After nearly 2 months on-site, I’m pleased to share some more details of our work on the Beverley Brook through Wimbledon Common which has been completed (for now!)
Why have we restored this stretch of the Beverley Brook? Read our introduction blog here.
As some of you will be aware, work started in mid-January and ran until the middle of March. Due to the flashy nature of the Brook, we were incredibly lucky to only lose a couple of days to high flows. It also seemed we experienced every season in those two months! Bitterly cold days with arctic winds and snow were replaced with t-shirt weather by the end of the project and there was even a hint of a tan!
The history of this project stretches back several years, and builds on the already completed restoration in Richmond Park. The two sites couldn’t be more different along the banks, but the channels themselves are largely the same, which is why we knew the Brook would respond well if the right techniques were used.
One of the main issues through Wimbledon Common was the lack of light.
Over the years, the river channel has become heavily shaded, mainly by oak trees of a similar age. As a result, ground and in-river flora was almost non-existent. Due to the amount of trees present, it was essential to get guidance from Natural England and an independent ecologist to determine which trees could come down with as little environmental impact as possible.
After these consultations, it became apparent that the number of existing trees were having a detrimental effect in the following ways:
- The number of trees was affecting the existing veteran oaks as a result of too much competition. Therefore thinning and haloing was encouraged to allow veteran trees to grow without hindrance.
- Due to the lack of light entering the river corridor, nothing on the ground layer, both on the banks and in the water, was growing. By opening up the canopy, this would hopefully encourage ground growth and create new habitats. Trees were carefully selected before felling and any with bat potential were left in-situ.
A channel constrained by wooden toeboarding
Another difference between Wimbledon Common and Richmond Park was the presence of toeboarding – long, cresote-coated wooden panels on either side of the channel. At Wimbledon Common, this meant that there was no interaction between the river and the bank, stopping natural processes such as erosion from happening. After removal of the toeboarding, the Brook will be able to find its own flow path rather than being so heavily constrained.
By the end of the project, we had removed over 2 km of toeboarding which filled eight 20m3 skips!
Creating a more natural channel with wood
It has been well documented how wood in rivers is hugely beneficial to boosting biodiversity and adding to the overall ecology of the surrounding area. We followed this approach by using the felled trees to create woody berms.
Left to its own devices, a river will naturally form berms, but due to the historic straightening of the Brook, and the addition of toeboarding, this natural process had been halted. With no connection between the river and the bank, and a uniform flow, berms were no longer able to form naturally. By removing the wooden toeboarding and adding berms, we gave the Beverley Brook a kickstart.
We used a few different techniques for building the berms, but the key aim was variation. By using large branches or even whole trees stacked on top of each other, we replicated what would happen naturally when fallen trees are not systematically removed from a river.
The berms were used to narrow the Beverley Brook to a more natural width, increasing the flow which cleaned the sand-smothered gravels. After all, clean gravels are an essential spawning habitat for the main fish species in the Brook – chub and dace.
Another benefit is the increased sinuosity the berms add to the channel. This will erode some areas, deposit eroded material in others, and lead to a diverse variation in habitat. The berms themselves also provide fantastic habitats for invertebrates and juvenile fish species. In fact, this is why we left the berms fairly open with space for fish to freely swim in and out.
Adding more wood!
Along with the berms, we also added Large Woody Material (LWM) to the channel. Before the project started, there were already a few naturally occurring pieces of wood along the Brook. The Beverley Brook is susceptible to very high flows which, combined with these large fallen trees, have created large scour holes and deep pools which in turn creates shallow gravel riffles just downstream.
All these naturally occurring pieces of LWM all had the same thing in common – they were very large and had a considerable number of fish sitting under them! The aim was to introduce lots more pieces of LWM and, as best we could, replicate the natural processes to create more areas of valuable fish refuge.
The work was completed by the first week in March and as I’m writing this, it is the middle of April. Spring has most definitely sprung and the restoration has had a month to bed in. Already, it is having some fantastic effects: sparkling clean gravels, areas of fast flow, deep pools, slack areas and the berms are starting to fill up nicely with deposits from the high flows experienced just after we finished on site.
After a summer’s growth, the plants should start colonising the berms and, thanks to the light now reaching the channel, plants will be able to flourish where it was once too dark for them to grow. We should also soon start to see in-channel plants growing, which provide essential food and cover for invertebrates, and in turn, will provide a buffet of food for bird life and bats.
A total of 1.3 km of the Beverley Brook has been enhanced with 60 new pieces of LWM installed as well as 43 berms. We also have the magical sounds of water tumbling around features which is quite mesmeric whilst strolling around. I for one am extremely excited to see how the river and surrounding ecosystem adapts over the coming months and years.
We will be re-visiting the site over the next few months to see how it is settling. We are also running a couple of events as part of London Rivers Week. If you fancy coming to hear more about this restoration project, or help us remove litter from the channel, check out our events page here!
We would like to thank the Environment Agency and Viridor Credits who funded the project. As well as the Wimbledon Conservators for their resources and support, and to Aquamaintain who helped with the delivery.