High waves, damaged dykes: which emergency measures will hold up?

The Netherlands is increasingly facing more extreme weather. Although our dykes are well maintained and regularly reinforced, it's important to be prepared for situations in which a dyke is damaged during high water and storms. In this test, we're investigating how much wave load the various emergency measures can withstand.

A breach in the dyke as the starting point for a new test

The trial builds on the ‘Clay Erosion’ study, which was carried out in June in the Delta Flume and during which high waves created an erosion pit on the outer slope of a dyke. That same erosion pit now serves as the starting point for this new study to test emergency measures used in practice. Among other things, a method known as ‘staking’ is being tested. This involves filling the erosion hole with sandbags or clay, covering it with geotextile and geogrid, and securing it with stakes.

Practising and measuring

During the trial, various combinations of emergency materials are installed and subjected to wave loads. In doing so, the researchers are gathering practical information on installation time, feasibility and safe working practices. Sensors record, amongst other things, wave height, wave pressure and current velocity; the tensile forces on selected cramps or anchors are also measured.

Water authorities have a great deal of experience in implementing emergency measures. Now we can see how long the emergency measure can withstand the force of the waves.

Arno Rozing, project leader at Deltares.

Wide-ranging collaboration

The idea for the emergency measures trial arose during a brainstorming session of the Water Safety Crisis Expert Team (CTW). The research is commissioned by the Foundation for Applied Research in Water Management (STOWA). Deltares is leading the project and is responsible for the test setup, support, measurements and reporting. Two water boards are closely involved in the implementation. Emergency response staff from the Hunze en Aa’s Water Authority and the Hollands Noorderkwartier Water Authority are assisting with the preparations and installing the emergency measures in the wave flume.

Gabriel Rammeloo, strategic policy adviser at the Hunze en Aa’s Water Authority: “This is a great opportunity for us to test how our reinforcement holds up against large waves. We have a plan and the materials to properly reinforce our sea dyke in the event of damage. Now we can test in practice whether this protection is also strong enough to withstand large waves.”

Theo Reuzenaar, Water Safety Adviser at HHNK: “This is a great opportunity for us, which we have seized to practise emergency measures in a realistic test setup. Not only the drills, but also the exchange of knowledge and experience with other water boards and Deltares is providing us with new insights. For example, we are learning about the practical feasibility of measures, the time they take to implement, and how we can best carry out our work safely.”

800 sandbags

Emergency response staff from the Delfland Water Authority and volunteers from the Delfland Dyke Watch are filling 800 sandbags using their sandbag-filling machine. This literally brings together practical experience, research and crisis preparedness in a single trial. Rotterdam University of Applied Sciences is also involved, and the trial forms part of a ‘Hydraulic Engineering’ minor for the Civil Engineering degree programme. As part of this, 21 students will attend lectures on water safety and carry out an assignment.

Faster and more effective response

The final results of the trial will help emergency response teams to act more quickly and effectively in the event of a real emergency. The trials will also yield new knowledge that can be used to further improve national guidelines for emergency measures. Above all, however, the trials will reveal the wave loads that the emergency measures can withstand