Environment
Retention areas best protection against flooding
The so-called closing structure of the Straussfurt flood retention basin. photo
© Martin Schutt/dpa
Rivers that have burst their banks can devastate entire regions, destroy towns or kill people. An EU study shows which protective measure could be the most efficient.
According to an EU study, retention areas are the most cost-effective method of reducing potential future damage from river floods. In the European Union and Great Britain, flood damage could increase to an estimated around 44 billion euros per year by the end of this century, the researchers write with a view to climate change.
Retention areas could reduce this amount to around 8.1 billion euros, as calculated by the team led by Francesco Dottori from the EU Commission’s Joint Research Center at the Ispra site in Italy. The number of people affected by flooding would then be around 80 percent lower than without flood protection.
The experts assumed that the global temperature would rise by three degrees by 2100. According to climate researchers, this happens if climate protection is not significantly strengthened. For Germany, they calculated an average of 383 million euros in required annual expenditure from 2020 to 2100 for the retention areas. The cost-benefit ratio is around one to four euros.
Water can be drained off in a controlled manner
According to the analysis, river floods in the EU and Great Britain currently cause an estimated 7.6 billion euros in damage every year. About 166,000 people are exposed to them each year. The researchers understand retention areas to be areas or basins in or on the course of a river into which water can be drained off in a controlled manner and temporarily stored when water levels rise sharply.
According to the researchers, the remaining protective measures such as dyke construction, flood-proof buildings and resettlement would be less cost-effective when viewed as a whole. Although dykes are economical, they have disadvantages for the environment, society and the economy if this method is used extensively. From a cost perspective, flood-proof buildings are more worthwhile selectively, but not over a large area. Resettlement is too expensive because new land has to be bought, old houses demolished and new ones built.
Floodplains can play an important role
The environmental protection organization WWF Germany referred to flood plains as ecological flood protection. “By restoring river floodplains, water retention in the area is improved by giving the river more space,” said WWF International Water Resources Officer Theresa Schiller. Such flood protection has a beneficial effect on the landscape water balance, which is gaining in importance due to increasing droughts.
Dottori’s experts pointed out that their results could only be of limited validity in practice. On site, a combination of multiple flood protection strategies, tailored to local conditions, should achieve the best results. They also mainly included the monetary benefits of the various measures, without taking social, economic or cultural aspects into account.