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Temporary flood water storage in agricultural areas in the Middle Tisza river basin - Hungary

Temporary flood water storage in agricultural areas in the Middle Tisza river basin - Hungary

The flood risk management strategy of Tisza River was  improved with the creation  of temporary flood water storage reservoirs. It proved its effectiveness, though the current prevailing land use prohibits unlocking its full potential. An up-do date cost-benefit analysis can inform future plans of more recurrent use of such polders to cope with more frequent peak flood events and provide a wider range of nature based solutions at the same time.

The observed increasing exposure to floods in the Tisza River floodplain is a consequence of the river regulation and land reclamation works that historically shaped the landscape of this area. During the last 150 years, an extensive flood defence and water management infrastructure has been constructed. Climate and land use change in the basin are increasing the frequency and magnitude of floods. The Hungarian Government has been pursuing a new flood defence strategy for the Tisza river basin incorporating the use of temporary reservoirs (polders) where peak flood-water can be released. A plan to build six reservoirs was adopted and implemented, with the option to build additional five. The six reservoirs proved to be effective in mitigating the risks of flooding during observed extreme weather events, protecting the downstream territory. At the same time, since a large part of the surface of reservoirs is located in agricultural areas and no land-use change was adopted, an economic compensation scheme was implemented by the Government. It aimed at remunerating farmers in case of damage to the agricultural soil and yield losses during flood events. A cost-benefit analysis of the selected strategy was performed. The analysis  revealed that it well represents a trade-off between efficiency in risk reduction and relatively low initial investment costs. The participation in the EU-funded project EPI-WATER stressed the importance of a more active stakeholder involvement in the design of the measures and in the compensation scheme.

Case Study Description

Challenges

Near the geographical centre of Europe, the Tisza river drains an area of 157,218 km2 with a population of about 14.4 million. On its route from the Ukrainian Carpathian Mountains to the with the Danube in Serbia, the Tisza mainly flows through Hungary’s Great Pannonia plain. The topography of the Tisza river basin  is characterized by high, narrow chains of mountains surrounding expansive, flat lowlands. With a length of 966 km and an average discharge of 794 m³/s, the Tisza is the Danube’s longest and second largest tributary. Most discharge is generated directly from rainfall but there is a contribution from both snowmelt and subsurface soil water. Serious floods can originate from the mountains when rainwater flows quickly down the slopes and accumulates in lowland areas. This problem has become more and more serious over time as deforestation and soil sealing had progressed and precipitation patterns changed due to climate change.

The river and its tributaries were regulated in the second half of the 19th century. The main purpose of this regulation was to increase the extent of agricultural land, in place of wetlands, marshes and areas at risk of regular flooding (Borsos et al., 2018). The length of the river was reduced by over 400 km as the meandering sections were cut through, while the size of the floodplain area decreased by over 90% as dikes were raised to protect against floods. River straightening, combined with other factors (sediment accumulation in some river sections, deforestation, land use change) has caused the continuous increase of  peak flood water levels.  Taking into account a few historical recorded flood events, peak water level was 753 cm in 1876, 909 cm in 1970 and 1040 cm in 2000 (Szlávik, 2005).

Today, the length of the flood defence dikes along the Tisza and its tributaries in Hungary is 2850 km. The size of the flood-protected territory is 16,000 km2, out of the total catchment area of the Tisza in Hungary of 47,000 km2. As the peak level of floods continued to increase during the last century and a half, so did the height of the dikes. A further rise of peak flood levels is projected for the 21st century as a consequence of climate change, and the current level of flood embankments will not be sufficient to provide adequate protection. Flood defence exclusively based on the enlarging and strengthening of embankments is estimated to be excessively expensive. In 1999, a research project funded by World Bank estimated that the cost of the remaining upgrade works would have been HUF 175 billion, equivalent to EUR 700 million at a 1999 exchange rate (Szlávik, 2005).

In the period 1998-2001 four serious flood events took place on the Tisza river with peak water levels exceeding all historical values. One of the events (2001) included the rupture of a dike and the flooding of areas that were supposed to be protected. This event made clear  that neither the height of the dikes, nor their strength were  adequate. Afterwards, a 4-year-long project was launched to investigate the validity of the flood risk projections used at the time (studies by VITUKI Environmental and Water Management Research Institute, 2006). The project applied  novel methods of time series simulation processes and used a revised historical hydrological database. It considered the impact of several changes (in forest cover, reservoirs, and flood embankments) within the different sections of the rivers passing through Hungary, also including climate change (Haase et al., 2006). The key conclusion of the project was that, compared to previous projections, there is increased uncertainty and higher expected water levels during floods. Water levels are expected to further increase as consequence of climate change. In this regard, a shift in pattern of rainfall events is observed in Central Europe. Even without a substantial change in average precipitation, more concentrated precipitation events  with higher discharges volumes are expected (Ungvári, 2022).

