It stops the Old Town from flooding, but how? Our marine impediment correspondent Angus Young dives in.
After the one on the Thames, Hull’s Tidal Barrier is the largest flood barrier in the UK. It’s not a surprising fact because after London, Hull is also the second largest UK city most at risk from being inundated by flooding.
Completed in 1980 at a cost of £4.3m, the barrier has certainly proved to be value for money having protected the city from flooding ever since. The giant structure’s finest hour to date came in December 2013 when it stood firm during a record storm surge on the Humber and kept everyone dry.
When a high tide is predicted, the barrier’s 212-tonne steel gate is lowered into the River Hull to prevent water from the estuary entering the low-lying River Hull Valley. Steel plays an important part in the structure because each of its two distinctive concrete towers also feature steel support columns. At the time, the 34 metre-long steel used for the columns was the longest ever rolled by British Steel.
The gate is powered by motors and is typically deployed using a hydraulics system 30 minutes before an expected high tide. In the event of a mechanical failure, it can actually be hand-cranked in position although this is never thought to have happened during a real-life incident.
When required to thwart a high tide, the gate moves from its normal stationary horizontal position and rotates 90 degrees before being lowered and locking into a sill built into the river bed. This movement has been likened to an up-and-over garage door. When locked into place, five sluice gates in the barrier control water flows into the river.
As with any machine of a certain age, the barrier needs regular maintenance. Last year specialist civil engineers carried out a major structural survey, inspecting 92 separate locations on the steel gate for signs of corrosion along with 260 welds and bolts. They also took concrete samples from 12 different parts of the two main towers for further examination. The results from tests on both the steelwork and concrete will be used to plan future maintenance work.
When it was built, the barrier was typically lowered around once a year but more recently that frequency has significantly increased reflecting rising tides on the Humber. Sometimes it is lowered once a month. Another recent change has seen the barrier being used to reduce the risk of flooding upriver in the River Hull Valley. This has seen it lowered at low tide to keep water from the estuary out of the River Hull to ease flood-inundated land north of the city.
As you would expect, Professor Stuart McLelland, of the Energy and Environment Institute at the University of Hull, is a big fan. He said: “The tidal surge barrier is an impressive structure and an elegant engineering achievement to help the city and the wide region live with the water that surrounds us. If it wasn’t there, those of use living and working in Hull would regularly get wet, or worse.”