Let's not pin down the delta - NRC Guest Blog by Dr Jeroen Warner

Dutch flood management policy benefits from a varied package of measures consisting of both ‘closed’ and ‘open’ hydrological interventions in the environment. This argument is voiced by Martijn van Staveren and Jeroen Warner, water policy researchers at Wageningen University. 

In a heavily populated and densely constructed delta such as the Netherlands, flooding can cause enormous economic and social damage. So it’s logical that the government is investing heavily in flood defence systems to prevent flooding.

The climate debate and the risk of extreme sea level rise have given a new impetus to the discussion about the nature and impact of those investments. Visionary images of the future presents various options to how we can deal with the consequences of these developments. These options range from mass migration to higher areas, to constructing tulip islands and huge climate-proof dikes. What is the best approach to keep the Dutch delta liveable and flood-resistant in the future?

The core question is whether to adopt a ‘closed’ or ‘open’ approach. The views regularly alternate. The closed approach is in line with the command-and-control principle, with many and especially high polder dikes, large civil engineering works, a hard coastline and trained riverbeds. The open approach advocates making room for the river, partially opening flood barriers, anticipating natural dynamics, temporarily depolderising and creating non-infrastructural policy such as evacuations.

The dynamics between these two approaches has become visible in Dutch flood policies developed these past few centuries. In recent editorials some argue that higher dikes will be insufficiently effective to protect the Netherlands against the rising sea level, whereas other experts claim that this will succeed when combined with the ‘closed’ approach and the necessary technical know-how.

Dutch flood policy favoured the closed approach until the mid-1990s. A shift occurred after the (near) flood disasters of 1993 and 1995. After this (near) flooding, an emergency programme was implemented to raise and strengthen many dikes, which resulted in fast and effective protection against flooding. At first, further construction was prohibited in the floodplains. However, the liberal Dutch aren’t fond of zoning: we want to be able to build in the floodplains, on weak ground and also below sea level.

But this was also the period in which ‘open’ ideas relating to Room for the River began to take shape, resulting in the Room for the River programme (2005-2017), in which dozens of measures were implemented to give rivers and nature more space: depolderisation to widen the river (e.g. Noordwaard near the Biesbosch, and the Overdiepse polder), compartmentalising polders and initiatives related to combined water safety, nature development and navigation (Hedwigepolder and Perkpolder). A city like Dordrecht began to think aloud about evacuation in the case of flooding.

Meanwhile, the closed approach seems to be the dominant one once again. In the framework of the High water protection programme the next few years will see hundreds of kilometres of dikes being raised, widened or strengthened in situ in order to comply with the stricter flood standards set forth in the Water Act of 2017.

What is the best approach to keeping the ‘Dutch’ delta liveable and flood-resistant in the long run? Open or closed?

In a dynamic delta system, the best approach probably involves a varied package of flood measures that anticipate the positive and negative points of both open and closed interventions. Flexibility and the ability to adjust to regional differences and changing situations are key.

On the basis of the slogan that summarises Dutch coastal policy (hard defences where necessary, soft defences where possible), we advocate ‘closed where necessary, open where possible’. In densely populated urban areas there are few options to prevent flooding other than storing, but also soon draining out flood water. However, along the rivers and the Dutch coast there are more possibilities of implementing open approaches to temporarily channelling through extreme amounts of water. The government should investigate what is and what is not possible more than they are currently doing.

Such a policy and its resulting mix of measures would create a flexible, resilient delta system with room for both human activities and unpredictable water dynamics.