GEOL. CROAT. 52/2 141 - 152 7 Figs. ZAGREB 1999

Quaternary Deposits as the Hydrogeological System of Eastern

Andrea BA»ANI 1, Marko ©PARICA 2 and Josipa VELI∆ 1

Key words: Hydrogeological system, Watershed, KljuËne rijeËi: hidrogeoloπki sustav, razvodnica, lito- Lithological continuity, Fault zones, Transmissivity, loπki kontinuitet, rasjedne zone, transmisivnost, rav- Plateau, Eastern Slavonia, . njak, istoËna Slavonija, Hrvatska.

Abstract Saæetak The area of eastern Slavonia, situated between the and U prostoru istoËne Slavonije, izmeu Save i Drave nalaze se tri rivers, comprises three geotectonic units: the eastern part of the geotektonske jedinice i to na sjeveru istoËni dio Dravske potoline, na Drava depression in the north, part of the Slavonia-Srijem depression jugu dio Slavonsko-srijemske potoline, a izmeu njih –akovaËko- in the south and the central –akovo- plateau together with vinkovaËki i Vukovarski ravnjak. Ravnjaci su u morfoloπkom i struk- the plateau. These units are separated by deep faults that turno-tektonskom pogledu sloæene timorske strukture, koje su od sus- reach the base of the Tertiary sediments. The first 200 m of Quater- jednih potolina odvojene sistemima dubokih rasjeda koji zadiru u nary deposits are saturated with fresh water. The aim of this study podlogu tercijarnih sedimenata. Zbog morfologije terena se duæ was to find out whether the faults form impermeable boundaries sepa- pruæanja –akovaËko-vinkovaËkog i Vukovarskog ravnjaka proteæe rating the waterbearing deposits into independent hydraulic systems, povrπinska i podzemna razvodnica koja istraæivani prostor dijeli u dva or if a singular hydraulic entity exists. Results of the analysis indicate sliva: Dravski na sjeveru i Savski na jugu. Cilj ovog rada bio je that lithological continuity of the aquifers exists along the fault zones istraæiti da li rasjedne zone izmeu ravnjaka i potolina predstavljaju on the margins of the –akovo-Vinkovci and the Vukovar plateaux, nepropusnu granicu koja naslage dijeli u dva odvojena hidrauliËka which means that there is no impermeable hydraulic boundary on the sustava ili one Ëine jednu hidrauliËku cjelinu. Analizom su obuhvaÊe- watershed between the Sava and Drava river valley. The part of east- ne kvartarne naslage koje sadræe vodu pogodnu za vodoopskrbu, a ern Slavonia between the Sava and Drava rivers is one hydraulic sys- koje zalijeæu do dubine od 200 m. Rezultati analize pokazali su da tem consisting of zones with different transmissivity values. In the litoloπki kontinuitet vodonosnih slojeva duæ rasjednih zona –ako- zones of reduced transmissivity, the hydraulic connections are weak- vaËko-vinkovaËkog i Vukovarskog ravnjaka nije prekinut, te da na ened, but not broken. Such zones exist not only along the fault zones razvodnici savskog i dravskog sliva ne postoji nepropusna hidrauliËka of the –akovo-Vinkovci plateau and the Vukovar plateau, but also granica. Prostor istoËne Slavonije izmeu Drave i Save smatra se jed- within the Sava and Drava depressions. The terrain morphology influ- nim hidrauliËkim sustavom unutar kojeg postoje zone s razliËitim vri- enced formation of both the surface and the underground watershed, jednostima transmisivnosti. Duæ zona smanjene transmisivnosti parallel to the extension of the –akovo-Vinkovci and Vukovar hidrauliËke veze su oslabljene, ali nisu prekinute. Takve zone nisu plateau. Therefore, within this single hydraulic entity, when the draw- prisutne samo duæ rasjednih zona –akovaËko-vinkovaËkog i Vuko- down reaches the watershed due to excessive pumping, the watershed varskog ravnjaka nego i unutar pojedinih depresija. U sluËaju da will be displaced from its natural position. sniæenje uzrokovano crpljenjem dosegne razvodnicu zapoËinje dotok vode iz podruËja s druge strane razvodnice, tj. razvodnica se premi- jeπta u odnosu na prirodni poloæaj udaljavajuÊi se od mjesta crpljenja.

1. INTRODUCTION of complex horst structures, that are separated from the neighbouring depressions by systems of deep faults The eastern part of the Drava depression in the (Figs. 1 and 2). With respect to the surface water and north and part of the Slavonia-Srijem depression in the groundwater, two drainage areas are defined - the Drava south, divided by the central –akovo-Vinkovci plateau drainage area in the north and the Sava drainage basin together with the Vukovar plateau, are deeply subsided in the south. The surface and subsurface watersheds structural depressions which were formed along region- between these two areas are located on the –akovo- al faults characterised by the horizontal displacement Vinkovci and the Vukovar plateaux. and movement of coherent tectonic blocks to the north- For construction of the geological map shown in east, which influenced the formation of large extension Fig. 1, the following sheets of the Basic Geological Map of SFRJ Scale 1:100,000 were used: Donji Miho- zones. The plateaux have the morphology and structure ljac (HE∆IMOVI∆, 1985), Naπice (KOROLIJA & JA- MI»I∆, 1989a), Osijek (MAGA©, 1987a), Odæaci 1 Faculty of Mining, Geology and Petroleum Engineering, University (TRIFUNOVI∆ & STOJADINOVI∆, 1985), Slavonski of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia. Brod (©PARICA, 1987), Vinkovci (BRKI∆ et al., 1 Institute of Geology, Sachsova 2, HR-10000 Zagreb, Croatia. 1989), BaËka Palanka (»I»ULI∆-TRIFUNOVI∆ & 142 Geologia Croatica 52/2

Fig. 1 Geological map. BaËani, ©parica & VeliÊ: Quaternary Deposits as the Hydrogeological System of Eastern Slavonia 143

Fig. 2 Geological cross-sections A-A’ and B-B’.

