The Netherlands: Deltares to Study Strength of Grass Covers on Dikes
Rijkswaterstaat is teaming up with the Rivierenland Water Authority and research institute Deltares to test a stretch of dike near Nijmegen near the Hollandsch-Duitsch pumping station and Millingen aan de Rijn.
The strength of the grass cover will be tested to see how it copes with overtopping resulting from combinations of storms and high water levels. To simulate those conditions, an overtopping simulator will be used.
The simulator can pour thousands of litres of water at a time over the dike. The testing near Millingen aan de Rijn will start on 10 January and end in mid-February.
The grass on dikes makes them stronger and it must be able to withstand waves and currents. The study will look at when the grass cover fails as a result of overtopping, and at the impact on objects like buildings and roads on the dike. The test will be conducted with a simulator located on top of the dike. The simulator is repeatedly emptied at a stroke, subjecting the dike to large wave forces. The repeated release of large wave volumes simulates high water in combination with hard winds. The wave load is increased until the grass covering shows signs of damage.
After the tests, the damage to the grass will be repaired immediately so that the dike will be safe for the coming winter. If the water level in the river is high, or if the forecast indicates that a period of high water is on the way, the test will be postponed in consultation with the Rivierenland Water Authority. Postponement will also be considered during storms or cold snaps.
Rijkswaterstaat will be conducting the study together with Rivierenland Water Authority, Deltares, Infram, Alterra and Van der Meer Consulting. The tests will start on 10 January 2013 and end in mid-February. They will be located on the Ooysedijk in Nijmegen and on C.R. Waiboerweg in Millingen.
Rijkswaterstaat is working together with research institute Deltares, on behalf of the Ministry of Infrastructure and the Environment (I&M), on the development of a new assessment method for the primary flood defences (the Statutory Assessment Instruments, WTI) that water authorities and Rijkswaterstaat will be using from 2017 onwards for checking whether their flood defences comply with the statutory safety standard.
This new method will look at various dike ‘components’. In this case, the focus is on the strength of the grass covering the dike. The results of the study will be used to improve the assessment instruments and, ultimately, to allow for a more precise assessment of flood defences. Dutch dikes undergo periodical checks determined by law.
Press Release, January 14, 2013