Objectives

The overall objective of the flood protection strategy for the middle Tisza river basin is to adopt cost-effective measures. The proposed measures aimed at ensuring an adequate flood protection level able to cope with the changing conditions of the river basin and the consequences of increasing peak flows. The strategy was designed to respond to the changes in local climatic variability and specific characteristics of the hydrological system.

Solutions

As a first reaction to the 1998-2000 floods, the government decided to speed up the on-going process of strengthening the dikes: the first plan (Government decree n.2005/2000) focused on the reinforcement of 740 km of dikes over a ten year period. In the second stage, the governmental strategy intended to intensify the process further by strengthening an additional 550 km of dikes, but in a shorter period of 5 years. The works started, but suddenly the programme was stopped.

A new Act was designed in 2004 with broader objectives: to increase flood safety  by the reactivation of former floodplain territories and the management of the water surpluses, the development of the regions with most disadvantageous status and the improvement of living conditions in these regions.

The new plan for flood safety included: the strengthening of the existing weak points of the dike system the restoration of the run-off capacity of the flood channel (the cross-section between the dikes) and the completion of temporary flood reservoirs (also known as “polders”) to reduce the peak of the biggest flood waves with a total capacity of 721 million m3 in the long term. The intention was to give room to the river using agricultural areas as temporary storage reservoirs for containing peak flow during extreme events. According to this plan, the area utilised for agricultural purposes in normal conditions, can be eventually flooded (intentionally and under controlled conditions) and utilised for temporary retention of flood waters in case of emergency. This system is designed to supplement the dikes to cope with floods with a return period of 100 years or higher. It allows buffering during extreme precipitation events and reducing flood wave propagation, with consistent beneficial implications for flood risk mitigation. A mechanism of economic compensation for the farmers involved in the construction of water retention reservoirs was put in place. Compensation is composed on two items: an upfront one-sum compensation for all the inconvenience and value loss associated with the scheme and an event-based damage compensation, to compensate possible economic losses due to the flooding of the agricultural area. The flood risk mitigation system, based on the temporary flood water storage in agricultural areas, proved to be extremely effective for the purposes of disaster risk reduction. It also revealed trade-offs for the agricultural production of the affected areas, that cannot be completely recovered with the compensation scheme.

The first polder was inaugurated in 2009, while all the other five planned temporary reservoirs were completed in the following years (2010-2015) with financial support, both from national and EU funds. One of these polders was successfully used in a 2010 flood event. Hydrological modelling results (Ungvári and Kis, 2022) show that using more than one polder at the same time for major flooding events further mitigates risks compared to the use of a single polder. The same study suggests that adding more polders to the current system can be effective in reducing risks with an acceptable investment cost range.

Relevance

Case developed and implemented and partially funded as a CCA measure.

Additional Details

Stakeholder Participation

The initial purpose of the plan was to include a wide, multi-disciplinary and multi-sectoral participation in the strategy planning process. This has not been fully accomplished in the implementation phase (Sendzimir and Magnuszewski, 2008). The flood mitigation project was designed with an approach aimed at minimizing the amount of agricultural land surface to be involved. In this way, policy makers tried to minimize the potential conflicts with farmers and landowners that could represent an obstacle for the development of the project. The design and implementation of the plan and the rules to operate the reservoirs were made by the central government (national level). The Government also identified the most suitable sites for the construction of the flood-water storage reservoirs. Farmers and landowners , not properly involved in the design of the strategy, were asked to accept the decision of the government (receiving an economic compensation for the potential losses) or be subject to the expropriation of their land for public use. In this second case, according to the landowners interviewed, the sum paid out by the government was considered consistent with the market value.

This case was analysed in the context of the EU FP7 funded project EPI-Water, Evaluating Economic Policy Instruments for Sustainable Water Management in Europe. Within this project, a compensation scheme able to better satisfy the requests of the agricultural sector and the needs of government was designed.

For the EPI-Water project, the participation of the stakeholders has been considered crucial. Landowners and farmers operating in the floodable areas and representatives from the regional water directorate were involved in the development of a compensation scheme that would have been able to more fairly compensate for the losses to the agricultural sector. The analysis conducted within the EPI-Water Project proposed to the farmers and government an Economic Policy Instrument based on a flat fee paid to the farmers plus compensation in case of flood. According to the project results, this scheme, not actually implemented, would have several benefits:

  • Improved farmers’ financial compensation with a scheme that could be perceived as more transparent and fair, increasing the public acceptance of the flood management strategy;
  • Incentive for the farmers to reduce the amount of value exposed to flood events. This could be realised by a different use of the floodable areas, lowering the value of the crop at risk within the reservoir. This would make the whole scheme cheaper in the long run;

Stakeholder consultations performed during the research project revealed that the parties involved had different interests: representatives of the government were in favour of modifications aimed at improving the scheme, while farmers had mixed opinions driven by their specific economic conditions. However, although for different reasons, both parties expressed scepticism about the viability and enforceability of long term agreements.