GALOVI∆, 1985a), BrËko (BUZALJKO et al., 1987) and the radioactive logs) were correlated in a north- and Bijeljina (VRHOV»I∆ et al., 1986). The structures south direction in order to depict the lateral relation- and other tectonic data were compiled after the works ships of the plateau sediments to the depressions. Due of HERNITZ (1983) and PRELOGOVI∆ et al. (1995). to the fact that there is a limited number of wells in the The aim of the study was to determine whether the marginal zones, the data set was complemented with fault zones between the plateaux and depressions con- interpretation of geoelectric measurements. The results stitute an impermeable zone that separates the Sava and obtained by utilisation of the mathematical models that Drava drainage area into two hydraulic systems, or covered the marginal zone were also taken into account. whether a singular hydraulic entity exists. The shallow- est 200 metres of sediments favourable for water-sup- ply were explored. 3. RESULTS

The results of comprehensive analyses of all the 2. DATA-SETS AND METHODS data that were at our disposal, originating from the sources mentioned above, can be grouped in accor- The work is largely based on the analysis of geolog- dance to the scientific disciplines - geological (strati- ical and hydrogeological data that were published in graphic, tectonic and palaeogeographic), hydrogeologi- scientific and professional papers and books, as well as cal and hydraulical data. Their synthesis solved the on the numerous reports in the archives of several com- problem of the continuity of the aquifer layers in the panies and scientific institutions. These data were inter- studied area of a relatively complex geological struc- preted together with fieldwork and laboratory investiga- ture. tions of the sediments drilled in 518 wells. The most important data obtained from the wells were the total 3.1. QUATERNARY GEOLOGICAL EVOLUTION depth, depth-intervals of permeable layers and the ratio of the thickness of permeable and impermeable layers. In view of the water-supply possibilities, the most The following hydrogeological parameters of the wells interesting sediments were deposited during the Middle were calculated: average hydraulic conductivity, trans- and Upper Pleistocene. This is the reason why this missivity, storage coefficient and leakage coefficient. overview of the geological history only covers the Qua- The drilling data and the well-logs (primarily the E-logs ternary period. 144 Geologia Croatica 52/2

