Tidal lagoon touted as Somerset flooding solution

Energy-generating tidal lagoons could help reduce flooding in areas like the Somerset Levels, according to engineers studying the technology.

A proposed tidal lagoon at Bridgwater Bay in Somerset could generate up to 3.6GW of renewable electricity by passing sea water in and out through a series of turbines located in a 16km-long wall around the bay.

But such lagoons could also keep the high tide out when needed, preventing tidal flooding from storm surges and effectively lowering the sea level to allow water from river flooding to run off the land more quickly, according to Prof Roger Falconer of Cardiff University.

Speaking yesterday at a briefing organised by the Royal Academy of Engineering and the Science Media Centre, he said a tidal lagoon at Bridgwater Bay would make a ‘huge’ difference to the nearby Somerset Levels, which have been severely flooded in recent weeks.

‘In my view it would be an ideal solution in the Somerset Levels,’ he told The Engineer. ‘The problem is they’ve got a horizontal water surface slope. [A lagoon] would allow us to drop the sea water level and therefore create a water surface slope.’

He added that dredging the area’s waterways – a key focus in the recent debate on flooding – would typically have a limited impact in the Levels because of the flatness of the land but that lowering the sea level with a lagoon would make dredging far more effective.

Swansea-based Tidal Lagoon Power Ltd is ‘actively examining’ plans to build a lagoon at Bridgwater Bay after recently submitting a planning application for a 240MW lagoon in Swansea Bay, which would be the world’s first scheme of this kind.

Peter Kydd, director of strategic consulting at Parsons Brinckerhoff, which worked on a 2010 government study on tidal power generation in the Severn Estuary, said the added bonus of flood prevention might make tidal lagoons more attractive but that the business case would have to be based on electricity generation.

‘The advantage is that a lagoon would pay for itself in terms of energy generation whereas most flood defence schemes are based on the probability of a flood occurring, so the cost of avoided damage would be much higher,’ he told The Engineer.

‘But it’s very difficult to quantify multiple benefits … Part of the reason for that is the electricity sector is privatised and therefore generation schemes have to be able to raise money from consumers, whereas flood defence is paid for by taxpayers.’

He added that the £12bn to £18bn cost of the Bridgwater Bay lagoon, as estimated by the government study, made it unlikely that the scheme would be chosen primarily for its flood defence benefits.

‘But it’s not just about a pounds and pence logic, it’s also about hearts and minds. So if there was universal support for a scheme, no doubt that would be taken into consideration.’