​ Combining data and deterministic modelling to monitor and predict seabed evolution in areas of marine aggregate extraction

Marine aggregates are a valuable and evermore consumed geological resource. In the Belgian part of the North Sea, increasing demands of aggregates since the 1970's has led to the closure of over-exploited areas and new sectors were opened. The activity has been continuously monitored, with high resolution depth recordings available since the early 1990’s, as well as spatio-temporal datasets on the extraction activities. Monitoring results suggested a local physical impact of the extraction but highlighted the unsustainable nature of the practice, calling for an improved assessment of the resource evolution. In this study, we explore the field data as well as results from a three-dimensional hydrodynamic model, a wave model and a sediment transport model in order to investigate seabed evolution in the exploited areas. On an aggregated basis, the data indicate that most of the variation in the bathymetry is explained by human extraction. Yet, at the detailed level, an important variability remains, showing that other factors affect seabed evolution. A higher resolution spatial analysis of the data is conducted to explore this variability. It stresses the importance of the scale at which data should be analysed in relation to seabed processes. Because several potentially explanatory natural factors (e.g., hydrodynamic regime, physical constraints at the seabed) are not available through direct observation, results from the various models are incorporated into the analyses. Empirical observations and results from a deterministic model are thus combined to construct a statistical model to determine whether and why areas are erosional or accretional under natural and anthropogenic pressures. This tool shall be used to guide a management plan for a more sustainable exploitation (TILES project, http://odnature.naturalsciences.be/tiles).