In northern Croatia, there is a continuation of like their transport capabilities, and by the shallowing of the depositional environments between the Pliocene depositional area. The wind forces took the dominant (Uppermost Tertiary) and the Quaternary, the Pliocene role in the transport of sedimentary material, while silt being characterised by large aquatic areas with sedi- and clay were deposited in the remaining lakes and ments of significant thickness, especially in the subsid- swamps. In some places, the aquatic environments ing depressions. It also means that the Pliocene - P l e i s- totally dried up which enabled the formation of palaeo- tocene boundary has not yet been defined with confi- sols. The related palaeogeomorphological circumstan- dence. Subsequent to the strong tectonic events bet- ces are explored, documented and explained in the ween the Pliocene and Quaternary, and to the break- works of VELI∆ & DURN (1993) and VELI∆ & SAF- through of the in the –erdap canyon, the lakes TI∆ (1996). and swamps gradually dried up, followed by formation The aforementioned depositional environments are of the drainage pattern. There are only scarce data on confirmed by fossil findings. The ostracods significant the Lower Pleistocene of the explored area. There are for the shallow stagnant waters were determined by no outcrops. The age was proved by fossil findings in a SOKA» (1976), SOKA» & HARTEN (1978), SOKA» small number of wells - in Otok (SOKA», 1976), Vin- et al. (1982) and URUMOVI∆ & SOKA» (1974). The kovci (SOKA» & HARTEN, 1978), Trpinja (MAGA©, characteristic malacological community of the swamp 1987b; MUTI∆, 1989), in Vladislavci and Osijek (MA- biotope was interpreted by TRIFUNOVI∆ (1985), and GA©, 1987b), in Erdut and Dalj (SOKA» et al., 1982) the important biotope for the fluvial-paludal environ- and also in Valpovo (KOROLIJA & JAMI»I∆, 1989b). ment was discovered by »I»ULI∆-TRIFUNOVI∆ & The Lower Pleistocene sediments are mostly clay, silt GALOVI∆ (1985b). Terrestrial species were deter- and some sand. Due to the fact that their contact with mined by POJE et al. (1995) and by MALEZ (1970, the Pliocene is not defined, it is also impossible to tell 1971, 1978). the thickness of these sediments. The Lower Pleisto- The majority of the clastic material was transported c e ne - Middle Pleistocene boundary is defined on the in the Slavonia-Srijem depression by the rivers and conditional E-log marker Q’ (Fig. 2). Above the Q’ streams from the Bosnian mountains and from Mt. Dilj. marker horizon, there is a domination of permeable sed- This is confirmed by the mineral composition of fluvial iments, sand with some gravel, while underlying sedi- sediments which originated from the serpentine zone in ments are of low permeability - silt and clay (URUMO- Bosnia (MUTI∆, 1993). The main direction of transport VI∆ et al., 1976, 1978). In the uplifts of the –akovo- from south to north correlates with reducing propor- Vinkovci and the Vukovar plateaux, the Q’ horizon lies tions of the coarse-grained clasts and grain size in the at depth of approximately 150 m, while in depressions same direction (URUMOVI∆ et al., 1978). In this way, it is mostly below 200 m, sometimes even 300 m in the southern part, along the Sava river, gravel was (HERNITZ, 1983). predominantly deposited, and in the northern sections sand (MILETI∆ et al., 1986a). The Middle Pleistocene sediments are also buried, The Drava river and the streams flowing down the apart from a small outcrop on the northern slope foot- slopes of Mt. Krndija are the main distributors of clastic hills of the Erdut hill (Fig. 1, TRIFUNOVI∆, 1985). material in the Drava depression. The Drava river trans- Nevertheless, these sediments are well studied due to ports the material eroded in the area of the Central the large number of water exploration wells, some of Alps, on the Pohorje and Kozjak massifs and from the them drawn on the geologic cross-sections (Fig. 2). It Slavonian mountains (BABI∆ et al., 1978; MUTI∆, was during the Middle Pleistocene that the main mass 1989). In eastern Slavonia the river mostly deposits of the hydrogeologically interesting permeable sedi- sand. The more frequently occurring gravel along the ments were deposited. The eastern Slavonia area was western margin of the study area was brought by the then covered by shallow lakes and swamps and the Mt. Krndija streams (URUMOVI∆, 1982). Apart from neighbouring Bosnian and Slavonian mountains were the rivers and streams, MAGA© (1987b) discovered the land areas exposed to strong denudation. The transport traces of lakes by the rivers and deep pools. In the and deposition of clastic material, respectfully several Erdut area, large shallow marshes existed where rivers cycles of redeposition, was also very dependent on the deposited sand in the high-water periods (VELI∆ et al., palaeoclimate. The most significant palaeoclimate char- 1985). acteristic was the alternation of the warm and humid In the Pliocene, the –akovo-Vinkovci and the Vu- periods with cold and very dry periods. During the kovar plateaux were mostly submerged uplifts charac- warmer interglacial periods, the high waters of surface terised by the deposition of mixed sedimentary materi- streams transported a lot of the coarse-grained clastic al. One of components was transported from the north, material and deposited it in the swamps and lakes. At respectfully the north-west, and another from the south the same time, the level of stagnant waters rose, so the or the south-west. In the Vukovar plateau area, the flu- swamps and lakes grew and covered a bigger area, until vial, lacustrine and marsh sediments were determined eventually they became interconnected. In contrast, the (»I»ULI∆-TRIFUNOVI∆ & GALOVI∆, 1985b). glacial periods are characterised by a draw-back of the Apart from the palaeoclimate conditions, sedimenta- surface streams into their river-beds, a reduction of tion was influenced by tectonic movements which are BaËani, ©parica & VeliÊ: Quaternary Deposits as the Hydrogeological System of Eastern Slavonia 145 still active in eastern Slavonia. The most important tec- to the lack of organic matter, it is interpreted that these tonic displacement is on the main faults that follow the sediments were deposited in relatively clean water. The northern and southern margin of the plateau and on the analyses of malacologic assemblages resulted in inter- secondary parallel faults of the WNW-ESE system. pretation of the water environment with land nearby There is also a marked displacement on the faults of the and marked oscillation of water level which produced NNE-SSW system (HERNITZ, 1983). This system has repeated floods and drying-up periods (GALOVI∆ et an especially pronounced horizontal character of dis- al., 1989). placement (PRELOGOVI∆ & VELI∆, 1992). Warming at the Pleistocene-Holocene boundary In the beginning of the Upper Pleistocene s i m i l a r caused a change in composition of vegetation cover. sedimentary conditions were preserved. The Riss- The steppe was gradually replaced by woods (POJE, Würm interglacial was still characterised by an influx 1986). Changes in wildlife are also documented. In the of coarse-grained clastic material, which is proved by early Holocene there are still grazing herds of North- palaeontological investigation of the topmost part of the European moose (Alces Alces) , gigantic deer (M e g a c e - gravely aquifer close to the Sava river (MUTI∆, 1993). ros) and European bison (Bison priscus), and during the It seems that the extensive transport of the coarse- Boreal there were common deer (Cervus elaphus), wild grained clastic material by surface waters stopped with oxen (Bos primigenius), bear (Ursus arctos ), wolf (C a - the beginning of the last ice age - the Würm glacial. nis lupus), lynx (Felis) etc. Domestication of some ani- The most remarkable Würm facies are the loess mals started in the Boreal. It was firstly the dog, then deposits that also cover a significant part of the study the goat, sheep, oxen and some other animals. In the area. Transported by strong winds, the loess grains Neolithic and the Bronze ages, it was the horse, don- were deposited everywhere - in the lakes, pools and key, hen etc. (MALEZ, 1979). shallower marshes as well as on the mild morphologic The climatic changes at the end of the Würm and land uplifts. In respect to that, the lake-marsh, marsh, the beginning of the Holocene caused the melting of ice marsh-continental and continental loess is differentiated in the alpine and perialpine area and inflow of large (Figs. 1 and 2). Different types of loess at the same time masses of water in and around the study area. Deposi- depict the contemporary distribution of the land and tion of fluvial sediments started, followed by formation water, which is of special importance for the recon- of river terraces. struction of the evolution of the plateaux. The typical continental loess is found only in the There are four genetic types of Holocene sediments: area of the Vukovar plateau, Erdut uplift and in the river and creek alluvium, proluvial deposits, aeolian restricted area near the Otok and Komletinci. This sands and marsh sediments (Fig. 1). means that land existed only in these areas at the time. The river and creek sediments are found in the river The loess on the –akovo-Vinkovci plateau was contem- channels of the Sava, Drava and Danube, and of their poraneously deposited in an aqueous environment. The larger tributaries. following tectonic movements led to the uplift of the Proluvial deposits cover the southern slopes of the Vinkovci area so that the loess that was in the begin- Erdut hill, as well as the northern margin of the –ako- ning deposited in water was gradually covered by conti- vo-Vinkovci plateau. They were formed by the surface nental loess (GALOVI∆ & MUTI∆, 1984; MUTI∆, erosion of the continental loess and accumulation of the 1990). The contact between the aqueous and continen- eroded material in the area of contact with the aquatic tal loess can be clearly observed in the quarry of the loess. The proluvial deposits are thin and made of loose Vinkovci brick-factory. During the entire Upper Pleis- silt containing limestone concretions. tocene, in the western part of the plateau (the –akovo Aeolian sands are determined in the surroundings of part) the wind-blown grains were deposited in the shal- Valpovo, in the marginal north-western part of the stud- low water environment. Due to neotectonic activity, ied area. Actually, the sediments of this genetic type are this part of the plateau became land only in the very common in the Drava valley west of the studied Holocene (MUTI∆, 1990). area, and it is only the tract with a maximal eastward In addition to the loess, the Upper Pleistocene sedi- reach that is encountered here. ments in the Drava depression are represented by river Although less than 2 metres thick, t h e s w a m p palaeoterraces and alluvial sands. The terraces are iden- d e p o s i t s cover large areas in the Brodsko Posavlje tified on the surface along the Drava flow between the region and in eastern Posavina. They represent the final Osijek and Sarvaπ and along the Danube from Dalj to phase of deposition of the lacustrine-marsh genetic type Vukovar, and the alluvial sand deposits lie in the mar- of sediments. In the Drava area, these sediments infilled ginal north-western part of the explored area (Figs. 1 the larger and smaller forms of negative relief, that and 2). were due to the stagnant water transformed into the A large part of the Sava depression area is covered swamps or swamp forests. In fluvial seasons, some of by marshy-lacustrine sediments of Upper Pleistocene the dried parts were again filled with water, and the age, deposition of which continued into the Holocene. depositional process renewed. This is ongoing today. Frequently, they are complicated to differentiate in the The swamp deposits consist of the humus-peat enriched field from the marsh loess (©PARICA et al., 1987). Due silt and silt with some sand, as well as of the silty clay. 146 Geologia Croatica 52/2

