A LONG-AWAITED report has laid the blame for floods that devastated Ruthin’s Glasdir estate in November on blocked culvert grills – and outlined a £250,000 scheme to stop it happening again.
The newly built Glasdir estate had a flood defence system in place, estimated to protect against a one in 1,000 year incident, yet 122 houses were badly flooded last November.
The report, by an independent panel of engineers, was commissioned by Denbighshire County Council (DCC) and its findings were revealed after a long wait yesterday.
These include raising the existing flood defence bund just over one metre, with an inspection and maintenance regime.
But it also recommends a long-term floodplain management scheme “with particular emphasis on the culverts”, plus a network of “flood wardens” and posts around the culvert entrances to catch larger debris.
Report author and civil engineer Jean Venables said the steps outlined should give peace of mind for residents.
“It gives confidence that they can sleep at night when it’s raining, gives confidence that they can buy and sell their houses and get insured,” she said.
The recommendations had been based on “very detailed” 3D modelling of the catchment area.
The amount of time it took to run the model using multiple different “iterations” was one of the reasons the Glasdir report took longer than the July report on flooding in the rest of Denbighshire, she said.
She said the estimated flow on November 26 to 27 was between 35.9 and 40.4 cubic metres a second – between a one in 100 and one in 200 year event. But the blockage to culvert screens was between 66 and 95 percent.
The screens were “of poor design”, “not complying with any recognised standard” and “not capable of being cleared in an emergency”, the report said.
Current guidance said such grills were not even necessary for safety reasons on such large culverts, and should be left off so debris - such as vegetation, shopping trolleys and “all sorts of rubbish that is left in ditches and brought down when it’s wet” – can flow through.
She said the Glasdir flood defences would have been “very effective” but for the blockage. The area had been previously estimated to be protected against all but a one in 1,000 year event - but that estimate had not factored in the effect of blocked culvert grills.
She said realistically in such a big catchment area it would not be possible to check all defences at the time of a flood warning.
“Hindsight is a wonderful thing, but we can’t see any evidence that the decisions taken at the time were not reasonable at the time,” she said.
It was not that the defences would have been considered substandard at the time, more that standards and understanding of flooding had changed, she said.
She said residents should also be made aware not to leave things which may contribute to a blockage, like piles of hedge trimmings, on the river bank.
Council chief executive Mohammed Mehmet said council officers supported all the report’s recommendations to be approved at the next full council meeting.
Mr Mehmet said no record could be found of if or when the culverts had been checked or cleared.
“I certainly think there are lessons for the council to learn,” he said, “this is not the end of it”.
Council corporate director Rebecca Maxwell said one of the lessons was that management documentation and priority lists must be “much clearer”.
Lead member for environment Cllr David Smith said he had asked for the head of highways to keep a “risk register” of culverts and report back on a regular basis.
He said the council had lodged for funding with the Welsh Government and in discussions with landowner Taylor Wimpey.
“We will get that funding,” he said.
FOR residents of the newly built Glasdir housing estate, answers have been a long time coming writes THOMAS MORTON.
Devastated by floods last November despite supposedly being protected, it’s no surprise they want to know who is responsible.
But Denbighshire County Council (DCC) chief executive Mohammed Mehmet said none of the flood investigations had been about apportioning blame, but rather to understand why the flooding happened, the likelihood of a repeat, and what needed to be done.
For the residents, yesterday’s Glasdir report was welcome, but did not go far enough in attributing blame.
Katie Morgan-Williams of the Glasdir Residents Association said: “We are grateful to the investigators for providing a solution which will hopefully make Glasdir a safe and desirable place for our children to grow up and for our community to enjoy.
“However we cannot forget the devastating impact that the flood had on our community - on the families with young children, on the mothers of expectant children and on the elderly.
“After a lengthy wait, for long anticipated answers to questions of causation, we have now been provided with a report which raises more questions than it answers.
“Accountability has clearly been avoided at every turn.
"What is clear from the report is that the flooding of our homes should simply never have happened and now we ask for those responsible to stand up and be accountable.”
But, said Mr Mehmet, the while report clearly said the blockage of culverts was a large factor, “What it doesn't say is how that blockage occurred. If that blockage was caused purely by lack of maintenance I think the finger is pointing at us...but it isn't that clear cut,” he said.
“I think there are lessons for us to learn certainly... but that doesn't equate to 'it was your fault'.
Though he admitted: “I think we are better as a result of this, and we should have been better in the past."
That DCC have no record of ever having checked the Glasdir culverts is embarrassing certainly, even if it’s unlikely there was anything much to clear before the flood.
As senior DCC engineer Wayne Hope said there was simply no “mechanism” for the culvert grills to get blocked up except for debris washed there by the flood itself.
Vegetation overgrowth for example was rooted to the ground and would not account for what Mr Mehmet called a “lorry load” of debris removed.
But what is also embarrassing that the grills over the culverts that caused all the trouble did not really need to be there at all, and the debris-build-up problem they would cause was not foreseen.
As report author Dr Jean Venables said, the only reason they were there was because “There was a feeling at the time that culverts should be protected in this way” - they serve no real safety purpose and the recommendation nowadays is not to have them.
Lessons are certainly there to learn, but perhaps after all extreme weather and acts of God are not entirely in the control of the DCC.