High river levels and rainfall caused flooding, council hears

FLOODING in Ennis last November was due to a combination of unprecedented high river levels in the Upper Fergus River and high volumes of rainfall over a period of three weeks. The information was given by senior executive engineer with Clare County Council, Eamonn O’Dea, in response to a query from Ennis East Councillor Tom McNamara.
He asked the council to confirm what progress had been made in identifying the reasons why areas of Ennis, and in particular Elm Park and Lifford, that never flooded before were flooded last November and what measures are been planned to prevent a re-occurrence of this very serious situation. Mr O’Dea pointed out that the reason that flooding occurred in Ennis was due to the level of rainfall during period from Saturday, October 31 to Friday, November 27, recorded as 468mm at Drumcliff.
“Rainfall from Saturday, October 31 to Monday, November 16 was 231mm and in the following three days, the recorded rainfall was Tuesday 30mm, Wednesday 41mm and Thursday 42mm. The rainfall recorded from November 20 to 27 was 121mm. The lower (below Knox’s Bridge) and middle (Knox’s to Mill Bridge) Fergus River levels were subject to variations due to retention of water during high tides,” he said.
He added that the no spring tide cycle had peaked at the weekend of November 14/15, which meant that the period of the retention of water behind the tidal barrage was reducing through the week.
“The very high river levels resulted in a combination of closure of flap valves or return flow through storm drains or infiltration, when combined with the heavy rainfall, resulting in an inability to discharge storm water to the river resulting in flooding in certain areas,” the engineer explained.
He stated that the records from the 1999 flooding in Ennis showed a peak flow of 60 cubic metres per sec (cumec) and the estimated 2009 peak flow was in excess of 90 cumec and the river flow did not drop below the 1999 peak flow level until early December.
“This area is in the Upper Fergus and is not affected by the retention of water behind the tidal barrage. The peak river level in this area would have been reached when the Claureen flow peaked on Thursday and Friday, November 19 and 20, however, the Fergus River did not peak at Ballycorrick Bridge until the following Tuesday, November 24 and the level reduced very slowly through that week. This resulted in unprecedented high river levels in the Upper Fergus River for a longer period,” he confirmed.
He also said that the higher ground between Westbourne housing scheme and Willow Park contained the river. “The road levels in certain areas of the Gort Road, Elm Park and Watery Road were approximately 0-.4 to 0.8 metres below the peak river level. The combination of high river level and rainfall resulted in flooding in these areas,” the engineer added.
He further commented that stage two of the River Fergus (Lower) Certified Drainage Scheme which covers the area from Bank Place Bridge to Doora Bridge is due to go to tender shortly and is programmed to start in May of this year. “This will help to deal with flooding in the future and will address at least some of the problem,” he said.
Councillor McNamara also asked the council what plans it has to prevent further flooding in the area of the Gort Road Business Park.
Mr O’Dea said that the council has engaged a hydrologist who has prepared a proposal, which has been submitted to the OPW under their small scheme programme. “The OPW are examining the proposal and anticipate a response soon,” he added.