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Long-term morphodynamic behaviour of the Maasvlakte 2 sand extraction pits and the influence on surrounding sand wave fields

Groen, Britt de (2015) Long-term morphodynamic behaviour of the Maasvlakte 2 sand extraction pits and the influence on surrounding sand wave fields.

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Abstract:The Rotterdam harbour is one of the largest harbours in the world and still expanding. The most recent expansion is called Maasvlakte 2 (MV2), which added 2000 hectares to the west of the existing port into the sea. MV2 was realised between 2009 and 2013 using sand dredged some kilometres o↵shore in the North Sea. A total of 200 million m3 sand was extracted from two sandpits with volumes of 170 Mm3 and 30 Mm3 . Those sandpits are located nearby the navigation channel to Rotterdam and surrounded by sand wave fields. Since sand waves have a migration rate in the order of 5 meters per year and a height of 5 meters, they can hinder navigation. Therefore it is important to know how sand wave fields behave. The purpose of this study is to determine the long-term e↵ects of the sandpits of Maasvlakte 2 on the surrounding sand wave fields. This is study is done by a data analysis of bathymetric data and secondly a model study for the long-term behaviour of sand pit and the sand wave fields. The bathymetric data is gathered from the anchorage area, a sand wave field 6 km away of the sand pits. These bathymetric data is analysed by a Fourier analysis (van Dijk et al. 2006) to calculate the specific sand wave characteristics. With a linear regression method the migration rate is determined for the sand waves. This is done for the period between 2006 and 2014, divided into two stages, one before and one after the realisation of the sandpits. The sand waves show a dynamic migration rate, with a range between 4.0-5.8 m/year. Before the realisation of the sandpit the range was between 3.9- 6.9 m/year and in the after stage a range of 2.6- 5.8 m/year. Because the calculation of these migration rates is very dependable of the place and angle, there cannot be made a conclusion based on this results. Modelling the long-term behaviour is done in two steps: (i) by modelling the sandpit in an idealized morphodynamic model (Roos et al. 2008) and, (ii) to use these results as input for a smaller-scale idealized sand wave model (Besio et al. 2006). The sandpit model is forced by tidal flow conditions as they apply near the sandpits, and the sandpit geometry is taken from recent surveys. Next, a simulation is carried out indicating how the pit will deform and migrate over the next century. Throughout this evolution, and at fixed locations, the tidal flow pattern and local depth can be extracted. This flow pattern and local depth are used as local forcing for the smaller-scale iii sand wave model. The sand wave model in the second step uses linear stability analysis to estimate the sand wave characteristics such as wavelength, orientation, growth and migration rates. Being driven by the gradually changing flow conditions and depth from the sandpit model, it indicates how the sand wave characteristics are a↵ected by pit evolution. The models show the following long-term behaviour of the sandpits: The edges will flatten out, the little pit will move to the larger sandpit and the pits will move with the dominant flow direction. When the navigation channel is also implemented into the model, the ridge between the pits and the channel will gradually vanish. This eventually results in one large pit. The dredging activities of the channel are not taken into account in the model. When looking again to the situation without the navigation channel, all sand wave fields surrounding the pits have crests with a north-east orientation. Those sand wave fields have the same response time as the Westhinder sand wave field, in the Belgium sea shelf. At the centre of the pit, sand waves will appear as well which have also crests with a north-east orientation. However, this orientation fluctuates with a small range throughout the years. If in reality there is silt present at the centre of the pit, which is most likely, no sand waves will arise. It can be concluded that the sandpits do not have a large impact on their surroundings. This is positive for the navigation maintenance, because no large changes will be expected over time.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:38 earth sciences, 43 environmental science
Programme:Civil Engineering and Management MSc (60026)
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