LEE VALLEY:THE ESB has strongly defended its role in the flooding of the Lee Valley and insisted it had no alternative but to release water from Inniscarra Dam due to unprecedented rainfall over a 24-hour period.
The semi-State company has been criticised by many in Cork over its decision to release a large quantity of water from Inniscarra last Thursday. Moreover, some politicians have called for an independent inquiry into the decision.
However, Inniscarra plant station manager Liam Buckley said it was only through action taken by ESB staff at Inniscarra and Carrigadrohid dams that a much greater flooding disaster was averted.
Mr Buckley said that the ESB monitors Met Éireann forecasts and changes in water levels in the 306sq mile catchment of the river Lee. The company was aware of high ground-water levels and forecasts of heavy rain for last week.
He explained that the normal capacity of the Lee Valley reservoir system is 35 million cubic metres of water with the Inniscarra reservoir accounting for 19 million cubic metres of this and the Carrigadrohid reservoir further upstream having a 16 million cubic metre capacity.
Other factors which must be considered with regard to the discharge from Carrigadrohid and Inniscarra is that some 40 per cent of the Lee Valley catchment is not governed by dams as both the Shournagh and Bride tributaries are downstream of Inniscarra.
On November 16th, with water levels starting to rise, the ESB issued a flood warning in accordance with the Local Authority Emergency Response Plans. It began discharging water from Inniscarra at a rate of 150 cubic metres per second, said Mr Buckley.
According to Mr Buckley, a discharge rate of approximately 150 cubic metres per second can be contained within the banks of the Lee downstream of the dam without a threat of flooding. But as water continued to enter the system, the ESB was forced to ramp out discharge.
Maximum allowable water level at the dam is 50.9m above sea level and levels, which had risen on Monday, were brought down to approximately 48.3m metres by Wednesday without any downstream flooding as discharges were kept at 150 cubic metres per second.
In the Lee Valley the ESB’s monitoring stations found 90mm of rain fell in a 24-hour period and a flood warning was issued before 11am, Mr Buckley said.
According to Mr Buckley, water entering the catchment rose to a peak of approximately 800 cubic metres per second, forcing the ESB to allow water levels behind the dam rise to 50.86m – 4cms below the dam’s maximum operating level.
The ESB was forced to further increase the discharge rate from Inniscarra in accordance with flood control regulations to a peak discharge on Thursday night of 535 cubic metres per second which kept water levels more than a metre below the 52-metre high crest of the dam, This peak discharge marked a one-third reduction in the magnitude of the flood which, given the water entering the Lee system, would, were it not for Inniscarra and Carrigadrohid, have led to uncontrolled flooding causing even more extensive damage to Cork city, he said.