Fig. 3 Hydrogeological cross-section I-I’.

About a century ago, when the struggle for reclama- According to core determination of the shallowest tion of this swampy land began, the lowest parts of the 200 m of sediments in the stratigraphic column, five to Sava and Drava depression were still covered by pools seventeen permeable layers can be discerned in the and swamps. There are works of PILAR (1876) on the Drava depression. The number of layers depends on swamps south-east of Osijek, and of BÖSENDORFER location, while some of them reach the maximal thick- (1952) on the pools and swamps in the areas of Karaπi- ness of 40 m (Figs. 3, 4 and 5). These permeable layers ca, and VuËica rivers, in the Bi- depres- are mostly composed of fine- to medium-grained sands sion, and in the areas of Berava, SpaËva and Studva. with some gravel occasionally, (usually encountered in They all had their maximal extent during the high the basal parts of thicker sandstone layers). Hydraulic waters of the Drava and Sava rivers. conductivity is commonly in the range of 10-20 m/day, There are also the archaeological findings that are with the exception of some of the wells in Osijek, worth mentioning, because they indirectly depict the where over 40 m/day was determined, and, in contrast distribution of aquatic surfaces. The oldest settlements wells in , Korog and Borovo which have less at present that were found in eastern Slavonia are from than 10 m/day. The storativity is in the range of 4 x 10-5 the Younger Stone Age - the Neolithic (6,000- 3 , 5 0 0 to 3 x 10-3 while the transmissivity depends on the depth B.C.) and pertain to the cultural layers named StarËevac of drilling and is in a wide range of 70-1000 m2/ d a y . and Sopot. These are the oldest settlements of farmers The distribution of the net thickness of permeable lay- that were located in groups on the more elevated dry ers in the entire studied area is shown in Fig. 6, where it terrain along the rivers and lakes, but out of the reach of clearly depicts the depositional conditions as described floods (MINICHREITER, 1992a, b). The remains of above. these cultures are found near the Stari Perkovci, Vrpol- The sediments of the Sava depression can be divid- je, –akovo, Vinkovci, Vukovar, Otok, Erdut hill and ed into two units with essentially different hydrogeo- near Osijek. logical properties. The first unit that lies in the south, along the Sava, consists of a single gravel aquifer (Fig. 3.2. HYDROGEOLOGICAL CHARACTERISTICS 2) with a maximal thickness exceeding 100 m. The lithological composition is dominated by fine- to medi- The permeable sediments saturated with drinking um-grained gravel with 10-50 wt. % of sand. This layer water were deposited during the Middle Pleistocene and has the most favourable hydrogeological characteristics part of the Upper Pleistocene, under conditions of in the triangle between the Velika Kopanica, Gundinci cyclic sedimentation followed by tectonic movements. and Kruπevica. In this area, the gravel rarely contains These depositional conditions resulted in pronounced more than 20 wt. % of sand, and the thinner beds of fin- lithological heterogeneity in both the horizontal and er material appear only sporadically. The more pro- vertical directions. nounced lithological inhomogeneity is found in the area BaËani, ©parica & VeliÊ: Quaternary Deposits as the Hydrogeological System of Eastern Slavonia 147

