A flood alleviation scheme that uses moveable weir technology entered service in Leeds, UK, in early October.

The scheme is intended to provide more than 3,000 homes, 500 businesses and 300 acres of development land with increased protection against flooding from the River Aire and Hol Beck.

The £50 million ($65.3 million) flood protection system includes three main elements: mechanical weirs, the merging of the river and canal, and flood walls and embankments stretching 4.5 km through the city center.

The project marks one of the first times that movable weirs have been used in the United Kingdom for flood alleviation. The weir gates are supported by inflatable neoprene bladders that can be lowered when high river flows are expected. Below is a video of the weirs being tested.

It takes around two hours for the gates to lower. Thanks to the weir gates, flood defense wall heights have been kept to a minimum, officials say.

The weirs have been installed at Crown Point in the city center and further downstream at Knostrop, where a new footbridge crosses the weir. The bridge reconnects a much-used trail to the north bank of the river, and provides users with a way into Leeds.

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. Some 180,000 tons of material excavated from the site has been reused on a local development site.

The earlier stages of the scheme included work further downstream, which was completed in 2015 and proved effective during floods in December 2015. Watch a video of the overall engineering project.

Weirs have previously been barriers, preventing species such as salmon migrating from the sea to the spawning grounds further up the river. Salmon have recently been spotted in the River Aire for the first time in 200 years, and now that fish passes have been installed on Knostrop and Crown Point weirs, as well as others on the River Aire, it is hoped that the chances of a spawning population of salmon will be increased in the future.

Otter ramps and holts have also been installed and are intended to support the local population.