In March 2007, the Coastal Division initiated an Integrated Master Plan for Coastal Safety (Masterplan Kustveiligheid) to protect Flanders against extreme flooding events in the present and in the future (2050). Extreme flooding events were defined as those associated with storms with a 1:1,000 years return period. The Master Plan aims to ensure the same level of protection under current conditions and in the case of a +30 cm sea level rise by 2050.
Before the Master Plan was finalised, an emergency plan for the execution of most critical works was in place between 2004 and 2010. This made it possible to resolve most pressing problems and cover short-term risks. Those risks were mapped by a study that was part of the Master Plan elaboration. In particular, implemented emergency measures have provided protection against storms with 1:100 years return period as a minimum along the entire coastline.
The Flemish government approved the Master Plan for Coastal Safety on the 10th of June 2011, after it was approved by the ten Flemish coastal cities and coastal communities.
Works started in 2011. The ambition is to protect the most critical areas as soon as possible. The website Kustveiligheid (Coastal Safety) provides information on specific measures planned in each coastal community as well as the relative work progress. The Master Plan includes both green and grey measures.
Green measures consist of beach and dune nourishment. The permit granted by the Federal Government, after environmental impact assessment, enables to extract about 20 million cubic meters of sand – taken from the Belgian part of the North Sea – over a period of 10 years, thus fully supporting beach and dune nourishment. Beaches and dunes are monitored every year to adapt their management accordingly. Beach nourishment efficacy is periodically assessed using a 6-year plan to respond to still occurring erosion and cope with future sea level rise. The volumes needed for maintenance are estimated around 500.000 cubic meters per year.
During the period 2011-2018, scheduled beach nourishments and repairs from heavy storm damage (e.g. after the “Sinterklaas” storm in 2013 or the “Dieter” storm in 2017) were completed in the risk areas identified in the Master Plan. Other smaller nourishment interventions were completed in other locations to strengthen the whole coastal area. Moreover, foreshore replenishment was carried out in October 2017 at Nieuwpoort. This foreshore nourishment aims to ensure the stabilization and growth of a bland intertidal beach (wet beach). This serves as a nature compensation intervention for works performed in and around the port of Ostend. On the other hand, it reinforces interventions performed in the neighbouring beach sections, delaying the erosion of the beach.
Sand replenishment or hydraulic-filling is performed as much as possible in an environmental friendly manner, to minimise possible disturbance to the coastal ecosystem. A monitoring programme was put in action for larger projects to assess the environmental impact immediately after the completion of the works and following the evolution of the environmental recovery with the time.
Grey measures (such as renovation of sea-dike and storm walls) have been implemented in areas where beach nourishment could not meet the desired safety standards. These protection measures have been designed to minimise their height and optimise their spatial integration, enhancing recreational opportunities. In Ostend, the reinforcement and renovation of Albert I promenade, with a mobile storm surge barrier was completed in 2012. The promenade was connected to the completed renovated Zeeheldenplein (sea heroes square). This is a “wave-damping” square that protects the city and offers, as an example of attractive architecture, recreational opportunities. The intervention is part of a wider plan to protect the city area at risk of flooding. This includes regular beach nourishment and the creation of a new large beach protected by a dam built perpendicular to the coastline.
Storm walls on renovated dikes were built at Wenduine (2015) as well as in the Marina of Blankenberge (completed in 2019), combined with a complete renewal of the two areas. The works for the extension of the dike protecting Zwin, the best known nature reserve of Flemish and Dutch coast, started in 2016 were completed as an important part of the large-scale works to preserve this reserve. In 2018, the construction of a rotating storm surge steel barrier in the harbour channel of Nieuwpoort begun, to protect the city and the hinterland against high water levels during heavy storms. The work will take more than three years.
In 2019, several studies were executed to design the necessary measures against storms in Zeebrugge, Mariakerke-Raversijde (Oostende) and Oostende (connection to Zeeheldenplein). These projects are planned to start-up in 2020.
Considering the dynamic evolution of the Flemish sandy coast, a comprehensive evaluation of the implemented measures is performed every six years to ensure that all the coastal sections, identified in the Master Plan, meet the following safety standards:
- At the storm peak, the seawater flow rate that can run over the security line must not exceed 1 l/m/s, ensuring that 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.
Coastal erosion and the effects of emerging storms are closely followed through plane flying over the beach (twice a year) and dune areas (once every three years). Using LiDAR technology (Light Detection And Ranging), height maps of the beaches and dunes are created, allowing control of coastal erosion and plan management interventions.
The second assessment was completed in 2017. It revealed that the level of protection has sharply risen in the areas where all planned measures have been implemented. In some other locations, where measures are not yet or not fully implemented or require constant nourishment, safety levels are not fully achieved. The next step towards coastal safety is the safety assessment of the existing harbour infrastructures like locks and gates to a 1,000 years storm event (corresponding to a probability of occurrence of such a storm of 0.1% in a year).