Erosion processes and bed level maintenance strategies in the tide-influenced branches of the Rhine-Meuse delta

Due to the closure of the Haringvliet in 1970 as part of the Delta works and the opening of the Beerdam in 1997, the course of the tidal flow in the Rhine-Meuse delta has changed. The tidal flow from and towards the Haringvliet is now completely taking place through the branches that connect the Haringvliet with the Nieuwe Maas and Nieuwe Waterweg. This causes these branches to erode by the increase of the tidal prism. The erosion problems occur in the central parts of the Rhine-Meuse delta, which, amongst other rivers, includes the rivers Spui, Oude Maas, Noord and Dordtsche Kil. The presence of sand, clay and peat layers in the branches causes the erosion mechanism to be rather complex. The alternation of sand and clay layers in the area causes the erosion to be non-uniformly distributed, resulting in deep local scour holes. The goal of this research is to determine an adequate maintenance strategy for the problem area. In order to do so the erosion processes are modelled in an existing Delft3D model. In this study, the morphodynamics in a depth averaged model, covering the Dordtsche Kil and a part of the Oude Maas, are calibrated in such a way that it quantitatively fits the existing long term erosion trend and that the qualitative processes of scour in the model simulations comply with the erosion occurring in reality. This is achieved by implementing multiple sediment layers simulating a bed topography where clay layers and local sand packages alternate. Subsequently modelling a variety of possible maintenance strategies has shown that several effective strategies are possible to deal with the erosion problems. Two strategies are suggested regarding the shortage of sediment in the system. The best way to deal with the local scour problems is to prevent further scouring of existing holes by fixation with riprap. Continuous nourishment in scour holes prevents the holes from scouring any further and moreover provides a solution for the long-term problem due to the fact that outflowing sediment diffuses and spreads out over the whole length of the river. A disadvantage of this strategy is the future obligation of continuous maintenance and monitoring for the whole Rhine-Meuse delta. The uncontrolled character of this strategy can also cause navigation nuisance. The other type of maintenance strategies considered is the reduction of erosive flow in the system. A situation where the Haringvliet gates are always opened, even during high tide, leads to a remarkable reduction in erosion. The scour holes still undergo erosion, but at a slower rate, and the erosion of the clay layer decreases to a negligible amount. A combination of fixing scour holes and opening the Haringvliet gates is also considered, which solves the problem for long-term erosion and the local scour, but comes at a high cost to implement. Besides in the Oude Maas, the erosion in the Spui branch is also alarmingly severe. In order to reduce erosion in this river branch, an option is to close it off. This causes the flow velocity in the Oude Maas to increase with approximately 10% and to reduce the flow velocity in the river Spui by half. It is strongly recommended to investigate the effects and possibilities of opening the Haringvliet sluices further. Further research should also be done with the extension of the Delft3D model to the Spui river, the downstream part of the Oude Maas and the Noord. Since the numerical model can become (even more) extensive with the implementations of 3 more domains, much more insight in the problems can be obtained with the interaction of the different eroding branches in a Delft3D model.

Subject

erosion
scour
Rhine-Meuse
Haringvliet
bed maintenance

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http://resolver.tudelft.nl/uuid:789c0aee-66f6-4a72-af87-6c1b98289147

Embargo date

2012-01-04

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Student theses

Document type

master thesis

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