Modelling hydrodynamics and sediment transport in the Grevelingen outer-delta in response to human interventions

Abstract

Many coastal areas worldwide have been shaped by humans for the use of ports, real estate, recreation or agriculture, especially in densely populated regions. In many cases the morphodynamics are altered due to these human activities. However, the understanding of morphodynamic evolution is limited due to complex non-linear interactions between the physical processes and the wide range on which these processes take place, both spatially and temporally. This thesis explores the assumption that changes in the hydrodynamics will impact the morphologic configuration. After the closure of the Grevelingen estuary inlet (Southwest Delta, the Netherlands) as part of the Delta Plan the morphodynamics shifted from tide-dominated to wave-dominated. Plans exist to restore tidal processes. However, with yet another human intervention in the form of a Tidal Power Plant (TPP) in the Brouwersdam it is unclear to which morphologic configuration the outer-delta will evolve and to what extent. The literature presents some morphodynamic relationships that help to determine whether a system is in morphodynamic equilibrium. Some coincide with the observed past mesoscale developments in the Grevelingen outer delta. However, equations describing the relation between the sand volume stored in the outer delta and the tidal volume do not agree with the observed developments. Furthermore, from the literature it is not evident to which configuration the morphology will evolve. To gain a better understanding of the sensitivity of the morphodynamics to a human alteration the hydrodynamics and sediment transport are simulated with a numerical model for 4 scenarios with different locations and different discharges of a TPP. Local undesirable effects as scour pits and beach erosion are likely to form in the proximity of the TPP. With a TPP in the South of the Brouwersdam the higher flow velocities and sediment transport are confined to the adjoining Brouwershavensche Gat channel. A TPP in the Northern part of the dam controls the tidal dynamics in the centre of the basin creating a channel and shoal system, whilst on the margins of the outer-delta wave processes prevail. Overall, the results show that the distribution of the change in hydrodynamics and sediment transport caused by the human intervention are largely controlled by the pre-existing morphology. This finding can aid coastal managers in predicting the amount of morphodynamic change in response to a human intervention in a similar coastal setting.