False barriers are used to block best flood plan

The proposed OPW flood relief project for Cork City is the culmination of 11 years of detailed scientific and engineering study carried out by experts, writes Valerie O’Sullivan.

False barriers are used to block best flood plan

The proposed OPW flood relief project for Cork City is the culmination of 11 years of detailed scientific and engineering study carried out by experts, writes Valerie O’Sullivan.

There has been a great deal of discussion over the past number of months about the proposed flood relief works for Cork City.

Much of the dialogue has been one-sided, and it seems that the opposing voices are loudest, although not necessarily in the majority. However, it is important to listen to all sides of the debate.

The flooding problem in the city centre is not straightforward. Cork suffers from both tidal flooding, and from fluvial (river) flooding.

Tidal floods are the more frequent of the events which disturb the city centre and can be hugely disruptive for the businesses and premises impacted. However, fluvial flooding can be equally devastating, as only too well known to all who recall the 2009 Lee flood event.

And because the flooding problem is not a simple problem, there is not a simple solution.

The proposed OPW flood relief project is the culmination of 11 years of detailed scientific and engineering study carried out by experts. It is unfortunate that a lot of misinformation has been put into the public domain about the OPW proposals.

The Lower Lee Flood Relief Scheme is being publicised by some opposition groups simply as a “walls” scheme, which will form a permanent barrier separating the citizens of the city from the river. This is disingenuous and is an unfair impression of the proposals.

The truth is that the actual proposed solution consists of a range of holistic measures, including:

  • A detailed flood forecasting system involving the installation, maintenance and real-time monitoring of a suite of gauges and sensors, recording rainfall and river levels across the Lee catchment area;
  • Revised dam operating procedures for extreme flood events, involving both Inniscarra and Carrigadrohid dams, and significant interaction with the ESB as operators of the dams;
  • Designation of upstream washlands in the floodplain to facilitate greater advance discharges (up to 300m³/s) from the dams.
  • A flow-regulation structure on the south channel of the Lee to reduce flow in south channel through the city during extreme events, critical to reducing the need for direct defences in the fluvially-influenced zone of this river channel.
  • Direct defences on north and south channel, comprising embankments, railings, ground level changes, and, in some locations, 1.2m-high walls — which is only just above waist height on most people.

Consider again each of the individual measures above. They are far too important to just scan and dismiss them.

The OPW project is a complete and integrated flood management solution bringing together many different management, engineering and process interventions to actively and appropriately manage flooding.

Many calls have been made for a tidal barrier. People seem to simply accept the opposing argument that a tidal barrier is the ideal solution, which, along with some upstream measures, would solve the flooding problem.

The argument against a tidal barrier is long and complex. The seeming simplicity of the solution is so attractive that many people do not want to hear that argument.

There are concerns associated with the location, alignment, and detail of the barrier proposed by the Save Cork City group. There are potential issues with navigation in the harbour, environmental and sedimentation problems, and of course, the costs.

The OPW has considered the Save Cork City proposals with a full consideration of the issues in Cork Harbour. In December 2017, the OPW published a report outlining the costs and the issues involved. The report really should be read by those who want a more informed view.

The cost estimates for a tidal barrier that have been publicised to date by Save Cork City are very much high level or preliminary costings, and appear to have been completed by experts who unfortunately have not had the benefit of the 11 years already spent on this project by the OPW.

The OPW has had the more recent report commissioned by Save Cork City reviewed and can confirm that this report actually validates the OPW position on the costs.

There are also claims being made that Dublin City has opted for a tidal barrier; this is simply not true. Dublin City Council has confirmed the scenario of a tidal barrier for Dublin City has been assessed a number of times, under various projects over the last 30 years.

This scenario has consistently been ruled out, primarily on economic grounds, but also for various other reasons including the development of Dublin Port, environmental considerations, social water sport activities, and tourism.

Flooding in 2015
Flooding in 2015

Dublin City has decided to tackle the threat of future floods by building flood walls and flood embankments.

Finally, it worth noting that for Cork City, a tidal barrier alone would not have served any purpose in the 2009 fluvial event, and the presence of a tidal barrier would still require riverside defences to an estimated €20.7m.

Upstream flood management measures have been proposed with the aim of “slowing the flow of the river”. The natural measures suggested, such as tree planting and attenuation areas, would have negligible impact on the volume of flow that comes down the river.

An assessment has been carried out, and a reduction of only 1%-4% may be achieved in river flow volumes. The Lee Catchment is approximately 1,150km² to the Lee Road Waterworks, and 69% of that catchment area is above Inniscarra dam.

When compared with the volumes that can be attenuated (or slowed) through a change in dam management, clearly the “natural” interventions to slow the flow are not the appropriate flood alleviation solution for the Lee.

As already mentioned, the actual proposed OPW scheme does include for revised dam operating procedures, which has a far greater impact.

There have also been calls for Dutch experts to be brought in to review the scheme. This is an unfair dismissal of the OPW’s years of experience in flood management throughout the country.

Many schemes have already been constructed successfully, Waterford City is of note, and Mallow and Fermoy are two locally impressive and successful schemes. The Dutch have their expertise, but why dismiss our own? The range of intended OPW measures outlines the complexity of the solution.

The OPW is the body responsible for refurbishment and maintenance of historic sites throughout the country. How many of us have been to Fota Gardens and Charles Fort here in Cork? To Ross Castle and Muckross House in Killarney?

Why would the OPW destroy our city? Would Cork City Council happily sit back and let them? No. The OPW proposes to invest over €20m in the existing quay wall structures, and yes, extend the quay walls where hard defences are required for flood protection purposes.

There is a landscape consultant and a Grade One conservation architect engaged for the detailed design of the scheme, to sensitively manage the final design.

How many of those opposing the OPW scheme have spent late nights and early mornings fighting floodwaters? How many have had to refurbish their properties time and time again, with no insurance cover? How many have spent time simply worrying over the risk of an event happening again?

Cork City requires urgent commencement of this work. It is a long time since the unprecedented flooding of 2009. There has been regular disruption to the city centre and devastation to homes and businesses since then, and with the associated stress and resultant costs, not least of insurance, for those affected, this scheme is simply critical.

The proposed scheme is the most appropriate solution for flooding in Cork. The solution was not arrived at quickly or without in-depth consideration of other options including tidal barrier and natural interventions. This solution is tailored to the Cork City situation.

The detail of how the OPW and Cork City Council go about implementing the scheme should be the point exercising people’s minds. How can the people of Cork benefit from the much needed investment and works that will be required along much of the riverside?

There is a vision for the proposed scheme to enhance all of our experiences with the river, through the creation of new riverside walkways, improving the existing access points to the river, and repairing and restoring the existing quay wall faces.

The two channels around the city centre are unique and the proposed scheme presents an opportunity to finally invest in and improve our frankly underutilised and underappreciated riverside.

The Lee is a beautiful feature of Cork City, and all we want is the best for the city and its inhabitants.

Valerie O’Sullivan is director of environment and recreation at Cork City Council

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