Monitoring en modellering van het cohesieve sedimenttransport en evaluatie van de effecten op het mariene ecosysteem ten gevolge van bagger- en stortoperatie (MOMO): activiteitsrapport 3 (1 april 2007 - 30 september 2007)

The "MOMO" project is part of the general and permanent duties of monitoring and evaluation of the effects of all human activities on the marine ecosystem to which Belgium is committed following the OSPAR convention (1992). The goal of the project is to study the cohesive sediments on the BCP using numerical models as well as by carrying out of measurements. Through this data will be provided on the transport processes, which are essential in order to answer questions on the composition, origin and residence of these sediments on the BCP, the alterations of sediment characteristics due to dredging and dumping operations, the effects of the natural variability, the impact on the marine ecosystem, the estimation of the net input of hazardous substances and the possibilities to decrease this impact as well as this in-put

MOnitoring en MOdellering van het cohesieve sedimenttransport en evaluatie van de effecten op het mariene ecosysteem ten gevolge van bagger- en stortoperatie (MOMO): activiteitsrapport 4 (1 oktober 2007 - 31 maart 2008)

The "MOMO" project is part of the general and permanent duties of monitoring and evaluation of the effects of all human activities on the marine ecosystem to which Belgium is committed following the OSPAR convention (1992). The goal of the project is to study the cohesive sediments on the BCP using numerical models as well as by carrying out of measurements. Through this data will be provided on the transport processes, which are essential in order to answer questions on the composition, origin and residence of these sediments on the BCP, the alterations of sediment characteristics due to dredging and dumping operations, the effects of the natural variability, the impact on the marine ecosystem, the estimation of the net input of hazardous substances and the possibilities to decrease this impact as well as this in-put

Monitoring of the impact of the extraction of marine aggregates, in casu sand, in the zone of the Hinder Banks

The far offshore Hinder Banks are targeted for exploitation of huge quantities of sand, mainly for coastal defence works. Here, up to 2.9 million m³ can be taken over 3 months, with a maximum of 35 million m³ over a period of 10 years. Large vessels can be used extracting 12500 m³ per run. South of the Hinder Banks concession, a Habitat Directive area is present, hosting ecologically valuable gravel beds. For these, it is critical to assess the effect of multiple and frequent depositions of fine material from dredging-induced sediment plumes.A monitoring strategy was set-up, tailored for assessing the importance and extent of physical perturbations that are created by the extraction activities. The monitoring design focuses on hydrodynamics and sediment transport with feedback loops between both modelling and field studies. Main targets are assessing changes in seafloor integrity and hydrographic conditions, two key descriptors of marine environmental status within Europe’sMarine Strategy Framework Directive. Seafloor integrity relates to the functions that the seabed provides to the ecosystem (e.g., structure; oxygen and nutrient supply), whilst hydrographic conditions refer to currents and/orother oceanographic parameters of which changes could adversely impact on benthic ecosystems.State-of-the-art instrumentation (from RV Belgica) has been used, to measure the 3D current structure, turbidity, depth, backscatter and particle size of the material in the water column, both in-situ and whilst sailing transectsover the sandbanks. In the Habitat Directive Area, gravel bed integrity (i.e., epifauna; sand/gravel ratio; patchiness) was measured as well. Most innovatively, an autonomous underwater vehicle was deployed (Wave Glider®, Liquid Robotics Inc.), resulting in quasi 22 days of current, turbidity and other oceanographic data.From a first data-model integration, and analyses against hydrometeorological databases, main results showed: (1) high spatial and temporal variability of turbidity, both current- and wave-induced; (2) important topography-induced resuspension over the sandbanks, especially under wave agitation; (3) spreading and deposition of dredging-induced sediment plumes; and (4) competitiveness of ebb and flood, meaning that deposition of fine sediments on the gravel beds is realistic. Field data on currents were used for the validation of a three-imensional hydrodynamic model. Results confirmed good model predictions of current magnitude and current directions in zone 4, critical for future impact assessment.Data will be integrated with results from the morphological and biological monitoring, respectively carried out by the Continental Shelf Service of FPS Economy and the Institute for Agricultural and Fisheries Research

Sediment plume monitoring in the Clarion-Clipperton Zone

OD Nature has a vast experience in monitoring and modelling Suspended Particulate Matter concentration in shelf areas. In the framework of the JPI-Oceans cruise with the RV Sonne in the Belgian, French and German concession zones for deep-sea mining in the Clarion-Clipperton Zone, this experience will be used to monitor sediments plumes, caused by deep-sea mning exploration activities

Modelling the effects of sand extraction, on sediment transport due to tides, on the Kwinte Bank

In recent years, the exploitation of marine aggregates is increasing. As an example, on the Belgian continental shelf, one particular sandbank (the Kwinte Bank) is exploited extensively; this has led to the creation of a 5 m deep depression along its central part. In the present contribution, the influence of these bathymetric changes, on erosion and sedimentation patterns are studied, using numerical modelling, in order to obtain an initial impression of the effect of such intense sand extraction on the stability of the sandbank. Different numerical models are utilised. Twodimensional and three-dimensional hydrodynamic models have been used to derive currents, whilst third generation wave models have been used to simulate the waves. Two different models are presented, which calculate the total load sediment transport as a function of the local currents and waves. These models have been used to investigate the erosional and depositional patterns. The use of two different sediment transport models has some advantages, since the results of sediment transport models are still subject to some important uncertainties. The hydrodynamic model results are validated using ADCP current data, confirming the good performance of the models. Likewise the wave models provide good results, comparing their results with data from a buoy. The sediment transport model results were compared to the residual transport patterns, derived from the asymmetry of dunes. The results obtained seem to be in general agreement with these observations. The numerical models are used to simulate the response of the sediment transport to extensive sand extraction from the sandbank. One ‘worst-case’ scenario and two more realistic scenarios were simulated, whilst the effect of these bathymetric changes on sediment transport was studied. The results show that the intense sand extraction does not seem to influence extensively the stability of the sandbank, but that, as a consequence, there is less erosion and deposition. The model results show, for all of the scenarios, a small amount of deposition on the top of the sandbank; this could be an indication of a regeneration mechanism. A trench, created perpendicular to the crest of the sandbank, could be slowly refilled again. The time-scale of this regeneration and the influence of storms remain uncertain. Although the main emphasis of the paper relates to tidal forcing, a brief discussion is included on the influence of wave action, on sediment transport