Study into riverbed helps predict river behaviour
Flooding in Limburg, 4 years ago, was the trigger for extensive research into the behaviour of the bed of the Maas (including the section that forms the border with Belgium). Rijkswaterstaat and Wageningen University & Research (WUR) worked together in this endeavour. The study gives insights into what happens on the riverbed and offers tools that will help improve predictions of future river behaviour.
Flooding in Limburg
During the flooding in 2021, Rijkswaterstaat started a special measurement campaign. As tree trunks drifted down the river, survey vessels were remapping the riverbed. On the 'Common' section of the Maas, a largely unnavigable section of the river in Limburg, large holes were discovered in the riverbed.
Those 'scour holes' can damage pipelines, slipways and river banks. 'Naturally, we wanted to study these phenomena so that we know better what to expect in future,' says Roy Frings (river morphologist at Rijkswaterstaat).
Research into scour holes
Frings studied the cause of scour holes together with Hermjan Barneveld (WUR researcher) and Ralph Schielen (consultant on water safety & hydro-morphology). The Maas has been widened in various places to reduce flood risk. This helps the river to drain excess water.
Widening of this kind was not possible everywhere. This naturally created a series of relatively narrower sections ('bottlenecks'), where the flow rate rose significantly as a result. During the flooding of 2021, this process created large underwater dunes that shifted back and forth over the riverbed.
In some places there is fine sand under the coarse riverbed. The deepest sections of the dunes delved through the layer of gravel, rapidly flushing out the fine sandy substrate. This created the deep scour holes. Barneveld: 'In addition to studying how the scour holes were actually created, we also wanted to learn where all the sand was carried to.'
Fieldwork in the various flood plains of the Maas, coupled with a special laser technique showed that 80% of the sand had been deposited on the flood plains, which is to say within 25 km of the last scour hole, at the Berg-Meeswijk ferry.
Future
Research shows that it is highly important to learn about the structure of a riverbed in greater detail. That way, sites with risk of erosion or scour can be identified, making it easier to determine appropriate measures for the river and the best sequence to follow when implementing them. Climate change means that extreme flooding events are more probable, so the Netherlands will have to deal with erosion problems more often.
One of the key focus areas of the Room for the River 2.0 programme is stopping riverbed erosion in the Maas and Rhine. 'The study gives us important insights into that,' says Schielen. Frings: 'This is how Rijkswaterstaat is working towards a safe and future-proof river system.'
Publication
The study was published on 10 July 2025 in the renowned science journal Nature. Read the article in full.