Dredging threatens the Dutch delta due to sediment loss

The rivers and ports around Rotterdam are already losing more sediment as a result of dredging, and that loss will increase even more in the next century, according to research by Utrecht doctoral student Jana Cox. According to her, the consequences for the Dutch delta are greater than the consequences of climate change.

Shipping channels in the ports and rivers that connect Rotterdam to the sea are It was dug to prevent large ships from stranding. This should go deeper and deeper, because the ships are getting bigger and bigger. At present, 2 billion kilograms of sediment are lost each year as a result. “That’s enough to fill De Kuip to the rafters every year,” Cox says.

The geologist from Utrecht University and others investigated the impact of climate change and human actions on the “sediment budget” in the Rhine-Meuse delta. This indicates that sediment loss will increase dramatically in the next century. In 2085 it will be at least 12 billion kilograms.

Cox concluded that due to climate change (more storms and floods), 20 to 30 percent of the silt will be supplied to the delta in the next 50 years than today, but dredging is removing a much larger amount of sediment each year. It concludes that “the escarpment, not climate change, is what determines the future of the Dutch delta.”

budget sediment
This annual loss of sediment is called a “negative sediment budget”: the amount of sediment leaving the delta is greater than the amount entering. The amount of sediment in the Dutch delta will be “red”, just like a bank account. This means the loss of valuable materials to protect the bank.

In addition, dredging can damage infrastructure, such as underground cables and flood defenses. “Precious southern landscapes could be completely lost in the future,” Cox said. “For example, Haringvliet, where unique birds live.”

She stressed that the problem was not only related to the Dutch. Much dredging is also required in other large deltas in China, Vietnam, the United States, and Australia with competing ports on the banks of rivers and lower river branches. As a result, it eventually lost the most important building block for maintaining this delta above elevated sea level.”

Solutions
However, according to the doctoral candidate, there are solutions to increase the passive sediment budget and deposit the sediment to a reasonable location in the delta to prevent subsidence and sinking in the future.

At Ems and Western Scheldt, for example, experiments are already underway to see if sediments can be used to strengthen banks and dams. So the next step in her research is to look at how to scale such local and small scale solutions to delta regions around the world.

“Another solution is to move the port of the largest ships to Maasvlakte 2 and from there to sail inland with smaller ships. Fortunately, this is already being considered.”

more information
Artikel “Climate change and human influences on sediment flows and sediment budgets in an urban delta: an example of the Lower Rhine-Maes delta distribution network”
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