Fig. 4 Hydrogeological cross-section II-II’.

Fig. 5 Hydrogeological cross-section III-III’. between the Babina Greda and ©titar and further to the from 2 to 11 in the shallowest 200 m of sediments. The east, where the gravel contains frequent interbeds of thickness of individual layers rarely exceeds 30 m. Lay- silty sand and clay. The mentioned aquifer has a ers are mostly composed of fine- to medium-grained hydraulic conductivity in the range of 30-³ 200 m/day, sand and occasionally of coarse-grained sand. As in the the transmissivity is between 423- 7344 m2/day, and Drava depression, the thicker layers of sand contain storativity between 1.7 x 10-4 and 8 x 10-3. some gravel in their basal parts, especially in the east- To the north and east of the gravel aquifer, lies the ern section, in the localities of Vranjevo, Otok and second hydrogeological unit of the Sava depression. It Slakovci. The hydraulic conductivity of these layers is consists of a system of sand aquifers that can number in the range of 5.5-37 m/day, the transmissivity is 148 Geologia Croatica 52/2

Fig. 6 Isolith map of permeable layers in the Quaternary aquifer system. BaËani, ©parica & VeliÊ: Quaternary Deposits as the Hydrogeological System of Eastern Slavonia 149 between 52- 706 m2/day, and storativity between 3, 4 and 5. The correlation of well data showed that the 1.3 x 10-4 - 4.3 x 10-3. plateaux have undergone a spatially and temporally In the first 120 m of sediments drilled on the –ako- non-uniform uplift that resulted in differences of sedi- vo-Vinkovci plateau, between 3 to 8 aquifers were ment deformation along the fault zones. The biggest determined in the stratigraphic column. Some of these displacements are registered on the southern fault zone, layers were found to have a maximal thickness of 30 m south of –akovo (Fig. 3). Thicker aquifers are bent and (Figs. 3, 4 and 5). These aquifers are made of fine- to thinned but their lithological (and hydraulic) continuity coarse-grained sand that often contains coarse-grained is not broken. It is noted that tectonics within the pla- gravel, especially in the western part of the explored teau itself contributed to sediment deformation even area. The hydraulic conductivity is in quite a wide more than the northern fault zone near Tomaπanci. Fur- range of 5-30 m/day, the transmissivity is between 52 ther to the east, in the area from Ivankovo to Vinkovci, and 413 m2/day, and storativity between 1.9x 1 0-4 a n d the aquifer layers remained practically undisturbed 4.4 x 10-3. along the fault zones, making the hydrogeological rela- The thickness of deposits that cover the eastern tions on the plateau the same as those in the depressions Slavonia aquifer system is shown in Fig. 7. The cover (Fig. 4). The correlation of wells across the Vukovar sediments over the entire area of eastern Slavonia are plateau showed a stronger deformation of sediments composed of silty-clayey deposits with lenses and along the northern fault zone than on the southern one interbeds of sand. The low-permeability sediments (Fig. 5). Some of the aquifers branch along the northern between the aquifers at depth are of the same lithologi- fault zone, but the continuity of the thicker layers is cal composition. The leakage coefficient there is in the intact. While observing the cross-sections in Figs. 3, 4 wide range of 1.3 x 10-5 - 4.3 x 10-3 day-1. and 5, a significant vertical exaggeration must be noted, Over the entire study area, the groundwaters are because it gives an impression of a higher deformation recharged by the means of rainfall infiltration. The in- of sediments than that which actually exists. filtration from the surface streams in natural conditions The same results were obtained by interpretation of can practically be neglected in the Drava depression. geoelectrical measurements that were performed on a The surface drainage pattern in the studied part of the number of occasions by the Geoelectrical Department Drava depression is such that it drains the groundwater of the “Geofizika” company from Zagreb. On the fault both in periods of high and low waters. The situation in zones, a few cross-sections have a characteristic reduc- the Sava depression is somewhat different. The Sava tion of the electric resistivity to a level of 5 Wm. There river channel is cut into the gravel aquifer, thus putting are bigger differences on the plateau itself. In the shal- it in direct hydraulic connection with the river. The lowest 100 m the zones were measured with resistivity high waters of the Sava are registered in the wells up to under 20 Wm, and those with more than 65 Wm. 5 km further north, as far as the area of Velika Kopani- In order to determine the hydraulic role of fault ca. During the low waters, the river waters are below zones between the plateaux and depressions, the results the groundwater level which means that the Sava drains of mathematical models that encompassed the plateau the aquifer. Alternatively, in conditions of extensive areas were analysed. Two models were calculated exploitation of the gravel layer, the inflow of Sava (MILETI∆ et al., 1986b, 1993), both of which tested waters would be the major recharge source. The rainfall the shallowest aquifer. In both cases, the model results infiltration on the plateaux is especially well developed showed that there is no hydraulic barrier along the fault in the eastern parts, because the aquifer system there is zones. Namely, the simulated and measured draw- covered by the continental loess that has a significant downs correspond only in the case of the supposed con- vertical permeability. tinuity of the aquifer. Putting the flow barrier along the Because of the terrain morphology, the hypsometric fault line in the model, or even the reduced transmissiv- levels of groundwater are the highest in the area of ity, would result in unrealistically large simulated draw- –akovo-Vinkovci and Vukovar plateau, which means downs in respect to the measured ones. that groundwater flows from the plateau in the direc- tions of the north-east and south-east, and there is the 4. CONCLUSION watershed along the plateau.

