The design is open source and already fitted to forty bridges.
Bolted to the underside of the stone bridge at Ardle Mill is a grey plastic box about the size of a sandwich. Inside are an ultrasonic distance sensor, a small circuit board, a solar cell and a battery salvaged from an old phone. Every five minutes, the box measures the distance from the bridge to the water below and sends the result over a low-power radio network to a server in Calder. The total cost of the parts was £9.40.
The design was developed by a group of six engineering students at Calder Technical College as part of a second-year project, and it has since been installed on forty bridges along the River Ardle and its tributaries. The plans, code and parts list are published online under an open licence, and community groups in at least three other regions have begun building their own.
From classroom to riverbank
The project began after the floods two winters ago, when several students watched water rise through their home villages with little warning. Official river gauges along the Ardle are spaced up to fifteen miles apart and are expensive to install, typically costing several thousand pounds each. The students set out to build something cheap enough to fit on every bridge, giving a far more detailed picture of how water moves through the catchment.
“We were told the official gauges were accurate to a centimetre. Ours are accurate to about two, which turned out to be more than enough when the alternative was knowing nothing at all.”
That is how Tunde Adeyemi-Clarke, one of the original six students and now a research assistant at the college, explained the trade-off. He said the hardest part had not been the electronics but the casing, which went through eleven versions before the team found one that kept out spray and condensation while letting the sensor see the water clearly.
How the system works
Each unit runs on a cheap microcontroller programmed to wake, take a measurement, transmit and return to sleep. The solar cell keeps the battery topped up even through dull winter weeks, and the units have run for up to eighteen months without maintenance. Readings are relayed through a mesh of community-owned radio gateways mounted on church towers, a pub roof and the water tower at Thornside, before reaching a server that publishes them on a public map.
The map shows each bridge as a coloured dot – green for normal levels, amber for rising water and red for levels close to the bridge’s historic flood mark. Residents can sign up for text alerts for individual bridges, and around 2,300 people have done so. During the heavy rain in October, the system recorded water rising at Coldwell bridge almost two hours before the nearest official gauge showed any change, and several households downstream used the warning to move cars and furniture.
The college’s head of engineering, Moira Delacourt, said the project had transformed how students thought about their work. Most engineering projects end in a report and a grade, she said; this one ended with a parish council asking for a sensor on its bridge.
Limits and next steps
The students are careful not to overstate what the system can do. The sensors measure only water height, not flow, and they cannot predict how quickly a flood will develop. They are also vulnerable to vandalism and to debris snagging beneath bridges, which can produce false readings. The regional environment agency has welcomed the data but says it will continue to rely on its own gauges for official warnings, while using the student network to help refine its flood models.
Funding remains a concern. So far, the parts have been paid for by a mix of college budgets, parish councils and a crowdfunding appeal that raised £6,000. Installation is carried out by volunteers, many of them retired engineers, who need permission from bridge owners and occasionally a ladder licence from the highway authority.
The next version of the sensor, currently being tested at three sites, adds a temperature probe and a small camera that takes a photograph of the water when levels pass a threshold. The team hopes to reach a hundred bridges by the end of next year, including several on the Selwyn estuary, where tidal surges complicate the readings. Each unit will still cost less than ten pounds, a rule the students say they have no intention of breaking.
