Doubts after the deluge

Serious questions have arisen about why the recent flooding in Cork was so bad given that the rainfall was not exceptional, according to an expert at University College Cork, writes DICK AHLSTROMScience Editor

THERE IS an urgent need to establish an effective flood forecasting and monitoring system for the River Lee catchment in Cork. Serious questions also remain about why the recent flooding occurred along the catchment given that the rainfall in the run-up to the floods was not exceptional, according to an expert at University College Cork.

Prof Ger Kiely of UCC’s Department of Civil and Environmental Engineering has begun studying why the flooding was so bad, to the point of requiring the shut-down of Cork city’s fresh water system.

The rainfall was not exceptional, says Prof Kiely who heads the university’s Hydromet research group looking at hydrology, meteorology and climate change. His team is hampered, however, by a lack of information even at this stage some weeks after the flooding.

“This is what we need to find out,” he says. “We have questions but we don’t have answers. We need to study this and get to the bottom of why they [the floods] occurred. As professional engineers we can’t say until we start getting the numbers.”

Even now his group has not got figures for rainfall and water volumes in the Lee catchment, he says. They do however have numbers for a neighbouring catchment, that for the River Blackwater.

The ESB only provided figures for water discharges from Inniscarra dam last Monday, the first indication that it had released unprecedented volumes of water into the Lee.

This was forced by the high levels of water building up behind the dam.

Some commentators had described the November storms which triggered the flooding as exceptional and so rare as to occur only once every 800 years. Prof Kiely dismisses this out of hand on the basis of the limited data available for the Lee and on figures from the Blackwater catchment.

A raingauge in Donoughmore on the upper Lee showed a rainfall of 51mm on November 19th, the day before the floods. The preceding 10 days had seen a combined total of 90mm.

A daily rain amount of 51mm is not unusual and has been recorded at Donoughmore one or more times each year, Prof Kiely says.

Raingauges along the Blackwater at Millstreet and Ballydesmond showed rainfalls on that day of 54mm, with a combined 125mm falling in the previous 10 days.

“We know it certainly was not an 800-year event, more like a 10- or 20-year event. We know from flow records,” he states. “If it wasn’t a big flood event on the Blackwater why was there such a flood on the Lee?”

He could not say what impact discharges from the Inniscarra dam might have had without having better rainfall and ground water run-off information in the wider Lee catchment.

The ESB defended its decision to increase discharges from the dam, when releasing figures last Monday. Discharges rose steadily through the evening of the 19th, eventually reaching an unprecedented 535 cubic metres per second, an effort to avoid uncontrolled flooding as water flowed into the lake at more than 800 metres per second, the company said.

The flooding damage in Cork, and of course in Galway and other centres, will run into the millions and makes it increasingly clear that a comprehensive response is required, Prof Kiely believes. It is also clear that the problem will become worse given the likely effects of climate change.

The west already receives 10 per cent more rain now than it did in the 1970s, Prof Kiely says. And contrary to popular belief it is not increasing because of higher rainfall rates per hour, but because of more hours of rainfall.

A proper response starts with good quality information, he believes. “Once you get the information and have a system for gathering it in place, it means you can develop a proper flood warning system.

“That is followed with a flood management system and flood forecasting system. If you know what is coming six, 12, 24 hours ahead of time you have time to give warnings,” he says.

“The Lee does not have such a system and building one is not a trivial cost,” he warns. Yet as this year’s round of floods has shown not investing may be more costly.