Strategy or Disaster : Flood Prevention Related Issues and Actions in the Tisza River Basin 3 Hungarian Geographical Bulletin 2009. Vol. 58. No 1. pp. 3–17. Strategy or disaster Flood prevention related issues and actions in the Tisza River basin Ferenc Schweitzer1 Abstract Changes in land use of the lowland landscape along the Tisza River have largely been shaped by processes that took place aft er fl ood control and regulation measures of that river. As a result fl uvial accumulation has either been eliminated or restricted to the fl ood plain. At present human sett lements extend to some segments of the low fl ood plain threatened by fl ood hazard. The amended Vásárhelyi Scheme focuses on raising embankments and extension of fl ood plain. Floods called the att ention to problems that have to be solved, such as the stability of levee slopes. To prevent slope slumps it would be reasonable to start studies on fl ood control embankments in order to reveal sections endangered by an extreme water pressure during fl oods. Key words: geomorphology, fl ood hazards, fl ood plains, Tisza River Valley Rising from the Northeastern Carpathians, Tisza River fl ows into the Danube aft er covering 946 km. The catchment of the Tisza (157,186 km2) opens up to- ward the W and SW. Within its 700 km long section across the Alföld (Great Hungarian Plain), the water level remains below 100 m a.s.l. Along the middle and lower reaches in the plain its valley is asymmetric: geomorphologically it fl ows in a trough-shaped depression upon its low fl ood plain. Tisza River emerged in the Late Pleistocene and initially it crossed the plain with its tributary Szamos (Someş) eastward from its present-day channel. Its terraces of Pleistocene age are to be found in the latt er regions. The river had been att racted to its present-day position by the Holocene depressions located east and north of Nyírség, the recent depression of Jászság and by the Szolnok–Titel trench. Its meandering channel changed frequently until the completion of water regulation, which were performed according to the concept of Pál Vásárhelyi. The fl atland is rich in microrelief forms as evidenced by the presence of cut-off meanders, double and triple channels (Fig. 1). Masses of water provided by fl oods stepping out on the left bank between Tiszadob and Tiszafüred, fl owing across ¹ Director, DSc, Geographical Research Institute, Hungarian Academy of Sciences, H-1112 Budapest, Budaörsi út 45. E-mail: schweitf@mtafk i.hu 4 Fig 1. Relief types in the southeastern part of the Alföld. – 1 = low flood plain; 2 = low flood plain of poor drainage; 3 = flood-free lowland (high flood plain); 4 = low alluvial fan covered with infusion loess; 5 = slightly rolling sandy lowland 5 swamps and transported by the Hortobágy stream reached the Berett yó marsh situated 30–35 km away. The shallow (30–40 cm deep) water and the swamps once formed part of the extensive wetland within the Tisza drainage basin. Hortobágy stream fl ows north to south in a ca 10–12 km wide clayey channel, fi lled up with 8–10 m thick fl uvial–alluvial sediments down to its tributary to Körösök. This minor valley used to be the track of the great fl oods; by now the area lying deepest within the Nagykunság and Hortobágy regions has been silted up. Nowadays huge masses of water originating from heavy rainfalls in the mountain frame and surging up in the plain create emergency situation during high stages. They cause fl oods of long duration and make large areas waterlogged in the Tisza valley. The sett lements along the rivers of the Alföld were located in the so- called high fl ood plain, which had not been inundated even during the most devastating fl oods. The ancient Tisza and its tributaries had fl ooded huge areas in the plain, a considerable part of which was occupied by marshy areas and backswamps (Fig. 2). The idea of the regulation of the Tisza River had been raised for the fi rst time during the reign of King Matt hias Corvinus, in the second half of the 15th century. It was he who issued the fi rst decree that levees must be erected in order to protect the land. The basis of water regulation was created much later: the Habsburg Emperor Francis II emanated a law in 1807 encouraging the organisa- tion of associations aimed at fl ood control and water regulation. As a result of mapping of the Tisza between 1834–48 led by Sámuel Lányi it had become obvious that high water endangered 854 sett lements in 18 counties, among them even some of those, which were located on the high fl ood plain and hitherto had not been inundated. It was a token of the low fl ood plain being silted up. As a consequence of forest clearance, rough grazing and land cultiva- tion along the river and probably enhanced by mining and quarrying activities within the drainage basin, runoff had increased and together with the risen high water levels they posed a serious threat for human sett lements. To protect the towns and villages, linear infrastructure and agricultural land the Tisza Valley Association was organised in 1846 under the guidance of Pál Vásárhelyi. It also pursued planning, co-ordination and implementation of activities on fl ood control and water regulation. Construction