It also defended the level of public consultation and range of expertise used in the preparation of what is the largest scheme of its kind in the history of the State.
As the city escaped yesterday with high spring tide-caused spot flooding in low-lying quayside areas, the OPW insisted that:
- Its proposed defence walls will not impact significantly on river views;
- Glass walls can’t be used more widely on cost and maintenance grounds and, in some cases, the supports needed for higher glass walls would be unsightly;
- ‘Green’ engineering solutions west of the city would not hold enough water to minimise flood risk in the city;
- A tidal barrage in Cork Harbour, priced at €400m, would not be cost effective and would do nothing to protect the city from fluvial flooding.
The OPW spoke out ahead of two human chain protests tomorrow by the Save Cork City Group, which fears the defences will turn the city into a storm drain and ruin river views.
However, in a detailed statement issued to the press and public representatives yesterday, the OPW said the group’s alternative suggestions would not provide effective flood protection. It said the proposed defence walls along the quays would not exceed 1,200mm and will not dramatically change a pedestrian’s view of the river.
“There will be five different wall types in use and it is the OPW’s and the city council’s view that they will not cut the city off from the river and indeed it was very much to the fore of the design team to ensure that this did not happen” it said.
“The strengthening of the quays which is to facilitate the installation of the defence walls will ensure the quays are preserved.”
It ruled out wider use of glass walls, revealing a €950 per metre cost for concrete walls and €2,000 price tag per metre of glass walls.
“Cost is not the only consideration, however. Glass walls require considerably more maintenance and become shabby looking in a short time if neglected,” the OPW said.
“Though robust, there have been instances where they have been damaged. Where glass walls are expected to defend to their full height they require quite large supports that can be somewhat unsightly even on relatively short stretches.”
It also said the design of embankments at Fitzgerald’s Park was given very careful consideration after ‘green engineering solutions’ were ruled out. It said the proposed scheme will reduce peak flood flows through the city during a 100-year flood event by 340 tons per second to 550 tons per second.
“This is a very significant reduction in flood flows but nevertheless the volume of water still to be conveyed would result in considerable damage in the city without the flood defence walls as proposed,” it said.
The OPW also confirmed that a contractor is due to be appointed in the second half of the year for the first phase of defence works around Morrison’s Island.
The detailed design of the rest of the scheme will be advanced for ministerial approval before the end of the year, with work expected to start in the first half of 2018, taking place in phases over up to seven years.