Success and Limiting Factors

The strategy adopted by the government has shown to be extremely effective in terms of flood risk mitigation, being scalable and flexible enough to cope with the uncertainty of future climate change projections. The retention of flood waters in the identified temporary reservoirs is crucial for the reduction of flood frequency and magnitude in the downstream areas, with considerable benefits for the cities located along the river. Unfortunately, as frequently happens in these cases, not all the stakeholders are enthusiastic about the solution adopted. Farmers claim inadequate consideration of their views and perspectives in the process that brought the government to use their land for temporary flood-water storage. Landowners are called to use their property for providing an important service, but they have not been involved in the design of the flood management strategy and the associated operating rules. This fact limited the acceptance of the measure by several stakeholders, hindering the success of the initiative.

Indeed, the current scheme revealed the existence of multiple problems, making the use of the reservoirs expensive for the government and, at the same time, leaving farmers and landowners dissatisfied. Limiting factors included the following unresolved issues about the compensation scheme:

  • Compensation is not adequate in comparison to the real amount of damages. It compensates the yield losses, but it does not take into consideration soil rehabilitation and the financial consequences due to the disruption of the seasonal production cycle. These extra costs are particularly significant for high value cultivations.
  • Long processing time, up to one year in some cases, for the compensation process to be completed.
  • High unpredictability of the compensation scheme cost over time, with potential high impacts on the national financial budget.

An increasing frequency of future floods, projected by the hydrologic models, is expected to increase the amount of damages to the agricultural sector. This could exacerbate the already delicate debate between local farmers and the government and increase the opposition to the construction of new retention areas.

Costs and Benefits

The use of polder systems offers many benefits in terms of flood risk mitigation. The solution is easily scalable and flexible (activation of a single  polder or different combination of two or more polders), able to face the wide range of uncertainty that features future projections of extreme flood events.

The solution adopted resulted in an overall cost of around 260 million Euro. The strategy has been implemented with the contribution from the European Regional Development Fund and the Cohesion Fund.

Several analyses have been conducted in order to assess costs and benefits of the chosen flood mitigation strategy. The results of a comprehensive ex-post cost-benefit analysis (Koncsos 2006) showed that the implemented scenario, with 6 reservoirs and no modification to the existing dike system, substantially reduces the risk compared to the baseline (no intervention). It represents a trade-off between efficiency in risk reduction and relatively low initial investment costs. The scenario analysis also highlighted that further investments in flood defence infrastructures are economically justified.

An up to date cost-benefit analysis performed in 2022 (Ungvári and Kis, 2022) showed that using most reservoirs is economically justified even for floods with a return period of 20-30 years. Hence, most reservoirs would  be advantageous even if they were used with a higher frequency than the originally planned one (100-years events). However it poses the issue of maintaining the current land use (with special reference to agriculture) or adapting it in the long term (towards a forested area) to accommodate new and more frequent use of polders as flooding reservoirs.

The designed flood protection strategies were planned as to be integrated into a wider process of regional development. It envisioned large scale landscape and social rehabilitation efforts. Those measures should be  combined with the restoration of the natural ecosystem of the region characterised by a complex system of wetlands.

The solution of establishing the temporary flood-water retention areas is in line with the requirements of the EU Water Framework and Flood Directives. The intervention adopts  a flood mitigation strategy that is respectful of the natural ecosystems and the natural hydrodynamics. However, since a large portion of the Tisza river basin is dedicated to agriculture, further constrains derive from the implementation of the Common Agricultural Policy and its system of subsides that influence landowner decisions.

The compensation schemes for farmers is established through a legal act. However, its implementation left a considerable uncertainty with regard to the agricultural production process, raising the direct costs as well as the opportunity costs for the farmers.

Implementation Time

The flood protection strategy with the realisation of six water retention areas was implemented during the period 2009-2015. An additional water retention area along the Tisza river was created in 2022.

Life Time

The water retention areas are planned to last more than 100 years.

Reference Information

Contact

Gábor Ungvári
Corvinus University of Budapest
Regional Centre for Energy Policy Research
Tel.: +36 1 4827073
E-mail: gabor.ungvari@uni-corvinus.hu

András Kis
Corvinus University of Budapest
Regional Centre for Energy Policy Research.
Tel.: +36 1 4827073
E-mail: andras.kis2@uni-corvinus.hu

Attila Lovas
Middle Tisza District Water Directorate
H-5000 Szolnok, Boldog Sándor I. krt. 4.
Tel.: +36 30 2797727
E-mail: lovas.attila@kotivizig.hu
Generic e-mail: tiszaoffice@kotivizig.hu

Published in Climate-ADAPT Jan 06 2023   -   Last Modified in Climate-ADAPT Jan 06 2023


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