The vital component of a storm surge barrier for one of Belgium’s ports is about to set sail
A storm surge barrier being built to protect 67 km of the Belgian coast that are at risk from flooding during heavy weather events has reached a major milestone, say the firms working on the seven-year project.
Marine civil engineer Jan de Nul is building the barrier and will immerse a major component, a concrete threshold, or sill, at Nieuwpoort as a major component that has been worked on in cooperation with marine construction specialist Herbosch-Kiere.
Last week, the companies announced that the building of the 23.5m x 42.1m concrete sill had been finished at Herbosch-Kiere’s Kallo facility and was about to be transported by sea to Nieuwpoort, where it will be installed in the harbour channel between both abutments of the storm barrier.
“Getting the threshold from Kallo to Nieuwpoort can definitely be qualified as special transport,” says Jan de Nul.
The threshold first must be built onto a pontoon that can be submerged then pulled by two tugboats along the Scheldt River, before sailing over the sea to Ostend, which will take around 12 hours.
“For the transport over the Western Scheldt and over sea, several links in the nautical chain work together closely,” says Herbosch-Kiere.
“The Common Nautical Authority gives approval for the river leg, and the Maritime Rescue and Coordination Centre issues the permit for the sea leg. For both parts of the ship, a pilot will be on board.
“Permits have been issued for this special transport, stipulating certain safety conditions.”
When the threshold arrives in Ostend, all of the seafastening safeguards that were preventing it from shifting or tipping over will have to be removed.
It will then be hooked on to a second pontoon, the Matador III.
“The concrete sill weighs more than 4,500 tonnes,” says Herbosch-Kiere. “Too heavy to lift for the Matador III. Bearing in mind Archimedes’ Law, that submerged objects are lighter to lift, the pontoon will be submerged so that the sill is entirely covered by water. The load to be lifted then ‘only’ weighs 1,210 tonnes.”
This operation will take up to 20 hours, and only when full checks have been completed will the threshold, suspended from the crane on the Matador III, be ready for the last six-hour leg to Nieuwpoort.
When the threshold arrives in Nieuwpoort, it will be lowered between the two abutments, which take around a day. It will then need to be anchored, and the entire harbour will be closed for around 10 days.
Divers will monitor the positioning throughout.
In the autumn, construction work will begin on bypass drains, lateral pipes in each of the abutments.
“They will ensure that the spring tide flow rate never exceeds three knots,” says Jan de Nul.
“Then the steel barrier still needs to be installed, as well as the mechanical parts and the fenders, and the service building will be installed on the abutment on the right bank.”
The firms say the works should be completed in 2025.
The works at Nieuwpoort are part of the coastal protection of the entire Flemish coast. In February, Jan de Nul began dredging and beach replenishment by the port of Ostend, moving 600,000m3 of sand to a 1.5km stretch between the western harbour dam and beach.