3.3. HYDRAULIC FUNCTION OF THE PLATEAU Based on the analysis of all the acquired geological and hydrogeological data, it must be concluded that In order to enable the analysis of lateral changes of there is lithological continuity of the aquifer layers sediments, especially on the contact between the plate- across the fault zones of the –akovo-Vinkovci and au and depressions, a number of the N-S striking hydro- Vukovar plateaux, which means that there is no hydra- geological cross-sections were constructed. The sec- ulic barrier on the watershed between the Sava and Dra- tions illustrate the results of comprehensive correlation va alluvial valley. of all the acquired drilling data and well-logs (mostly The area of eastern Slavonia between the Drava and E-logs) in the area of –akovo-Vinkovci and Vukovar Sava rivers is regarded as one hydraulic system that plateau. Only characteristic sections are shown in Figs. contains zones of different transmissivity. Along the 150 Geologia Croatica 52/2

Fig. 7 Isopach map of low-permeable aquifer system roof. BaËani, ©parica & VeliÊ: Quaternary Deposits as the Hydrogeological System of Eastern Slavonia 151 zones of reduced transmissivity, the hydraulic connec- list Vinkovci L34-98.- Geol. zavod Zagreb (1987) tions are weakened, but not broken. Such zones exist & Geoinæenjering Sarajevo (1979), Sav. geol. za- not only along the fault zones of the –akovo-Vinkovci vod, Beograd, 49 p. and Vukovar plateau, but within the depressions and the HE∆IMOVI∆, I. (1985): Osnovna geoloπka karta SFRJ plateau itself. 1:100.000. List Donji Miholjac L34-73.- Geol. za- The terrain morphology influenced the formation of vod Zagreb (1981-1984), Sav. geol. zavod, Beo- both the surface and the underground watershed, paral- grad. lel to the extension of the –akovo-Vinkovci and Vuko- var plateau. In a hydraulic sense, the watershed repre- HERNITZ, Z. (1983): Dubinski strukturno-tektonski sents a streamflow line. That is why, in order to con- odnosi u podruËju istoËne Slavonije.- PhD Thesis, struct a mathematical model of a certain drainage area Jugosl. komitet svjet. kongr. za naftu, “Nafta”, (or of a part of the drainage area) with a marginal line Zagreb, 221 p. along the watershed, the watershed has to be defined as KOROLIJA, B. & JAMI»I∆, D. (1989a): Osnovna a “zero flow boundary”. Because of the single hydraulic geoloπka karta 1:100.000. List Naπice L34-85.- entity, in the case of the draw-down reaching the Geol. zavod Zagreb (1988), Sav. geol. zavod, Beo- boundary due to the excessive pumping, the groundwa- grad. ter will start flowing over the margin of the model. The bigger the draw-down at the margin, the bigger the KOROLIJA, B. & JAMI»I∆, D. (1989b): Osnovna flow, making the watershed more displaced from its geoloπka karta SFRJ 1:100.000. TumaË za list Naπi- natural position. ce L34-85.- Geol. zavod Zagreb (1988), Sav. geol. zavod, Beograd, 40 p.

