Thames Barrier’s mid life crisis raises retirement questions

Turning 40 is a tricky time for anyone, but even more so when you are the barrier protecting 1.4 million Londoners and £321 billion of property from a deadly deluge. On 8 May 1984, the late Queen officially opened the Thames Barrier, which had actually been in operation for the previous 18 months.

Despite being 520 metres long and consisting of 10 steel gates each weighing some 3,100 tonnes, it is not in the average Londoner’s radar in the way that the Houses of Parliament, the O2 Millennium Dome and the London Eye — all of which the barrier protects from aquatic destruction — very much are. Paying a visit on Saturday 12 May, I saw few others coming to have a look.

Over its 40 (or 42) year life, it has been closed 221 times and has not, it seems, ever suffered a technical failure. As the government, which paid 75 per cent of the £2.4 billion cost in today’s money, said “without the barrier, storm surges and frequent tidal flooding … submerge buildings along the river as well as the Underground”.

But the barrier will go into retirement at some point; it was originally envisaged to need replacing in 2030, but a reassessment has extended its working life to 2070 when it will be 86.

A decision about the Thames post-2070 must be made in 2040. The Environment Agency, which has responsibility for flood protection, has identified seven options. The first is to upgrade the existing barrier. The review is silent on merits and demerits, but that is unlikely to happen. Raising the height of the gates will involve a very complex and expensive operation that would mean effectively reconstructing the entire structure.

The second alternative is a second set of gates at the existing site plus locks to allow boats to pass during closures.

There are then three options for new barrier downstream of the existing one. The nearest  ones are at Long Reach, with a single set of gates, matching the incumbent, and another with a second set of gates and locks. A few miles towards the sea are a set of two matching proposals at Gravesend in Kent. Again, no details, so no costs.

Finally there is a proposal for four tidal flood storage areas on four marshes along the estuary that would store flood water, enabling the barrier (which would be upgraded “at a later date”) to cope with surges.

Nature based solutions

One of the big debates within academia is over the growing prominence of engineering solutions such as dykes and barriers over more nature based solutions (NBS) such as flood reservoirs. Given that the engineering solution was selected in the 1970s out of 31 designs —were any of them NBS? — it is hardly surprising that it will likely be a battle of the barriers.

But the presence of at least half an NBS option is a relief. It would be interesting to know if a full NBS option without a barrier upgrade was ever on the table. The barrier has been a great success and imitated by other cities. But as sea levels are forecast  to rise and tidal surges more likely thanks to climate change, will the UK need yet another, longer barrier further downstream after another 86 years.

Given that the decision is still 15 years away, there is still an opportunity to start a debate about the potential for NBS such as floodplains, rainwater harvesting, sustainable urban drainage systems, and flood retention systems within the city itself.

It is the least we can do as the Thames Barrier enters the second half of its life.