of a system of embankments along the Danube and Tisza rivers and tributaries also involved the construction of artifi cial channels, cutt ing off meanders and reclamation of swampy areas through the operation of drain- age canals. These measures have been and still are considered one of the most radical contemporary interventions in the natural conditions of Europe. These measures were taken for the solution of tasks set by the socio-economic demands of the time. 6 As it is well known, initiation of water regulation along the Tisza was the merit of Count István Széchenyi and implemented partly according to the plans elaborated by Vásárhelyi. These activities were based on the hydrologi- cal law of Vásárhelyi, the validity of which for the middle stretches of great rivers had been recognised internationally. For instance, fl ood control and water regulation of the Middle Rhine and Mississippi valleys were executed on its basis. What was the main point of this law? Vásárhelyi's att ention was drawn by the facts that during mean water the Tisza is in equilibrium and does not Fig. 2. Waterlogged areas in the Tisza valley prior to water regulation (Ihrig, D. 1952). – 1 = outlet of water from the river channel and direction of currents; 2 = inundated areas 7 build sandbars. He had come to the conclusion that eff ective measures on regulation are only feasible if: a) the river is shortened by cutt ing through the braided channels (me- anders), b) fl oods provide a rapid drainage (travel time) similar to that of mean water which means that between channel width and depth of fl oods there should be an identical ratio as between those of mean water. Taking into account the above considerations, Vásárhelyi calculated the average distance between the embankments, and found it to be 750 m (changing between 500 and 1900 m depending on local factors). This caused serious commotion among the concerned public because close embankments could involve higher levels of fl oods with a growing hazard of the failure of dikes. This uncertainty and panic mood had been the reason why the Italian engineer Pietro Paleocapa had been invited as an expert. It was he who pro- posed the system of fl ood protection applied for the Po River i.e. shaping of a wide fl ood bed to be inundated by the great fl oods and of inner dikes along the river to hold back the lower summer fl oods. However this system has a defect of its own: due to silting up of the fl ood bed by high waters year aft er year, the levels of fl oods rise as well. Nowadays the Po fi lled up its fl ood bed to an extent that low water of the river fl ows higher than the roofs of the houses in Ferrara. From this short historical review it becomes clear that the optimum ex- tension of the fl ood bed between dikes and levees has been a controversial issue since the time of Vásárhelyi and Paleocapa. So was the number of meanders to be cut through. Vásárhelyi planned 102 meanders to cut off , whereas Paleocapa found it necessary to shorten the channel by 15 meanders. Thus the river had been shortened (from 1420 to 977 km) whereas the stream gradient increased and the character of beds of low and medium discharge slightly shift ed toward the upper reaches. Rivers leaving mountain and hill regions suddenly acquire lower section character owing to an abrupt fall in stream gradient. In natural conditions sediment load of watercourses accumulates in alluvial fans (in a way the Nyírség or the Maros fan emerged) but it has recently been enforced to deposit in relatively narrow fl ood beds between the levees. The Tisza and tributaries have always been rich in sediment load. Even the most ancient sett lements situated on high fl ood plains were inundated some- times because the low fl ood plain in their surroundings had been silted up. Natural sediment transport probably has grown with the progressing urbanisation and during 150 years of fl ood control the process of silting up and relief evolution of fl ood beds with the emergence of point bars accelerated. The updating of maps along the Tisza started in 1974 but later it was postponed. Preparation works called att ention to the process of silting up (Sass, J. 1981). Nevertheless, fi lling up of the fl ood bed and formation of point 8 bars had been neglected up to the turn of the millennium. It might sound absurd, because Vásárhelyi’s concept was a controversial issue, just on the basis of this problem. Though some experts did take into account the rise of high water stages on the fl ood plain pressed by the embankments, the rate of sedimentation was underestimated. Nowadays this has led to a situation when the embankments need to be raised regularly and if the present conditions are going to survive, this problem is here to stay (Fig. 3). According to the measurements and joint mapping activities of the Geographical Research Institute HAS and KÖTIVIZIG, the fl ood bed of the Tisza river at Szolnok has been silted up in a thickness of 200–240 cm since the water regulation measures. During the same period the fl ood plain of the Körösök has raised by 160–180 cm. The 5, 10 and 13 cm thick sediment layers accumulated by the fl oods of the past years or decades are clearly