Bristol Avon Rivers Trust, alongside a team of local volunteers have been out restoring river habitat along Stoke Brook, a tributary of the Bristol Frome, which flows through Forty Acres in Stoke Gifford.
The watercourse underwent extensive alterations in the past, having been artificially straightened to accelerate the flow of water. Over time, the stream has significantly degraded, losing crucial habitats for fish and aquatic organisms.
The main goals of the restoration project aimed to enhance conditions for macrophyte and macroinvertebrate (such as aquatic insects) communities and to establish habitats for both larger and smaller fish species, including the European eel and bullhead. These improvements are vital to the health of the brook, as it is currently failing under current Water Framework Directive assessments.
During Autumn 2023, 16 brushwood berms were installed to a 300 metre stretch of the Stoke Brook through Forty Acres Nature Reserve in Stoke Gifford. Constructed within the river, brushwood berms are wooden structures designed to promote natural processes, enhancing flow dynamics, and creating habitat diversity for the wildlife inhabiting the river.
To build the structures, large amounts of brushwood (small branches) were harvested from adjacent woodland, carried and floated down by volunteers then carefully positioned into the river behind a larger tree limb used as a flow deflector. Over time, this introduces flow variations that reshape the riverbed, scouring gravels and forming habitats like riffle pools. Once positioned, the brushwood was secured in place using cross braces (tree limbs) and were wired down to chestnut stakes that were hand driven into the riverbed. The process was physically challenging, a bit damp and chilly during early winter, but the dedication by the volunteers was truly inspiring!
BART was joined by several corporate groups undertaking volunteer days with BART, a number of local volunteers and members of the local Three Brooks Conservation group. The teams were briefed on how to undertake the work safely and using the correct techniques.
The watercourse is known to be extremely flashy, meaning water levels can rise very quickly after a rainfall event. The berms were designed to over-top and could be underwater for months at a time. As water swiftly courses through and over them, these structures will trap sediment, gradually accumulating to create a lower-level extension of the riverbank. As the brushwood berms capture silt and become self-sustaining, vegetation will establish on them and create a more diverse river cross-section, creating deeper pools where flow is quickest, scouring silt from the riverbed which provides valuable habitat for fish. Where the energy from the brook lessens, sediment will be deposited forming small islands which provides a different habitat type, which supports marginal vegetation to establish which will attract invertebrates and fly life.
It will take a few years before the berms begin to flourish, and the restoration site settles into its new equilibrium. When it does it will provide a more resilient habitat for the species which depend on a variety of habtiat types.
A big thank you to South Gloucestershire Council for funding and supporting the restoration works throughout the council’s land
