Coastal safety-
case studies in
Flanders
Duinkerke, June 12th 2018
MDK-Coastal Division
ir. Daphné Thoon
Content
1. Introduction
2. Coastal Safety Masterplan - status
3. Management of the sandy coast
4. Case studie ‘Ostende- Mariakerke and Raversijde’
5. Case studie ‘seawall Middelkerke’
1.Introduction
A low-lying hinterland
5
Low lying hinterland
More than 85% of the polders beneath +5m TAW (average storm)
Urban areas
Harbors
Dunes
A ‘man-made’ coast line:
beaches and sea walls
Harbor areas: quaywalls, locks &
weirs
Non urban areas: beaches and
dunes
Storm 1953
2. Coastal Safety Masterplan
Safety assessment and risk calculations:
2007-2008 Norm: No victims due to a 1000-year storm surge event: • Limited overtopping: 1l/m/s • No breaching of dunes and seawalls • No erosion that threatens protected buildings
• Weak links (1000 year ARI): 1/3d coastline + harbors
• Mostly at locations with sea walls and quay walls
Safety Assessment 2007-2008
2007: start voorbereiding Masterplan
Kustveiligheid
Aim:
protect the Flemish coastline and the hinterland against the impact of a 1000 year ARI storm surge and prevent large scale floodings by taking into account climate changes till 2050
estimated sea level rise in 2050: 30cm
Coastal Safety Master Plan
Coastal Safety Master Plan
Types of measures
‘Soft’ measures
‘Hard’ measures
Soft measures
• Beach nourishments
• Dune nourishments
Hard measures
Sea walls and quay walls: storm walls or elevation
Reinforcement of locks and weirs
Stilling wave basin
Storm surge barrier
• study Master Plan started in 2007
• Master Plan and proposed measures approved by the Flemish government in 2011
• estimated cost: 300 millions €
• works started in 2011;
Coastal Safety Master Plan
11/06/2018 │20
Anno 2011: measures to be executed
Beach
nourishment
Dune
nourishment
Storm wall/ storm
surge barrier
Stilling wave
basin
11/06/2018 │21
Anno 2018: Measures to be exectuted
Beach
nourishment
Dune
noruishment
Storm wall/ storm
surge barrier
Stilling wave
basin
3. Management of the sandy coast
Coastal Safety Masterplan: Management
Sandy flood measures: management is required
• Dynamic environment: natural sand transport + maintenance is needed after heavy storm surges
Coastal Safety Masterplan: Management
Sandy flood measures: • Topographic and bathymetric measurements: 2 times/year
• 6 yearly detailed safety assessment: 2015
• Safety assessments after every heavy storm surge
Results safety assessment of 2015
Safety assessment conclusions
• No breaching of dunes and seawalls • Weak zones remain ‘weaker’ but are much better • Nourished zones that don’t comply to the standard:
the norm is just exceeded, so maintenance is needed
4. Case studie ‘Ostende – Mariakerke &
Raversijde’
Ostende ‘Mariakerke & Raversijde’
1. Reinforcement of the coastal defence 2. Reduce sand blowing on the sea wall and coastal road 3. Create added value to inhabitants and tourists
Design of flood measures: 3 goals
Cooperation of MDK en City of Oostende
Design is almost finished
1.Beach nourishment and storm walls
2.Reduce excessive eolian transport
Dune creation for reducing eolian transport
3. Added value
5. Case studie ‘Seawall reinforcement of
Middelkerke’
Middelkerke
1. More ‘protection’ 2. More ‘experience’ 3. More ‘sun’ 4. More ‘green’
Design of flood measures: 4 goals
Cooperation of MDK en Town of Middelkerke
1.More protection: combination of soft
and hard measures
2.More experience
3.More sun
4.More green
Questions
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