Photo Photo by Maeslantkering. Source: Tineke Dijkstra
In the area around Rotterdam and Dordrecht, the four storm surge barriers are a crucial part of the flood protection measures: the Hollandsche IJsselkering, the Haringvliet locks and the Hartel and Maeslant barriers protect more than two million inhabitants from flooding. In the event of a violent storm at sea – which can cause high water levels – the flood control is closed, which causes lower water levels in the rivers. Sea level rise creates further challenges in the use and maintenance of the four defences. The question arises: how long will the flood protections still provide an adequate level of protection?
After the reassessment of the preference strategy in 2020, partners in the Rijnmond-Drechtsteden region are busy with the regional implementation of the Delta program and preparations for the new recalibration in 2026. An important part of this is the sustainability and flexibility of the current system of storm surge barriers and dykes that protect the area from flooding.
Thirteen partners work together in the Rhinestuary Drechtsteden Delta program: the province of South Holland, the state (Ministry of I&W: DGWB and Rijkswaterstaat), the Delfland and Schieland and Krimpenerwaard water councils, the Hollandse Delta water council, the Port of Rotterdam and the municipalities of Rotterdam, Dordrecht, Hardinxveld-Giessendam, Krimpenerwaard , Hoekse Waard and Voorne aan Zee.
A bit of history…
The area contains both the oldest and the most modern flood barriers in the Netherlands. In 1958, just five years after the flood disaster, the Hollandsche IJsselkering was ready for use. Since 1971, the Haringvliet locks have provided flood protection in two ways: as a storm surge barrier during storms at sea and as huge outlet locks during high discharges of the rivers. In 1997 – 25 years ago – Maeslantkering and Hartelkering (together Europoortkering) were completed. The design of the four barriers differs enormously, as does the frequency with which the barriers close: the Haringvliet locks “work” every day, the Hollandsche IJsselkering closes on average two to three times a year (already ten times this year) and the Europoort barrier closes in 25 years. Only closed twice during storms (2007 and 2018). That is why Maeslantkering and Hartelkering are also called “sleeping giants”.
What’s next for us?
Due to targeted management and maintenance, the high water protection can last approximately 100 years. At least that was the idea during design, construction and delivery. The rise in sea level more often results in water levels where the flood control must close (the closing levels). The increase in closing frequencies means, for example, that access to the port of Rotterdam is blocked more often. One or a few times a year is manageable, but what if it becomes 20 to 30 times a year? This figure is reached when the sea level rises by about one and a half meters compared to the beginning of the century. Furthermore, this may also have an impact on the period when necessary maintenance is carried out. Rijkswaterstaat now carries out maintenance outside the ‘storm season’ in the period from mid-April to the end of September, but that period may be shorter in the future because the closing levels will then also be exceeded. In short: the technical lifespan may be 100 years, but is the functional lifespan as well?
How do we handle it?
To answer this question, Rijkswaterstaat and the partners in the Delta program Rhine Estuary-Drechtsteden are starting a study of the functional lifetime of storm surge barriers, starting with the Maeslant barrier. The study examines which aspects determine and limit lifespan. The researchers are also looking at improvements and whether the effects of those improvements can have a positive effect when the flood defenses have to be replaced by new defenses or alternative strategies, such as closing the rivers with locks.
The results are also used as input to the Knowledge Program on Sea Level Rise, where track 2 examines the sustainability of the current strategy and its flexibility.
The preferential strategy for the Rhinestuary-Drechtsteden Delta program now assumes that the Maeslantkering and the Hartelkering will provide sufficient protection against flooding until at least 2070. The research into the functional lifetime can lead to different estimates, of course also depending on the speed of the soap level rise. The six-year cycle of re-evaluation of the preference strategy ensures that we know in time when to intervene to ensure the long-term protection of the region’s inhabitants against flooding.