Monitoring of the dune for dike pilots. Evolution after 3 years

At the beginning of 2021, the MDK Coastal Division, and the municipalities of Ostend and Middelkerke built up dunes on the dry beach in front of a sea wall at four locations: Spinoladijk and Raversijde (Ostend), Westende (Middelkerke) and Knokke. Intensive monitoring at these Nature-based-Solution (NbS) sites was carried out from the beginning of 2021 (except in Knokke from 12/2023) to 04/2024 to investigate the development of the built dunes and to follow closely their morphology and planted …

At the beginning of 2021, the MDK Coastal Division, and the municipalities of Ostend and Middelkerke built up dunes on the dry beach in front of a sea wall at four locations: Spinoladijk and Raversijde (Ostend), Westende (Middelkerke) and Knokke. Intensive monitoring at these Nature-based-Solution (NbS) sites was carried out from the beginning of 2021 (except in Knokke from 12/2023) to 04/2024 to investigate the development of the built dunes and to follow closely their morphology and planted vegetation. This report documents the evolution of the morphology of the dune for dike pilots until the 3rd year after construction. A progressive evolution of the four pilot sites occurred over the entire monitoring period. A substantial accretion took place in the 1st year in the zones where marram grass and/or brushwood fences were installed. These allowed to capture effectively the aeolian sand transport. Since the 2nd monitoring year , there has been a reduction in sand trapping, which could be related to the saturation of the vegetated boxes as well as a difference of wind conditions over the monitoring periods. At Raversijde, this reduction could be further caused by a diminished sand availability after the nourishment in 2021. Further monitoring surveys will help to understand the observed relationships between accretion in the upper part of the dry beach and erosion dominating its lower part above the low water mark. These would also confirm the temporal behaviour and evolution of the NbS sites.