The designer of a £45M scheme to protect Leeds from a 1 in 75 year flood has claimed that the project could have saved parts of the city from being submerged in December’s 1 in 100 year event, had it been completed.
As reported previously in New Civil Engineer (17 December, 2015), construction work on the Leeds Flood Alleviation scheme was underway at the time that storms Eva and Frank struck over the Christmas period. The works began in January 2015 and are scheduled to finish in March 2017.
The £45M project was decided upon as a low-cost alternative to an original design for a £190M flood defence scheme which was scrapped because of the prohibitive cost and because it removed views of the River Aire from the city.
Had the earlier scheme been approved it could have conceivably started on site in 2012 and the designer of the new £45M scheme thinks it would also have prevented flooding in the city “by the skin of its teeth”, had it been finished.
Crown point weir
Arup global flood resilience leader David Wilkes said: “It was never badged as scheme to protect against all events and it’s a bit early to call it without all of the data, but the indications are that had those works been completed they would have probably done their job with no room to spare.”
Wilkes explained that the landscape defences in the scheme were designed with an additional 300mm of free board to allow for any differences between the 1 in 75 year model level and the absolute height of such a flood. He thinks that this free board would have saved those parts of the city that were going to be protected by the new landscape defences.
In addition to the construction of 4.5km of landscape defences, the Leeds Flood Alleviation project consists of replacing 200-year-old masonry weirs in the River Aire with bottom-hinged flap gates which can be lowered or raised by a series of air-inflated bladders. Flood levels are to be reduced further by the removal of Knostrop Cut Island, an 800m length of land between the Aire and Calder Navigation and the River Aire. This will create additional flood water storage and help facilitate the flow of water.
Wilkes revealed that the works had been hit by the Christmas flooding.
“There’s been a breach between the river and the canal, works have been washed out and there’s a lot of mud and damage,” he said. “Our contractor Bam Nutall is on top of that and is already moving to be able to pick up speed later this week to get the job back on programme.”
This article was amended on 12 January 2016 to include information about when the £190M flood defence scheme would have gone ahead had it been approved.