Improving the Dollis Brook through an innovative approach

Dollis Brook is a tributary of the River Brent which rises in Moat House Open Space in Dollis Hill, North London.

Dollis Brook is a beautiful space, but experiences similar pressures to many of the rivers in Greater London, with large stretches of modified concrete channels and culverts, as well as water quality issues created by road runoff, misconnections, and urban pollution.

Over the years, this river has been changed and altered for a variety of reasons. For instance, in the 1970s, timber toe-boarding was added to both sides of the Brook for flood protection, which made the river straight. Although the intentions were good, this initiative had negative consequences. For instance, it restricted the river waters to a smaller area, resulting in faster movements and more sediment, which in turn increased chances of flooding. Moreover, a natural river should meander and bend, slowing the water’s flow, creating more space for fish and other aquatic wildlife.

To address these issues, Thames21 initiated a project to improve the health of the Dollis Brook for wildlife and for people. The removal of the toe-boarding will also allow for a better connection between the river and its floodplain.

In fact, the prime focus of the initiative was to remove old (1950’s-based) wooden toe-boarding which had been soaked in coal-tar creosote. To be precise, removing around 500m meters of toe-boarding from both sides of the river.

Creosote is produced by heat treating coal under pressure to produce a tar which is then distilled and was widely used in the past as a wood preserver. Today, this is considered a toxic substance and is banned for most uses as it is harmful to our environment, especially in water and can remain in the environment for decades.

Not only would it appear that the toe-boarding was covered in creosote, but the surrounding whole installed structure was also soaked in it.

The structure was created by sandbagging the river into the centre, digging back the banks each side, posting in the upright posts, fitting the long toe-boarding (shuttering) on, and back filling back the earth and removing the sandbags.

Thames21’s Catchment Partnerships (CP) team bid for and received Water Environment Improvement Fund (WEIF) funding from the Environment Agency to remove continuous sections of toe-boarding through Brook Farm Open Space (BFOS) – a public space in North London. The start point of toe-boarding on the Dollis Brook is BFOS which will be a trial site for the toe boarding removal methodology. The goal is to work downstream to restore large sections of the Dollis Brook back to a more natural river, with the objective to improve the riparian habitat for flora and fauna that inhabit the margins.

 

The Thames21 team have (Jo Goad and I)been working with local groups and volunteers, some local, and some from across London, (even some from Manchester!), to provide public volunteering events to take out the toe-boarding from the river.

Methodology

The project team had to come up with a completely new methodology to remove the toe-boarding on this project, as there wasn’t an existing template for this work that the team could use. This made the project an exciting challenge for us.

The team first tried using manual winches as a method as this has been used successfully before on smaller sections of river. However, this project required a consistent means of removing the most challenging sections of toe-boarding quickly enough to merit the funding, and for it to be something we could invite volunteers to take part in safely.

For this, the team came up with the idea of using hi-lift jacks, and wide base plates to support the jacks on the soft sands, gravels, and sediments in the channel. They also used cordless drills and wooden blocks to create lifting blocks that we could bolt through the upright posts that were holding the long wooden boards in situ. When possible, the team used chains to “choke” free standing posts instead of having to drill and fix our lifting blocks to every post, this was an opportunity to teach a lot of new skills to staff and volunteers alike.

The specific focus was to remove the upright posts first because they are the key to the whole dismantling process. When the team saw that the new methodology worked exactly as planned, they were overjoyed because some of the posts were buried up to 2m vertically into the riverbed and were installed with posting machinery.

Working with our volunteers and supporters, the team were able to carry out this unique in-channel demolition activity. A great example of collaborative river restoration work.

Our volunteers have voiced many kind remarks about how much they have enjoyed the process, especially in stating how they felt that they were “really making a difference to the brook”.

Progress and benefits

So far, the team have managed to remove all the toe-boarding from a section of the Dollis Brook through Brook Farm Open Space approx. 400m long more than ten events through the winter of 2023-24, reconnecting the Brook back to the floodplain and allowing the marginal habitats a chance to be restored.

The benefits of this are many, slowing down the brook and reconnecting it to the floodplain is a big one, but restoring marginal habitats is also vital. There are many benefits, such as providing food and homes to invertebrates, these provide their own natural services to our ecosystems, like pollinating native plant species, which provide food for butterflies and other insects. These insects help clean up our ecosystems, provide food for larger creatures like fish, birds, and small mammals.

We also have plans to help the river to breathe by tackling the plant Himalayan Balsam, which can block out other wildlife and space along the river.

Conclusions

So, you see removing toe-boarding isn’t just about removing the toe-boarding, but it is helping to restore and balance our endangered waterways for the environment, and that in return can have profound benefits for us.

It is hoped that this project will continue in the autumn and winter of 2024 to remove more toe-boarding and help increase the Brook’s habitat range. All in all, the team has been lucky and grateful to have a fantastic, dedicated group of volunteers who have worked hard on the project and enjoyed the work immensely. A huge thank you to all of you and to all of our wider team, supporters and partners. Essentially, they have become part of the crew and Thames21 family. We hope to see more of them soon and we hope to see new volunteers join them. All are welcome!

For more information on how to get involved, please watch out for our Dollis Brook events on our ‘What’s On’ page here: https://www.thames21.org.uk/events/

Alternatively, email our Dollis Brook team via the following email addresses: michael.oneill@thames21.org.uk or jo.goad@thames21.org.uk or carolina.pinto@thames21.org.uk

Acknowledgements

I was the engagement lead for this project and Jo Goad was the project officer lead. However, there were other contributors on this project that also deserve credit. Thames21’s Miguel Sanabria and Tyler Randall helped with some of the delivery of this project. While Thames21’s Hannah Reid and Carolina Pinto were pivotal with developing the project scope. Our former colleague Josh Hammond also helped create the original project proposal.

By Michael O’Neill, Thames21’s Engagement Officer.