Modelling the Morphodynamic Response to Sand Extraction from Tidal Sandbanks in Sediment-Scarce Environments

Tidal sandbanks are large-scale bedforms with heights of 5-30 m, lengths of 5-60 km and crest spacing of 2-15 km [1] and tend to exist in sandy continental shelf seas throughout the world, e.g., the North Sea, East China Sea and Irish Sea. They can form when tidal flow velocities are sufficiently large, and evolve on a centennial timescale. Tidal sandbanks have been explained as free instabilities of a flat, sandy seabed subject to tidal flow [3].
Marine sand is needed for coastal nourishments, land reclamation and the construction industry. However, in some marine systems, the total amount of sand is limited and depleting. This includes the Belgian Continental Shelf (BCS), located in the Southern Bight of the North Sea, where most of the sand that is available is located in tidal sandbanks [2].
The underlying clay layer is exposed in the troughs between the banks, often together with gravel. In turn, sandbanks form attractive locations for sand extraction and a significant portion of mined sand is extracted from sandbanks. However, these extractions may threaten the morphological balance of the environment with adverse impacts on future sand stocks, sediment quality, foundations of wind farms and protected Natura 2000 areas. Here we present an idealised process-based modelling study that aims to understand the morphodynamic response to sand extractions from tidal sandbanks, in sediment-scarce systems such as the BCS.