Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM [1][1] Changes along the Belgian part of the North Sea BelSPO-SSD Strategic Research Network

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [2][2] Surface area: 3600 km² N Increasing human pressure Maes et al., 2005 Marine Aggregates Average m³/yr Coastal protection may demand > m³ Disposal of dredged material 2006: TDM R. Janssens, 2009 In Quest4D compilation of distribution and intensity of human activity, incl. the extent of fisheries’ impact on the seabed Quantitative analysis of fishing marks, based on multibeam backscatter data Example Thornton Bank ?Cumulative impact?

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [3][3] Main problems in impact studies  No baseline information - No historic reference points  Significance of impacts? Time-scale of change?  Cumulative impacts? – Far field influence?  Links between cause and effect?  Threshold of habitat change?  What is natural and what is anthropogenically-steered???

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [4][4] Changes in bathymetry Changes in sediments Changes in macrobenthos Partner: RBINS, Dep. Invertebrates / Ghent University, Marine Biology Section

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [5][5] Long-term vs. short- to medium-term changes  Decifering natural vs anthropic change –Natural change:  Sediment volumes and bedform changes against hydro- meteorological conditions  Influence of storms on sediment transport –Anthropic change:  Analysis of short- to medium-term changes against intensity data of anthropic activities (e.g. data on disposal of dredged material and aggregate extraction)

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [6][6] Natural evolution Sediment volumes vs hydro-meteo from measuring piles (Flemish Authorities)  Wind  High- and low frequency waves  Currents  Water levels Natural vs anthropic Event–driven vs. yearly-averaged changes Decifering threshods of ‘natural’ change Van Lancker, in prep. Findings along ‘undisturbed’ near coastal small sandbank: (1) Enhanced SW conditions bring in sediment (2) Persistent NW and NE conditions evoque erosion (3) Overall shallowing of the area Scenario’s will be used to predict sediment transport changes, due to climate change

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [7][7] Anthropic change : case study on the disposal of dredged material Stiff clay from maintenance dredging works and increase of mud pebbles Vibrocore

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [8][8] Analysis of bathymetric data Analysis of corresponding data on the disposal of dredged material Active cooperation end-users Regional sedimentation beyond the disposal grounds, in the direction of navigation channels Analysis of vibrocores: top cm highly dynamic natural vs anthropic sedimentation patterns 12 3 Decifering thresholds of ‘anthropic’ change Short-term impact Medium-term impact

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [9][9] Sediment change analysis

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [10] Sand fraction is generally well-sorted Poorer sorting associated with gravel or shell hash areas Period around 1900

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [11] Wide-spread worsening in sorting: esp. around harbours, near disposal and aggregate extraction sites Present-day

Management Unit of the North Sea Mathematical Models MUMM | BMM | UGMM Ocean Dynamics [12] Changes in skewness Mostly enrichment of (very) fine sands in the areas with more poorly sorted sediments Present-day