In the Rotterdam harbour, we are at risk of dredging our own graves

The consequences of further and further deepening waterways in the harbour of Rotterdam are bigger than those of rising sea levels for the time being, geographer Jana Cox argues.

The harbour of Rotterdam: a lively cargo harbour where over a hundred thousand ships arrive and depart to deliver goods and products every year; not just for the Netherlands, but also for the rest of Europe. In order to ensure that ships can travel safely through the waterways in and around Rotterdam, dredging is going on throughout the entire year. During this process, enormous amounts of mud and sand are removed and dumped in the North Sea.
 

Between 2000 and 2019, we annually dredged up enough to fill stadium De Kuip up to the edge with. In 2085, we will probably be dredging up enough to fill the stadium every other month.

This loss of sediment is called a ‘negative sediment budget’: the amount of sediment leaving the delta area is bigger than the amount entering the delta area. And exactly that sediment is valuable material for shore protection and an important element to keep our delta above the rising sea level.

Bigger container ships

Dutch innovations in dredging technology make it possible to make deeper and deeper waterways, and that is needed because container ships are getting bigger and bigger. But recently, the amount of sludge has increased enormously. Between 2000 and 2019, we annually dredged up enough sediment to fill soccer stadium De Kuip up to the edge with. In 2085, we will probably be dredging up enough to fill the stadium every other month.

Annually, sediment enters the harbour from the Rhine, the Maas and the North Sea. The sediment used to be equally divided across the delta. That kept the waterways stable. But the construction of the Delta Works resulted in changed water and sediment flows, and the deposits of silt became more concentrated in the very deep Nieuwe Waterweg and the harbour network around Rotterdam. This led to a shortage of sediment for other branches of the system (including the Haringvliet). This leads to many problems. The shores and riverbeds have cables and tunnels, and there are water barriers and fortified shores to protect Rotterdam and the surrounding cities from water damage and floods. Sediment protects these structures in a natural way from soil erosion caused by fast-flowing water. Currently, nearly all the sediment coming in from the rivers and the North Sea ends up in the harbours, where dredging is an expensive and time-consuming job.

Dredging or biodiversity

It is not just the infrastructure and the safety measures against floods that are at risk. Sediment is also the most important element in nature reserves (marshes and flood plains) against rising sea levels. Without this sediment, many species of plants, birds and fish will lose their habitats. In order to stay competitive, the harbour of Rotterdam has to be able to receive bigger ships, and that could mean more has to be dredged in the future. The dredging fully overshadows all climate effects we are going to see when it comes to sediment, such as additional provision from the coast. The Dutch are ahead of the curve in large-scale dredging of deltas, but the rest of the world is not far behind now that big harbours like Shanghai and Singapore are gaining on Rotterdam as busiest harbour. They follow the example of Rotterdam and deepen the waterways; harbours all over the world want to be the most efficient, with as much ship traffic as possible.

Climate change is a complex and difficult to solve problem, but dredging is something we can control. But that does require making serious choices about our priorities. There are already solutions to address this problem. Such as reusing the dredged up sediment and depositing it in risk areas that are in danger. Or have the largest ships only dock at the second Maasvlakte. This is something that the Rotterdam region seriously has to get to work on, or it is not the climate that will be our downfall, but our choice to dredge our own graves.

Correction (10 December 2021): it was originally stated that millions of ships annually enter and leave the harbour of Rotterdam. That has been corrected, as the harbour counted 120,722 visiting ships in 2020.