Inability of watercourses to deal with rain to blame
Tuesday, July 10, 2012
THE inability of watercourses to deal with prolonged intense rainfall was a primary cause of the recent widespread flooding in Cork City — and not the non-cleaning of gullies or drains.
The localised concentrated nature of the rainfall was "unpredictable and unprecedented", a review of the flooding has found.
Met Éireann records confirm over 30mm fell in three hours from midnight, with 18.3mm between 1am-2am across Cork City and surrounding area.
The total rainfall of 52.3mm over the 48-hour period of June 27-28 had, however, been less than a 58.7mm total that fell in a 48-hour period, two weeks earlier. "This clearly indicates that the cause of the devastating early morning flooding on Thursday, June 28, was due to the nature of the rainfall in terms of its concentrated level over a short duration in the early hours," the review suggested.
City Hall management acknowledged, in the case of Blackpool, flooding did occur due to a lack of capacity in the culvert to handle the heavy rainfall. They conceded that it was "not possible, therefore, to formulate at this time, measures to guarantee a non-recurrence."
The report also said that without sophisticated warning systems on all rivers it is not possible to predict or give warnings of possible flooding.
However, the report — Review of Flooding Events of June 28 — ruled out any commercial rates’ reductions for city businesses hit by the storm.
"The issue of rate relief and the difficulties that some property owners may have in securing adequate insurance has been raised," said city manager Tim Lucey in the report. "In the case of rates, it is not proposed to offer reductions. Rates are effectively a form of local taxation and the council has not varied them in the past in light of specific or differing individual circumstances.
"However, the council has a good record in engaging with our rate payers and, indeed, we encourage those experiencing difficulty to engage with us early so that we can assess each individual circumstance and agree appropriate schedules of payment arrangements where such is warranted.
"In the case of insurance, this is a matter for private property owners to pursue with their insurers."
The report continued: "In all cases, the flooding that occurred was not contributed to by reason of the non-cleaning of gullies or drains.
"The council has an active and continuing programme of gully and drain cleaning in place which would have positively contributed to the management of rainfall and preventing more widespread flooding in many areas.
The primary cause was the inability of the watercourses to contain the massive amount of rainfall that occurred over a short timeframe.
The review stated: "The river channels and culverts affected were unable to cope with the concentrated level of rainfall that entered their respective catchments over a short period.
"Flooding occurred within an extremely short timeframe at different locations in the city, without warning and of a "flash flood" nature.
"In any circumstances, without the benefits of sophisticated flood warning systems being in place on each of these rivers, it would not be possible to predict the impact of the rainfall and give adequate advance notice to the affected areas.
"In the circumstances, the City Council could not have been in a position to give more specific advance flood warnings."
The review said: "Any suggestion that the affected areas could have been adequately warned of flooding through the more widespread direct dissemination of the severe weather warnings received from Met Eireann is misplaced."
In the case of Blackpool, meanwhile, inspections of culverts are continuing. "It is not possible to be definitive at this time whether the rainfall event is outside the designed capability of the culvert or that there is a inhibition of the culvert capacity due to a restriction within the system," the report said.
The report showed, in the month of June, four weather warnings had been issued by Met Éireann. The June 27 warning stated: "Heavy rain will develop overnight and there will be some torrential and possibly thundery downpours. These falls may lead to localised flooding. Rainfall totals of 30 to 50mm are likely, but due to the thundery nature of the rain localised totals of up to 70mm are possible."
Arising from the intense rainfall, there was widespread ponding and heavy stream flows on roads and streets across the city which arose from the incapacity of the road gullies and sewers to cope with intensity.
Manhole covers were forced up at various locations.
Following the review, a number of planning actions are to be taken:
* The need for the National Major Emergency Management Office in conjunction with Met Éireann to examine the nature of the weather warnings issued to local authorities.
* A text alert system to be introduced immediately, offering the general public the opportunity to receive an SMS alert advising that a weather warning has been received from Met Éireann.
* Weather warnings once received will be disseminated via the city council’s twitter account.
* The council’s website and twitter account will be updated with relevant information as it becomes available during severe weather. It is not proposed to engage in a dialogue-type communication.