State’s €140m plan ‘will not solve’ Cork’s flooding problem

The €140 million Office of Public Works flood relief plan for Cork will not solve the long-term problem of flooding in the city, according to an expert in climate and coastal science.

The plan relies too heavily on building flood defences in the city centre and fails to address the tidal component of flooding, according to Emeritus Professor in Geography at UCC, Prof Robert Devoy.

Prof Devoy said that the published OPW plan does not place sufficient emphasis on developing a fully integrated river catchment management plan for the Lee, but instead relies heavily on flood defences in the city centre.

For any flood protection scheme to be successful, it needs to address both ends of the flooding problem – both an integrated river catchment management plan and a tidal barrier to remove the marine storm surge component of flooding, he said.

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A tidal barrier in Cork Harbour, as advocated, for example, by the Save Cork City group, would also help reduce the effect of increases in storm waters coming down the 95km length of the Lee under future climate warming impacts, he added.

“The OPW plan to build river channel embankments, walls and pumping elements, isn’t appropriate in terms of what Cork needs – it requires a more integrated, larger scale view and spending €140 million on building walls will not provide the desired future flood protection for the city.”

A lead member of a working group on the Intergovernmental Panel on Climate Change (IPCC), Prof Devoy said the OPW plan was based on a 10-year old study of flood risk on the Lee. “Given this time lag in its publication, it should be looked at again.”

Under the OPW scheme, the building of flood defences in the city centre, along with the provision of 46 pumping stations, would allow a major increase in the safe discharge levels at Inniscarra Dam to 550 cubic metres per second without causing flooding in the city centre.

However, Prof Devoy said that while providing such discharge rates appears as precise, a more appropriate approach would involve “a return to first principles”, which looks in greater detail at the impact on the city region of increasing discharge levels through embanked river channels.

According to Prof Devoy, the OPW should not have dismissed the idea of a tidal barrier downstream of the city as such a structure is going to be essential to help alleviate the city from future flooding under sea-level rises.

Rise in sea levels

He pointed out that sea levels were projected in the mid-2000s to rise around Ireland by 40-55cm by 2100, but researchers now consider that this projection is likely to be too conservative a forecast, particularly in the face of future land ice melt in western Antarctica.

Land ice melt in such areas could lead to global average sea level rises of six metres in the future and while this has to be adjusted regionally, any flood protection plan for Cork would need to cater for a sea level rise of at least one metre, he said.

Prof Devoy said that the figures quoted by the OPW for the cost of a tidal barrier, ranging from €450 million-€1billion, were based more upon examples of developed barrage schemes elsewhere, and the costings may not apply to the situation in Cork.

The option of a barrier, including its exact height and appropriate location within Cork Harbour, require detailed examination and accurate costings as an engineering option and as part of an integrated flood protection plan for Cork city, he added.