Visiting engineer gives talk on coastal sea defences
AN ENGINEER from the UK has given islanders an insight into how the south coast is preparing its sea defences for the future with multi-million pound investment.
It comes as Guernsey grapples with its own challenges for coastal defences, as global warming brings more extreme weather and rising sea levels.
Marc Bryan is major projects manager for Coastal Partners, a joint partnership between five local south coast authorities – Portsmouth, Fareham, Gosport, Chichester and Havant – covering some 153 miles of coastline.
He was in the island at the invitation of the Channel Island Group of Professional Engineers to talk about his work generally and two Portsmouth-based coastal defence projects in particular, which are set to cost about £225m.
‘Portsmouth is a very low-lying island, it’s the UK’s only island city and it’s very densely populated,’ he said.
Its oldest defences date from the 15th century and some of these are classed as being of historic interest, so as well as replacing some sections, others will be protected by new defences.
In addition, there are sections which are too low to offer long-term protection and need raising.
The sort of term being talked about is 100 years, said Mr Bryan, based on an estimate of a sea level rise of just less than one metre during that time.
While this is a worst-case scenario, he said it made sense to use it as a benchmark since with the area being so densely populated and the amount of disruption likely to be caused, it would avoid having to do more work again in the near future.
Like in Guernsey, there have been situations where the defences have been breached. ‘We’ve had a number of quite major failures of the current defences over the last 10 years and spent about £5m. patching them up.’
Research had been done on extending the life of the existing defences. ‘In the majority of cases, unfortunately, it wasn’t feasible, you’d have had to do so much work to extend and get them to where they need to be, that it’s been more economic to build new.’
The work will involve some 200,000 tonnes of granite being shipped in from Norway and some pre-cast units from Northern Ireland.
But not all sections of coast can be protected and this has to be accepted, said Mr Bryan.
‘As climate change takes effect we are going to have to let some areas go.’
While Guernsey could have similar issues, in some respects the island was in a worse position.
‘You have a lot more exposed conditions, while we’re protected by the Isle of Wight,' he said.
‘But in principle, everyone’s facing the same issues.
‘We’ve got rising sea levels and ageing defences, a lack of space behind defences to do different things.
‘We’re all grappling with the same issues.’
