Wading through opposing sides of the Cork flood defence plans

The OPW and a voluntary campaign group are at odds over how to combat flooding in Cork. Eoin English examines what may be coming on stream.

Wading through opposing sides of the Cork flood defence plans

BATTLELINES have been drawn over the State’s largest ever flood defence project, with fears on one side that it will destroy a city’s character, and fears on the other that objections could delay it.

On one side are Office of Public Works (OPW) engineers and their consultants Arup who are trying to design a solution to minimise flood risk for the thousands of Cork City traders and residents who live in fear of every flood alert.

On the other side is the vocal voluntary campaign group, Save Cork City, led by architects, engineers, and heritage experts, who are opposed to the scheme’s reliance on direct defences, and to the damage they say the new and raised walls will do to the city’s heritage and character.

Despite their late arrival on the pitch, their high-profile campaign led directly to the hosting of a public forum on the flood scheme on Friday.

The OPW has insisted that while direct defences are the only viable and cost-effective option, it is still open to considering changes to the look and feel of the defences in certain areas.

The agency launched a robust defence of the scheme at Friday’s forum, pointing out the city’s long history of flooding, with vast areas and an estimated 2,100 properties exposed to the risk of tidal flooding from the east and fluvial flooding to the west.

The urgent need for a major flood defence plan was brought into focus following the devastating 2009 flood when the city suffered an estimated €100m in damage.

Another devastating flood in early 2014, which prompted a visit by President Michael D Higgins to affected traders, fast-tracked the design process.

The OPW finally unveiled details last December of the overall design concept for public consultation. It features a suite of measures, with hard and soft engineering solutions, including:

  • Designation of upstream washlands to facilitate greater advance discharges from dams;
  • Construction of direct defences at Inniscarra Bridge, Ballincollig, Carrigrohane, and Inchigaggan;
  • Construction of direct defences, including walls, embankments, and the raising of existing quay walls, on the north and south channels of the river;
  • Construction of flood gates at some footbridges and boardwalk locations;
  • The installation of localised surface water pumps to deal with minor flood issues in other locations.

It also includes the development of a detailed flood forecasting system; a flood warning service; and revised operating procedures at the Inniscarra and Carrigadrohid dams, in the event of extreme flood events.

There also plans to build a large river barrier west of Cork City, close to the Kingsley Hotel, to control the flow of flood water into the south channel of the River Lee, and to divert water into the north channel, which engineers say has spare capacity.

It is this decision to divert fluvial flood waters into the north channel, resulting in the need for quay walls here to be raised to a height of 1.2m, which has triggered controversy.

The OPW says the entire flood defence plan will minimise flood risk for about 2,000 properties — 1,227 commercial properties and 878 homes — which will be defended from a once-in-a-century flood event.

A further 1,079 properties not at immediate risk of severe flooding — 613 commercial and 466 residential — will benefit from a significant reduction of flood risk.

Michael Collins, assistant chief engineer with the OPW and who chaired the steering group which oversaw the design process, said a long list of options was considered, including upstream storage and land use management, flood forecasting and warning systems, revised dam operating procedures, direct flood defences, channel widening, and/or deepening, individual property protection, and a tidal barrage.

“But the only viable, cost effective, and sustainable scheme includes direct defences as currently presented,” he said.

The forum was told the key issues for the design team included keeping defence heights in the city to a minimum and below guarding height in the city centre and designing a functional, effective, but sensitive scheme with the collaboration of the city architects, planning, environment, and parks sections.

He said the team also sought to design a scheme that maintained, and if possible, enhanced connectivity to the river for citizens and visitors.

The forum was told the scheme will deliver a lot of positives, including minimising flood risk, incentivising investment, provision of almost 1km of new river walkways, and a €20m investment in the city’s quay walls which could be at serious risk of collapse in places.

While opponents of the scheme have suggested the construction of a tidal barrage, and a “farming the flood” approach to flood attenuation upstream (effectively allowing vast tracts of farmland west of the city to flood) the forum was told these options are not viable.

“While a tidal barrage would certainly deal with the tidal flooding problem in the city, it would not deal with the fluvial problem, and the fundamental problem is that it is not economically feasible as the cost would be expected to be between €400m and €1bn, which is way beyond the current value of benefits of the scheme, which is under €200m,” said Mr Collins.

The price tag would consume the State’s entire flood protection budget for the next decade.

Farming the flood is not a viable solution for Cork either, said the OPW.

Studies have shown it is effective in small flood events, but brings almost no relief from mid-range or extreme flood events, from which is what Cork is most at risk.

To deal with the fluvial flooding situation upstream, an area of 20sq km would have to be flooded to a depth of an extra one metre of flood water, with some modelling showing that up to 40sq km of land would be required for farming the flood.

OPW engineer Ezra McManamon told the forum there has been an “overstatement and a good deal of misinformed comment” about the scale of the quay walls, and the impact the defence scheme will have on flood water levels.

Walls will be no more than a safeguarding height (1.2m), he said, slating Save Cork City campaigners over claims the scheme would actually make flooding worse.

Mr McManamon said the flood levels on the stretch of river from Inniscarra Dam to the Tyndall Institute will be reduced by an average of 0.5m, and to a maximum of 1m.

Downstream of the Tyndall on the north channel, where flood levels are dominated by the tide, design flood levels increase by an average of 20cm to a maximum of 0.5m, which is why quay wall heights are being increased, he said.

The OPW also defended the public awareness and public consultation on the scheme which started in 2013, and included a public information day when the emerging preferred option was identified in 2014.

“Approximately 500 letters were issued to registered and reputed property owners whose property or property related rights may be directly affected by the scheme works,” it said.

The public consultation process, extended twice to April 7, still gives the public the opportunity to make suggestions, it said.

Changes have already been made to the scheme on Lee Rd, Patrick’s Bridge, and Grand Parade as a result of submissions already made.

The OPW has said it is very open to positive proposals particularly in relation to the look and feel of the flood defences in areas like Fitzgerald Park, North Mall, and Sullivan’s Quay.

It is hoped 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 Lee Fields, starting in 2018, and work between Wellington Bridge and Grenville Place starting shortly after.

It is hoped these three phases will be completed by 2020, providing the majority of protection to the city.

Drawings and photomontages can be viewed on the project website, www.lowerleefrs.ie.

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