Removing unexploded ordnance for dredging works

Unexploded ordnance had to be removed prior to dredging works. Credit: Port of Kokkola

Dredging and reclamation works are often interrupted by unexploded ordnance (UXO). This is especially an issue encountered around the North and Baltic seas, but also in lakes, rivers, and land.

According to Germany’s Fraunhofer Institute for Chemical Technology, there is “an estimated 1.6 million metric tonnes of conventional and 220,000 metric tonnes of chemical warfare agents” dumped at sea decades ago, mostly at the end of World War II, and now decomposing, posing explosion and pollution hazards. As indicated below, some UXO dates from the first World War. 

Boskalis subsidiary Heinrich Hirdes EOD Services, a hydraulic engineering company that works with UXO, has echoed the estimated figure on conventional UXO, and has pointed out that the construction of offshore wind farms and their connecting cables to land side is creating new dangers when encountering the objects. 

As a sign of the extent of the UXO problem, Belgium’s Flemish regional governmentspecifically the Department of Mobility and Public Works, Maritime Access Division  in 2018 launched a programme to hammer out the parameters of a test of ways to efficiently remove UXO in the North Sea. A market consultation session was held in October 2019 in Brussels.  

The government is targeting an estimated 35,000 metric tonnes of dumped conventional and chemical ammunition dating from World War I that sits in a sandbank called De Paardenmarkt off the coast of Knokke-Heist, about 90 km from Antwerp. According to the government, “to date, there is no danger to the marine environment or public health, but there is a constant risk” of chemical UXO oxidising or breaking open in collisions with vessels, either of which would “result in heavy chemical pollution”. 

The government has specified several key technologies as being of interest, including precision detection, environmental monitoring, sediment dredging, and robot technology to raise and remove the UXO. Depending on what approaches are eventually selected, the government is planning a test that would demonstrate ways the UXO “could be cleaned up safely and time- and cost-effectively” in a full-scale project.  

In recent years, the UXO is being discovered in greater numbers with the use of technologies such as magnetic probes and sonar, as Fraunhofer pointed out. However, divers often are required to dispose of the UXO – a dangerous activity. Further, some objects cannot be removed and must be detonated in place, with explosions and toxins posing risks to people and marine life alike, as Fraunhofer described.  

To address this multi-pronged problem, Fraunhofer reports that it has worked with other organisations in a German government-funded programme, co-ordinated by Heinrich Hirdes EOD Services, to develop what Fraunhofer calls “a robotic underwater salvage and disposal process for the disassembly of ammunition in the sea”, or RoBEMM for short.  

Fraunhofer declined to comment further on the specifics of the technology and its ongoing development but does indicate that the goal of RoBEMM is to provide a semi-automated process that renders underwater UXO “harmless directly where it is found”, replace divers, and dispose of such objects in an environmentally sound way. Testing is under way, according to Fraunhofer. 

N-Sea, a Dutch company, in 2017 announced its own system, called Magsense, which reportedly is a vertical gradiometer array designed for accuracy in a variety of conditions and undersea terrains. In late 2017, the company reportedly won a contract from 50Hertz, an operator of transmission systems, to detect and remove UXO from the route of two to three such cables for planned wind farms in the Baltic near Lubmin, Germany.  

While Fraunhofer is applying what it calls its areas of expertise  safety and characterising UXO substances  to the RoBEMM project, Heinrich Hirdes provides various services to find, recover, and destroy UXO.  

As the company describes, its applications include, among others, sounding in waters and on land, radar, side scan and multibeam sonar, magnetometers, electromagnetic surveys to investigate UXO, remotely operated vehicles and electromagnets and divers to recover them, and bubble curtains to buffer explosions when destroying UXO at sea.