Tuesday 21 November 2017

City's location on River Lee is both a blessing and a curse

Rescue workers take doctors and nurses to Cork’s Mercy Hospital during flooding in the city in 2009. Photo: Daragh McSweeney
Rescue workers take doctors and nurses to Cork’s Mercy Hospital during flooding in the city in 2009. Photo: Daragh McSweeney
Ralph Riegel

Ralph Riegel

For more than a century, Cork has ranked as Ireland's most flood-threatened city.

Built on low-lying islands and marshlands where the River Lee splits into several channels, the city's location is both a blessing in terms of its visual appeal and a curse in terms of the tidal flooding threat it regularly poses.

That was graphically illustrated on November 20, 2009, when a combination of factors left the city facing the worst flooding in its 800-year history. One city centre quay wall collapsed, a hospital had to be evacuated, and the city's main water treatment centre was swamped, leaving more than 50,000 people without drinking water.

Dozens of businesses closed due to flooding and never reopened. The damage was estimated at close to €100m - and major losses were also suffered by both the city's main courthouse and University College Cork.

Since then, Cork has suffered further floods - albeit far less severe in nature - in October 2012 and in both January and February 2014.

One prompted a personal visit by President Michael D Higgins, who wished to show solidarity with the devastated traders involved.

The city is now the focus of the most ambitious flood relief scheme in the history of the Office of Public Works (OPW). Originally costed at around €80m, the scheme is now estimated to cost €144.7m and will take more than four years to complete.

The OPW estimates that almost 2,200 properties are at flooding risk in Cork city centre and some suburbs. With the city's population of 125,000 expected to grow to 150,000 over the next decade, the scale of at-risk properties is set to increase unless the major overhaul of flood defences is completed.

Barrier

To protect against tidal flooding surges, the Government and OPW opted for a plan based on riverside defences rather than a Thames-style tidal barrier, because the latter could cost up to €1bn. This sparked controversy with the Save Cork City (SCC) group, which opposes high quay walls as damaging to the city's visual heritage. SCC claimed that the tidal barrage would cost closer to €200m - and is the best solution to the flood problem.

Flood Defence Works Interactive Map

This tool sets out the cost of installing flood defences, the damages which might arise and number of properties under threat, in the most at-risk areas across the State.

It is based on data from the draft Flood Risk Management Plans, produced by the Office of Public Works (OPW), following extensive surveys of 90 coastal communities, and more than 6,500kms of river channel.

The country is divided into 29 Units of Management (UoMs), which are areas covered by a single river basin or covered by a group of smaller rivers. Given its size, works required along the Shannon are set out in three UoM.

Clicking on the icons show the works required in each area.

The urban area is highlighted at the top, and the UoM beneath. The cost of proposed works is set out in €m. The ‘damage uncapped’ figure relates to the total cost of damages to properties and infrastructure which would arise if nothing was done.

The ‘damage’ figure is based on the value of the properties at risk. This figure is used to determine if a scheme should go ahead – if the cost of the damage is less than the cost of providing defences, the scheme may not go ahead. This is the cost-benefit ratio. If it’s less than one, the scheme doesn’t make financial sense.

The final figure is the number of properties protected.

Some icons contain less information. For example, Tullig in Kerry is part of the Castleisland flood defence scheme so no information is contained. The OPW has also identified other areas as being at low risk, or says the existing flood defence regime should be maintained. In other cases it notes the need for a forecasting system, or says if a scheme is underway.

Further information is at http://maps.opw.ie/floodplans/


However, OPW Minister Sean Canney said he was confident the OPW scheme will deliver. The OPW denied that the new quay walls will leave the city centre enclosed within a concrete ring.

Its plan also includes the covering of some vulnerable culverts and work to both bridges and drains to enhance water flow at peak discharge periods.

All open railings around the city quays will either be replaced with walls or supplemented by portable flood barriers. The scale and complexity of the scheme has meant plans have taken much longer than expected to prepare. The OPW plan will also involve careful water management between Cork councils and agencies, such as the ESB, which operate dams in the upper Lee valley.

Irish Independent

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