Sediment and morphodynamics of a siliciclastic near coastal area, in relation to hydrodynamical and meteorological conditions: Belgian Continental Shelf = De sediment- en morfodynamiek van de kustnabije zone in relatie tot de impact van hydrodynamische en meteorologische factoren in een silicoclastische omgeving, Belgisch continentaal plat

The Belgian near coastal area is characterised by shallow marine sandbanks lying more or less parallel to the shoreline. Research activities were focussed on the sediment- and morphodynamics of the Stroombank, the Nieuwpoort Bank and the Baland Bank, supplemented by a comparative investigation along the interaction zone with the Flemish Bank system. To study the sedimentological and morphological behaviour of this macrotidal environment (-5 to -15 m MLLWS) an integrated research strategy was set up covering different spatial as well as temporal scales. Sediment transport calculations showed that the tidal currents are generally competent enough to resuspend the in-situ sediments. The surficial sediments of the near coastal zone are mainly characterised by fine to very fine sands. Still, medium sands occur in the areas witnessing an intense tide-topography interaction. Striking is the correlation with the presence of bedforms. Deeper than roughly -6 m the surficial sediments are most likely enriched with mud. An interactive model is proposed whereby the transport of sediment is mainly dependent on the swale configuration. Especially when the tidal currents are funnelled, sandy deposits are being washed out and stored along the slopes of the banks. Part of the accumulated sediments is subsequently winnowed out and transported upslope the sandbanks by the combined action of currents and waves. In time, the above mentioned observations and interpretations can be confirmed. From the chronosequential measurements an indication could be given of the vulnerability of the coastal system. It can be stated that there is a clear relation between the observed morphological changes and the ruling hydro-meteorological conditions. Generally the lowest sediment budgets correspond with summer and autumn conditions, whilst the winter months witness the highest sediment volumes and are characterised by an abundance of fine sandy sediments. Sediment transport is most intense when the direction of storminess parallels with the configuration of the swales. From the observations, it can also be deduced that the duration of stormy conditions is more important than the strength. Moreover, the sedimentary pattern in the near coastal area is characterised by a quick recovery after stormy periods. From the spatial and temporal differentiation, the near coastal area can be regarded a self regulating sediment transport system dominated by longshore sediment fluxes. The origin of the Coastal Banks is likely constrained to a time period having hydrodynamic characteristics comparable to the nowadays situation</p

Mapping the seabed of the Belgian part of the North Sea to assist in a science-based approach to management

Knowledge of the spatial distribution of sediments, the impact of human activities on the seabed and the natural evolution of the seabed is important to assist in a more sustainable management of the Belgian Part of the North Sea (BPNS). Sediments are an essential part of any aquatic system and are the key for a better understanding of the marine ecosystem; moreover, they are a valuable socio-economic resource for construction material and beach nourishment; therefore, they are extracted increasingly. Research on sediment nature and processes are important also for the optimisation of dredging and dumping activities, the implantation of windmill farms, seabed constructions, cables and pipelines, the designation of marine nature reserves and, generally, any spatial planning initiative.Related to the BPNS research, the Renard Centre of Marine Geology (RCMG) of Ghent University has been/is actively involved in various inter- and multidisciplinary projects. Throughout these projects, a research strategy is followed that balances between process/modelling studies, and the optimization of the use of various acoustical and sampling techniques.Results from three research projects, related to the mapping of the seabed of the BPNS, will be presented. During the Marebasse project (Belspo, SPSDII; http://users.ugent.be/~vvlancke/ Marebasse/), significant new sampling and acoustical data was acquired in typically mud-, sand- and gravel-dominated areas (Van Lancker et al., 2007). On the scale of the BPNS, new thematic maps, related to the bathymetry, sedimentology and morphology, were produced. Automated modelling of these physical data layers, based on advanced geostatistical methods, have resulted in physical habitat maps with ecological relevance. On a smaller scale, impact studies of aggregate extraction and dumping of dredged material were performed on selected sites, integrating results from geo-acoustical surveys and terrain verifications. Results have shown that, on a short- to medium-term, the effects seem relatively localised. All results are integrated into a Geographical Information System GIS@SEA (The physical seabed GIS to support Studies and Environmental Applications).As the Marebasse project focussed on the spatial variability of the seabed nature and the short- to medium-term impact of human activities, knowledge of the natural evolution of the seabed, its response to sea-level rise and the long-term anthropogenic impact remains poor. These issues are investigated now in the QUEST4D project (Belspo, SSD; http://www.vliz.be/projects/Quest4D/). Through quantification of erosion/sedimentation patterns, the natural evolution will be compared against the impact of human activities. Results will be presented of the area north of the Vlakte van de Raan, including the dumping ground Br&W S1. Acoustical maps of the seabed reveal different sedimentation and erosion patterns, originating from natural processes and human-induced activities (Van Lancker et al., 2008). The socio-economic importance of seabed resources is further dealt with in theRESOURCE-3D project (Belspo Targeted Action), in which a 3D reconstruction of the internal structure of sandbanks is aimed at. A case study on the Kwinte Bank will be presented

