Outline of floods as well as flood prevention and flood protection activities in Hungary

Transcription

1 AARMS Vol. 10, No. 1 (2011) TECHNOLOGY Outline of floods as well as flood prevention and flood protection activities in Hungary RÉKA MAGDOLNA RÁCZ Miklós Zrínyi National Defence University, Budapest, Hungary The article tends to give useful ideas about the reasons and features of the floods in Hungary as well as the ways and potentials of flood prevention and flood protection. My purpose is to make the readers recognize the importance of the up-to-date state and improvement of flood protection, the complexity and relevance of flood prevention and protection. Due to the climatic and geographic features of Hungary the high level flood risk has permanently had to be considered. Floods in Hungary Comparing Hungary s territory with the country s flood area, the flood risk is the highest in Europe, because the 23% of Hungary s territory is made up by flood areas along river valleys, while its 10% along minor streams. 1 Due to its climatic and geographic features, over its history Hungary has always been exposed to flood risk. The reasons are various. Hungary is situated in the drainage basin of the Danube, in the deepest part of the Carpathian Basin. Besides, it is a flat country. Nearly 70% of its territory lies lower than 200 metres, only 1% rises above 500 metres. Its eastern part is the deepest with its metres elevation above sea level. 2 Most rivers of the Alps and the Carpathians flow into the two major rivers of Hungary: the Danube and the Tisza. Consequently, the sudden melting of snow in the above mentioned mountains or a huge amount of the falling precipitation result in flooding in Hungary. (This incident is especially dangerous in the area of the Upper-Tisza and its tributaries, and the rivers of Körös, as the water level might rise by 10 metres within hours after the rainfall. Besides, the floodwaves might be combined as consequences of the melting snow and precipitation. The flowing component the flowing quantity of precipitation can be increased by the following factors: saturated soil frozen soil inclined surface of the drainage area Received: January 19, 2011 Address for correspondence: RÉKA RÁCZ reka.racz@katved.hu

2 lack of vegetation or rare vegetation cold weather which decreases evaporation steamy air. The next types of floodwaves of the Danube, the Tisza and their major tributaries are identified: 3 floodwaves arising from precipitation or snow melting, which increase each other s effect accumulating floods of main streams and tributaries, coming from precipitation or snow melting floods raised by redamming caused by ice-jam other waters coming from redamming floods as results of man-made interventions. The vast majority of the rivers in Hungary spring in foreign countries, so their water output is formed and influenced by rivers of drainage areas in other countries. The rivers in Hungary are divided into the Danube and the Tisza water system. Depending the hydrographic features of the drainage area, on the Hungarian reach of the Danube two types of flood might rise. One is the result of snow melting, and appears in late winter or early spring. The other appears in summer after the extensive, huge rainfalls in the high parts of the Alps. Due to their water output summer floods are more dangerous. Considering the water output the Hungarian reach of the Tisza is devided into two sections: the Upper and Middle-Tisza. The Upper-Tisza is featured by three types of floodwave: spring, May and autumn floodwave. At the mouth of the Szamos the first and second ones merge, and meet the floodwaves of the Körös and Maros, the two major tributaries of the Tisza. High floods of long extension in the Middle-Tisza might often result dangerous situation. Additionally, we might face icy flood. Its development depends on the quantity and quality of ice brought by the river and due to the temperature, the water output, the water speed as well as the extent of the water surface, which are morphologic features. The icy flood is impossible to predict, because it s the consequence of ice jam or ice block. That s why icy flood is especially dangerous. 124 AARMS 10(1) (2011)

3 Figure 1. Ice block 4 All in all, Hungary has got four types of flood: winter-spring flood green flood summer-autumn flood icy flood. Relying upon former statistic figures Hungary faces minor or medium floods every 2 3 years, major floods every 5 6 years, and extreme floods every years. 5 The quarter of Hungary s area lies under the overflow level of deluge. These areas include 700 settlements with 2.5 million people. Also, these areas take in one-third of the croplands, 15% of the railways, and 30% of gross domestic product is produced on these flood affected areas. 5 Flood prevention in Hungary Flood prevention means the activities which prevent flood plain from inundation. Facilities of flood prevention are called flood prevention works. Flood prevention activities include the regulation of the rise of flood and the regulation of flowing of flood. Regulation of the rise of flood means e.g. setting of the drainage basin (e.g. guard dam building, terrace building) and the regulation of the land use. The latter is based on forestration and plantation of vegatation which retards the flowing. Regulation of flowing of flood means: 1.) the setting and conrol of the riverbeds 2.) bigwater control (bed cutting, dyke building, flood plain setting) 3.) use of flood decreasing drains and flow-control reservoirs. River control aims at counterbalancing the riverbed and the waterflow. River control has got three types: major-water control medium-water control minor-water control. AARMS 10(1) (2011) 125

