Newton Emerson: What can save Belfast in the face of rising sea levels?

People in Belfast, in my experience, do not really think of themselves as living by the sea. They know the sea is there, and they may stroll along the newly developed waterfronts where the river Lagan approaches Belfast Lough, but intervening port and industrial areas disguise the fact the sea is right there, almost literally at the bottom of the High Street.

This may explain the muted reaction to this week’s Intergovernmental Panel on Climate Change report on climate change – or perhaps it is simply too overwhelming and depressing to contemplate. The report’s most optimistic projection is for a 0.5m sea level rise plus heavier rain by the end of the century, with centuries of unavoidable sea level rises thereafter.

That is enough to threaten imminent disaster and ultimate doom for Belfast, one of the few settlements of any size in Northern Ireland to be so vulnerable.

The risk from the sea must have been clearer to the populace before 1970, when high tides and heavy rain could cause occasional serious flooding in the city centre. Better drainage solved the problem, which has now vanished from shared memory. It seems inconceivable to me that water once sloshed around City Hall and Great Victoria Street.

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A sea level rise, with a commensurate water table rise, will also cause Belfast to sink

I remember the pungent smell at low tide from the Lagan mud flats which stretched around the city centre. That problem was solved in 1994 by the Lagan Weir, a mini-Thames Barrier. Its five gates are raised mainly to keep the river level behind them up, although they have also been used to keep high tides out, protecting inner-city housing. The weir was not built to protect the city centre, however. Exceptional tides already lap less than half a metre from the quaysides below it.

The first part of Belfast to disappear below the waves will presumably be Sydenham, a densely-populated neighbourhood beside the airport. In 2014, residents were told to prepare for evacuation due to a storm surge. The warning proved unnecessary and the authorities came in for criticism for creating a drama, but their fears were understandable: Sydenham is less than 1m above sea level, with a tidal river running through it behind embankments as high as its Victorian houses. Across the Lough in north Belfast are more swathes of almost equally vulnerable housing. The Harbour Estate, one-fifth of the city’s surface area, is all on reclaimed land.

The city centre itself is built on notoriously infirm ground – the silty Belfast sleech. When the Victoria Square shopping centre was built 15 years ago its underground car park had to be made watertight, like the hull of a ship, then anchored down to stop the entire complex trying to float. Construction of the new Ulster University campus was delayed when the hole dug for it filled up with water. A sea level rise, with a commensurate water table rise, will also cause Belfast to sink.

What, if anything, can be done to save it?

If the Dutch can get the Rhine to the North Sea, even Northern Ireland should be able to get the Lagan to Newtownabbey

The Lough is about 5km wide along its length and very shallow: 5m to 10m almost everywhere. It is no “Boris Bridge” fantasy to imagine some kind of barrier across it, at least as a protection from high tides. Protecting land permanently below sea level would be a different proposition: the barrier would need huge locks for shipping, or the harbour would have to be relocated outside it. Then the full outflow of the Lagan would have to be pumped or diverted over it. This is technically feasible but would it be economically viable for a provincial city of half a million people?

Such engineering projects could become the economic motor of a warming world, with Belfast considered fortunate in its manageable geography.

Alternatively, global urgency to protect coastal cities could make flood protection more difficult and expensive, and force countries to ruthlessly prioritise.

It is natural to look to the Netherlands for hope. If the Dutch can get the Rhine to the North Sea, even Northern Ireland should be able to get the Lagan to Newtownabbey. The Dutch would not only build a barrier but reclaim the land behind it, making themselves even safer and wealthier.

However, I find my thoughts turning to Seattle, another rainy city built on tidal mud flats. After a fire in 1889, it took the opportunity to solve its flooding problem by raising the city centre one storey. Walls were built along both sides of streets up to first floor level, filled in with waste and rubble and paved over. Ground floors became basements, for those who could be bothered to occasionally pump them out.

An arresting sight on a tour I took of these basements 20 years ago were the toilets people had desperately raised up on bricks, almost to the ceiling, to stop sewage backing up.

Raising Belfast one floor would buy us another 100 years. It feels much more like something we might do.