Our volunteers were incredibly busy back in February carrying out River Restoration on the Beverley Brook and Wandle.
Wimbledon Common River Restorers
At the start of 2020, a new group of volunteer River Restorers came together to learn about natural river processes and how heavily modified waterbodies (like the Beverley Brook) have been altered over time. These changes stop the natural processes which would usually shape a healthy river ecosystem, leaving us with a degraded river that has few, good habitats for wildlife.
Early in 2019, we carried out a large-scale restoration project along 1.3 km of the Beverley Brook through Wimbledon Common. Our River Restorer volunteers came on board to help us extend the work upstream – this time using people power alone!
We worked together to plan and design the work, ready to deliver as a team in mid-February. After the design phase, we applied for and were granted a Flood Risk Activity Permit from the Environment Agency giving us permission to proceed.
Prior to the practical work, we also carried out surveys of the stretch to enable us to measure the change we make over time. We used a methodology called MORPh and our results are now shared online: modularriversurvey.org/map/
The survey results highlighted the problems this stretch of the river faces:
- Heavily over-shaded so that very little in-channel or bank-side vegetation was able to establish.
- Toe boarding constrained the river along both banks, preventing the natural processes of erosion and deposition.
- The channel was uniform and artificially straight leaving the river devoid of habitat and flow diversity.
With a baseline established, it was time to get on the ground and deliver our river improvements!
We had 2 days in the river (with a 3rd cancelled due to heavy rain) and our volunteers put in hours of hard graft to get the job done. Our attention was focused on narrowing the channel by constructing an enormous brash berm. To speed up the process of our work bedding in and becoming a natural extension of the bank, we decided to start work in an area where some trees had already been cleared to allow light in, which should help plants to thrive here.
Brash berms re-define the line of the bank, and when constructed in a sequence on alternating banks, help create a narrower, more natural, meandering channel. The densely packed brash slows the flow of water through the berm, causing any sediment carried along by the water to drop out of suspension within the berm. With time, the berm will fill with silt and create a fantastic substrate for riparian plants to grow.
To kick-start the process of vegetation, we transplanted some hardy sedge plants from elsewhere that will hopefully take root and speed up the naturalisation process.
Our wonderful berm altered the flow of water down the previously straight channel. To allow the river to move as it would naturally, we also removed many metres of toe boarding that was lining the channel along both banks.
The finished work looks fantastic and extends the restored section of the Beverley Brook through Wimbledon Common by another 50 metres! Well done to all the River Restorer volunteers who helped with this work and a massive thank you to Wimbledon and Putney Commons Conservators for their support of the project.
Morden Hall Park River Restorers
Alongside our preparation for the Wimbledon Common River Restorers volunteer project, we were running workshops and surveys to carry out a similar project on the Wandle in Morden Hall Park.
Morden Hall Park is now owned by the National Trust but was once a deer park for a country estate. With the Wandle splitting into many meandering channels, the park remained as a green oasis throughout the river’s industrial heyday.
The River Restorers project within Morden Hall Park focused on part of the river that was artificially straight and very over-wide for the amount of water flowing along it. Due to these modifications to the channel, the stream power was insufficient to move small particles of sediment along the river and keep the gravel riverbed clean. This means the classic chalk stream gravels we’d expect to see were choked with silt and fine sand, making a poor habitat for invertebrates and spawning fish.
Our plan for restoration focused on narrowing the channel by creating brash berms and adding in pieces of large woody material to create a variety of riverbed features including deeper pools and shallow gravel riffles.
Day 1 saw a lot of the groundwork go in for the creation of a very large brash berm which would narrow the over-wide channel to two-thirds of its original width. Our volunteers worked very hard to knock in dozens of posts and remove some remaining toe-boarding along our working area.
With achy arms and tired muscles, we headed home for a good rest ready for the second day.
Day 2: The weather was less than kind, with bits of snow drifting in during the morning but that didn’t stop our amazing volunteers! We worked like a well-oiled machine to pack the berm with brash. This will slow the flow of water through the berm helping it to trap silt.
Day 3: We installed a chunky wood deflector, finished the berm & transplanted clumps of sedge to kick start the vegetation process. You can see in the videos below, the brilliant effects our work is having to create a variety of flow patterns and give the river enough energy to clean up the gravels and improve this vital habitat.
A huge round of applause for the Wandle River Restorer volunteers for their hard work and unwavering enthusiasm throughout the 3 days (apart from the short crisis when the hot water wasn’t ready in time for tea break on the third day!) and to the National Trust for their work to facilitate the project.
Thank you to Thames Water who funded both of these volunteer-led restoration projects through their Community Investment Fund.