A TIDAL barrier flood solution for Cork is “unsafe” and would cost millions of euros per year to operate, according to the experts leading defence plans for the city.
Ken Leahy, of Lower Lee Flood Relief scheme project consultants ARUP, has dismissed claims that the Office of Public Works (OPW) €140 million flood defence system, based on containment and pumping, will fail.
The Save Cork City group has been campaigning for a tidal barrier at Lough Mahon and claim international experts have concluded that a tidal barrier is a more economical approach to protecting Cork and provides greater advantages for the city in terms of safety.
However, while Mr Leahy concedes a tidal barrier would solve tidal flooding, he said it would not protect Cork from fluvial [rainfall] flooding which the OPW says accounts for almost three-quarters of flood events across the city.
Dams at Inniscarra and Carrigadrohid were opened to release water which caused millions worth of damage in 2009. However, Mr Leahy claims a tidal barrier would not have offered any relief in this event.
“In the 2009 event, a tidal barrier would have made little or no difference to flooding because it was generally a result of the lack of capacity in the western channel,” he said.
“Unfortunately, a tidal barrier is just unsafe. It could have significant environmental impacts. While it would prevent tidal flooding, it will not solve fluvial flooding.
“If it was to be installed, it would have to be complemented by the lower level defences in this scheme. Generally, tidal barriers are installed in places where the only alternative is walls that are two or three metres high. Cork is nowhere near that at this stage,” Mr Leahy added.
Rising sea levels will be dependent on climate change action and Mr Leahy estimated Cork has up to five decades before it needs to consider a tidal barrier, while the current design offers an “adaptable and flexible approach” with an ability to adapt a series of interventions in the future.
“We have 40 to 50 years of time before we are forced to look at doing something in addition to what we are proposing now,” he said.
Mr Leahy has also criticised a tidal barrier concept developed by experts working for Save Cork City.
“The gate is too narrow. We’ve modelled it and you have velocities of three metres per second which is double the top of the scale for the design level of navigation. It’s just unsafe,” he said.
“There are only two places in the world where velocities are quite high and the context is very different.
“The example of San Franciso has been given but the difference there is that the navigation channel is straight for about three kilometres on both sides. Save Cork City are proposing to navigate a ship in Cork through a 60-metre opening.
“At those velocities, it’s like driving your car at 200-miles an hour on an eight-lane autobahn that is empty versus driving up a narrow road in West Cork.”
The OPW has previously dismissed costings presented by Save Cork City and UK hydro-engineering company HR Wallingford on a tidal barrier at Lough Mahon, costing up to €170m. OPW consultants ARUP say the capital cost would be closer to €1.6bn and would cost 0.3% of the building cost every time it was opened.