Dublin City Council is to advance work on flood defences in the areas of the city worst affected by last week's flooding of the Tolka pending the completion next May of a full survey of the river.
The Dublin city engineer, Mr Michael Phillips, told The Irish Times that the work was likely to involve building embankments and raising or strengthening walls in the Ballybough and Drumcondra areas.
But he cautioned that even such precautions would not have withstood the ferocity of last week's flood, which was rated at a one in 200-year storm - the worst since the Tolka burst its banks in 1954.
Mr Phillips conceded that the river had not been dredged for decades, even though earlier floods would have carried silt down to its estuary, probably building up mudbanks underwater off Clontarf.
However, he denied that last week's flood was exacerbated by the five culverts through which the river runs in a causeway providing access to the East Point business park or by works on the Dublin Port Tunnel.
He said interim flood defence works were first proposed for the Tolka following heavy rain in November 2000, "but there was concern at the time that we would be just shifting the problem upstream".
On the advice of the arterial drainage division of the Office of Public Works, a survey of the whole river from its source beyond Dunboyne, Co Meath, to the sea was commissioned from consulting engineers.
Currently being carried out by M.C. O'Sullivan, in conjunction with P.H. McCarthy, the Tolka survey is one element of a wider Greater Dublin drainage study, designed to support strategic planning objectives.
Following an interim report by the consultants on areas prone to flooding, including Drumcondra, Mr Phillips said a number of "small schemes we can advance" would be identified within the next 10 days.
These works may include the construction of embankments, walls and one or two small holding ponds "to offer some security to people living in these areas without transferring the problems elsewhere", he said.
More extensive works are expected to be recommended by the consultants in their final report next May, including "attenuation measures" such as the creation of larger retention ponds upriver.
Mr Phillips said these ponds were likely to be designed to cater for one in a 100-year storms. They would also provide some compensation for the green areas lost to concrete through suburban development.
While not commenting on the rezoning two years ago - against planning advice - of land in Dunboyne which was flooded again last week, he said planning policy needed to take account of floodplains.
"Three weeks ago, we had a one in 70-year flood on the Dodder. At the beginning of October, we had a one in 100-year flood on the Liffey.
"Last week's flood on the Tolka was a one in 200-year storm", he said.
"The rain that fell so far in November was 140 mm, compared to an average for the whole month of 64 mm. Of that 86 mm fell on Thursday and Friday. No drainage system could have catered for that."
