The first phase of delivery in the South Brook catchment has been delivered by BART, aiming to ‘slow the flow’ of surface water during peak rainfall events. In 2018 & 2019 BART carried out natural flood management (NFM) walkover surveys with the overall aim of identifying opportunities to implement ‘nature based solutions’ in the South Brook Catchment near Melksham, Wiltshire.
The South Brook NFM walkovers aimed to complement existing work programmes by identifying opportunities to work with natural processes in order to benefit localised hydrology in response to rainfall events, particularly in the South Brook headwaters. BART found that measures such as improved land and soil management and flow path attenuation may benefit localised hydrology while also delivering multiple benefits such as reducing sediment runoff and improving water quality issues in the river network.
Lauren (Project Manager), George (Senior Project Officer) & Alex (Volunteer)
As part of a suite of measures planned in the catchment BART delivered the installation of leaky dams, or ‘log jams’, in an active, spring-fed stream using locally sourced woody material. The leaky dams are carefully designed to allow a continuous base-flow to pass beneath the structures so that connectivity of water, sediment and aquatic biota is not impacted during average to low-flow conditions. In effect, the leaky dams will only function during higher flow conditions.
The leaky dams were secured in place using chestnut posts and small quantities of galvanised steel wire, used to secure timber to the chestnut posts, creating secure structures that will survive high flows. The structures are a considerable height in order to provide maximum benefit in the deeply incised channel.
“Our work will help contribute towards ‘slowing the flow’. The accumulative impact of multiple small-scale interventions is likely to benefit localised hydrology in response to rainfall events.”
Having identified opportunity to intercept a further flow pathway through a small woodland upstream of the leaky dams, BART introduced large woody material to the woodland floor to ‘slow the flow’ of surface water runoff from an adjacent field before it enters the watercourse. This measure is part of the pilot project to see the impacts of woody material in slowing runoff by encouraging the spreading of water across the natural low point of the woodland. This could increase the water storage capacity of the woodland and promote greater habitat diversity.
BART will be delivering further measures in the area later this year to include tree planting along the riparian corridor to increase the infiltration of surface water and promote biodiversity, and increasing the storage capacity of an existing pond-like feature, which collectively aim to contribute towards storing flood waters on their natural floodplain.