Increasing suburbanisation and changes in agricultural practices are blamed by hydro-geologists for the severity of recent flooding. But there is little sign that the potential threat has been taken seriously by most local authorities.
Even housing estates built within the past decade have been flooded because the risks were never properly assessed when they were going through the planning process. Some houses, indeed, were built in areas prone to flooding in the past, including the floodplains of major rivers.
Householders who bought or built homes near a river or stream, because it was such an attractive amenity, have suddenly discovered that it's no fun when this "amenity" bursts its banks and flows into their gardens, kitchens and living-rooms, saturating carpets and timber floors.
"People who live beside a river should expect to get their feet wet now and again," said the late Noel Carroll, spokesman for Dublin Corporation, after Hurricane Charlie caused the Dodder to overflow in Ballsbridge in 1986. It sounded like a callous comment, but it was true, too.
Not much can be done about Clonmel, in Co Tipperary, which has been sitting in the floodplain of the River Suir since medieval times. The real question is whether steps can be taken to avoid building new houses, factories or motorways in areas prone to flooding.
Travelling around Ireland, geologists are amazed at the number of houses built in low-lying, often flat, alluvial floodplains. "They're just asking for trouble," one of them commented. In most cases, however, there was no assessment of flood risk before approvals were granted.
This lacuna in the planning process was cruelly exposed in south Galway a few years ago when bungalows that should never have been built in the first place had to be demolished - the area around Gort, a low-lying version of the Burren in geological terms, was far too prone to flooding.
County councillors who thought they were doing people favours by pushing through Section 4 motions directing that permission be granted for this or that bungalow were, as things turned out, visiting untold suffering on their constituents. Flood risk assessment simply did not arise.
Mr Donal Daly, of the Geological Survey, who compiled its report on the flooding in south Galway, said there was no doubt some of the houses had been "built in the wrong place". And when bungalows built within the previous 20 years had to be demolished, it was "a hard lesson".
The Gort area is unique because it is so low-lying and the only outlets for heavy rain are turloughs or underground watercourses. Though the Geological Survey found a significant increase in rainfall over recent years, it did not recommend extensive works to prevent flooding in the area.
Mr Mark Conroy, a hydro-geologist with Tobin Environmental Services in Dublin, said that unless flood risk assessments are requested by the local authorities, they are not going to be carried out. Yet it is only in the Shannon basin, because of its history of flooding, that these are done.
He also pointed out that increasing urbanisation has a direct effect on the water table, simply by taking up more and more land. "In general, if you build a house, you cover 50 per cent of the site area with concrete and the capacity of the soil to absorb water is correspondingly reduced."
Changes in agricultural practices have also had an impact. The use of JCBs to dig deeper drains may improve the viability of marginal farmland, but it simply creates "fast tracks" for storm water, which will inevitably find its way to the nearest river, stream or lake, swelling water levels to flood.
One possibility to avoid flooding on housing estates would be to install storm water retention systems, such as lagoons which would also have an amenity value, Mr Conroy suggested. "Building dykes to keep water out only means that it would be diverted somewhere else," he said.
The long-term solution may be provided by a draft EU Water Framework Directive, which will require river catchments to be examined in a more "holistic" way, taking account of such issues as surface water drainage, pollution threats and where new development should best be located.
But it is not just local authorities which are learning from oversights. One of the unexpected casualties of the heavy rainfall was the M4 motorway, near Maynooth, Co Kildare. It had to be closed to traffic after the local Meadowbrook stream flooded the road surface.
A spokesman for the NRA said yesterday that the risk of flooding had been taken into account in designing this motorway. What the engineers did not expect was that the nearby Royal Canal would burst its banks, flooding the Meadowbrook and, in turn, a stretch of the M4.
"The area around Maynooth is very flat and quite a lot of housing development has taken place there since the motorway was built, which wouldn't have helped," he said. "But what happened at the weekend was exceptional and all we can do is hope that it won't happen again."