PROPOSED measures to combat lower Lee flooding were outlined to members of the public at a heated meeting in City Hall on Friday.
Ken Leahy of Arup Consulting Engineers discussed the €140m plans, which he stated will defend in the region of 2,100 properties currently at risk of tidal and river flooding events.
“The problem in Cork is twofold,” Mr Leahy explained.
“There is fluvial risk evidenced by the recent event in 2009 and there is also a more frequent tidal risk, the most recent event being in 2014. It is important in that context that the scheme deals effectively with both risks.
“The vast majority of the central island where a significant proportion of residential properties are are at risk of flooding from one or both. In context, in 2009 it is estimated that there was a loss to business in the order of €1.2m.”
The brief for the flood relief plan, he outlined, was to develop a viable, cost-effective and sustainable flood relief scheme with the required standard of protection of a one in 100-year fluvial flood and one in 200 year tidal flood.
The proposed solution involves the designation of upstream washlands to facilitate greater advance discharges from hydroelectric dams and direct defences downstream of Inniscarra Dam and through the City.
A flow regulation structure is proposed for the South Channel of the Lee to reduce flood risk while a number of flood gates at some footbridges and boardwalk locations and localised surface water pumps are also proposed.
Revised Dam operating procedures have also been outlined. In advance of a predicted extreme event, new procedures would involve increased advance discharges of water to create storage in advance of the flood. During rising floods along the river, continued increased discharges, not exceeding the threshold of flooding, will ensure that dam storage is retained until it is needed at the peak of the event while new rules will also allow dam discharges to be managed effectively in conjunction with the tidal cycle.
Major controversy surrounds the erection of defensive walls along the river, 27% of which will reach a height of 1.2 meters.
While Arup state that circa €20m will be invested to repair some four kilometres of historic quay walls, concerns have been raised by local campaigners that this will block views of the river at certain points, notably the North Mall.
"We’ve been asked if direct fences could be avoided entirely if the dams were managed differently and unfortunately the answer is no," Mr Leahy said.
"The dams in Cork are quite small relative to the flood volume so they cannot on their own provide a solution. They reduce the peak flow into the city in the order of about 40% and without them we wouldn’t be able to create a scheme with such a low impact in terms of wall defences."
Mr Leahy added that “a key requirement from the outset was to ensure that defence heights were minimised and maintained at no height higher than guarding height so that views of the river were not obstructed and that access to and the relationship with the city and the river is maintained”.
He also noted that “almost one kilometre of new walkways will enhance the connectivity for the people of Cork with the river”, while the overall plan “will incentivise significant investment into the city and encourage business to come into the city create local employment".