by Luc Ponsioen
November 11, 2019
Storm-surge barriers are a vital element in the Dutch flood defence system: they protect us against high water at times when it is truly necessary. Currently, such circumstances occur sporadically. The Maeslantkering in the port of Rotterdam area is such a storm-surge barrier. Since its commissioning in 1997, it has only been closed on two occasions in response to a storm situation. But despite its limited use, the barrier needs to fulfil safety standards at all times. In order to meet these standards a Risk-based management and maintenance strategy has been implemented to ensure the barrier’s optimal condition. After all, each component of the barrier represents a potential risk (chance of failure) of the storm-surge barrier’s malfunctioning. Essential components are therefore implemented redundantly so the chance of failure is reduced significantly. With these measures we believe to have created a coherent system that guarantees the flood safety of a large part of the Netherlands. To-date, we haven’t spared a penny or effort on this. After all, it is our safety that is at stake – as well as safeguarding the economic continuity in the south-west of the Netherlands, an area that locates one of the world’s biggest ports.
At the same time, we have to ask ourselves, given the challenges of climate change, how much longer this system remains functional and secured. With rising sea levels and increasingly violent storms, the storm-surge barriers need to close more frequently. It is very well possible that within the next ten years the Maeslantkering will not close once every ten years, but once every three years. And within the next twenty years, it might close yearly. For the Eastern Scheldt barrier, also located in the south-west of the Netherlands, it could very well be that during the storm season the barrier closes once a month. This leads to significant consequences for the barriers’ maintenance regime. The conduct of maintenance under risk-based management, as it is done today, will therefore take on added importance. This means higher costs and, moreover, the ecological impact on the local intertidal zone will be considerable because of the alternating salt-salt regime. And we haven’t yet pointed to the economic consequences of closing a storm-surge barrier. Just think of the economic damage caused by having to temporarily keep ships from entering the port of Rotterdam because the Maeslantkering is closed.
If the trend continues, then we’ll need to ask ourselves how long, and under what external conditions, today’s storm-surge barriers will continue providing a sufficient safety guarantee. This of course depends a lot on the climate scenario. The Delta Programme, the strategic framework within which this kind of infrastructure currently functions, assumes a maximum rise of one meter in sea levels this century. But scientists are far from comfortable with this figure. Early this year, an article in the Dutch news magazine, Vrij Nederland, caused quite a stir. Leading scientists argued that the extrapolation of current climate trends will present the Netherlands with a number of existential questions and possible courses of action. These included a couple of business-as-usual and two other pretty extreme scenarios. The latter included one in which the Netherlands would organise its defences further to the west, with islands in the sea, and one in which the Netherlands would withdraw to the, currently still, higher situated eastern half of the country. But in all of these scenarios the most crucial question today is: How can we, whatever the dynamic scenario, continue to successfully make use of our infrastructure? And which no-regret vision will we follow in adjusting the existing infrastructure and in designing a new one. Because, however extreme the scenario, in all cases the road towards it is an incremental one – and, of course, one paved with an increasing risk of negligent action. In this regard, one of the challenges over the next decades will be to establish in detail the usability and adjustability of the current and future water safety infrastructure. This will also involve building associated digital systems, in which the traceability of the design, and the management and maintenance, are organised in a comprehensive and optimal manner.