OPW engineer defends Cork flood defence plan amid criticism

Cork City Council confident issue behind overflows at Atlantic Pond resolved

The Office of Public Works has defended its decision not to include a tidal barrier as part of its flood protection scheme for Cork amid criticism by a climate scientist that the scheme relies too heavily on building flood barriers in the city centre.

Emeritus Professor of Geography at UCC Prof Robert Devoy expressed concern that the €140million OPW flood relief scheme is based on a flood risk study that is eight years old and fails to address the tidal flooding component particularly in the event of climate change and sea level rises.

But OPW chartered engineer, Ezra MacManamon disagreed with Prof Devoy’s analysis of both the problem and the OPW plan, saying that the plan as designed is suitable to protect against a 1-in-100-year fluvial flood and a 1-in-200-year tidal flood as currently envisaged.

Mr MacManamon said the scheme is designed, as are all flood relief schemes, not to protect against long-term climate change but “is adaptable to provide greater protection in the future if the need arises as a result of climate change”.

He rejected Prof Devoy's assertion the scheme was based on a 2009 Lee Catchment Flood Risk and Management Study, pointing out it had since been updated by the OPW and its consultants as necessary to evaluate the magnitude of the flooding problem and identify a preferred solution.

Tidal component

Prof Devoy said that the OPW plan failed to address the tidal component of flooding in Cork but Mr MacManamon said that this was simply not the case as the plan provided protection against tidal flooding in the city including protecting more than 850 properties.

He said that over the 50-year lifetime of the scheme, it would provide a benefit of €40 million in terms of protecting properties from damage caused by tidal flooding so to suggest that the scheme failed to address the tidal component of flooding was “simply totally untrue”.

A tidal barrier was only one possible form of defence against tidal flooding and the OPW scheme, involving the construction of defences in the city, was both “technically feasible and economically viable whereas a tidal barrier is not economically viable at this time,” he said.

Prof Devoy said it appeared the OPW costings for a tidal barrier, which ranged from €450 million to €1 billion, were based more on examples of developed barrage schemes elsewhere than a costing for Cork but Mr MacManamon defended both the OPW’s approach and its figures.

“It is considered these estimates provide a good indication of the order of magnitude of the cost of a barrage. There is little benefit in carrying out more extensive work to refine the estimate of cost for such a structure when it appears that it would not be economically viable by a factor of 10 to 25.”

Mr MacManamon said the cost of a tidal barrier (€450 million-€1 billion) to give a benefit of €40 million did not make it economically viable but this may change in the future with the effects of long-term climate change and the economically viability of a barrier could be reconsidered.

He said he could see no way in which the construction of a tidal barrier would have any impact on reducing fluvial flows into the city in a future climate change scenario and he reiterated that the construction of flood defences within the city were essential to any solution.

“It is possible that such a barrier would have some reducing effect on flood levels where they are caused by a combination of tidal and fluvial effects but this is only in a part of the area where defences are required, and it would not eliminate the need for defences.”

Páirc Uí Chaoimh

Meanwhile, Cork City Council has expressed confidence that it has resolved a flooding issue at the Atlantic Pond area of Blackrock after it was flooded several times over the past few weeks.

The pond, located just east of Páirc Uí Chaoimh, is a popular amenity but several times over the past three weeks, water levels rose and flooded walkways.

The surrounding pathway was frequently flooded to a depth of 30cm (1ft) or more as water spilled out some 6m (20ft) beyond the pond’s side.

The result was that even when the flood waters receded back into the pond, the grassy areas immediately surrounding the park were turned into impassable tracts of mucky ground.

Some locals questioned whether the flooding may have been related to the €78 million redevelopment of Páirc Uí Chaoimh stadium.

However, Cork City Council in a statement have confirmed that the flooding was caused a problem with a flap valve on a channel linking the Atlantic Pond with the River Lee at the nearby Marina.

“The purpose of the flap valve is to let water out of Atlantic Pond into the River Lee at low tide and to prevent water from entering the Atlantic Pond from the River Lee at high tide,” said the council.

“The repair to the existing flap valve was completed by the Cork City Council Drainage Section on Wednesday. This has been successful in remedying the issues at Atlantic Pond,” it added.