Banging the drum against road runoff at the UK Rivers Summit

Banging the drum against road runoff at the UK Rivers Summit

Brown trout were able to return to the River Wandle and breed successfully for the first time in nearly 100 years thanks to the South East Rivers Trust’s work, Co-CEO Dr Bella Davies told the UK River Summit on Tuesday. Ian Lamont, our Communications Officer, reports.

An enthralled 100-strong audience at the second annual Summit heard that road runoff had been stopping trout spawning on the Wandle. The summit brought together campaigners, NGOs, politicians and industry experts to debate issues affecting rivers, in the historic setting of the National Trust’s Morden Hall.

Dr Bella Davies talks at the UK River Summit
Dr Bella Davies talks at the UK River Summit about preventing road runoff

Bella explained that a mechanical device called a hydrodynamic vortex chamber – effectively a big drum – had proven to be the solution to help brown trout thrive once more. It had been fitted to key parts of the river to filter out numerous chemicals and pollutants before they reached the Wandle.

Bella urged a captivated audience at the Summit to “implore policy makers to listen, investigate and do something about,” road runoff because the “solutions are there” to stop contaminants from roads reaching our rivers. She outlined the struggles to bring back brown trout, an iconic species, to the special habitat of this chalk stream, one of only about 220 such rivers globally.

The trouble trout had in the Wandle

A “top predator” and “keystone species” in the eco-system, brown trout had struggled to thrive in the Wandle because of pollution, with the last one caught there in 1934. The industrial revolution was huge in bringing about that scenario, but modern day road runoff had become the modern culprit, she explained.

One of the first projects run by the Wandle Trust (which later became SERT) was Trout in the Classroom, said Bella. School children helped breed the species, but after the fish were released they did not breed successfully in the river, surveys proved, despite Environment Agency data showing that the water quality was high.

Those who saw the Wandle regularly noted that the water turned black every time it rained. Conclusions were drawn that the cause was road runoff. A commissioned study by a Queen Mary university student identified 15 types of Polycyclic aromatic hydrocarbons (PaH) pollutants and copper in the river.

So how could the issue be solved?

Road runoff pollution filter
A giant hydrodynamic vortex chamber filters our road runoff and sends clean water into the River Wandle’s Carshalton Arm

A hydrodynamic vortex chamber was selected to capture the pollutants before they reached the river – and a year after its installation another EA fishery survey found there were 67 juvenile trout on a 200m stretch of the river.

“Urban pollution and road runoff are one of the three main sources of pollution in Britain alongside agriculture and sewage. It is the reason that 18% of water bodies fail their target of good ecological health. It is also massively underestimated and under-monitored,” Bella explained.

She added that road traffic sends about 300 toxic chemicals, for example from catalytic converters in vehicles, into rivers via drains. Microplastics, tyre wear, paint, rust, pesticides, road chemicals and garden runoff are other examples of sources of such pollution washed in by the rain.

Bella said about road runoff: “It’s toxic and much of it can’t be broken down by micro-organisms in the water environment. It’s persistent and it builds up in the sediment and can affect the entire eco-system.

“The impacts of road runoff are widespread and very scary. We know they can cause harm to insects and to human health. The PaHs are particularly nasty – they can affect an animal’s ability to reproduce…and can cause death outright, especially in the summer when it hasn’t rained for a while. When it rains, we often see fish kills because the contaminants have washed straight into the river.”

Describing how the vortex chamber worked, she said that dirty water goes into the device at the upstream side, the “big drum” retains the sediment and then cleaned water is sent into the river.

These had never been retrofitted into roads before, so our project leaders worked closely with manufacturers to make them work and fitted them on to the three main surface water drains coming into the Carshalton Arm of the Wandle.

“That was the first time trout had spawned successfully on the river for almost 100 years,” Bella stressed.

Other solutions to road runoff, she said, included nature-based ones such as wetlands, such as the  Chamber Mead on the Hogsmill. Ideally both would be in place, with wetlands bringing amenity, flood and biodiversity benefits.

‘It gives me hope, but policy has to change’

Removing pennywort
Removing pennywort at Morden Hall Park during the UK Rivers Summit

Bella concluded: “These solutions give me hope that it is possible to tackle road runoff, but we need to do it everywhere. It is estimated that there are a million outfalls in the country and that’s probably underestimated. They are completely unmeasured and unregulated.

“I implore the policy makers to listen, investigate and do something about it. We have to shout louder to make sure this actually happens. We know there are effective solutions out there so let’s build them quickly.”

In her welcoming remarks, Bella invited people to “celebrate all rivers” but in particular the Wandle. “It’s unusual to be a chalk stream, it’s even more unusual to be an urban chalk stream and it’s even rarer to have one with a footpath all the way alongside it,” she said, referencing the Wandle Trail.

