UK: Northern Divers Complete Year-Long Project in Humber Estuary

Specialist divers battling strong tides and zero-visibility have completed a year-long project to cover parts of an exposed underwater pipeline in the Humber estuary.

Teams from Hull-based commercial diving and underwater civil engineering company Northern Divers worked up to 60ft below the surface of the river.

The divers coated a section of pipeline with special concrete covers, called fronded mattresses, to ensure the route can better withstand the estuary’s notoriously harsh conditions.

Because the riverbed in the Humber is very mobile, with strong tidal streams, the protective trench where the pipeline was originally laid has been gradually eroded – exposing parts of the infrastructure.

Two teams of 12 men from Northern Divers worked 24 hours a day in a wide stretch of the river and battled the tides and pitch-black conditions to lay the concrete mattresses, each weighing about four tons, over the industrial pipeline.

John Sparrowe, managing director of Northern Divers, which was established in 1963, said: “As a company, we’ve been working in the Humber for more than 40 years and know about the unique issues and dangers it poses.

“For this project, we had to contend with strong, six knot tides and zero visibility – meaning the divers had to use their sense of touch to feel their way around laying the mattresses over the pipeline.

“The divers were also working in a very busy shipping lane, so had to be extremely aware of large vessels passing close to them.”

The mattresses are lowered to the riverbed by a floating crane, with global positioning satellite (GPS) technology used to find the right location in the estuary.

However, because of the lack of visibility beneath the surface of the water, the divers then have to use their sense of touch to accurately fix the mattresses in place and connect them together by hand.

Each mattress is anchored to the riverbed and features a textured coating on its top, known as a frond. This resembles strips of grass and is designed to collect silt in the water – creating an additional, natural, protective coating over the pipeline.

About 1,300 mattresses were lowered into position during the 12 months of the project, which began in January last year.

The section covered was 770 metres in length, by 35 metres wide.

Northern Divers is equipped with the most up-to-date diving, inspection and maintenance technology and carries out a variety of projects, from inland and coastal work, to harbour repairs, hydrographical surveys and cable installations around the world, including on a Dutch offshore wind farm in 2006.

Mr Sparrowe said: “Each project presents its own challenges to us as divers. For example, when covering the pipeline in the Humber, we were restricted in how we could work because of the tides, shipping and weather conditions.

“On one day you may have got the opportunity to dive four times, but on others just once.

“So, with a job like this, it’s always a case of having a good deal of patience, using your specialist knowledge of an area and being very well prepared.”

Northern Divers, which has purpose-built headquarters in Hull and operates worldwide, has recently targeted more energy-related projects on its own doorstep.

The company believes the business is perfectly positioned to offer its specialist support as major wind turbine companies, such as Siemens, E.ON and RWE, look to base large-scale operations in the Humber area.

However, the work on wind farms is just one part of a diverse portfolio of projects and clients that has seen the company’s divers already complete several, complex, marine civil engineering and salvage schemes across the UK over the last year.

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Subsea World News Staff , February 24, 2012;  Image: Northern Divers