Watch as workers abseil down Hull's tidal barrier to carry out nuts and bolts inspection

For the past few weeks they've been working on the 44-year-old structure, which is second in size to the Thames Barrier and has successfully protected the city from flooding since it opened in 1980.

Routine maintenance continues all year round, but close-up, forensic inspections only occur around once a decade. People have been getting a good view of the work as they cross the river Hull from The Deep. Contractors from specialist rope access firms CAN and RSK can be seen working, while safety operatives watch on a walkway 90ft above the river Hull.

The team have been grinding layers of paint off the welded joints so the welds and steelwork can be inspected.

Environment Agency adviser Adrian Robinson said some nuts and bolts will be taken out and sent to the lab where they are X-rayed for wear and fractures that are not visible to the naked eye. He said: "The structure is 212 tonnes and moves a lot, it is metal so it contracts and expands, so we always need to ensure its integrity. This is a really good way to do a visual and touch inspection."

In 1969, the council decided a barrier was needed to stop high tides entering the river Hull from the Humber after widespread flooding. It is used around 25 times a year but last winter operated around 40 times more than usual to help drain floodwater.