More than a century ago, the Eemshaven-Delfzijl dike in the north of the Netherlands was covered with 70,000 m2 of Norwegian boulder stone, which came to the Netherlands in the last Ice Age. The revetment was strengthened later by filling up the gaps between the stones with concrete. Unfortunately, on the basis of current knowledge, we cannot say whether this revetment can cope with design storm conditions. However, under the Dutch Water Act, we have to prove that the dike is stable or overhaul the revetment.
Deltares tested the revetment for the Wadden Sea Dikes POV (a Trans-Project Review of the Flood Protection Programme, a joint project involving the Noorderzijlvest Water Authority, the Hunze en Aa's Water Authority and the Friesland Water Authority). The complexity of a study of this kind means that it cannot be conducted on a small scale or using a computer and so we turned to the new Delta Flume.
We built an exact replica in the Delta Flume of a section of the stone revetment on the Eemshaven-Delfzijl dike. The question was: can the revetment sustain the violent impact of a superstorm (waves that occur once every 3,000 years)? Deltares conducted the first series of tests in October and November. The test dike with Norwegian boulder stone was covered with pressure sensors. The final tests looked at short and long waves. We tried to break down the revetment by battering it with increasingly higher waves. The thinking is that if you know when and in what conditions the revetment fails, you also know the revetment can protect the coast of the Wadden Sea. It was concluded that the revetment was strong enough and that no upgrade was required. So the study in the Delta Flume saved EUR 25 million for the water authority.
A final experiment will be conducted in 2016 to determine the extent to which the results can be extended to the rest of the Netherlands, potentially producing even greater savings.
This study once again demonstrates the importance of experimental research as the birthplace of new knowledge that can lead to major savings
Thanks to the tests in the Delta Flume, we could leave the boulders in place, and we saved enormous amounts of time and money.
In this project Deltares worked together with the following partners: