26 October 2010

Gothenburg protected from submergence

Gothenburg will be flooded if the sea level rises by 90 centimetres. Simultaneously, there will be extreme high tides (surges) as a result of stormy weather. Mistra Urban Futures’ plan is ‘defence, attack and retreat’.

Rain and storm surges are not what are causing the rise in sea level off the coast of West Sweden. The cause is low pressure as such, according to GT/Expressen (the Gothenburg edition of Expressen, the national evening paper) online. A marked dip in pressure can ‘release’ the sea, making it rise by more than a metre. ‘Extreme high tide’ currently means that the water rises 1.8 metres above its normal elevation.

In the Netherlands, the UK and Japan, research on the consequences of rising sea levels is far advanced. Japan has, for example, a floating airport — one kilometre long.

In Gothenburg a pilot project is now under way to yield answers to two questions: ‘How will the city be affected when [NB not if] the sea level rises as a result of climate change?’ and ‘What should be done about it?’

Research centre
The latter project is under way under the aegis of Mistra Urban Futures, an interdisciplinary research centre for sustainable urban development started in Gothenburg by Mistra, the Swedish Foundation for Strategic Environmental Research. It is headed by the municipality, the City of Gothenburg, in cooperation with various partners including Chalmers University of Technology and the Swedish Environmental Research Institute (IVL).

Ulf Moback, a landscape architect at the urban planning department, and Philip Thörn at IVL are jointly serving the project management. Moback explains the situation as follows.

‘The scientists think that in a hundred years’ time, the sea level will have risen by one metre — although no one knows for sure, of course. I think it will be even more,’ he tells GT/Expressen. ‘Frihamnen (the inner harbour) in the Port of Gothenburg has been selected as a kind of pilot area, and the aim is to find out how the city is affected economically, socially and ecologically.’

Mobile structures
‘We’ll have a report ready by October next year,’ Moback continues, ‘and after that there will be seminars at which we discuss how to proceed in terms of three different notions: defence, attack or retreat. “Defence” means that the city builds walls and dykes or levees to give protection at times of extremely high water. “Retreat” means that it will be all right to stay in the area for the next 50 years or so, but that we then may have to withdraw from it. This can be done with prepared mobile structures. And “attack” means that the city will build despite the rise in sea level but use floating structures or build on pillars.’

Extremely high water
‘The plan is that the city should be capable of withstanding extreme highs of up to 3.8 metres above the normal level,’ Moback adds. ‘During the 21st century there has been extremely high water on two occasions, including the “Gudrun’ storm.’
The Göta älv was then, at most, 1.75 metres above the normal level in the central reaches of the river. But what about the rise in land height, then? Doesn’t it cancel out a one-metre rise in sea level over a century?

Ulf Moback says: ‘No, the rise in sea level that’s already been ascertained exceeds the rise in land height.’

Mistra Mistra