5. REFERENCES MAGA©, N. (1987a): Osnovna geoloπka karta SFRJ 1:100.000. List Osijek L34-86.- Geol. zavod Zagreb BABI∆, Æ., »AKARUN, I., SOKA», A. & MRAZ, V. (1981-1987), Sav. geol. zavod, Beograd. (1978): O geologiji kvartarnih naslaga porjeËja rije- MAGA©, N. (1987b): Osnovna geoloπka karta SFRJ ke Drave.- Geol. vjesnik, 30/1, 43-61, Zagreb. 1:100.000. TumaË za list Osijek L34-86.- Geol. za- BÖSENDORFER, J. (1952): IstoËna granica Tomisla- vod Zagreb (1986), Sav. geol. zavod, Beograd, 54 p. vove, Kreπimirove i Zvonimirove Hrvatske u sav- MALEZ, M. (1970): Izumrli sisavci Slavonije.- Zbor- sko-dravskom interamniju.- Rad Jugosl. akad. znan. nik radova I. znanstvenog sabora Slavonije i Bara- umjet., 286, 143-170, Zagreb. nje, 101-105, Osijek. BRKI∆, M., GALOVI∆, I. & BUZALJKO, R. (1989): MALEZ, M. (1971): Kvartarogeoloπke karakteristike Osnovna geoloπka karta SFRJ 1:100.000. List brodskog Posavlja.- Radovi Centr. org. nauËn. rada Vinkovci L34-98.- Geol. zavod Zagreb & Geoinæe- u Vinkovcima, Jugosl. akad. znan. umjet., 1, 373- njering Sarajevo (1979-1985), Sav. geol. zavod, 383, Zagreb. Beograd. MALEZ, M. (1978): Paleontoloπka i kvartargeoloπka BUZALJKO, R., VUJNOVI∆, L. OLUJI∆, J. & MAR- istraæivanja u 1973. godini.- Ljetopis Jugosl. akad. KOVI∆, S. (1987): Osnovna geoloπka karta SFRJ znan. umjet., 78, 559-572, Zagreb. 1:100.000. List BrËko L34-110.- Geoinæenjering Sarajevo & Geol. zavod Zagreb (1985), Sav. geol. MALEZ, M. (1979): Kvartarna fauna Jugoslavije. zavod, Beograd. Praistorija Jugoslavenskih zemalja 1. Paleolitsko i mezolitsko doba.- Akad. nauka Bosne i Herceg., 55- »I»ULI∆-TRIFUNOVI∆, M. & GALOVI∆, I. (1985 79, Sarajevo. a): Osnovna geoloπka karta SFRJ 1:100.000. List BaËka Palanka L34-99.- Geol. inst. Beograd & MILETI∆, P., BA»ANI, A., MAYER, D. & CAPAR, Geol. zavod Zagreb (1972-1980), Sav. geol. zavod, A. (1986a): Prilog poznavanju hidrogeoloπkih zna- Beograd. Ëajki prve hidrogeoloπke zone na podruËju istoËne Slavonije.- Geol. vjesnik, 39, 137-150, Zagreb. »I»ULI∆-TRIFUNOVI∆, M. & GALOVI∆, I. (1985 b): Osnovna geoloπka karta SFRJ 1:100.000. TumaË MILETI∆, P., HEINRICH-MILETI∆, M. & BA»ANI, za list BaËka Palanka L34-99.- Geol. inst. Beograd A. (1986b): Pristup interpretaciji podataka pokus- & Geol. zavod Zagreb (1983), Sav. geol. zavod, nog crpljenja.- Geol. vjesnik, 39, 151-164, Zagreb. Beograd, 46 p. MILETI∆, P., HEINRICH-MILETI∆, M. & BA»ANI, GALOVI∆, I. & MUTI∆, R. (1984): Gornjopleistocen- A. (1993): Konceptualni hidrogeoloπki model za ski sedimenti istoËne Slavonije (Hrvatska).- Rad hidrogeoloπki sustav istoËne Slavonije.- Rud.-geol.- Jugosl. akad. znan. umjet., 411 (Razr. prir. znan., naftni zbornik, 5, 65-73, Zagreb. 20), 299-356, Zagreb. MINICHREITER, K. (1992a): StarËevaËka kultura u GALOVI∆, I., BRKI∆, M. & BUZALJKO, R. (1989): sjevernoj Hrvatskoj.- Unpublished PhD Thesis, Uni- Osnovna geoloπka karta SFRJ 1:100.000. TumaË za versity of Zagreb, 104 p. 152 Geologia Croatica 52/2

