Storm surges are one of the main natural threats in the North Sea region. Today, coastal ports are most at risk of flooding in case of heavy stormy weather. To protect the coast and hinterland from heavy storms, the Flemish Government approved the Masterplan for Coastal Safety in 2011. This plan includes the building of a storm flood barrier at the mouth of the river Yser in Nieuwpoort. After in-depth studies, a horizontal sector gate with a clearance width of 38 meters was chosen.

Rotating steel barriers

The movable steel barrier is a construction that rotates around a horizontal axis. When parked, the barrier is sunk in a concrete sill at the bottom of the river Yser. The steel barrier rotates between two cast steel shafts which are anchored in concrete abutments connected to the banks of the Yser.

Maintenance of the barriers

For maintenance purposes, the barrier can be rotated 180 degrees into the horizontal maintenance position. Alongside the sector gates, large lateral ducts (bypass sewers) will be built in the abutments. These can handle additional flows, keeping the current velocity at spring tide below 3 knots and limiting the impact for recreational boating.

Construction and products

The two building pits for the abutments were made of combined walls. Each pit consisted of 53 tubular piles Ø1,420 x 21.6 mm in S 460 MH, 31.5 m long and infill sheet piles AZ 28-700 in S 240 GP, 26.5 m long. The tubular king piles were installed with a vibratory hammer PVE 2350 VM and driven to final elevation with an IHC Hydrohammer S150. Due to the high water pressure on the combined walls, the C6 interlocks of the tubes and the middle interlocks of the sheet piles were filled with sealant Beltan® Plus.

For each pit, 42 tubular foundation piles Ø 1,270 x 16 mm in S 355 J0, 12.9 m long were installed with an overlength of 8.6 m to drive them with a vibratory hammer, above the water level. They were driven 9 m into the tertiary clay, using a vibratory hammer PVE 250M.

Apart from the building pits, other steel combined walls, sheet pile walls and tubes were installed for the quay walls at both embankments, current conducting walls, a construction pit for the bypass sewers, an undercurrent screen, guiding walls and dolphins.

The project started in February 2018 and will be completed in 2025.