The Summit also gave us the chance to show attendees our volunteers’ work on the River Wandle at the National Trust-owned park. About a dozen people donned waders to cross the river and head to the main park for a guided river wade to see how our volunteers have turned a straight river into one flourishing with wildlife. Participants also had the chance to remove pennywort from the river next to Morden Hall, appropriately during Non-Native Invasive Species Week, which highlights how plants and animals that have come into our rivers cause them harm.

Click below to hear Bella’s full speech about the road run-off solution.

Helping nature bloom at Morden Hall Park

Working in river restoration, there’s nothing more satisfying than being able to see the difference made when you return to a site – and then embark on further improvements.

That feeling is heightened all the more when you return with volunteers and witness their delight, as they too see improvements, especially when their previous activities included put odd-looking obstacles in the river which, to the untrained eye, could look out of place.

So it was on the River Wandle earlier this year. We led two days of work as part of our ongoing Morden Hall Park restoration project, on a section of the river that is fairly hidden from view when the public visit this National Trust property.

Removing pennywort

Removing pennywort
Removing pennywort – just one of the boatloads taken away at Morden Hall Park in spring 2023

Since 2015, we have been taking volunteers out to this patch every spring and autumn, to carry our river improvement work. Activities have ranged from removing invasive vegetation and taking out toe boarding (which stops animals and fauna making their way from river to land and prevents natural river processes from occurring) and adding more natural looking riverbank materials such as berms – a ridge, made in this case of branches, sticking out from the bank into the river.

Back in the spring, working with the Morden Hall Nature Group, we started two days of work with a litter pick and general tidying. However, the main focus of the first day was to remove a significant amount of pennywort, an invasive species that regularly occurs at the site in large quantities.

We loaded up our small boat several times in our attempts to rid the river of this fast-growing plant, which smothers other important habitats and reduces biodiversity by crowding out native plants – taking oxygen from fish and insects.

Our hardy group of 20 volunteers then set about installing some sizeable deflectors – large tree trunks that protrude into the river – into the river channel.

These will help to improve the river. In this area, the Wandle has been widened and straightened, reducing the energy in the river. This means that silt and sediment settles to the riverbed and smothers natural gravels. Clean, loose gravels are a vital part of rivers, providing spawning habitat for fish as well as habitat for invertebrates and aquatic plants.

Deflector work was tough going

A deflector at Morden Hall Park
Volunteers take a deflector up the River Wandle at Morden Hall Park

Deflectors help to remove sediment and silt from the riverbed by reshaping the water flow and increasing the diversity of the river’s flow. Instead of being straight, the water now meanders around these impediments as it would have done when the watercourse was formed naturally. This work varies the flow in the river, scouring gravels and creating pools behind the deflectors, giving respite to fish and allowing them to hide, spawn and thrive.

Through this work, funded by the Environment Agency, we were able to put in four sizeable deflectors made from ash trees which the National Trust had stockpiled for us when undertaking Ash Dieback work.

Knocking in these large tree trunks into place (a pair at a time) after dragging them up the river and moving them into position, was hard work! The posts to attach them were driven into the riverbed, to make the deflectors look as natural as possible.

A deflector secured in place at Morden Hall Park. Picked for its ability to host birds
A deflector secured in place at Morden Hall Park. The wood was picked for its ability to offer a perching place for birds

Blooming the berms

Adding plants to a berm
Volunteers added plants to a previously installed berm at Morden Hall

Not as heavy work, but equally as important, was planting golden flag iris into one of the berms that we had installed on a previous visit. These berms are made of tree brash that has been pushed together and secured, to give fish and invertebrates another refuge in a varying flow river. The golden flag iris has beautiful yellow flowers in summer, which might still be in bloom by the time we return later in the year, as part of our continued work.

Having worked at this site repeatedly over time, it is amazing to see what a difference our work has made to the riverbed. In this once straight channel we have varied the flow by creating a meandering pathway. Instead of silt covering the whole riverbed, the deflectors and berms have helped to create clean areas of loose gravel; perfect for fish to spawn in and prosper – and now water crowfoot, is also thriving.

Typical of a globally rare chalk stream such as this, this aquatic plant thrives in fast flowing water, providing habitat to invertebrates and is a good source of food. It can also act a bit like the deflectors by redirecting water and increasing local speeds to create clean places in the gravel.

Biodiversity is certainly booming – and we couldn’t do it without our volunteers.

This summer, we made a short video of how our work since 2020 is having an impact on this section of river, changing it from a straight river into a habitat-rich one where a variety of wildlife can thrive in a river that has varied flow speeds.