ASSESSMENT OF THE SEA DEFENCE STRUCTURE
The objective of the Master Plan for Coastal Safety is to protect the Flemish coast and the hinterland against the impact of a storm surge with a return period of 1000 years. Since the approval by the Flemish Government of the Master Plan for Coastal Safety in 2011, the Coastal Division already carried out various protection measures at the level of sea dikes and dunes along the coast. Where possible, the choice was deliberately made for beach nourishments, whereby the beaches were heightened and broadened. This causes the waves to be broken on the beach and lose their energy before they cause damage to the dikes and the building area behind.
In view of the dynamic nature of our sandy coast, the Master Plan for Coastal Safety includes a comprehensive evaluation every six year of the safety level, the so-called review of the seawall structure, to ensure that all 255 coast sections meet the following safety standards:
- The flow rate of the seawater that at the peak of the storm can run over the security line must not exceed 1 l/m/s. At this flow the stability of adjacent buildings is not endangered.
- Eventual erosion of the dunes during the storm must not extend to the first residential area.
- The volume of the remaining dunes after the storm impact must be sufficient to avoid a breach in the dunes’ belt.
- The lining of the sea dike should remain stable during a storm to avoid a breach.
The second assessment of the seawall structure was completed in 2017. It was based on the latest scientific findings and calculation methods. The study checked whether the already tackled zones still meet safety standards and where protection measures are needed.
Result of the review
On the locations where all measures within the framework of the Master Plan for Coastal Safety have been carried out, the level of protection has risen sharply. In some locations, however, measures are still necessary to meet the intended level of safety. This is because the planned protection measures are not yet or are not fully implemented or because the beach needs a maintenance nourishment.
In particular, at the level of dikes and dunes the following measures have already been carried out or planned:
- Ostend Centre and Mariakerke: maintenance replenishment carried out in the spring of 2018.
- Knokke-Heist: implementation of the planned replenishment from the Master Plan Coastal Safety in the autumn of 2018
- Ostend – Mariakerke – Raversijde: construction a storm return wall on the dike – start of works foreseen end 2018
- Sea dike Middelkerke: renewal of the dike – design study is ongoing