Huge financial over-runs in the Kilkenny City Flood Relief Scheme mean that Carlow, Clonmel and Waterford, which also suffer from severe flooding, will get smaller schemes in the next few years.
This was revealed in a review of the River Nore scheme in Kilkenny city carried out by the Office of Comptroller and Auditor General.
The comptroller had questioned the Office of Public Works (OPW) about why the cost of the Kilkenny scheme jumped to an estimated €48 million from an initial estimate of just €13.1 million in 1998.
The OPW said costs spiralled out of control partly because of unexpected archaeological finds and partly because of the contamination of the river with dangerous chlorine compounds.
The OPW revealed that the flood relief scheme in Kilkenny will not now be repeated in other cities because the cost of protecting Kilkenny went so far beyond budget.
That means Carlow, Clonmel and Waterford will now get smaller schemes over the next few years.
The OPW admits in the report that the rise in costs is "not acceptable" but blamed environmental considerations that prevented the agency from building during the summer months when salmon spawn in the river. The OPW also blamed the unexpectedly high cost of compensating landowners. Those costs will take several years to calculate.
The still unfinished scheme was first mooted in 1994 when many parts of Ireland were flooded.
The first report into the Nore and its tributary the Breagagh was written in 1995 when the government of the day agreed Kilkenny should be protected.
A consultant's report at the time said archaeological costs would be just €630,000 or 6 per cent of the original budget.
The cost so far has been €4.82 million.
The OPW gave no explanation as to why it expected costs in Kilkenny to be so low, despite records of settlements dating back thousands of years.
Archaeologists have unearthed artefacts ranging from coins and tombstones to an entire wooden structure that may have been used for some form of primitive worship.
The OPW admits that archaeological costs normally amount to between 5 per cent and 10 per cent of a project. The total cost of the delays was about €28 million.
The report gives no breakdown of the cost of the various reasons behind the delays.