosion and the formation of winding riverbed. In the past it often caused minor or bigger floods in Potisje, and somewhere even- the formation of marshes and spongy ground. Cutting of 136 meanders (23 on our territory) shortened the flow for 453 km or 31,9 %, which caused the increase of river fall and the velocity of its runoff into the Danube. The velocity of the water on the Tisza River is small and it is about 1 m/s. The value of average discharge is 870 m3/s. (Bjeljac, Kovačević, Milanović, 2003). High water level of the Tisza River is in April, because of snow melting from the Carphatians Mouintains, and the lowest water level is in October. During the high water level The Tisa River influences the level of water on the Danube River. Table 1.– Hydro – sistem Danube – Tisza - Danube Canal name Overall length (km) Navigable(km) Begeč – Bogojevo 90,0 90,0 Vrbas – Bezdan 90,0 89,9 Novi Sad – Savino Selo 80,9 80,9 Bajski kanal 39,1 39,1 Odžaci – Sombor 12,7 12,7 Bački Petrovac – Kravukovo 52,0 52,0 Prigrevica - Bezdan 31,7 31,7 Kosančić – Mali Stapar 21,1 21,1 Jegrička 65,4 - Banatska Palanka – Novi Bečej 147,3 147,3 Begej 34,6 34,6 Plovni Begej 31,4 31,4 Stari Begej 37,1 - Kikindski kanal 50,3 32,0 Zlatica 35,0 - Tamiš 116,8 3,0 Karašac 5,8 - Brzava 19,9 - Moravica 17,4 - Rojga 12,6 - Total 929,0 603,7 Other rivers cut their valleys in the river terraces and loess plateaus. Contrary to the Danube and the Tisa which during the whole year have lot of water, smaller rivers dry up during summer or partly turn into bogs, while in spring and in rain seasons significantly rise. It will be mentioned some smaller rivers: the Čik River, the Krivaja River , the Mostonga River, the Zlatica River, the Begej River , the Tamiš River, the Karaš River and the Nera River. The route of the main canal of the hydro-system Danube-Tisza –Danube starts from Bezdan, where large electric sluice gate was constructed, and then it goes in the direction Prigrevica-Srpski Miletić- Savino Selo-Vrbas and it continues until the entry into the Tisza River at Bečej. This part of the hydro- system is known under the name Veliki Bački Canal. Downstream from Novi Bečej, on 62 km from its confluence with the Danube, the Tisza River is dammed with large sluice gate with ship lock. The sluice gate enables gravitational turning of the necessary quantity of water in Banat`s part of the route of the main canal, which then goes into direction Novi Bečej-Jankov kamen-Klek-Botoš (here canal is BALWOIS 2010 - Ohrid, Republic of Macedonia - 25, 29 May 2010 2 cut by the Tamiš River)-Potpotoranj-Banatska Palanka, where canal enters the Danube River. The branches of the main canal were constructed in such way that river canals, bogs and other recesses in the ground are maximally used. That is how the canals of the Mostonga River, the Jegrička Bara, the Zlatica River, the Galacka River, the Stari Begej River, the Tamiš River and the Karaš River were used. The network of the main canal also included already existing canals, whose muddy canals were deepened, as well as canalled flow of the Begej River (Dukić, 1976). Figure 1. Water quality of hidro – system Danube – Tisza – Danube in measuring profiles Irregular and unequal quantity of river water created huge problems during the whole year. In time of maximal water levels, rivers drained, flooded inundation planes and went deep into the areas of low altitudes. This water remained almost during the whole year and damage the cultivation of soil. The biggest floods were when the maximal water level of the Danube River was decreasing in time of the maximal water level of the Tisza River, or when the maximal water level of the Tisza River was late and it coincided with the maximal water level of the Danube River. Then the water accumulated at Đerdap`s gorge, runoff was slowed down and vast quantity of water overflowed not just alluvial planes but river terraces as well, all of which caused disastrous floods. At the same time, with high water level of rivers, groundwater appeared on the surface. It also caused floods. Terrains which were flooded by groundwater were considerably lower than surrounding ground, so there were no runoffs towards the rivers. The quality state of rivers and canals in DTD system Although the emphasis in this paper will be directed to the canals of the DTD hydro-system, in the beginning of this chapter it is necessary to briefly give the state of the water quality of the most important rivers on this territory.