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Why we need to start focusing on road runoff pollution to protect our rivers

03 November 2023

Thames21’s Zara Visanji explains how the Road Pollution Solutions tool is identifying at-risk areas to help plan interventions.

Why we need to start focusing on road runoff pollution to protect our rivers
Tackling road runoff pollution can help us keep our rivers clean. Image credit: Thames21

The nation’s rivers are polluted.

There are many reasons for this: untreated sewage released by water companies, illegal waste dumping and littering, and misconnected drains.

There’s also another type of pollution known as road runoff.

Pollutants, such as residue from oils spills, and tyre and brake wear from vehicles, will settle on the road and build up during dry weather events.

These are then washed into nearby rivers and streams when it rains.

The 'Cinderella’ of pollution

Road runoff pollution has long been one of the most challenging diffuse pollutions (the pollution of water that happens through a variety of land-use activities) issues to identify, quantify and resolve.

There currently isn’t a national, real-time monitoring network that measures the impact of this type of pollution.

It’s often the ‘Cinderella’ of pollution topics, because it receives far less public attention than sewage or agricultural causes.

Road runoff pollution doesn't get as much attention. Image credit: Thames21
Road runoff pollution doesn't get as much attention. Image credit: Thames21

Road Pollution Solutions

The mayor of London, Transport for London and Thames Water commissioned environmental charity Thames21 to conduct a study in 2019 measuring the amount of road pollution entering our rivers.

The first phase of the study categorised roads in terms of potential to contribute towards pollution of London’s rivers and helped to identify the best locations for interventions to address this issue.

Four years later, we’ve led the second phase of the project with our partners to create an online, interactive and evidence-based decision tool, known as Road Pollution Solutions.

This tool predicts the level of pollution risk posed by London’s strategic road network and identifies pollution pathways into the river.

It also shows the locations where the runoff could be filtered with natural barriers, also known as nature-based solutions.

These include specially designed wetlands or channels built alongside the busiest roads to prevent pollution flowing into rivers and streams.

This study focuses on nature-based solutions because they can provide additional benefits to local communities. For example:

  • flood risk mitigation
  • enhanced biodiversity
  • green spaces for public enjoyment
Road Pollution Solutions. Image credit: Thames21
Road Pollution Solutions. Image credit: Thames21

Priority pollutants should be captured at source by sedimentation devices like grit separators and oil/water separators which can capture up to 80% of the suspended solids in the runoff.

The modelling focuses on London’s larger rivers and is limited to outer London, which has a separate surface water drainage network.

It also doesn’t include all of London’s road network, due to data availability.

Check out the Road Pollution Solutions tool

Expanding the tool

The methodology used to build the tool has been semi-automated, allowing us to replicate this work across other areas.

The data layers used to underpin the tool can be easily expanded to other locations, along with the traffic model that’s been created for this next part of the project.

We’ve already expanded the tool to include the Maidenhead-Teddington catchment and Surrey area.

This will be released before the end of the year and added to the existing platform.

How can you use the tool?

This project has identified a significant level of road runoff pollution is contributing to the poor health of our rivers.

The outputs of this work can be used by decision makers to tackle pollution levels at source by prioritising road locations for action.

It may be used by bodies such as:

The outputs will also help deliver water quality improvement interventions.

Similar to those delivered using sustainable drainage systems – a nature- based solution designed to temporarily store water during storm events.

How is Thames21 using the tool?

Thames21 is currently using the tool to determine if road runoff is a potential problem when thinking about future projects.

It does this by examining the predicted road runoff concentrations in an area.

For example, wetlands are being installed in Gallions Lake, in south-east London, to treat a known road runoff pollution problem.

Thames21 is also working with local councils to overlay their project ideas with the tool to determine whether treatment options need to be altered to include road runoff pollution.

We hope community groups will be able to use this tool alongside local authorities by using their specific knowledge to support the planning and delivery of projects within London boroughs or catchments.

For any question or queries regarding the decision support tool, please contact Zara Visanji at Thames21.

Find out more about the tool

  • Zara Visanji, evidence project manager at Thames21