Flood Risk Mitigation in the Tisza Valley by Deep Floodplain Reservoirs: the Effect on the Land Use

Journal of Environmental Science and Engineering B 1 (2012) 34-40 Formerly part of Journal of Environmental Science and Engineering, ISSN 1934-8932 D DAVID PUBLISHING Flood Risk Mitigation in the Tisza Valley by Deep Floodplain Reservoirs: The Effect on the Land Use Zsófia Derts and László Koncsos Department of Sanitary and Environmental Engineering, Budapest University of Technology and Economics (BME), Budapest H-1111, Hungary Received: July 13, 2011 / Accepted: August 8, 2011 / Published: January 20, 2012. Abstract: The actual situation of the Tisza Valley traditionally used for land farming is basically determined by the consequences of the river regulation of the nineteenth century which aimed at the extension of the intensive agriculture, by the extreme water regime of alternating periods of flood showing a deteriorating trend and drought related to the climatic change; and by several environmental problems induced mainly by the land use. The objective of the article is to prove the regional advantages of a proposed technical solution to mitigate the flood risk with a special regard to the land cover. Hydrodynamic modeling results prove that the best technical solution is given by a combination of different strategies containing the inundation of deep floodplains-areas regularly covered by water before the river regulation works and, globally, by an important mitigation of flood damages, the costs of solution would be surely covered in the longterm. By means of its natural-resembling operation, the regular water cover would allow a multiple use of water, contributing to the solution of the simultaneously existing aridity problem, and, the development of the floodplain landscape management would help improve the ecological and the economical upgrading of the region. Key words: Aridity, deep floodplain, flood control, land use, landscape management. 1. Introduction geographical centre of Europe [2]. The Tisza River can be divided into three sections (upper, middle and The Tisza Valley in Hungary has suffered of grave downstream section) [1] from which in Hungary flood damages and, looking back to the extreme flood mostly the middle and downstream sections can be events of the past decade, the risk shows a found, both characterized by a meandering platform deteriorating trend. What is more, the situation of [2]. According to its hydrological situation, the these areas, characterized by flood damages is precipitation in the Hungarian Tisza Valley is less aggravated by aridity and environmental quality problems related to the land use. than 500 mm per year. The mean annual discharge at 3 The main objective of this article is to propose an the mouth of the Tisza River is 792 m /s [2]. The effective technical solution for flood mitigation, to Tisza Valley has an extreme water regime: smaller analyze the limits of its execution with the current flood events occur in every 1-2 years and larger ones land use and to give a suggestion for the complex in every 5-6 years [3] regularly alternating with issues of the Tisza Valley. drought within short periods. 1.1 Geographical Situation of the Tisza Valley 1.2 Human Impacts The 157,000 km2 large Tisza River basin takes part In Table 1, the actual problems of the Tisza Valley of the Danube River basin [1] and can be found in the mostly related to human activities are summarized. 1.3 Possible Technical Solutions Corresponding author: Zsófia Derts, Ph.D. student, main research field: environmental modeling. E-mail: [email protected]. The following interventions are possible to solve Flood Risk Mitigation in the Tisza Valley by Deep Floodplain Reservoirs: The Effect on the Land Use 35 Table 1 Problems of the Tisza Valley related with causes and issues. Causes Problems Issues Increased frequency, occurring period Flood protection, water supply for Climate change [4] and level of flood events; aridity of ecological and agricultural (human) inner areas needs Material damages from flood levels Deficiencies of the actual flood Development of the flood protection exceeding the dykes and from protection system [5] system geotechnical catastrophes Degrading the water exchange between Sedimentation of the floodplains [6] the main river bed and the floodplain; Increasing flood risk Improving water exchange between the Necessity of raising dyke levels [1]; Tisza and its flood area; improving the Regulation works: meanders cut, river sinking of the main river bed leading to hydraulic conductivity of the floodplain length shortened, slope increased, the decline of the groundwater level; by regular maintenance velocity increased, cross-section 167 larger and numerous smaller reduced [1] oxbow lakes disconnected [2] 96% of the original 25,900 km2 ancient