Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

[1]

Changes along the Belgian part of the North Sea

BelSPO-SSDStrategic Research Network

2007-2011

vera.vanlancker@mumm.ac.be

Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[2]

Surface area: 3600 km²

N

Increasing human pressure

Maes et al., 2005

Marine AggregatesAverage 1.5 106 m³/yr

Coastal protection may demand

>10 106 m³

Disposal of dredged material

2006: 12 106 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 dataExample Thornton Bank

?Cumulative impact?

Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[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 ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[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 ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[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 ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[6]

Natural evolutionSediment volumes vs hydro-meteo from measuring piles (Flemish Authorities)

WindHigh- and low frequency wavesCurrentsWater levels

Natural vs anthropic Surveys 96099611961297029709971198029803maximum

change9609   0.05 0.03 0.09 0.01 0.05 0.05 0.04 0.09

9611   -0.02 0.03-0.04 0.00 0.00-0.01 -0.04

9612   0.05-0.02 0.02 0.02 0.01 0.05

9702   -0.08-0.03-0.03-0.04 -0.08

9709   0.04 0.04 0.03 0.04

9711   0.00-0.01 -0.01

9802   -0.01 -0.01

9803   0.00maximum

change0.00 0.05 0.03 0.09 -0.08 0.05 0.05 0.04

Baland Bank bathymetric surveys.Matrix of all the intersurvey volume differences per surface unit (m³/m²). The maximum differences are indicated in italic. Surveys are indicated as YYMM.

Varying sediment volumes over sandbank areas

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 ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[7]

Anthropic change: case study on the disposal of dredged material

Stiff clay from maintenance dredging worksand increase of mud pebbles

Vibrocore

Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[8]

Analysis of bathymetric data Analysis of corresponding data on the disposal of dredged

material

Activecooperatio

n end-users

1976-1979 1981-1985

Regional sedimentation beyond the disposal grounds, in the direction of navigation channels

Analysis of vibrocores:• top 25-50 cm highly dynamic• natural vs anthropic sedimentation patterns

1 2

3

Decifering thresholds of ‘anthropic’ change

Short-term impact

Medium-term impact

Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[9]

Sediment change analysis

Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[10]

Sand fraction is generally well-sortedPoorer sorting associated with gravel or shell hash areas

Period around 1900

Management Unit of the North Sea Mathematical ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

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 ModelsMUMM | BMM | UGMM

http://www.mumm.ac.be/

Ocean Dynamics

[12]

Changes in skewness

Mostly enrichment of (very) fine sandsin the areas with more poorly sorted sediments

Present-day