Perfect storm of factors caused river to burst its banks

Combination of astronomical spring tides, a tidal surge, and strong south-easterly winds led to city floods

A combination of high astronomical spring tides, a tidal surge, and strong south-easterly winds caused the River Lee to burst its banks in the low-lying Morrison’s Island area at high tide at 8.30am on Tuesday, sending floodwaters surging towards Oliver Plunkett St, affecting up to 100 business premises.

Most had heeded flood warnings, and property damage was minimal.

When certain meteorological conditions combine with a high spring tide, a water level of up to 2.3OD (ordnance datum) is enough for the river Lee’s southern channel to overspill the quay walls at Morrison’s Quay and wet the wheels of cars parked in the area.

Water levels peaked at around 2.57OD at high-tide at 8.15pm on Monday, causing relatively minor spot flooding on the roads. 

But winds veered south to strong south easterly at around 5am Tuesday, and helped push water levels at high tide to 2.8OD by 8.30am.

City centre exposed

The city centre, in a saucer-shaped depression, is very exposed to small changes in water levels, and this increased level was enough for the water which poured over the quay walls to rush down several side streets and cross the crest of the South Mall, and down into the Oliver Plunkett St area.

The northern channel also overflowed the quays, flooding Kyrl’s Quay and Cornmarket St where property damage was less severe.

In February 2014, when water levels peaked just 10cm higher at 2.9OD, the floodwaters swept through Oliver Plunkett St and on to St Patrick’s St, affecting between 200 and 300 properties.

The ESB said that while its dam discharges went from a previous low-level of around 6.4 cubic metres per second to normal rates of between 70 and 80 cubic metres per second by 2pm on Monday following heavy rainfall in the Lee catchment on Sunday night and Monday morning — with up to 35mm of rain recorded at some of its gauges — it had no impact on the tides.

Yesterday’s flooding follows several near-misses in recent months, including an incident last November when a last-minute change of wind direction meant the water did not reach the crest of the South Mall, and most businesses remained unharmed.

Pharmacist John Minihan, whose premises on Oliver Plunkett St normally bears the brunt of the torrent of water which flows from the Mall down Pembroke St, said he had taken precautions and had escaped significant property damage.

Let’s call a spade a spade — we could have avoided this morning if the flood defences on Morrison’s Island were done. 

“This, coming on top of everything else, it’s just so difficult. We are just getting tired now of flooding," he said.

“We can argue about the theory of what to do, but we have to make decisions. They won’t always be the right decisions, but anyone who doesn’t make a decision won’t achieve anything.

“We’re getting too accustomed to trying to please everyone. We have to look at what we can afford and what can we do immediately."

Cork City Council chief executive Ann Doherty said it is time to deliver certainty for city centre traders and residents.

“We have a solution,” she said. "The time has long passed now for it to be delivered. We have the means to deliver that certainty."

The council’s director of operations, David Joyce, said the scheme could be delivered within 12 months if it clears the legal hurdles.