Environmental impacts resulting from the disposal of dredged material at the S1 dumping site, Belgian Continental Shelf

To guarantee a safe access to harbours, dredging of the maritime access channels is needed. Moreover, shipping channels have to be adapted to the continuously increasing size of vessels. In some cases, the dredged material is reused for beach nourishments or infrastructure projects, but mostly, it is dumped on offshore dumping sites. The efficiency of a dumping place is determined by economic, physical and ecological criteria: (1) dumping places need to be situated close to the navigation channels; (2) a low recirculation of the dumped material towards the dredging places is aimed at; and (3) a negligible effect on the ecosystem should be ensured. The goal of this research is providing baseline information on the impact of dumping on the morphology, sedimentology and biology and the adaptation after cessation of dumping. Both the dumping site as its environment have been considered. The investigated dumping site S1, the largest on the Belgian Continental Shelf, and its surroundings were surveyed with a multibeam echosounder (RV Belgica) providing bathymetrical and backscatter data. Additionally, seabed samples were taken for sedimentological/biological analyses with a box corer, a Reineck corer or Van Veen grab. Finally, chrono-sequential single-beam echosounding was used to investigate the morphodynamic evolution from 1995 until 2002. Generally, the results reveal that on a short- and medium-term, the impact of the dumping of dredged material on the morphology, sedimentology and ecology is drastic, but localised. After the cessation of the disposal of dredged sediments, it seems that the site has restored a morphodynamic equilibrium, both from a morphological, sedimentological point of view, however this is hard to say for the biology (cf. nine stations are devoid of macrobenthos)

Translation of biological and sedimentological point data towards habitat suitability maps of biological communities and EUNIS level 5 maps. Part 2: From habitat suitability maps of biological communities towards EUNIS level 5 maps

The full coverage habitat suitability maps of the macrobenthic communities serve as an input to apply the EUNIS classification on the Belgian Continental Shelf and to translate the maps into EUNIS habitat types (EUNIS level 5 maps). The whole analysis was performed within a GIS (Geographic Information System). The habitat suitability maps were classified by means of the natural breaks classification scheme. Two derivative maps were generated, respectively exceeding probabilities of 60% and 70%. Subsequently, the derived habitat suitability maps were translated into EUNIS habitat types. A large proportion of the Belgian shelf is covered and assigned to EUNIS classes. Each defined EUNIS habitat type has a habitat suitability percentage exceeding 60%. So far, only the Macoma balthica community matches within the current EUNIS classification. The other communities do not exactly match classes within the EUNIS classification. As such, only temporary codes are created and those need an expert review. The Habitat model (Degraer et al., in prep.) does not foresee transitional communities; as such they cannot be mapped. Once these are defined, a complete full coverage EUNIS map can be attained

Geostatistical modelling of sedimentological parameters using multi-scale terrain variables: application along the Belgian part of the North Sea

In the nowadays highly pressurized marine environment, a science-based approach to management becomes increasingly important. In many cases, the sediment nature and processes are the key to the understanding of the marine ecosystem, and can explain particularly the presence of soft-substrata habitats. For predictions of the occurrence of species and habitats, detailed sedimentological information is required. This paper presents a methodology to create high quality sedimentological data grids of grain-size fractions and the percentage of silt-clay. Based on a multibeam bathymetry terrain model, multiple sources of secondary information (multi-scale terrain variables) were derived. Through the use of the geostatistical technique, Kriging with an external drift (KED), this secondary information was used to assist in the interpolation of the sedimentological data. For comparison purposes, the more commonly used Ordinary Kriging technique was also applied. Validation indices indicated that KED gave better results for all of the maps

Acoustic habitat modelling for the mapping of biological communities

In the framework of the MAREBASSE project (‘‘Management, Research and Budgeting of Aggregates in Shelf Seas related to End-users’’, EV/02/18, Van Lancker et al. 2005) and the MESH project (“Mapping European Seabed Habitats, Interreg IIIb; www.searchmesh.net), biologically relevant habitat maps are produced, based on multibeam acoustic datasets, ground truthed with physical and biological samples. The habitat map production comprised of the following four key steps: (1) getting the best out of the ground truth data; (2) selecting and deriving the best available input and most appropriate data coverages; (3) using the most appropriate techniques for interpreting the data through integration and modelling, and; (4) designing the map layout to create a map fit for purpose. Results are presented where classes derived from acoustic seabed classification are translated into habitat maps. Cross tabulation is used to correlate biological ground truthing data with the acoustic classes. Finally, habitat maps are produced, representing the likely occurrences of the different macrobenthic communities occurring on the Belgian part of the North Sea (BPNS). For the study areas of Oostende, Hinder Banken, Sierra Ventana, habitat maps of macrobenthic communities have been created. The habitat maps are based on a cross tabulation of acoustic backscatter classification of the multibeam images, overlaid with biological samples worked out on a macrobenthic community level