Morphodynamic modelling of the Galgeplaat

Morphodynamic modelling of the Galgeplaat

Das, I.L.L.

Stive, M.J.F. (mentor)
Wang, Z.B. (mentor)
Hibma, A. (mentor)
Van der Werf, J.J. (mentor)
Eelkema, M. (mentor)
Volp, N.D. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2010-05-10

Since the completion of the Eastern Scheldt project in 1987, in the south-western part of The Netherlands, there has been a decrease of tidal volume, range and current in the Eastern Scheldt estuary. This has led to morphologic changes in the basin. The channels are in demand of sediment and as the Eastern Scheldt barrier itself blocks most of the sediment transport from the North Sea to the basin, this sediment comes from the intertidal areas inside the basin. As a result, the intertidal areas inside the Eastern Scheldt basin are eroding with consequences for ecology, safety, shipping, recreation and fishery. One of the larger shoals in the Eastern Scheldt is the Galgeplaat. The Galgeplaat is eroding at a high rate. So far the governing processes behind channel-shoal interactions for accretion or erosion of intertidal areas such as the Galgeplaat are not exactly known. The main objective of this research is to get more insight into these processes. A conceptual model of the Galgeplaat is developed which explains the morphologic changes of the Galgeplaat, since the closure of the Eastern Scheldt, with the occurring processes. First, a data-analysis is performed to determine the morphologic changes of the Galgeplaat for the last two decades. After that, a detailed 2DH Delft3D model is set up for the Galgeplaat, including tide, wind and waves to determine the effect of each process on the intertidal area. For wave simulations an online coupling is made with SWAN. The model is roughly validated for water levels, flow velocities in magnitude and direction and wave heights. Several simulations of a spring-neap cycle are performed including the different processes of tide, wind and waves. These processes are switched on or off to stipulate the influence of each process. It is believed that tides are responsible for shoal accretion and waves cause degradation of intertidal areas. This was the case before closure of the Eastern Scheldt and shoals like the Galgeplaat were in morphodynamic equilibrium; there was no net accretion or erosion over time. A performed simulation with today’s tidal characteristics does not show shoal accretion. A simulation conducted with increased tidal velocities, which is thought to represent the tidal flow before the closure, shows that shoal accretion above mean low water does occur. Simulations confirm that waves are the main driving force behind the degradation of intertidal area of the Galgeplaat. During both calm and storm weather conditions the intertidal area is eroding. During calm conditions this erosion is limited, while during storm conditions there is severe erosion. During storm conditions the sediment, brought into suspension due to wave breaking, is mainly transported by the dominant wave-induced currents from the shoal into the channel. The main conclusion of this research is that the tide in the Eastern Scheldt does not have enough shoal building capacity to withstand the destructive forces of the waves. This results in rapid loss of intertidal areas, such as the Galgeplaat. Local nourishments might be able to maintain the intertidal area and thus preserving the values of these areas.

Galgeplaat
Eastern Scheldt
Intertidal area
Delft3D
Channel-shoal interactions
Conceptual model

http://resolver.tudelft.nl/uuid:56998e1f-729c-4924-9a4b-67003c1355ff

Student theses

master thesis

(c) 2010 Das, I.L.L.