Sea level rise and its danger for the Belgian coast

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Sea level rise and its danger for the Belgian
coast

• ir. Toon Verwaest
• ODINAFRICA course 13 november 2006 Oostende

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• What is Flanders Hydraulics Research?
• Definition(s) sea level rise
• Measurements sea level rise
• Coastal defence from the perspective of sea level
  rise
• The coastal landscape from the perspective of sea
  level rise

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
What is Flanders Hydraulics Research?

• service of the Flemish administration (ministry
  Mobility and Public Works)
• internal consulting
• knowledge area is water (ship maneuvring in
  undeep water, coastal defence, ports, navigable
  waterways, sluices)
• physical models, numerical models, measuring
  networks in situ, databanks, laboratory
  experiments

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Definition(s) sea level rise

• Reference level on land relative sea level
  (3 different reference levels)
• Relative sea level movements (ca. 10 different
  phisical processes, taking place on very
  different timescales and spatial scales)
• time scale lt 1 year
• time scale gt 1 year ? mean sea level

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Bewegingen relatieve zeespiegel op tijdsschaal lt
1 jaar
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Bewegingen relatieve zeespiegel op tijdsschaal gt
1 jaar
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Measurements of relative sea level rise

1. Relative to the top of quay walls in harbours
   maregraphs (100 year data set)
2. Relative to the top of pleistocene subsoil
   quartair-geology (10.000 jaar data set)

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
18 cm / eeuw
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
7 cm / eeuw
70 cm / eeuw
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Coastal defence from the perspective of sea level
rise

• Scenarios of relative sea level rise in 21st
  century from only 10 cm to almost 100 cm
• and the next centuries of the 3rd millenium
  10 m in the year 3000
• Increase floodable land (the coastal lowlying
  areas)
• Increase failure probability of the coastal
  defence

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Increase floodable land
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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• Increase failure probability of coastal defence
  ca. 0,5 m higher sea level translates into a
  factor 10 increase in failure probability !
• this is because the failure probability of a
  coastal defence is determined (in large part) by
  the storm surge level
• in addition, there are expactations that the
  storm climate in the North Sea will worsen more
  (frequent) extreme winds

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• COASTAL DEFENCE POLICY GROW WITH THE SEA using
  SAND NOURISHMENTS
• To protect 1 km of coast for every 10 cm sea
  level rise 100.000 m3 sand
• flexibel technique (lt-gt hard coastal defences
  such as sea dike structures)
• maximum societal benefits
• recreational beach
• ecology
• landscape
• Work with nature sedimentation of natural sand
  transport
• Important increase of finances for coastal
  defence ( factor 3 in 2050 !)
• seaward solution

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
The coastal landscape from the perspective of sea
level rise

• 21st century
• Damages of the coastal defence caused by storm
  surge (erosion of dunes, damages to buildings on
  the coastal defence)
• seaward solution with sand nourishments (to
  grow with the sea)
• 3rd millenium
• managed retreat change the functions of the
  land near the coastline ( a different spatial
  planning)
• landward solution (lt-gt seaward solution)

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• SAND NOURISHMENT, example
• De Haan

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• SAND NOURISHMENT, example
• Oostende

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• MANAGED RETREAT, example
• UK nature areas in stead of farmland

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• MANAGED RETREAT, example
• COMCOAST european project

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006

• Other type of MANAGED RETREAT
• Controled flooding areas alongside rivers,
• Thereby also decreasing the water level in the
  river

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Sea level rise and its danger for the Belgian
coast ir. Toon Verwaest 13 november 2006
Other type of MANAGED RETREAT Projects to create
nature areas (not triggered by a coastal defence
problem)
Sea inlet slufter (1 ha) near borderwith
France
Increasing the Zwin salt marches (100 ha)
near border with The Netherlands