discernible (Figs 4 and 5). Based on VITUKI (1983) data each fl ood of the Tisza between 1976 and 1983 left an average 30 cm thickness of deposits, in spite of the miti- gating eff ect of the Kisköre water reservoir. During the great fl ood of spring 2000, 14 cm thick sediment was deposited upward Szolnok. This process will lead to the situation when fl ood waves occur higher than the level of the low fl ood plain prior to fl ood control measures, which used to be inundated regularly. E.g. now the Tisza does not fl ow along the deepest line of the valley but upon a silted up fl ood bed so once it steps out to the fl ood plain, the return of its water to its elevated channel is made impos- sible. It seems the same is happening to the Tisza and its larger tributaries as it has occurred to the Huang He in China or to Po River and its environs in Italy (Fig. 6). Fig. 3. Rising of the embankment along Tisza (Schweitzer, F. 2000) 9 Fig. 6. Bloc-diagram showing silting up of the channel of Huang He, China (aft er Cholnoky, J. 1900). The initial height of the embankment was 14 m and the fl ood bed was fi lled up to 11.5 m. The distance between the dikes was ca 11 km (Schweitzer, F.–Nagy, I.–Alföldi, L.) Fig. 4. Profi le of the fl ood bed sediment sequence along the Körös River in Takácszug. – 1 = grey micaceous sand; 2 = grey silty sand; 3 = dark brown clay; 4 = stratifi ed silty clay; 5 = grey silty fi ne sand; 6 = grey fi ne sandy silt; 7 = greyish-brown hydromorphous soil; 8 = hydro- morphous soil formed prior to fl ood control measures; 9 = infusion loess (Schweitzer, F. 1999) Fig. 5. 137C distribution in the sediments of (fl oodway) point bar (I.) and Marótzugi-Holt-Tisza (abandoned me- ander, II.), aft er Braun, M.–Dezső, Z.–Hadady, Gy. 2001. – A = depth; B = 137Cs activity concentration; 10x = tenfold magnifi cation 10 An extreme rate of silting up of fl ood beds is described in the book writ- ten by Jenő Cholnoky entitled 'The land of dragons' (1900, p. 293) in relation with the Huang-he at Kaifeng. He writes: "I approached the big river from the large sett lements stretching at the mountain foothills and reached it on 13th January. The height of the embankments is14 m but the river fi lled up the channel so that they are only 2.5 m higher above the fl ood bed. Terrible situation! No wonder that the failures of the dikes along the Huang He are so devastating!" ( It is widely acknowledged that in 1999 and 2000 dike failures could be prevented along several sections of the Tisza and its tributaries in the Great Plain only with the involvement of enormous material expenditures and hu- man eff ort. However, in 2001 in the Bereg environs a dike failure occurred at Tarpa (Fig. 7). On the map compiled by Ihrig, D. (1952, Fig. 2) the most critical places and the extent of the waterlogged area can be seen. Fig. 7. Geomorphological sketch of the environs of Tarpa (comp. by Balogh, J. 2001). – 1 = rim of the high fl ood plain; 2 = high fl ood plain; 4 = fi lled up former meander; 5 = cut-off me- ander, waterlogged; 6 = slope, undistinguished; 7 = higher summit level between 160–180 m; 8 = lower summit level between 140–150 m 11 Fig. 8. Geomorphological sketch of the section between Tiszakécske and Csongrád. – 1 = low fl ood plain; 2 = high fl ood plain; 3 = sett lement; 4 = embankment 12 13 No chance must be given to what occurred repeatedly in the 20th century (1919, 1925, 1940, 1948, 1970, 1974, 1998, 1999, 2000) that the high water reached or overgrew the crest of dikes and levees. The latt er were constructed for a prob- ability of the occurrence of the highest fl oods once in 50 years. Owing to the silting up of the fl ood bed they are either to be raised time and again (which has been the practice so far) or it must be completed by another solution. The opening of the fl ood bed in places where the emergency storage is allowed by geomorphologic, economic and social geographical conditions and by the infrastructure would contribute to the revival of quasi-natural conditions (Schweitzer, F. 2001, fi gs 8 and 9). The construction of detention reservoirs is considered part of the amended Vásárhelyi Scheme (Váradi, I.–Nagy, I. 2002, Fig. 10). Also this could provide solution for a nation-wide strategic problem because emergency situations threaten the security of life and property of nearly 1.5 million people. To counterbalance a permanent rise of fl ood levels dikes and levees must be enforced and raised periodically. As it was the case during the high water stages of the Tisza in 1999 and 2000, a system of more than one hundred years' age is slowly improved at the price of incredible hu- man eff ort and material means. The question however is if the whole system is able to meet the security requirements during the forthcoming centuries. Large hydrological schemes must be supported with huge investments and they are to serve for long duration; their substitution is highly expensive and time consuming. Along the Körösök a very narrow (50–70 m wide) fl ood bed was left during water regulation in the late 1800's (Alföldi, L. 1999). It con- tinues into the 150–200 m wide fl ood bed on the Transylvanian part of the valley. This funnel-shaped confi guration has resulted