This weir is moveable to help control flood waters and replaced an older fixed weir. The construction of the weir included a footbridge across the weir to allow pedestrians and cyclists to cross from one side of the river to the other.
"The first ever use of the innovative ‘moveable weirs’ in the UK has hit a major milestone as all three weir gates have been installed as part of the Leeds flood alleviation scheme.
The weirs have been installed at Knostrop Weir on the River Aire as part of the first phase of the project and can be raised or lowered to control the flow of water depending on river level.
The weirs are controlled by deflating and inflating ‘bladders’ fabricated from a bullet proof neoprene material under each gate, which act like giant air filled pillows. This raises or lowers a gate to control water levels, preventing flood water from reaching the city.
It has been designed and built by BMM joint venture comprising contractor Bam Nuttall and consultant Mott MacDonald with consultant Arup as technical advisors.
The scheme has cost around £50M and is being led by Leeds City Council in partnership with the Environment Agency. Phase 1 of the scheme was initially designed to protect Leeds city centre (between Leeds station and Knostrop weir) from a flood event with the likelihood of occurring once every 75 years. However, an injection of funding in 2016, allowed protection to be increased to provide protection against a more major one in 100 year flood event.
Testing of the technology has already been carried out and work to finish the defence will now focus on removing the remaining cofferdam ahead of it becoming a fully operational flood defence later in May.
As part of the scheme, new fish and eel passes are also being constructed. The structures consist of a number of shallow trays which the fish and eels can swim and jump up, allowing them to migrate upstream. The Environment Agency said this was a huge improvement on the previous weir which was stone and 3m high creating a barrier for fish and eels moving up the River Aire."
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The level of water in the river was controlled by the moveable weir for the first time in March 2019 after heavy rainfall.
"The Leader of Leeds City Council has reiterated the need for further flood defences across the city after a weekend when the Leeds Flood Alleviation Scheme was successfully put into action for the first time.
With heavy rainfall falling on already-saturated land, the trigger point was reached for the moveable weir at Knostrop to be lowered on Saturday for the first time since it was installed in 2017 as part of the £50million first phase of the Leeds Flood Alleviation Scheme.
By lowering the weir, the on call Leeds Flood Alleviation Scheme incident team from Leeds City Council supported by the Environment Agency were able to control the flow of the River Aire in order to effectively protect city centre properties from the threat of flooding.
As river levels continued to rise, the team considered also activating the second weir at Crown Point, with the trigger level there coming within approximately 70mm of needing to be lowered, before the river level slowly stabilised as conditions improved.
Together with additional flood defence measures recently put in place to protect homes and businesses along the riverside at Stourton, the scheme proved successful in preventing properties in the city centre from flooding. Some low lying riverside footpaths were flooded as these areas are not protected by the scheme, which focuses on protection to properties and infrastructure."
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