The £50 million flood alleviation scheme in Leeds which uses moveable weir technology – a first for flood risk reduction in the UK – has opened.

Led by Leeds City Council in partnership with the Environment Agency, the scheme will provide more than 3,000 homes, 500 businesses and 300 acres of development land with increased protection against flooding from the River Aire and Holbeck.

The first phase of the award-winning Leeds Flood Alleviation Scheme, delivered by the BMM jv (BAM Nuttall and Mott MacDonald), not only uses state-of-the-art flood defence engineering techniques but is one of the largest river flood alleviation schemes in the country.

The scheme comprises three main elements: state-of-the-art mechanical weirs, the merging of the river and canal and flood walls and embankments stretching 4.5km through the city centre.

It is the first time that moveable weirs have been used in the UK for flood alleviation purposes. The new weir gates are supported by giant inflatable neoprene bladders that can be lowered when high river flows are expected. It takes around two hours for the gates to lower - thanks to the installation of these weir gates, it has been possible to keep flood defence wall heights to a minimum so as not to spoil views of the city centre waterfront.

The weirs have been installed at Crown Point in the city centre and further downstream at Knostrop, where a new locally manufactured bridge has been installed across the weir connecting the diverted Trans Pennine Trail with the north bank of the river.

In addition to these measures, the removal of a manmade island, known locally at Knostrop Cut, which separated the canal and river has been removed to improve a bottleneck for flows. 180,000 tonnes of material excavated from the site has been reused on a local development site and also on diverting the Trans Pennine Trail which previously went across the manmade island. Reusing this material has saved the project in the region of £6 million.

Project Manager for BAM Nuttall, Andy Judson, said:

 ‘We’ve constructed two moveable weirs, one at Knostrop and one at Crown Point. We’ve provided 36 separate zones of the linear works up through the city centre. The project's main innovation is the moveable weirs, controlled by air bladders.

“This is the first time this has been used for flood alleviation in the country. We’ve had a really strong ‘one team’ ethos on this project. We’ve all been co-located and understood that by working together, we would get the job finished on time and on budget.’

More than 22,000 jobs will be safeguarded over the next 10 years due to the increased level of protection and through the scheme’s development and construction, 150 jobs and apprenticeships have been created.

The scheme, which sees work on the River Aire now substantially complete and work at Holbeck continuing into autumn, is being officially opened by the Leader of the Council Cllr Judith Blake CBE and Chair of the Environment Agency, Emma Howard Boyd.

Judith Blake CBE, said:

‘We are delighted to see this much-needed first phase of the Leeds Flood Alleviation Scheme opened. We’d like to thank everyone involved in this phase of the scheme and look forward to developing the plans for phase two and beyond, as only through an entire catchment and citywide approach can we protect all communities in Leeds from the threat of flooding.’

Chair of the Environment Agency, Emma Howard Boyd, said the scheme was one of many in the Defra programme which would see £430 million invested to reduce flood risk across Yorkshire before 2021.

“We’re always looking for new ways that we can use technology to reduce flood risk so it’s exciting that this scheme is also a first for flood risk management in the UK thanks to the use of the moveable weirs which can be lowered when river levels are high.” she added.

Boxing Day 2015 saw Leeds experience significant and widespread flooding with some of the highest river levels ever recorded. The flooding affected nearly 3,000 residential properties (including indirect impacts to high-riseaccommodation) and 700 commercial properties.