Influence of the partial closure of estuaries on the residual sediment transport and trapping

Bachelor thesis (2020)

Authors

F. Sindy Electrical Engineering, Mathematics and Computer Science

Contributors

H.M. Schuttelaars Mathematical Physics - EEMCS (supervisor 1)
S.R. de Roode Atmospheric Remote Sensing - CEG (supervisor 2)
Faculty
Applied Sciences
Copyright: © 2020 F. Sindy
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Published Date

19-08-2020

Language

English

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Faculty

Applied Sciences

Abstract

In this thesis the water motion and sediment dynamics are investigated in a periodically closed and opened estuary. The water motion in an estuary is mainly driven by the semi-diurnal tide with an period of 12h25m and river discharge. An example of such an estuary is the Ems-Dollard estuary. Recent observations show an increase in tidal range (height difference between high and low tide), suspended sediment concentration and the depletion of oxygen levels (consequently harming the ecosystem). A possible solution, periodically closing and opening the estuary, is investigated. The water motion in a periodically opened and closed estuary is described by the linearised cross-sectionally averaged equations which give the sea-surface elevations and tidal velocity when solved with the eigenfunction expansion method. It was found that the sea-surface elevations and tidal velocity for a periodically opened and closed estuary are again 12h25m periodic. For the sediment transport, when no overtide is considered the residual sediment transport is seaward directed if the estuary is closed at low water and landward directed if the estuary is closed at high water. The barrier location determines the magnitude of the residual sediment. When overtide is included in the forcing of the system no relation is found
between the direction of the residual sediment transport and the closing height and closing position. The location of the barrier and closing height both determine the magnitude of the residual sediment transport and direction. By introducing a barrier that periodically closes and opens we intended to achieve a seaward directed residual sediment transport in the Ems-Dollard estuary. The results suggest that this is not possible. Further research is needed with more
extensive models to confirm this. For future Research I recommend to extend the model to a two-dimensional model with the eigenfunction expansion method. Other possibilities may be to consider a spatial dependent erodible bed.