MINICHREITER, K. (1992b): RanoneolitiËka arhitek- ©PARICA, M., BUZALJKO, R. & PAVELI∆, D. tura sjeverne Hrvatske.- PoroËilo raz. pal. neol. ene- (1987): Osnovna geoloπka karta SFRJ 1:100.000. ol. v Sloveniji, 20, 17-26, Ljubljana. TumaË za list Slavonski Brod L34-97.- Geol. zavod Zagreb & Geoinæenjering Sarajevo (1986), Sav. MUTI∆, R. (1989): Korelacija kvartara istoËne Slavo- geol. zavod, Beograd, 56 p. nije na osnovi podataka mineraloπko-petrografskih analiza (IstoËna Hrvatska, Jugoslavija). Dio I: Drav- TRIFUNOVI∆, S. (1985): Osnovna geoloπka karta ska potolina.- Acta geologica, 19/1, 1-60, Zagreb. SFRJ 1:100.000. TumaË za list Odæaci L34-87.- Geol. inst. Beograd (1972-1983) & “Nafta-gas” MUTI∆, R. (1990): Korelacija kvartara istoËne Slavo- (1973-1983), Sav. geol. zavod, Beograd, nije na osnovi podataka mineraloπko-petrografskih 54 p. analiza (IstoËna Hrvatska, Jugoslavija). Dio II: Les- ni ravnjak.- Acta geol., 20/2, 29-80, Zagreb. TRIFUNOVI∆, S. & STOJADINOVI∆, P. (1985): Os- novna geoloπka karta SFRJ 1:100.000. List Odæaci MUTI∆, R. (1993): Korelacija kvartara istoËne Slavo- L34-87.- Geol. inst. Beograd & “Nafta-gas” Novi nije na osnovi podataka mineraloπko-petrografskih Sad (1984), Sav. geol. zavod, Beograd. analiza (IstoËna Hrvatska). Dio III: Slavonsko-sri- jemska potolina.- Acta geol., 23/1, 1-37, Zagreb. URUMOVI∆, K. (1982): Hidrogeoloπke znaËajke istoË- nog dijela Dravske potoline.- Unpublished PhD PILAR, Gj. (1876): Podravina, Djakovπtina i Dilj- Thesis, University of , 138 p. gora.- Rad Jugosl. akad. znan. umjet., 33, 38-57, Za- greb. URUMOVI∆, K. & SOKA», A. (1974): O kvartarnim naslagama Æupanje (istoËna Slavonija, SR Hrvats- POJE, M. (1986): Ekoloπke promjene na vukovarskom ka).- Geol. vjesnik, 27, 319-330. prapornom ravnjaku proteklih cca 500.000 godina.- Geol. vjesnik, 39, 19-42, Zagreb. URUMOVI∆, K., HERNITZ, Z., ©IMON, J. & VELI∆, J. (1976): O propusnom mediju kvartarnih te gornjo POJE, M., JURI©I∆-POL©AK, Z. & ©PARICA, M. i srednjopliocenskih naslaga sjeverne Hrvatske.- (1995): Srednjopleistocenska malakofauna Glogov- Zbornik radova 4. jugoslavenskog simpozija o hid- ice kod Slavonskog Broda (Slavonija, Hrvatska).- rogeologiji i inæenjerskoj geologiji, 1, 395-410, In: VLAHOVI∆ I., VELI∆, I. & ©PARICA, M. Skoplje. (eds.): First Croatian Geol. Congr., Opatija, Pro- ceedings, 2, 459-464, Zagreb. URUMOVI∆, K., HERNITZ, Z. & ©IMON, J. (1978): O kvartarnim naslagama istoËne Posavine (SR Hr- PRELOGOVI∆, E. & VELI∆, J. (1992): Correlation of vatska).- Geol. vjesnik, 30/1, 297-308. Quaternary Sediments and Tectonic Activity of the Eastern Part of the Drava River Depression.- Geol. VELI∆, J. & DURN, G. (1993): Alternating Lacustrine- Croatica, 45, 151-162. Marsh Sedimentation and Subaerial Exposure Phas- es During Quaternary: PreËko, Zagreb, Croatia.- PRELOGOVI∆, E., JAMI»I∆, D., ALJINOVI∆, B., Geol. Croatica, 46/1, 71-91. VELI∆, J., SAFTI∆, B. & DRAGA©, M. (1995): Dinamika nastanka struktura juænog dijela Panon- VELI∆, J. & SAFTI∆, B. (1996): Dubinskogeoloπki skog bazena. - In: VLAHOVI∆ I., VELI∆, I. & odnosi podruËja smetliπta “Jakuπevec” - Ëimbenik ©PARICA, M. (eds.): First Croatian Geol. Congr., sanacije.- Zbornik radova IV. meunarodnog sim- Opatija, Proceedings, 2, 481-486, Zagreb. pozija “Gospodarenje otpadom - Zagreb ‘96”, 197- 205, Zagreb. SOKA», A. (1976): Pleistocenska fauna ostrakoda iz VELI∆, J., DRAGI»EVI∆, I. & PRELOGOVI∆, E. nekih buπotina u istoËnoj Slavoniji (sjeverna Hrvats- (1985): Geoloπki odnosi kvartarnih naslaga okolice ka).- Geol. vjesnik, 29, 159-172. Erduta (istoËna Hrvatska).- Geol. vjesnik, 38, 87- SOKA», A. & HARTEN, van D. (1978): Ilyocypris 100. slavonica n. sp. (Crustacea, Ostracoda) from the VRHOV»I∆, J., MOJI»EVI∆, M., AN–ELKOVI∆, I., Pleistocene of Vinkovci (Slavonia, north Croatia) MARKOVI∆, B., PAVLOVI∆, Z., RAJ»EVI∆, D., and of Tegelen (The Netherlands).- Geol. vjesnik, PRTOLJAN, B. & GALOVI∆, I. (1986): Osnovna 30/1, 219-223. geoloπka karta SFRJ 1:100.000. List Bijeljina L34- SOKA», A., DRAGI»EVI∆, I. & VELI∆, J. (1982): 111.- Geoinæenjering Sarajevo, geol. inst. Beograd Biostratigrafske i litoloπke odlike neogenskih i kvar- & Geol. zavod Zagreb, Sav. geol. zavod, Beograd. tarnih sedimenata nekih buπotina okolice Osijeka.- Geol. vjesnik, 35, 9-20. ©PARICA, M. (1987): Osnovna geoloπka karta SFRJ 1:100.000. List Slavonski Brod L34-97.- Geol. za- vod Zagreb & Geoinæenjering Sarajevo (1986), Sav. Manuscript received September 23, 1999. geol. zavod, Beograd. Revised manuscript accepted November 12, 1999.