Modelling the Morphodynamics of the Kwinte Bank, Subject to Sand Extraction


Briere, C. and Roos, P.C. and Garel, E. and Hulscher, S.J.M.H. (2010) Modelling the Morphodynamics of the Kwinte Bank, Subject to Sand Extraction. Journal of coastal research (SI 51). pp. 117-126. ISSN 0749-0208

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Abstract:The North Sea is, to an increasing degree, subject to human activities and interests; a particular example of a user function of this environment is sand extraction. In order to satisfy the demand for sand, tidal sandbanks in some sectors of the North Sea act as a source of sediment, this may lead to the creation of large-scale pits on these bedforms. Sandbanks, which provide protection to adjacent stretches of coastline, are therefore worthy of investigation, especially when their potential as a source of aggregates is taken into account.
To investigate seabed dynamics, in general, and to predict the long-term morphodynamics of tidal sandbanks subject to sand extraction, in particular, process-based modelling is a commonly-used method. Different approaches can be considered: (i) based on complex numerical simulations; (ii) or applying an idealised model, designed specifically to describe sandbank dynamics. Herein, the first approach is applied to a case study of the Kwinte Bank; this is a tidallymaintained sandbank, located on the Belgian continental shelf. The modelling is set up using the complex processbased model Delft 3D – Online, the waves were not taken into account.
Numerical results and experimental data from a field campaign (undertaken in March 2004) are compared and show good agreement. Analysis of residual currents indicates a predominance of ebb flow over the bank. However, the residual sediment transport pattern is flood-dominated. The predicted residual sediment transport pattern shows that the Kwinte Bank should be regarded as part of a system of swales and sandbanks.
Finally, the long-term evolution is discussed, considering complementary approaches that combine the benefits from the complex numerical modelling with the idealised one. The evolution of a tidal sandbank, after removing an amount of sand, is difficult to predict. No clear tendency is evident in the evolution of the depression area on the basis of the long-term full process-based modelling. However, on the basis of idealised modelling, the anticipated long-term trend of an excavated area is the recovery of the depression, resulting in an equilibrium of the sandbank, over a time-span of a few centuries.
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