floodplains isolated [10]; decrease of Changing the land cover by taking in groundwater level [2]; Extension of drained areas for intensive account the nature and the original local leading to the disadvantageous agriculture [7-9] circumstances; and by satisfying human modification of the water balance and needs for nourishment to the extension of arid areas; decrease of biodiversity; Application of inappropriate technologies and of excessive amounts Diffuse nutrient loads runoff and soil Adequate technologies, development of of chemicals in agriculture; deficiencies erosion increased [2], decrease of the sewage and waste water treatment of the sewage and waste water groundwater quality [11] system treatment system [11] Establishments (residential and other Material damages caused by major Revision of the permission system for buildings) in areas anciently covered by flood events constructions water Revision of the agricultural financial Further extension of intensive support system, and research for one Agricultural financial support system agriculture land use that supports land uses more adaptive to the nature the flood risk problems: water storage in deep floodplains (anciently regularly The correction of the flood levees among the covered by water) during flood waves would be a Tisza by repairing the problems of designing and of technically efficient way to mitigate flood risk. Our technical condition; objective is to analyze the feasibility of this idea in the Amelioration of the hydraulic conductivity of the aspect of the land cover. floodplain; 2.1 Available Information Emergency flood reservoirs filled up in every 30-40 years as an average in case of extreme flood For our research work the following georeferenced waves [12]; digitalized maps, GIS data and descriptive literary Regular Inundation of low elevation areas called information were available: deep floodplains which used to be covered by water The former (nineteenth century) [7, 8] and for 2-4 months per year before the nineteenth century present (CLC 50) land cover of Hungary [9], Google regulation works [13, 14], to increase the efficiency maps, 50*50 m cells morphologic model for the Tisza of the shrinkage of floods. Valley; GIS data for drought and flood risk (provided by 2. Methodology VITUKI Environmental Protection and Water According to our previous research work [15], Management Research Institute of Hungary); 36 Flood Risk Mitigation in the Tisza Valley by Deep Floodplain Reservoirs: The Effect on the Land Use The Hungarian map of the areas anciently comparative analysis of the ancient and current land regularly covered by water (flooded areas and covers and the potential risks for each chosen deep wetlands); floodplain. Historical landscape and ethnographical 3. Model Analysis and Calculation Results descriptions of the Tisza Valley [16], descriptions and modeling results concerning the flood risk and its As a result of the 2D hydrodynamic simulations, a influencing factors in the Tisza Valley [3-6, 14] etc.. sum of 2.5 milliard m3 of regularly inundatable deep floodplain capacity has been found for the Hungarian 2.2 Hydrodynamic Modeling and Inundation Tisza section without affecting seriously the Frequency Calculations surrounding settlements (see Fig. 3). In a previous phase of our research [15], the The water level decreasing efficiency of the deep potential technical solutions and their combinations floodplain reservoirs was compared in case of several were compared by computer models connected with settings for historical flood records of the last fifteen each other: years, and it has revealed that however each flood 2D hydrodynamic model based on the equations wave is different; the average flood level mitigating of shallow waves [17] resulting connected water level, effect would have always exceeded 1.0 m on the reservoir volume and water surface data; Hungarian section of the Tisza River. The 1D hydrodynamic model based on the optimization of the studied system has resulted that Saint-Venant equations [12] calculating the flood 20-30 meters large sluices and continuous and level decreasing effect of the deep floodplain bidirectional operation would be ideal in a way that reservoirs in case of different operational settings; the sluices would be closed when the water level A flood risk model determining the normal exceeds the maximum allowable level at the entering distribution intervals of different types of material point (to prevent flood damages in the settlements and damages in actual and designed conditions in establishments). different scenarios by Monte Carlo simulations [11]. From the flood damage cost statistics given by The results of the mentioned modeling analysis Monte Carlo simulations of 5,000 generated flood processes constituted

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