Huge barrier-type structure to stem the flow of flood water in Cork City
A huge river barrier-type structure will be built west of Cork City to control the flow of flood water into the south channel of the river Lee.
Details of the huge structure, which has been earmarked for construction close to the weir at Carrigrohane, is one of several engineering solutions proposed under the €140m Cork City flood defence plan unveiled for public consultation yesterday.
The flow regulation device, which will be operated remotely, will, in times of river flood, reduce the flow of water into the south channel of the river Lee, diverting water instead into the north channel, which engineers said has spare capacity.
The structure will replace an existing footbridge, and will feature an opening for canoeists and other river users to facilitate ongoing amenity use of the river.
Ken Leahy of Arup engineers said that this structure, combined with several other proposed flood defence works, emerged following a long and detailed screening process.
The preferred flood defence plan, which has gone on public display for six weeks, features a suite of measures, including the development of a detailed flood forecasting system; a flood warning service; revised operating procedures at the Inniscarra and Carrigadrohid dams, in the event of extreme flood events.
It will also involve the designation of upstream washlands to facilitate greater advance discharges from the dams; the construction of direct defences at Inniscarra bridge, Ballincollig, Carrigrohane, and Inchagaggan; the construction of direct defences, including walls, embankments and the raising of existing quay walls, on the north and south channels of the river; the construction of flood gates at some footbridges and boardwalk locations; and the installation of localised surface water pumps to deal with minor flood issues in other locations.
The entire project will minimise flood risk for about 2,000 properties — 1,227 commercial properties and 878 homes — which will be defended from a one-in-a-century flood event, Mr Leahy said.
A further 1,079 properties not at immediate risk of severe flooding — 613 commercial and 466 residential — will also benefit from a significant reduction of flood risk.
It is hoped that enabling works will start in one of the most flood-prone areas of the city — around Morrison’s Island — next year, with work on defences on the western city outskirts, from Ballincollig to the Lee Fields, starting in 2018, and work between Wellington Bridge and Grenville Place starting soon afterwards.
Mr Leahy said the hope is that these three phases will be completed by 2020, providing the majority of protection.
The other phases targeting high-priority tidal reaches, and protecting the rest of the north and south channels of the Lee, will take place over the following three to four years.
Minister of state at the Office of Public Works, Sean Canney, said the entire scheme could take up to six years to complete.
He described the publication of the plans as a “milestone” for the city which has been devastated by several major floods since 2009. And he defended the length of time it has taken to produce it.
“This project is the single biggest flood defence project in the country,” he said. “There were a lot of challenges, environmental, engineering, and logistics required in doing a project of this size.”
Once the public consultation is finished, the feedback will inform the detailed design of the overall scheme.
Mr Canney emphasised the important contribution that local knowledge can play in the detailed design stage, and he encouraged as many city-dwellers and business owners as possible to visit the public exhibition and make comments and submissions.
The proposals will be on display for six weeks until January 20, 2017 with comments being accepted from the public until February 17.
To ensure the public is aware of the Lower Lee (Cork City) Drainage Scheme and its effects, copies of the plans will be available for inspection, until January 20, at the following locations:
Members of the scheme’s engineering design team, its environmental consultants, and representatives from the Office of Public Works will be in attendance at City Hall’s Millennium Hall to explain the scheme to the public today, from 3pm to 9pm, on Tuesday, December 20, from 3pm to 9pm, and on Thursday, January 19, from 3pm to 9pm.
Details, maps, and photo montages of the scheme are also available on www.lowerleefrs.ie.
Submissions on the proposed scheme can be made up to February 17.
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