in a bott leneck and led to fre- quent dike failures, threatening with piping and extension of waterlogged areas during each fl ood. To prevent this hazard either fl ood beds should be broadened along the Hungarian section or the dikes must be relocated (Fig. 8). ← Fig. 9. Geomorphological map of the outlet of Körösök to the Tisza (comp. by Balogh, J. 2001). – 1 = low fl ood plain; 2 = high fl ood plain; 3 = cut-off meander, intermitt ently waterlogged; 4 = cut-off meander, permanently waterlogged, with reed-sedge vegetation; 5 = cut-off meander, intermitt ently waterlogged, with reed-sedge vegetation; 6 = fi lled up former me- ander, intermitt ently waterlogged; 7 = fi lled up former meander in fl ood-plain gallery forest; 8 = fi lled up former meander in fl ood-plain gallery forest, intermitt ently waterlogged; 9 = fi lled up former meander cultivated as cropland; 10 = = fi lled up former meander, drained; 11 = alkaline, waterlogged fl at; 12 = wind blown sand; 13 = sand dune. Man-made landforms: 14 = row of pits on the fl ood bed (for dike construction); 15 = row of pits for dike construction with gallery forest coverage; 16 = kurgan; 17 = fl ood levee; 18 = highway; 19 = railway; 20 = sett lement; 21 = boundary of natural microregion; 1.7.23 = Tiszazug; 1.8.12 = South Tisza Valley; 1.12.22 = Csongrád plain; 1.13.23 = Körösszög 14 Fig. 10. Detention reservoirs in the Tisza Valley according to the amended Vásárhelyi Scheme (Váradi, I.–Nagy, I. 2002) 15 Further development of the Vásárhelyi Scheme (2002) is aimed at the lowland storage of water transported by fl oods (Fig. 10) Another opportunity is the enlargement of fl ood beds up to the geomorphological levels of the high fl ood plains (fi gs 8 and 9). This solution would contribute to the safe fl ood con- trol and improve the biological habitability of the landscape if on the protected side (low fl ood plain) reservoirs of integrated use (accommodating abandoned channels) were constructed. These storage facilities as organic part of the natu- ral environment (e.g. Bodrogzug, Köröszug, Tiszanána, Cserőköz) would play the ecological role of the swamps of past centuries. The realisation of similar schemes is the responsibility of academic research. The temporal perspective of these investigations is some hundred years. 150 years ago Pál Vásárhelyi outlined a nearly perfect scheme meeting the contemporary demands, yet leav- ing behind quite a number of problems to be solved in the near future. In the fi rst step a number of questions must be answered by scientifi c research which have been outlined by the author in an earlier study (Schweitzer, F. 2000): Studies on the evolution of the Tisza valley over the past ca ten thou- sand years with mapping of buried and current channels and their intersec- tions, since the latt er pose a piping water hazard; Exploration and measurements of the rate of silting up of the fl ood bed, a survey of changes having taken place since fl ood control and water regulation measures; measurements on pollutants transported from the catch- ment area to the fl ood bed and accumulated there; clearing out if sediment accumulation is uniform over the diff erent parts of the fl ood bed and if there is a proven relationship between the distance from the dike and the rate of sedimentation; Mechanism of the evolution of point bars and natural levees and their relationship with the silting-up process over the fl ood bed; Investigations into historical changes of forest coverage of the moun- tainous sections of the drainage basin of the Tisza and its tributaries; Mapping and evaluation of the confi guration of high fl ood plain (high bank) and levees; study on the opportunities to extend fl ood bed, in some places elimination of embankments, function of which could be taken over by high banks in the future; or (as an alternative) construction of levees in more distant areas, investigations into the storage capacity of the extended fl ood bed; Geoecological-geomorphological investigations over the fl ood plain and fl ood bed aimed at the rapid conduit of fl oods and at an adequate storage of excess waters; Adequate treatment of the vegetation spreading over the fl ood bed. The gradient of the channel along the middle reaches of Tisza is 3 cm per one km and the current of water is slowed down by the emerging thick shrub; Economic and social geographical studies. – – – – – – – – 16 In the Tisza Valley the length of embankments of primary and sec- ondary categories is 1320 km, to this 119 km high bank section is added mak- ing up 1439 km as the total length of fl ood levees. In the course of the river regulation measures the length of the Tisza was reduced from 1420 km to 977 km. At present the 600 km long Hungarian section of the river is fl anked by 1085 km long embankment. If raising of crests of dikes is to enjoy priority, it will have to be ex- ecuted in the future more frequently than previously, owing to the intense silting up of the fl ood bed. REFERENCES A Tisza vidék problémái és fejlesztési lehetőségei. – FVM–MTA RKK ATI. Kézirat. 2000. Alföldi L. 2000. A magyar vízgazdálkodás stratégiai kérdései. – MTA Stratégiai kutatások. 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