Influence of Tidal Turbines on the Sediment Transport in the Eastern Scheldt

Abstract

There is a growing interest in tidal energy, thanks to its constant availability in comparison to other renewable energy sources. Also in the Netherlands, tidal turbines have been installed. This has been done in the storm surge barrier that is positioned in the inlet of the Eastern Scheldt. These turbines have an impact on sedimentation. Therefore, the objective of this study is to analyse the effect of tidal turbines on the sediment transport in the Eastern Scheldt. Within this research, there is a distinct focus on how the tidal situation plays a role in this. Literature research has been carried out to gain knowledge that is needed to fulfill this objective. From this literature research it could be concluded that the effect of tidal turbines on sediment transport is much greater when the tide is (horizontally) asymmetric. It means that the maximum flow velocity in ebb-direction does not equal the maximum flow velocity in flood-direction. This results in a net sediment transport in one direction. It can be concluded that the greater the tidal asymmetry, the greater the net sediment transport. Now, it was time to qualify the aspects of the tide where the sediment transport depends on. This has been done by analytical elaborations of the relation between sediment transport and flow velocity. From this, it could be concluded that the sediment transport is depending on the wave height amplitude, discharge amplitude and the phase difference between the wave height and the discharge. The obtained relation was implemented into a Matlab model that computes the wave height and the discharge due to arbitrary tidal waves. The model has been extended to a network of channels that represents the Eastern Scheldt. With the extended model it was possible to simulate a net sediment transport, due to tidal asymmetry. The storm surge barrier and the tidal turbines could be implemented in this model, represented by a higher resistance. This resulted in a lower wave height- and discharge amplitude and with that also the net sediment tranport decreased. Since the net sediment transport is directed seawards, a decrease meant less erosion of the channels. But from the literature research it was concluded that the construction of the storm surge barrier and of the tidal turbines resulted in more erosion of the channels. An explanation for this difference in results may be that in the model, only sediment transport due to tidal asymmetry is taken into account. Other forms of transport are not considered. Also, many assumptions have been made in the model and there is still room for improvement to represent the reality more accurate with this model, which could be subject to further research.