Controlling burrowing beavers

Wild boars, badgers, rabbits and, above all, beavers cause damage to flood defences through their burrowing. "Beavers had become extinct in the Netherlands, but were reintroduced to the Biesbosch in 1988 and now there are between 6,000 and 7,000 beavers living in the rivers of our country", says dike expert Frans van den Berg of Deltares, outlining the situation. "Beavers start digging below the waterline, which means that dyke managers often don't see that the beavers are making tunnels in the dyke."

Water authorities have sounded the alarm and are looking for measures to minimise the risk of flooding. This is because animal burrowing can have a major impact on the strength of flood defences. In Germany and Italy, dyke breaches have already been caused by animal burrowing.

Controlling flood risks

Deltares is collaborating with water authorities (WSRL, WDOD, Hunze en Aa's, Aa en Maas) and Stowa on various studies into animal burrowing in order to gain a better understanding of the stability of flood defences. This has resulted in guidelines and risk assessments to manage flood risks caused by burrowing.

This allows water authorities to see which animals are causing what damage, what detection and repair options are available, and what measures can be taken. Innovative methods such as artificial intelligence (AI) and fibre optics are used for detection. Fibre optics, which are present in the subsurface for other purposes, act as sensors and can detect the slightest vibrations.

Learning to work together

The aim of the collaboration is to establish a uniform method for all water authorities that describes the impact of animal burrowing on flood defences and the associated measures, and translates this into the likelihood of flooding. This enables the dyke manager to estimate the extent of the damage and take appropriate measures.

Frans emphasises that the beaver is a protected animal and that close cooperation with zoologists is therefore essential. Together with Vilmar Dijkstra of the Mammal Society, among others, the behaviour of beavers in the river area is being studied, especially during high water. "By working with zoologists to understand the behaviour of beavers, we want to discover how they respond to the measures we take. After all, the beaver is here, so we have to learn to work together and live with it."

It's not so much a question of whether things will go wrong, but when. So let's get to work together!

Vilmar Dijkstra, beaver expert at the Mammal Society

"You can install wire mesh in the dike, dump stones in places where beavers come or modify the dike so that it is no longer attractive to beavers," Frans lists some measures. Another solution being developed is high-water refuges: alternative places that have been made extra attractive for beavers to settle during high water.

Risk assessment

These and other recent findings are being compiled in a new safety framework, which is being implemented within the Knowledge and Innovation Agenda of the Flood Protection Programme. The Flood Protection Programme is involved in order to reinforce its reinforcement task (reinforcing 1,500 kilometres of flood defences by 2050). This framework allows the water authorities to carry out the research themselves according to a step-by-step plan.

"They have to deal with many locations where animals dig, so it is impossible to take measures everywhere,’ says Frans. ‘You can determine which dykes are most at risk of flooding and which are least at risk. The places with the highest risk can then be tackled first."

Collaboration

Deltares will test the updated safety framework with various water authorities. It will also work closely with Stowa and the Zoogdiervereniging, and the knowledge gained will be pooled via the Beaver Knowledge Centre. Deltares hopes to make this method available to all water managers.