Temporary Flood Water Storage in the Middle Tisza River Basin
The Tisza River, near the geographical centre of Europe, flows mainly through Hungary’s Great Pannonia plain. The Tisza River Basin (TRB), with a population of 14.4 million had been increasingly experiencing the challenge of flooding due to a series of changes made to the landscape. To address this challenge, a major project has since been implemented using the combined effect of different adaptation measures to reduce the risk of flooding and make sure that the area can cope with a changing local climate into the future. By improving river defences, restoring parts of the flood plain and creating temporary reservoirs for to contain flooding in agricultural areas, the flood risk has been significantly reduced and cities along the river are protected.
The Adaptation Journey
The positive impact
Between 1998 to 2001, four serious of floods occurred in the Tisza River Basin, including a rupture to dike flood defences which caused flooding in areas that should have been protected. This demonstrated that the dikes, walls along the river that hold back water, were not high nor strong enough to protect the basin from flooding. To protect the cities of the river basin and reduce the risk of flooding, cost-effective adaptation measures were adopted.
From 2007, weak areas of the dikes which had never been strengthened in previous attempts were improved, while to complement the dike flood protection system, the run-off capacity of areas between dikes was restored, and temporary reservoirs were created in agricultural areas that could be flooded when the river flow was high. In this way, more of the basin is protected from flooding and the areas chosen as reservoirs can still be used for agriculture at other points during the year, while during extreme rainfall the flooding frequency has been significant reduced. For example, in 2010, one of the reservoirs was successfully used during a flood event. By combining a mix of strategies, a balance was found between reducing the costs of the measures and avoiding taking too much land away from agriculture and other uses.
How does it work?
The temporary flood water storage in reservoirs on agricultural land works by giving the river room to flood specific areas with water during extreme flooding events. The reservoirs have a total capacity of 1 – 1.5 km3 and are used for agriculture in normal periods. During extreme rainfall events, the reservoirs provide a buffer for water flow, and reduce flood wave propagation by temporary allowing the river to flood them during emergencies.
The plan for implementing the reservoirs was supported by a new Act in 2004, which has the following objectives: Increase flood safety (partly) by the reactivation of former floodplain territories, the management of the water surpluses, the development of the regions with most disadvantageous status and the improvement of living conditions in these regions.
In addition, the participation of people to be impacted by the changes was crucial. Landowners and farmers operating in the floodable areas, alongside representatives from the regional water directorate, were involved in the development of a compensation scheme. This meant that land owners were paid for the losses to the agricultural sector due to the flood storage in reservoirs.
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 volume of 794 m³/s of water flowing through it, the Tisza is the Danube’s longest and second largest river tributary. Most water 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 the removal of soil by construction has increased, and precipitation patterns changed. The changes caused an increase in the water level during extreme events, which leads to flooding, and is expected to become an increasing challenge due to climate change.
Operation and maintenance
The lifespan of the measures implemented is expected to be 100 years. From an engineering perspective the strategy proved to be successful, however maintenance is required with respect to environmental damages within reservoirs. This has not yet been addressed in the project.
Obstacles and challenges
A major challenge for the plan was in the compensation scheme with landowners and farmers Problems with the present scheme which can make the use of the reservoirs expensive for the government and, at the same time, leave farmers and landowners dissatisfied. This includes the following:
• 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.
• It can take a long time, up to one year in some cases, for the compensation process to be completed.
• There is a 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 central government and increase the opposition to the construction of new retention areas.
In addition, some farmers have claimed that their views and perspectives were not fully considered, and feel dissociated from the design and operation of the flood management strategy. For similar projects in the future, active stakeholder involvement will be important to the process of developing a payment scheme that is more satisfactory for both parties than the currently existing process of compensation of the losses suffered by the agricultural sector. Through stakeholder involvement, the process and scheme would gain additional credibility and there would be increased acceptance of the effect of climate change on the future frequency of reservoir use.
How much did it cost?
The solution adopted resulted in an overall cost of around 260 million Euro, and the strategy was implemented with the contribution from the European Regional Development Fund and the Cohesion Fund.
Revitalization of water elements Agriculture landscape Flood control measures Floods and torrential rainfall Soil erosion