A clever technology that uses sound waves to measure the flow in storm overflow pipes could help prevent the pollution of UK rivers and seas.

Public concern about the unacceptable amount of sewage entering rivers and seas has prompted the UK Government to demand that every water and sewerage company in England has a clear plan of action for every storm outflow, particularly those near swimming spots or precious wildlife habitats. A storm overflow occurs when the capacity of a wastewater system is exceeded due to heavy rainfall, with the excess water being discharged into local watercourses - this in turn can lead to pollution and environmental damage.

According to the Environment Agency, in 2022, the duration of monitored storm overflow events in England totalled 1.75 million hours, with 91% of sites carrying out monitoring. With extreme weather events becoming more commonplace due to climate change, the problem is only set to increase, but it is impossible to manage storm outflows without measuring not only the duration of the event, but also the rate of flow.

Getting that data from the inside of fast flowing pipes can be tricky, but a clever device called a clamp-on ultrasonic flow meter can make it much easier. Ultrasonic flow meters use sound waves to measure the rate of flow and they can operate from outside of the pipe.

This means there is no need to cut or modify the pipe, making installation simple and cost-effective. Because there is no contact with the fluid being measured, there is absolutely no risk of workers or the environment being contaminated

Real-time data on the flow rate of storm outflows is valuable for pollution prevention, but is essential in managing flood risk and ensuring the safety of local residents, infrastructure and wildlife. The flowmeters help operators manage challenging and fast-changing situations.

Bigger penalties

At present, any water company that illegally pollutes waters can face enforcement action from the Environment Agency, but the prosecution process can be lengthy. In May, the economic regulator Ofwat said it will be issuing targets for reducing the average number of spills from storm overflows, and where water companies do not meet those targets, they will be subject to financial penalties.

Aileen Armstrong, senior director at Ofwat said, “Companies need to reduce the use of storm overflows.

"We want to introduce measures to hold them to account for this and to ensure companies are effectively monitoring their use of storm overflows. We will continue to use all the powers we have to drive companies to get to grips with this issue.”

According to ultrasonic flowmeter manufacturer Flexim, dynamic clamp-on flowmeter data monitoring provides a crucial early warning of overspill. This helps to prevent untimely discharges from stormwater retention tanks, meaning the number of discharges into local watercourses is greatly reduced.

How do ultrasonic clamp-on flow meters work?

Ultrasonic clamp-on flow meters use two transducers to transmit high frequency sound waves that help calculate the flow rate of a fluid. Transducers are devices that convert one form of energy into another.

In this application, one transducer emits ultrasonic signals into the fluid and the other receives them. The flow rate is calculated by measuring the difference in time that it takes for the signal to travel with the flow and against the flow. This results in a time difference that is directly proportional to flow rate.

It is also possible for the flowmeter to measure the speed of the fluid and the direction of flow. Both transducers are safely and securely fixed to the outside of the pipe with a permanent clamp-fitting.