Our summers are getting hotter and more water is evaporating. So we should try to retain rainwater for longer, especially on the drought-prone sandy soils. Water boards are trying to restore meandering streams, make banks floodable and install extra weirs and even sandbags. But they also get help from the natural dam builder.
The beaver naturally belongs in the Dutch river delta. But the largest rodent in Europe disappeared from our country in 1828 due to hunting. At the end of the eighties, beavers were released in De Biesbosch and the Gelderse Poort. And they have been steadily increasing since then.
A few thousand beavers now live along the Rhine and Meuse, and smaller streams are now being colonized again. And that has consequences for water management: the animals up to 1 meter 30 long gnaw down entire trees with great ease, which they then use to dam water courses.
The appearance of such beaver dams is in principle positive,” drought expert Niko Wanders of Utrecht University told NU.nl. “Behind the dam, water is retained for longer. That also ensures that more water seeps into the soil, so that the groundwater levels rise.”
Brabant brook no longer runs dry
That groundwater is the water supply of the soil. If this is replenished in the winter, drought problems will arise less quickly in the summer. And the arrival of a fresh beaver dam can make a measurable difference, says Jeroen Helmer of ARK Nature Development.
“A good example of beaver work on sandy soils is the dam that beavers built two years ago in the Astense Aa in North Brabant. That stream still ran dry in 2018, but the beaver has kept things wet ever since – with all the consequences for groundwater levels. .”
Are beaver dams better than human interventions? At least for nature, says Helmer. “There are quite a few weirs in the Netherlands that are not passable for fish. Often a fish passage is made with hard partitions to bridge the difference in height.”
“Beavers can offer a much more natural solution, which fish can often still pass through. We are therefore developing a plan to use the help of beavers for better water management in an area near Den Bosch.”
Beaver dams overflow when water is too high
A problem with beavers is that they can sometimes be a little too enthusiastic. Then you can get high water levels where you would rather not have them.
Surfaces can then be flooded, says Wanders. “But beavers also keep an eye on high water levels. Because too much water behind the dam also creates a danger of their dam collapsing. So they ensure that in extreme situations there is an overflow to drain water. Otherwise, the dam damage.”
Where beavers return, streams often overflow. All sorts of other species can benefit from this.
Where beavers return, streams often overflow. All sorts of other species can benefit from this. Photo: Jeroen Helmers/ARK Nature Development
beaver deceiver can provide a solution
If things do get out of hand, administrators can also take measures themselves, says Helmer. “For example with a beaver deceiver. That is a tube that is placed in a beaver dam to lower the water level again.”
In any case, Helmer hopes that the beaver will have more space to retain water in stream valleys. “Until now we have been busy discharging rainwater to the sea as quickly as possible. But with the fourth dry summer in five years, we have to ask ourselves whether that is such a good idea.”