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Deltares | R&D Highlights 2015
Testing of ancient
block revetment in
the new Delta Flume
After a period of three years, the construction of the new Delta Flume on the Deltares campus in Delft was completed in 2015. The new flume is 300 metres long, 9.5 metres deep and 5 metres wide and it replaces the 35-year-old flume in Marknesse. The length means gradually rising coasts can be modelled, the depth makes it possible to generate waves up to 4.5 metres high. This major advance requires a 10-metre-high wave board that is moved to and fro using hydraulic cylinders. After the grand opening of the flume in October in the presence of ministers and other dignitaries, the first project involved studying the stability of a specific type of block revetment under wave attack: grouted boulders. Particularly in the north of the Netherlands, a number of dikes have been protected with this type of revetment, which is made from round natural stones (boulders) transported to our region by the glaciers in the last Ice Age. The stones used on Dutch dikes range in size from 30 cm to 90 cm and are often grouted with concrete. Craftsmen used to position these stones on a gravel bed of crushed bricks, forming a relatively smooth revetment.
The need to know more about the stability of boulder revetments of this kind became urgent because a lack of knowledge made it impossible to assess the stability of the dike between Eemshaven and Delfzijl as required by the mandatory periodic safety assessment for Dutch dikes. This particular dike is approximately 11 km long, and 9 km is protected with grouted boulders. Old documents show that this revetment was already in place in the 19th century. Due to positive experience with the block revetment on this dike, the water authority was convinced that stability was adequate and decided to perform a model experiment to prove it.
The block revetment was built in the Delta Flume on a dike with an outer slope of 1:3.6 and with a height of 11 m. Experienced craftsmen were hired to make a realistic model revetment. The tests were carried out on almost prototype scale (1:1.3). The wave height was increased step by step to find the maximum wave conditions in which it was stable. The test showed that the block revetment is stable enough for the dike Eemshaven - Delfzijl and that the safety margin is more than adequate. This result saved the water board approximately €10 million that had been earmarked for the renovation of this revetment.
Further reading:
Mourik et al (2015). Stabiliteit van met beton ingegoten Noorse steen, Deltares report 1220204
Flood Risk
mark.kleinbreteler@deltares.nl T +31(0)88 335 8244
