Special waterway transport: Enormous concrete sill for flood barrier from Kallo to Nieuwpoort

Within the next few days, a special transport will leave our site in  Kallo. A pontoon carrying an enormous concrete sill. Final destination: Nieuwpoort harbour channel. This is a major component of the flood barrier currently under construction by Herbosch-Kiere and Jan De Nul Group. This flood barrier will protect Nieuwpoort against extreme storm surges. Minister for Mobility and Public Works Lydia Peeters came to have a look at how this enormous sill is being completed.

23.5 metre wide, 42.1 metre long and five metre high, that is the size of this concrete sill that was under construction at Kallo over the past few months. This sill will soon be installed in the harbour channel at Nieuwpoort between both abutments of the flood barrier. Later, it will hold the steel barrier in normal, open position.

“The construction of the flood barrier is unique in our country,” explains minister Lydia Peeters. “When I see the sill lying there, then the transport alone can be considered a real feat. Many different parties worked together to get the sill safely at its final destination. Everyone who took part in this project has a right to be proud of being involved in the process as a whole.”

“The flood barrier is necessary to protect Nieuwpoort and the hinterland against floods,” says minister Lydia Peeters. “Nowadays, coastal harbours are the most at risk of floods when storm surges occur. Nieuwpoort too is currently still unprepared for the high water levels that can occur during heavy storms. For the protection of Nieuwpoort, at the Flemish Authority we are currently investing M€ 58 in the construction of flood barriers in the Yser estuary. The infrastructure is one of the measures in the Coastal Safety Master Plan that will protect our whole coastline against heavy storm surges until 2050.”

Benny De Sutter, CEO Herbosch-Kiere: “Since the works were performed in our premises in Kallo, we have the privilege of monitoring its progress on a daily basis and seeing it grow. That was a special experience for our people, here at the office. The activities on this impressive and gigantic structure went very smoothly and we are proud of our colleagues who devoted their efforts in a flexible and professional manner over the past period. We are absolutely ready tor this adventurous journey to the final destination of the sill in Nieuwpoort.”

Dirk Van Rompaey, Director Civil Engineering Works at Jan De Nul Group: “Our Belgian coast is vulnerable to rising sea levels. The flood barriers being constructed by Jan De Nul in Nieuwpoort fit in a series of public measures aimed at protecting 67 km of coastline. It is a unique hydraulic structure in which civil engineering and maritime technology know-how and expertise join forces. Quite fitting for Jan De Nul. The Immersing the concrete sill is a major milestone in this project. An exploit achieved by Jan De Nul in cooperation with Herbosch-Kiere.”

Water transport

 Getting the sill from Kallo to Nieuwpoort can definitely be qualified as special transport. The sill is built onto a pontoon that can be submerged. Two tugboats first pull the pontoon through the Scheldt, and then over sea to the harbour in Ostend. A trip that will last about twelve hours.

For the transport over the Wester Scheldt and over sea, several links in the nautical chain work together closely. The Common Nautical Authority (CAN) gives approval for the river leg, and the Maritime Rescue and Coordination Centre (MRCC) issues the permit for the sea leg. For both the part of the trip on the Scheldt and over sea up to Ostend, a pilot will be on-board.

Permits have been issued for this special transport, stipulating certain safety conditions.

Upon arrival in Ostend, everything preventing the sill from shifting or tipping over during transport (seafastening) is removed. Then, the sill is hooked onto a crane on a second pontoon, the Matador III. The concrete sill weighs more than 4,500 tonnes. Too heavy to lift for the Matador III. If you still remember Archimedes’ Law, you will know that a submerged object is lighter to lift. Therefore, 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 takes 16 to 20 hours. A number of checks will still need to be carried out. Only then will the sill, suspended from the crane on the Matador III, be ready for the last leg of the trip to Nieuwpoort. This journey takes approximately six hours.

Once the sill has arrived in the harbour channel at Nieuwpoort, it is lowered between two abutments. This takes approximately 1 day. Finally, the sill still needs to be anchored. For this, the harbour channel will be closed off completely for about 10 days. During the whole process in Nieuwpoort, divers are present to check that the positioning happens correctly.