So many wrecks

The Netherlands must provide adequate access to Belgium?s largest port, Antwerp, according to a long-standing arrangement between the two countries. To this end, the Dutch government has undertaken to give larger ships access to the port of Antwerp by deepening the navigation channel on the river Scheldt. By the time the work is completed, over 50 wrecks will have been cleared. “The project is about to move into its final stage,” says Arnold Warmerdam, a consultant with the Netherlands-based Touw group of surveying and consultancy companies, who has been overseeing the technical aspects of the project on behalf of the Dutch government. The Scheldt project started in 1997, when the wrecks of eight riverboats were cleared under the watchful eye of Touw?s salvage consultant Kommer Tanis. In 1999, when Warmerdam came on board, one inland and three ocean-going vessels were removed, and last year an additional three ocean-going ships were cleared. “It has not been easy,” says Warmerdam. “The river Scheldt is a busy commercial river and has not been closed for shipping during the project. To coordinate removal work and vessel traffic, close links have been forged between pilots, river authorities and local government.” The main challenge was to assess what needed to be removed. “We had to develop new techniques to determine the precise location of the wrecks, as most of them were completely submerged in the sediment,” says Warmerdam. These new techniques enabled the position of the top and bottom of the wrecks to be pinpointed. When a wreck is not completely covered by sand, it can easily be detected using multi-beam echo sounding, used in conjunction with advanced GPS. When the wreck is submerged, magnetometer equipment is used. This detection method measures anomalies in the earth?s magnetic field that are caused by iron masses in the riverbed. Warmerdam says, “Once the wrecks had been located, we brought in a hopper dredger to clear away the sand around the vessel, creating a moat around a pedestal that contains the wreck. A huge wreck removal grab on sheerlegs was then used to pull up the wreck, piece by piece. A jet flow unit was used to clear the wreck from the sand and to keep the moat around the wreck free.” Tanis and Warmerdam had to contend with strict Dutch and European environmental legislation, in addition to the technical aspects. “All the dredged material had to be analysed before disposal. Special permits had to be obtained to dispose of some of the sediments,” says Warmerdam. For Touw, the Scheldt project has been a valuable learning experience. “This type of project is a once or twice in a lifetime event. But we are now in a position to utilise our knowledge for other projects around the world,” says Warmerdam. The knowledge gained during the project has led to Touw setting up a specialised wreck removal and salvage team headed up by Tanis. Tanis says, “The unique nature of the Scheldt project has meant developing a level of technical and procedural knowledge that few in the wreck removal business can rival.”