Dried-up reservoirs and fish ponds. This year has shown that they do not work as protection against drought

2018 - 12 - 01
Dried-up reservoirs and fish ponds. This year has shown that they do not work as protection against drought

The extreme drought that hit Central European countries this year has revived the debate on the construction of new reservoirs and fish ponds. But this year’s high temperatures have also shown that these methods of retaining water in the landscape do not work.
Indeed, this year’s precipitation was so low that even numerous reservoirs lost their water, as did many fish ponds. Even ponds that still retained water showed significantly lower water levels and, moreover, since August dangerous and poisonous blue-green algae covered bodies of water in many places.

“Water needs to be retained in the landscape, not in reservoirs. We must return to the natural forest structure as quickly as possible, since deciduous and mixed stands, and hence their soils, retain significantly more water than coniferous vegetation,” notes Miloslav Jirku from the Biological Centre of the Academy of Sciences of the Czech Republic.

“Farmland management must be improved, too. The use of heavy machinery compacts the soil, making it far more difficult for precipitation to seep into the soil. As a result of the use of chemical sprays, earthworms and other soil organisms which increase the infiltration of water two- and threefold have disappeared from the soil. Due to farming on large blocks of land, there are no obstacles to water as it flows away while taking topsoil with it,” adds Jirku.

For several years, scientists have been pointing out that healthy soil could, for example, retain 8.4 billion m3 of water in the Czech Republic. Currently, however, it retains 3.3 billion m3 less water – roughly 5.04 billion m3 in total – due to poor management. For comparison, one of the reservoirs under discussion in recent years would retain a mere 15 million m3 of water. Similar conclusions regarding the capacity to retain water can be drawn when comparing reservoirs and forests. According to environmentalists, three times more water was held by the three last remnants of alluvial woodlands and meadows in the eastern half of the Czech Republic during the 1997 floods than by all of the reservoirs in the same part of the country.

Measures leading to better soil management are thus of key importance. For example, according to Jirku, fields need to be split into smaller sections where different crops will be rotated. Grassy or uncultivated belts must be planted, especially where water needs to be retained so that it does not run off quickly with the topsoil.

“Every time floods or droughts occur, engineers dust off plans for reservoirs that weren’t built in previous decades, but it is precisely these massive interventions in the landscape that are one of the causes of the current situation. Reservoirs are not a solution to the problem – they are part of the problem,” says Dalibor Dostal, director of the conservation organization European Wildlife.

Improving the condition of forests and soil is not the only measure that can help water retention, and there are also other steps that would bring about a change for the better. For example, drainage should be stopped. This measure was taken for land reclamation projects particularly in the second half of the twentieth century, both in agriculture and forestry. Even at this moment, with Europe facing the issue of drainage, public funding can be used for this purpose in some European countries.

“It is precisely artificial drainage of the landscape that increases the pressure to retain water in other places by means of reservoirs. Engineering interventions in the landscape are extremely costly and never work as well as natural processes, proven by millions of years,” Dostal added. Building reservoirs is also an activity that consumes massive amounts of concrete. Concrete includes cement and steel – two raw materials whose production creates significant amounts of greenhouse gases that cause climate change, which in turn is one of the causes of the current drought. “In addition, the cost of building a single reservoir amounts to hundreds of millions or even billions of euros. This is money we desperately need for implementing truly effective measures in the landscape,” Dostal added.

One of the reasons for the lack of water in the European landscape involves the control of rivers. In the Czech Republic, for example, the length of rivers has been reduced by an average of one-third; in some watercourses, it is even by two-thirds. This was the result of rebuilding naturally meandering flows lined with alluvial plains into straightened canals surrounded by embankments and drained landscapes. Water flows quickly through such places without having any time to enter the surrounding landscape.

“Controlled, straightened flows need to be returned, at least to some extent, to the natural shape with a curved channel with room to flow out during high levels of water that need space and time to infiltrate rather than quickly flow off and cause damage,” concludes Jirku.

Foto: Wikimedia / josefstuefer

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