Groundwater data essential for safety Dutch flood protection works - Case Study
The Grebbedijk is a levee located between the municipalities of Wageningen and Rhenen in the Netherlands and protects 250,000 residents in the Gelderse Valley adjacent to the waters of the Lower Rhine (Nederrijn). The Grebbedijk does not comply with the latest strict safety standards. In 2023 the more-than-5-kilometre-long levee will be reinforced as part of the Flood Protection Programme, to ensure that the hinterland will remain safe if the water flowing through the Rhine in the future increases due to climate change. The Water Board is extensively monitoring the levee to collect as much groundwater data as possible for this purpose.
Reindert Stellingwerff, Policy Advisor Water Defences at the Vallei and Veluwe Water Board, is involved in the Grebbedijk reinforcement project. ‘We want to prepare an optimal design for the Grebbedijk. This requires data. The installation of the measuring network on the levee ultimately enables us to better predict the required strength of the newly to be designed levee in the event of peak discharge.’
‘As a Water Board, we manually measured groundwater levels near the levee for 20 years, but at a much lower frequency. The new measuring system Eijkelkamp Soil & Water installed, will provide us with much more data. During the installation of the measuring array, we experienced peak discharge of the Rhine River in January 2018. Due to fast and effective action on the part of Eijkelkamp Soil & Water, the measuring points outside the dike were extended, enabling us to continue measuring during the high water conditions. It is not always possible to take elaborate measurements in the start-up phase of a project. But that happened here. We were lucky to be able to conduct measurements under high water conditions right from the start.’
‘Levee managers want to know as much as possible about a levee. That makes measuring and monitoring an essential activity. Even in areas that do not immediately require reinforcement. All levee maintenance managers in the Netherlands are busy with the periodic Safety Assessment. By performing calculations we assess the strength of our levees. This requires data about the groundwater levels below the levee and in sand layers located at greater depths. And preferably for the entire year. This helps us understand how a dike behaves during high water conditions. We aim to translate this data into extreme scenarios to test the levee and monitor it in case that situation actually occurs.’
‘Our measuring array has been configured by Eijkelkamp Soil & Water for continue measuring and monitoring over the coming years. After all, as maintenance manager, my goal is to have data series spanning several decades. The data we acquire is transmitted to the Dike Data Service Centre, a platform for storing dynamic measurement data within and around dikes. This platform enables us to store, analyse and review large quantities of dynamic measurement data, geographically as well as in the form of tables and graphs. We developed the Dike Data Service Centre together with five water boards and the Directorate-General for Public Works and Water Management (Rijkswaterstaat). We are hoping that increasingly more dike managers will join this platform so that we will end up with safe, future-proof dikes throughout the Netherlands.’Flood Protection Programme
Working together to restore levees that during the safety assessment were declared non-compliant. That is the essence of the Flood Protection Programme: a programme in which the national and regional water authorities collaborate intensively to protect the Netherlands from flooding. The Programme is updated annually and developed for a period of six years at a time, with a longer-term twelve-year perspective. The Flood Protection Programme forms part of the Delta Programme. For more information, please visit hoogwaterbeschermingsprogramma.nl.Vallei en Veluwe Water Board
The Vallei en Veluwe Water Board is responsible for providing safe levees, clean and sufficient surface water and treated wastewater in the region bordered by the IJssel River, the Lower Rhine River, the Utrecht Hill Ridge and the Bordering Lakes. As such the Water Board oversees an area of 245,644 hectares and serves 1.1 million residents.