THE GOVERNMENT should establish an independent inquiry by external technical experts to examine the ESB’s handling of the November floods on the river Lee which caused up to €100 million worth of damage in Cork, a local TD has urged.
Cork South Central Labour TD Ciarán Lynch said independent experts were necessary to assess the ESB’s handling of the flood and in particular whether changes to the Carrigadrohid dam may have affected storage capacity of the Carrigadrohid reservoir.
Carrigadrohid dam, 27km upstream of Cork city, is the smaller of two dams on the Lee and has a reservoir capacity of 16 million cubic metres, while the larger Inniscarra dam, 13km upstream of Cork city, has a reservoir capacity of 19 million cubic metres.
The ESB has consistently stated it was left with no option but to discharge record volumes of water from both dams on November 19th last because of unprecedented levels of rainfall in the Lee catchment area.
In 1991, the ESB, following a review of its handling of a major flood in the Lee valley in August 1986, built a 50 metre-wide spillway on the southern side of Carrigadrohid dam to enable it to deal with a one-in-10,000-year flood.
Mr Lynch raised the issue of the Carrigadrohid spillway when ESB officials appeared before by the Oireachtas Committee on the Environment, Heritage and Local Government last month.
ESB technical risk manager Tom Browne told the committee the spillway was set at 65.2 metres above sea level, which meant once the water level in Carrigadrohid reservoir exceeded 65.2 metres, whatever came into the reservoir flowed over the spillway.
“Once the water reaches a certain level there, it automatically spills into the Inniscarra reservoir,” Mr Browne told the committee. “Effectively that spillway came into operation on November 19th – this meant that no more could be contained in Carrigadrohid.”
Mr Browne’s contention that no more water could have been contained within Carrigadrohid has been supported by surveyor Paudie Barry, MD of Baseline Surveys, who has taken over 600 GPS readings on water levels in the November 19th flood.
Mr Barry, who has surveyed high-water marks from the November flood at both the Inniscarra and Carrigadrohid reservoirs, said the highest high water mark he could find in Carrigadrohid was 65.3 metres – just 100mm above the sill level of the spillway.
However, asked by The Irish Timesif construction of the spillway reduced the storage capacity of Carrigadrohid, the ESB said the relationship between reservoir size and storage capacity was not straightforward.
“Compare the reservoir to a bath and the spillway to the overflow pipe. The level in the bath can still rise above the overflow. In fact, the overflow will only discharge if the level is above the overflow,” said the company in a statement.
“If there is a large amount of water coming into the bath, the level only stabilises when the water is high enough above the overflow that a balance is reached between outflow and inflow so ‘capacity’ above the overflow is being utilised as part of the water control.”
According to the ESB, in the case of a very large flood such as a one-in-1,000 year or 10,000-year flood, the water level in the Carrigadrohid reservoir would rise significantly above the spillway level such would be the amount of water entering the reservoir.
Mr Lynch said the ESB reply to The Irish Timesthat water could rise above the spillway appeared to contradict Mr Browne's contention that there was no extra capacity at Carrigadrohid above the spillway and highlighted the need for an independent inquiry.
The inquiry would assess whether the adaptation of the dam to include the spillway “may have contributed to the faster release of water into Inniscarra and to the flooding which hit Cork”, he said.