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