Multi-Year Field Measurements Eems-Dollard

Are the uncertainty allowances and robustness in the Hydraulic Preconditions (HR) of the dike improvement Eemshaven – Delfzijl correct? Or have they been overestimated resulting in increasing costs? To prevent over-investment, the Noorderzijlvest Water Board has decided to shorten the time until the next dike reinforcement from 50 to 25 years. And they want to start with a 12 to 15-year measurement programme that is expected to demonstrate that the uncertainties and safety measures used (with regard to water levels and waves) are indeed too great. Infram Hydren is involved in the installation of the wave overtopping tanks, data analysis, calculations and the translation thereof into the design.

The questionCost-efficient, multi-year field measurements for effective dike reinforcement

With the Multi-Year Field Measurements Eems-Dollard, the water board aims to prevent over-investment and to contribute to effective dike reinforcement in Eemshaven – Delfzijl. As a result, the current uncertainties in the hydraulic loads that form the basis of the assessment and design of the primary flood defence system are minimised. The challenge is to carry out the measurement programme in such a way that it has an effect on the entire Eems–Dollard area and the eastern Dutch Wadden region. So this is a broad approach, in which the water board asks for a contribution to:

• better calculation models and a general refinement of wave overtopping calculations,
• new insights into the combination of wave height, wave direction, wave run-up and wind direction/strength (wind climate) and thus new insights for designing or assessing the flood defences in the Dutch coastal zone,
• cost-saving and effective flood protection programmes.

Our contribution and resultMaximum reduction of uncertainties in the hydraulic load

Together with Van der Meer Consulting, Infram Hydren is setting the bar for reducing uncertainties regarding the effects of wave run-up and dike overtopping. To achieve this, we measure wave overtopping directly at two different locations (where the hydraulic conditions are also measured). We place two tanks at different levels in the existing dike profile at each location, so that we can monitor a range of storm surge levels. As a result, we achieve a significant reduction in uncertainty when translating the wave conditions at the toe of the dike to the overtopping over the dike (depending on the size of the overtopping). As a knowledge and development partner, Infram Hydren is not only responsible for installing the wave overtopping tanks, but also for collecting and processing the data, and for managing and maintaining the wave overtopping tanks.

We also developed an innovative measuring system in which we perform wave run-up and wave overtopping measurements using laser scanners. We do this during high water on the dike.

Research

A number of papers have been published about this project. Two examples of this are shown below:

• J.W. van der Meer, J.W. Nieuwenhuis, G.J. Steendam, M.J.J. Reneerkens, H.J. Steetzel, & G.Ph. van Vledder, "Wave overtopping measurements at a real dike", Coastal Structures 2019
• P. Oosterlo, B. Hofland, J.W. van der Meer, M. Overduin, & G.J. Steendam, "Calibration and preparation of field measurements of oblique wave run-up and overtopping on dikes using laser scanners", Coastal Engineering 2021