4 Hungary prefers major-water control, because it provides better draining conditions for flowing floods. Also, it prevents the spreading of floods on the flood plain. To provide better draining conditions it is needed to convert the riverbed, to cut the curves, and to stabilize the bed. A possible way to divert floods is to apply flood decreasing canal. This method is applicable in case of fitting relief and waterflow. The flood decreasing canals have got three types: passing flood decreasing canal paralel flood decreasing canal evading flood decreasing canal. Applying a passing canal the water of the river is lead to another river in order to prevent the area below the passing from flooding. It only operates in case of suitable relief and flowing. In Hungary the floods of the Répce are lead to the Rába in order to prevent the lower section of the Répce. Using a paralel flood decreasing canal the flood of the river is devided in a section, then this canal in an upper segment is driven back to the river. In Hungary, applying this method, the Lajta has been prevented from flood. A special variant of paralel canal is evading canal. It s applied in big cities, where the river crosses the city. Through the canal the flood is lead out of the city, then evading the city it is lead back in a lower section. Flood protection in Hungary Technical and financial components make up the complex operation of flood protection. The objective is to recover as well as decrease the loss caused by flood. The following flood protection system operates in Hungary: primary flood protection works (total length: 4181 km, out of it 4027 km dirt dyke, 30 km flood protection wall, 124 km high bank) 6 flood decreasing canals (Lajta, Rábca, Répce) emergency reservoirs on flat areas secondary (locating) protection works. Flood protection means three types of operations: 7 1. When the water overflows the top of the dyke. Protection method means emergency dams, patrol service or both combined. The protection power of the primary works might be reduced by: ice drift, ice jam distortion of riverbed, alluvium 126 AARMS 10(1) (2011)

5 rolling water at high water level lack of local height measurement. Protection methods against ice drift and ice jam due to icy floods are prevention through river control as well as emergency dam i in order to increase the dyke. Figure 2. Emergency dam made from sandbags 8 Protection against rolling water has got three ways: floating works on water, reinforcement of dykes by building temporary cover, and protecting walls made from sandbags. To raise the top of the dyke means further increasing of the dyke through secondary structure as well as building emergency dams and crib dams. 2. Operations when water attacks the body of the dyke. Table 1. The effect of flooding and the way of protection 3 Effect of flooding Decrease of stability Slip of slope Infiltration of layer Infiltration of sole Crackings Erosion caused by rodents Way of protection supporting dyke on protected side ribbed supporting ribbed supporting supporting by natural-stones building berm filling up the gap e.g. with cofferdam network of leaking trenches, leaking berm counterpressing basin swelling of dyke i Various types of emergency dam: ED made from earth, ED made from sandsacks, ED made from sandsacks secured against rolling water, ED made from earth packed in geotextile, ED made from sandsacks with earthsupporting, ED with twigs filling. AARMS 10(1) (2011) 127

6 3. When water attacks through subsoil flood effects are as follows: soil gets soft on the protected side splitting of top-layer spring deliquescence of subsoil. Flood effects in the subsoil and ways of protection: Table 2. The flood effects in subsoil and the way of protection 3 Flood effects in subsoil Getting soft Spring, splitting of top-layer Deliquescence of subsoil Way of protection extension of infiltration length counterpressing basin cutting off granular load counterpressing basin ribbed load or load with permeable material Conclusion The National Disaster Management Strategy has rated the greatest risks for Hungary in the near future. Transportation of hazardous materials is the first, hydrologic risk is the second, impacts of extreme weather is the third. In my view, the climate change will result more intensive and more frequent rainfalls, which will increase the danger of flood, consequently requires to improve flood prevention operations. The Summary of the joint project called Change, Effect, Response (in Hungarian: VAHAVA) carried out by the Ministry of Environment and Water offers as for solutions: The experience of recent years has not only highlighted the complexity of draughts, inland waters and floods but also the possible remedy for them. Recent events have cleared up that the struggle of dykes with the height of flowing water can no longer be the single way of protection. Complex solution is needed, meaning to speed up the major water flowing, to break down partially or completely the summer dams, to change the agricultural-horticultural use of the areas, to develop water-basins, to let out the major waters, to improve the international connections with the transboundary catchment areas, to reinforce and look after the dykes. Urgent change in approach and complex flood protection operations are required by the events aroused be extreme weather, e.g. minor-major inundations, landslides, overflow of local waters, mudavalanches, violent storms, difficulties in sowing and harvest AARMS 10(1) (2011)

7 References RÉKA PALÁSTHY: The Tisza Extreme floods, Technical University of Budapest VAHAVA Summary. 6. BEÁTA OLGA FELKAI: Ecological issues of flood protection, Szent István University PhD thesis, GödöllR, AARMS 10(1) (2011) 129