Two underwater deposit areas to store sediment dredged from the Elbe River, Germany, as part of a deepening project to make it navigable for larger ships, were completed in November 2019.
Permanent relocation of the dredged material is vital to ensure it will not be washed back into the Elbe River or the North Sea. As a result, Germany’s Federal Waterways and Shipping Administration (WSV) commissioned Belgian dredging and offshore major Jan De Nul (JDN) and Dutch hydraulic engineers Van den Herik (VdH) to build the underwater deposit areas (UDAs) at Neufelder Sand and Medemrinne, respectively. Both are in the Elbe estuary funnel, near Neufeld and Sankt Margarethen, and close to the port of Cuxhaven.
The overall project logistics requirements and portside infrastructure were provided by Cuxhaven Port Authority member Machulez, with Cuxhaven’s Hansakai site acting as a base port. Machulez’s tasks included working with JDN and VdH on the import of over a million tonnes of rock from a Norwegian quarry to build the ‘bunds’ (dams) creating the UDAs. The rocks arrived in Cuxhaven between March and September 2019 aboard more than 40 ships and were delivered to the construction sites in two independent logistics cycles, each with three construction site ships.
“The biggest challenge of the project was to organise the multiple parallel handling of all ships involved, as well as the related pre-carriages and on-carriages,” a Machulez representative told DPC. “But we were able to do this without any delays.”
JDN was responsible for the bigger of the two UDAs, Neufelder Sand, the bund measuring 6,700 m with the top fixed at -4.60 m Normalhöhennull (normal height zero or NHN). About 800,000 tonnes of rock – with grading up to 200 mm – was needed.
Speaking exclusively to DPC, JDN project manager Dennis Veeckman described the challenges.
“Cuxhaven is located in a semi-diurnal region, which means that two high tides and two low tides occur every 24-hour cycle. The tides influenced the planning of our loading and dumping activities. In order to define the right combination of ‘load-tide to dump’, a constant follow-up was required.
“The big rock delivery vessels were able to discharge their cargo via their own conveyor belts directly into our two large split hopper barges [SHBs], L’Etoile and L’Aigle. Thanks to this unconventional loading method, no re-handling of the rock was required, and the loss of fill material could be minimised.
“Based on the calculations of volumes needed on the dump location, we were able to optimise each load in the SHBs,” Veeckman continued. “This would seem to be time-consuming, but that was not the case because of good planning. It even became a ‘plug-and-play’ exercise, which resulted in a very quick turnaround time for the cargo vessels.”