Flooding that took place shortly after a multimillion-pound road scheme was completed was a one-off caused by construction debris blocking the drainage system, a Tynwald committee heard.
And the Manx Utilities Authority rejected the idea that the surface water drainage system should have been upgraded as part of the Peel Road scheme - insisting the costs would have been too high.
A section of the newly relaid Peel Road had to be closed on May 10 this year when heavy overnight rain caused flooding.
Back in July, Infrastructure Minister Phil Gawne told the Environment and Infrastructure Policy Review Committee which is investigating the Peel Road and Finch Road improvement schemes: ‘We should have engineered the scheme to ensure the capacity was there. But MUA are the responsible agency for this.’
But giving evidence to the committee this week, Peter Winstanley, retired chief executive of the Water and Sewerage Authority, said he didn’t believe capacity had been the problem.
Asked why the flooding had taken place on May 10, he said construction debris had blocked the highway drainage and got into the downstream surface water system.
Jetting had cleared the blockage but CCTV investigations revealed a significant amount of debris still left in the system.
He said the contractors should have cleared the debris before hand over: ‘In my opinion that made a significant contribution to the flooding on that day.’
Also giving evidence was Neil Caine, who is responsible for projects and flood risk with the Authority. He said the contractor had failed to prevent debris getting into the drainage in the first place.
The witnesses said they had thoroughly evaluated the option of replacing the old 450mm surface water drainage pipe but concluded the benefits would have been outweighed by the costs.
Mr Caine said it would have been extremely difficult as it is very deep - about 4 metres - and the area was congested with other services including high voltage cables.
He said no practicable solution has been found to allow the water to run directly into the Douglas River.
In any event, the flooding only affected the highway and not neighbouring homes or businesses.
‘It does rest with DoI whether they felt it’s a problem or whether it’s acceptable,’ he said.
Ultimately, however, it was the then director of highways’ decision not to replace the surface water drainage as part of the Peel Road scheme, Mr Winstanley said.
He said the end result would have been the same.
Asked if lessons had been learned, he said more time could have been allowed a ‘more considered approach’.
He said the road scheme had started while the evaluation and analysis were still being carried out and if it had been decided to replace the surface drainage system it would have delayed the road construction programme.