Verbeterde kwantificering van sedimenttransport in laaglandrivieren

Outcome

Improved quantification of sediment transport in the river Waal through improved field methods and application of transport formulae.

Figure 1: Collecting water samples during a field campaign with Rijkswaterstaat-CIV. Photo by Jan-Willem Mol (Rijkswaterstaat).

Motivation and Practical Challenge

River management aims to ensure flood protection, guarantee safe infrastructure and facilitate navigation. Especially since climate change and sea level rise will impact the Dutch delta, thorough understanding of the river as well as the ability to predict future change through numerical models is important. Both rely upon information of sediment going through the river. This study aims to improve the methods to measure sediment transport and to calculate sediment transport. This is achieved by analyses based on data that has been gathered over the past years for monitoring as well as data from additional field campaigns. We specifically focus on the role of multiple scales of dunes migrating through the river and how dune tracking can lead to large scale estimates of bedload sediment transport.

Research Challenge

How can the quantification of sediment transport in the Dutch river Waal be improved?

Innovative Components

In the first study, we have observed that a secondary scale of small dunes are superimposed on the larger primary dunes in the river Waal. These small dunes migrate very fast, resulting in a large associated sediment transport rate, which is similar , or even exceeds the transport rate connected to primary dunes.
In a second study, we built upon this work and study when and where this secondary scale of dunes is present in the river Waal. To analyze a large multibeam echosounding dataset, a tool has been developed to separate dune scales and identify and characterize primary and secondary dunes.
Results indicate that the two dune scales coexist throughout the river Waal and for a large range of discharges. Currently, we aim to understand the competition and interaction between these two scales. For the final study, a large dataset has been created based on a field campaign in the river Waal, near Tiel. Based on this dataset, both suspended and bedload sediment transport will be quantified and used to validate transport formulae.

Relevant for whome and where?

Increased understanding of river dunes and improved quantification of sediment transport is relevant for river managers as well as researchers as a basis for numerical modelling, predicting flood risk, understanding the river system to prepare for future developments.

Findings and practical application

An important finding is that a secondary scale of dunes is very important in the river Waal, since they occur over space and time, and associated transport is similar to, or even exceeds that by primary dunes. In the next steps, we determine the implications for sediment transport quantification and develop field methods to quantify transport as well as improve the application of transport formulae.

Status for day to day practice

The tool can be used to identify and characterize dunes based on river bed elevation scans.
Knowledge that a secondary scale of dunes is present at range of discharges throughout the Waal. This secondary scale migrates fast, so has a large impact on sediment transport.

Next Steps

How multiple scales of dunes relate to large scale sediment transport quantification. Relevance of dune tracking and impact on how different sediment transport formulae should be applied.

Last modified: 09/11/2022