‘Strange and irritating’ noise from Yorkshire river and bizarre lines on water mystify residents

A mystery noise emitting from the River Ribble has drawn complaints from residents as the team from Yorkshire hydro scheme Settle Hydro scrambled to get to the bottom of the baffling sound.

The “strange and irritating” noise, which occurred when the river level was moderately low, was described as a low-frequency rumble which gradually increased in intensity and then stopped.

After approximately 30 seconds the rumble would gradually build again.

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Furthermore, during the intermittent periods of rumbling, a series of horizontal lines would “dance and flutter” across the face of the weir.After complaints from residents, Steve Amphlett, chairman of the board of volunteers at Settle Hydro, a clean electricity project which draws water from the River Ribble in the area, was anxious to address the problem.

SHS volunteers working on the weir to disrupt the nappe vibrations

It was initially assumed the noise was coming from the Archimedes screw which powers the turbine at the hydro scheme - but the noise continued even after the team manually turned off the hydro generator.

“We were amazed when the noise continued and realised it seemed to be emanating from the river itself, which seemed very peculiar,” he said.

“We then pinpointed the sound to the weir upstream of the hydro.”

But it was a Google search by Mr Amphlett’s wife, Sue Amphlett, that led the team to crack the mystery.

Settle Hydro volunteer works on the weir

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She typed “strange rumbling noise coming from weir” into the search engine, and discovered several academic papers about a phenomenon known as 'Nappe Vibration' or 'Nappe Oscillation'.

In 2021, work was completed on essential repairs to the weir boards, which achieved a “perfect flow over the weir”.

However, this also created ideal conditions for a Nappe Vibration.

The meter passes the 1,000,000 kWh mark

Mr Amphlett explained: “Having established the cause, we needed a way to mitigate the problem, as turning off the River Ribble was not really an option!

“The next step was to see if disturbing the flow over water over the weir would have an effect, so we tried temporarily placing several sandbags on the weir crest.

“Hey presto, the noise stopped.”

The hydro team are now in the process of designing a permanent solution which will involve attaching boards at intervals along the length of the weir boards, and protruding above the weir crest.

This will create a series of gaps in the nappe to disturb the conditions that create the vibrations.

As well as solving the mystery of the strange sound, Settle Hydro has recently marked the milestone of having generated one million kWh of clean, green renewable energy.

The community project, which was commissioned in January 2010, generates electricity by drawing water from the River Ribble through a sluice gate to power nearby homes, with surplus energy sold into the National Grid.

Mr Amphlett said “It is a wonderful feeling to have generated over one million kWh of clean electricity – it really is a special milestone which shows that even small communities can take action to help reduce the carbon emissions responsible for climate change.”