A total of £10 million should be spent on flood protection measures in Ennis, Co Clare, to cater for damaging fluctuations in the water levels of the river Fergus, a report has concluded.
The study was commissioned following the worst flooding in recent memory which destroyed the ground floors of business and residential premises over the Christmas period last year.
At the time, residents blamed the mini-building boom of recent years, resulting in some traditional flood plains being built on. But the report states developments on "the perceived flood plain" did not cause or contribute to the flooding.
However, it recommends the lower Fergus continue to be designated a managed flood plain. While normal flood protection is designed to deal with a flood which has a frequency occurrence of once in 100 years, Ennis could have protection for a once-in-500-year frequency for an additional £1 million.
Last year's flood had a relatively low frequency of one in 15 years and could have been contained if the low-lying town's walls and embankments were waterproof. All drainage pipes should have non-return valves to prevent back flows from the river, according to the study.
The study was compiled by two consulting engineering companies, John B. Barry and White Young Green Ireland, along with Prof Conleth Cunnane of the Department of Engineering Hydrology, NUI Galway, and KT Cullen & Co, consulting hydrogeologists.
It notes the past decade has been the wettest on record, leading to serious flooding in 1995 and 1999.
The river Fergus was tidal in the town until 1954 when a barrage was built at Clarecastle. This allows river water to be discharged at low tide and prevents high-tide waters from entering the river.
The rock-hewn channel below the barrage also needs to be improved and construction works are necessary to augment the natural drainage systems of the limestone (karst) landscape around Ennis.
"Development works should be prohibited within well defined zones at all karst features where flooding/ecological sensitivities pertain," the report adds.