Improved knowledge on the sediment balance of the Meuse River and on how to model sediment transport and morphology for the next century helps to plan sustainable river measures.
Figure 1: huge amounts of sediment deposits after the flood. Where does all sediment come from? (Photo by Hermjan Barneveld)
Motivation and Practical Challenge
Most rivers are supply limited, meaning that the sediment load to the river channel is less than what can be transported by the flow. Together with other causes like river straigthening, narrowing and dredging this causes ongoing riverbed erosion. To mitigate problems related to ongoing erosion, better knowledge on the sediment balance of the river and longterm impact of measures is required. This situation is current in many rivers worldwide.
In my career at research and consultancy institutes these problems were an important trigger to many of the projects. My PhD research offers me the opportunity to in-depth investigations on the determining processes and best numerical modelling techniques, taking into account the uncertainties involved.
How does the sediment balance of the Meuse River of the last 25 years look like?
And how can we model sediment transport and morphological changes with analytical techniques, or do we need numerical models? If so, how to apply them?
Based on the governing equations for flow and morphology, I developed an analytical approach for assessing celerity and damping of large sediment waves on the river bed. Can this approach be used as quick assessment tool?
And could we perhaps even simplify the equations so we can use faster numerical morphological models for long-term simulations?
For the assessment of the sediment balance data on river bed changes, bank erosion, floodplain deposits, dredging, supply from tributaries and sediment transport capacity has been collected and analyzed. After the extreme summer flood of 2021 field work has been carried out to assess volumes and composition of floodplain deposits and bank erosion.
Numerical modelling of the sediment transport and morphological changes is required to assess impact of past and future measures on river bed development and consequently water levels. As morphological changes are generally slow, simulations for the next century are required to design no-regret river interventions. Including uncertainties in these simulations is essential.
Relevant for Whom and Where?
Rijkswaterstaat is preparing plans for the period up to 2050 (with a view to the next century) and wants to know what the impact will be on riverbed and all functions in the river.
Findings and Practical Application
Analytical approaches as rapid assessment tool are possible in lowland rivers when the Froude number is moderate (<0.3) and the morphological changes smaller than 10% of the average water depth.
The supply of alluvial sediment to the Dutch part of the Meuse River is hypothesized to be negligible because of the large weirs just upstream of the border. This hypothesis has to be validated with bed sediment analysis in Belgium. For the sediment balance the riverbed changes, dredging volumes and bank erosion are for now thought to be the main components. During large floods the deposits of sand on the floodplains is also important for the balance.
Status for Day to Day Practice
Data on the components of the sediment balance should be better documented to further improve the balance. This also includes sampling and analysis of the river bed sediment and sediment transports.
The hypothesis on negligible sediment load at the Belgium-Dutch border needs to be validated, at least with information on the river bed composition. In addition bed level information in the region between river bed and river bank could help to improved the sediment balance.
Last modified: 23/06/2022
Accuracy Assessment of Numerical Morphological Models Based on Reduced Saint-Venant Equations
In this paper we investigate under which conditions numerical morphological models can be simplified to speed up simulations, and still provide accurate predictions of riverbed dynamics. We show that popular simplified models based on the quasi-steady approach are highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. We provide diagrams (see example below) for assessing the accuracy of simplified models (quasi-steady and diffusive wave) for various combinations of Froude number, sediment transport and dimensions of riverbed waves.
18/12/2023 by Hermjan Barneveld et al.View details
Can Linear Stability Analyses Predict the Development of Riverbed Waves With Lengths Much Larger Than the Water Depth?
In this paper we evaluate the use of analytical relations, based on linear stability analyses of the St. Venant-Exner equations, as rapid assessment tool for migration and damping of large riverbed waves. Supported by numerical simulations with a 1-D numerical model (markers in chart below) we prove that for Froude numbers ≤ 0.3 the results from linear stability analysis are valid for predicting the propagation of low riverbed waves. For larger Froude numbers riverbed waves are more diffusive and migrate slower in time than predicted from linear stability analysis.
03/03/2023 by Hermjan BarneveldView details