The dikes that prevent water from entering towns and protect people in the Netherlands are prone to risks caused by burrowing animals. It is essential to monitor dikes for animal burrows as they undermine the structural stability and safety of the earthen dikes, writes Frances Kannekens.
Who doesn’t know the story of Hansje Brinker, the little boy from Haarlem, who saved the Netherlands from a dike breach by plugging the hole with his finger. The present-day scenario plays out differently, with the dikes having a different vulnerability.
It was a sunny spring day, with a clear blue sky, when a group of enthusiastic civil engineering students arrived at the Prosperpolder near Doel. The thermometer reading showed 23 degrees.
Doel is a picturesque place near the Dutch-Belgian border. On one side of the Doeldike lies the green polder, teeming with diverse birdlife, while on the other side lies the bustling harbour of Antwerp, with its imposing infrastructure and large cargo ships. The dike, spanning nearly a kilometre, appears strong and sturdy and acts as a separator of the two different worlds.
In the Netherlands, water is almost everywhere, making it an intriguing subject for research, particularly in the domain of water safety. At the HZ university, diverse research groups work on various projects related to water safety and nature-based solutions. The objective of the trip to Doel was to gain insights into dike management, since the present-day dikes confront vulnerabilities that are different from the days of Hansje Brinker.
Left: students work as a team to track and record the burrows on the Doeldike. Photos: Frances Kannekens
Animal burrows a threat to dikes
Doeldike, like the other dikes in the Netherlands and Belgium, is a man-made earthen barrier and an integral part of the local country's flood protection systems. The dikes protect not only our economic activities, but also millions of people against the danger of floods.
Mostly built of earth, with a vegetation cover on top, the dikes attract animals, especially the burrowing kind. These animals dig tunnels, holes and shelters to live in. While they make a safe home for themselves, their homes pose a significant threat to the dikes.
The presence of these holes and tunnels can compromise the structural integrity of the dikes, leading to hydraulic changes and surface erosion. Such risks underscore the importance of dike monitoring.
Though the burrows pose a threat to levee stability, they are not easy to detect.
Importance of dike monitoring
To shed light on the issue of animal burrows within dikes, the field trip immersed students in the practical aspects of dike monitoring.
Under the guidance of field experts, the students embarked on inspecting the Doeldike for animal burrows. The students were divided into teams – with one team searching for animal burrows, the second team creating a grid in the grass and another transferring the same information onto paper.
The assigned area spanned 3 metres in width and extended 20 metres down to the toe of the levee. In this small section of the dike alone the students found 23 animal burrows! The burrows were of varying sizes too. The students had not expected it to take so long to monitor a dike for these animal burrows.
What happens if we don’t act
For their concluding assignment, students assumed the roles of crisis coordination experts, specifically simulating the responsibilities of dijkgraafs or dike wardens. Their task involved addressing the imminent collapse risk of a damaged dike, compromised by animal burrows.
Under extreme time pressure, they had to delve into crisis management and address pressing questions. Would the dike withstand the presence of animal burrows? How much time remained before a breach? Should evacuation be considered? Would emergency services arrive on time?
The students realised that answering these questions was exceedingly difficult without the knowledge of the dike's condition and within such a short time. Gaining a deeper understanding of animal behaviour within the dike and its impact on failure mechanisms became crucial for assessing water safety and dike stability.
Additionally, finding answers to questions such as what to do with the animal burrows and the inhabitants posed further challenges. While removing the animals and repairing the dikes promptly seemed necessary for water safety, it was vital to identify a safe area where the animals wouldn't compromise other flood protection systems.
These field visits were organised to raise awareness among HZ students about the harmful effects of animal activity in dikes. Moreover, it provided a valuable opportunity for students to collaborate with and gain experience alongside field experts.
Left: students present their crisis management plan, pretending to be dike keepers on a stormy night with rising water and heavy rain. Right: a field expert explains the different safety measures such as using sandbags, depending on the severity of the situation. Photos: Frances Kannekens
Beyond hypothetical emergencies
While the students had to manage a pretend-crisis, the actual monitoring is done by watchful wardens who navigate the dike through stages – from assessment to emergencies. With a deep understanding of the dike's conditions, they respond to the design high water and extreme precipitation.
The monitoring strategy deploys instruments outlined in the ‘National Crisis Plan for High Water and Floods’ that guides crisis management in the Netherlands.
In high-water events, mayors consider preemptive evacuation, overseen by the police. The process involves the Water Management Centre, the Departmental Coordination Centre and the National Coordination Centre, and active communication through various channels.
Critical questions such as risks during non-evacuation arise during emergencies. Evacuation's essence lies in the balance of time, often within a 48-hour window. The risk-prone area undergoes scrutiny, residents are categorised, and coordination phases unfold, advised by operational leaders. Emergency measures, developed based on residual strength, dike type and environmental factors, stand ready.
After a breach, predictions of growth allow preventive measures ranging from erosion-resistant thresholds to reinforced toe constructions.
Safeguarding the Netherlands’ dikes necessitates more individuals like Hansje Brinker, as the task of managing the animals within the dike cannot be shouldered by one person alone. And that is what the dijkgraafs are doing effectively.
