DENBIGHSHIRE County Council was responsible for maintaining culverts left 85per cent blocked ahead of flooding at the Glasdir estate in Ruthin.
That was the revelation following an Environment Agency investigation into the causes of severe flooding there on November 27.
But Mohammed Mehmet, chief executive of the council, told the Free Press he disputed the extent of the blockage and would be commissioning an independent inquiry into the flooding.
Flood experts produced a model of the event to replicate the flooding and help them reach their conclusions. They also investigated the site, used evidence from eye-witnesses, photographs from the site and images taken from the air.
This found that the culverts would need to have been 85per cent blocked in order to cause the flooding of the estate.
A spokesman for Environment Agency Wales, who produced the report for the Welsh Government, told the Free Press: “Denbighshire County Council was responsible for the culverts.”
Dr Mehmet said: “What they’re saying is that their model suggests the culvert would have been 85 per cent blocked.
“We’ve got aerial photos which show water was flowing at the other end. The culverts definitely were partially blocked but to what extent is disputed by us.
“In my view the debris there is more likely to have been washed there by the flooding.
“There was grass and growth there but I think that would have been flattened by the flooding.”
Dr Mehmet said the council had questions about the maintenance of the river and also about the lack of warning the authority and residents at Glasdir were given
about the flooding by the Environment Agency.
“If we’d been warned about the flooding people would have been there to clear the culverts, we only got to know about it after it happened,” he said.
“What is clear is there was blockage in front of the culvert. What is far from clear is what caused it.”
He added that the council had checked records and had no complaints recorded about the culvert being blocked for the two weeks before the floods.
The report explains floodwater is directed to the culverts under the link road towards the Mwrog Flood Alleviation Channel and northern floodplain.
The culverts are designed to ensure that floodwater can pass from the floodplain south of the link road to the floodplain north of this road.
“There is evidence that the flooding which occurred on the Glasdir estate was due to an obstruction which impeded the floodplain from functioning, stopping the floodwater draining from the south to the north,” says the report.
“The culverts were blocked to some extent by debris collecting on the safety screens around the upstream entrances and this would have caused water levels to rise upstream of the culverts on the southern floodplain.”
As well as the culverts, the investigation examined an earth bund located to the east of the Glasdir estate, which it says is “owned by a yet to be determined third party”.
The investigation found this did not fail and the bund had no structural damage following the floods.
The report concluded that a combination of factors caused the flooding of more than 100 homes:
- debris blocking culverts stopped flood water from draining to the floodplain on the other side of the dual carriageway.
- gradients on the opposite side of the culvert meant that flood water could not drain to the wider floodplain and flood relief channel.
- heavily saturated ground in the lead up to the event as well as the sheer length of time the River Clwyd was in flood were also important factors.
- Glasdir residents have demanded to know why houses were built on a known flood plain in the first place.
Dr Mehmet said the estate had been through a “rigorous planning process” before permission was granted to developers, Taylor Wimpey.
“It was always known that it was a flood plain,” he said.
“It was the expert view from the Environment Agency that it would be OK to build there providing we had mitigation in place.”