The Roads Service is to set up an early warning system with the Met Office to avoid future flooding on the scale of the summer deluge in August which paralysed much of Northern Ireland’s transport network, it emerged today.
This is one of a series of recommendations made by investigators probing the cause of floods that left the Broadway underpass on Belfast’s Westlink under 20 feet of water.
An interim report into the disaster revealed that work to raise the banks of the Clowney Water upstream of the junction had not been completed when the underpass was opened to traffic this summer.
When torrential rains hit Belfast on August 16, the river overflowed at the entrance of a newly built culvert and poured into the underpass, filling it to the brim.
Roads Service had advised building a flyover as part of the revamp of the Westlink, but instead a public inquiry recommended an underpass on environmental grounds.
This morning, Transport Minister Conor Murphy welcomed the independent report into the flooding and said some of the recommendations have already been put in place.
Work to raise the banks of the Clowney Water upstream of Broadway to 500mm above the 1-in-100 year designed flood level has now been completed and will provide capacity to delay any future flooding event, he said.
The report revealed that the newly installed drainage system did not perform in accordance with its required design capacity of a 1-in-100 year flood event.
It’s believed the August storm was between a 1-in-50 and 1-in-70 year flood event.
Other factors contributing to the disaster may have included debris blocking the trash screen at the entrance to the new Clowney culvert, restricted discharge from the overflow structure at the bottom end of the culvert and restriction of flow by a valve at the entrance to the Blackstaff culvert, below the Clowney culvert.
The investigators have recommended completing the work to raise banks, developing better procedures to include more regular inspection of the Clowney Water and introducing an early warning system that will alert Roads Service to high water levels to ensure public safety until the works are completed.
A specialist hydraulic team will also be building a 1-in-20 scale model of the junction, which will be used to test flows in a bid to discover why the waterway became restricted. This investigation is expected to take six months.