Beneath the Amsterdam-Rhine Canal: exploring its connection to the subsurface

Between Nigtevecht and Breukelen, seepage causes wet farmland, unstable ditch banks, and restrictions on land use. By conducting measurements, analyses, and field tests, we are developing the knowledge needed to efficiently eliminate the causes of flooding or limit their impact. In doing so, we not only map the relationship between the canal and the groundwater system, but also bring together different disciplines and areas of expertise.

How does the canal affect groundwater levels?

The Amsterdam-Rhine Canal lies higher than the surrounding polders and therefore forms an important part of the regional water system. However, the connection between the canal, the subsurface, and the groundwater level near the surface is complex. To better understand this interaction, we measure groundwater pressure at many different locations around the canal.

Together with engineering firm TAUW and supported by local expertise from the Amstel, Gooi, and Vecht Water Authority, Teun van Woerkom, a Deltares expert in groundwater and infrastructure, is investigating how groundwater pressure varies across the study area.

“This project is unique because of the large number of groundwater monitoring points we have set up. Through intensive measurements, we have gained a much better understanding of regional differences,” says Teun. “We are also seeing that the relationship between the canal and the groundwater is not always equally strong. In summer, more water appears to flow out of the canal than in winter.”

These measurements do not stand alone but, together with a newly developed groundwater model, form a tandem for investigating the canal’s role in the groundwater system.

“This research is important to Rijkswaterstaat, both for the Amsterdam-Rhine Canal area and for the further development of our knowledge. We want to efficiently minimise the canal’s impact on the surrounding area. At the same time, the project also generates a great deal of broader knowledge about the canal itself. Together with Deltares, we are carrying out various canal research projects to expand our knowledge. This project is an important part of that effort,” says Roel Brugman, geohydrology adviser at Rijkswaterstaat.

The role of the canal bed and subsoil

Previous research by the water authority indicates that the properties of the canal bed likely play an important role in the interaction between the canal and the subsoil. Analysis of the measurement data and model results shows that the resistance of the canal bed is very low in certain sections of the canal.

As a result, water can seep into the subsurface and from there flow into the surrounding polders. To reduce the amount of seepage reaching the surrounding polders, Deltares is investigating the effectiveness of various measures.

Sealing the canal bed

One of the options being investigated is applying an additional sealing layer to the canal bed. Together with Lynyrd de Wit, an expert in flow dynamics and sediment transport at Deltares, various materials and mixtures are being tested in the laboratory.

In doing so, Deltares is investigating how permeable these materials are, how stable they remain under the influence of water movement caused by passing ships, and how their properties change over time.

The initial results are promising, says Lynyrd: “Fine sediment such as bentonite or silt can be used to make the canal bed less permeable. Using a relatively simple setup, we can investigate the impact of water movement caused by passing ships and determine the minimum settling period required after installation. These are key factors in determining whether application in the Amsterdam-Rhine Canal is feasible.”

From measurements to measures

The results of these tests by Lynyrd, together with a groundwater model developed by Teun, form the basis for incorporating measures into the canal. “Combining this knowledge creates valuable synergy,” says project leader Hans Landwehr, a geotechnical expert at Deltares.

“This allows us to assess the effectiveness of promising measures in reducing flooding in the surrounding area, both in the short and long term.”

The assessment of potential measures is currently underway, with the results directly supporting Rijkswaterstaat in addressing the challenges in the Amsterdam-Rhine Canal area. In addition, the project generates knowledge that can also be applied to similar issues along other Dutch waterways.

In this way, Deltares not only maps the relationship between canals and the groundwater system, but also brings together different disciplines and areas of expertise.