A large part of BART’s work includes practical habitat restoration, including weir removal, where we make physical changes to the river to restore natural processes to make them healthier, more naturally functioning environments which support more wildlife. There are many different ways in which we improve river habitat, but the aim of all techniques is to reduce the environmental impact caused by mankind.
See below for some examples of the work we carry out across the catchment:
Many of our rivers have historically been heavily modified by overwidening and straightening for navigation, industry, hydropower and other forms of land use. Modifying river channels this way has reduced the quality of habitat available to support fish, invertebrates and other forms of aquatic life. Secondly, no ‘meanders’ (bends in the river) results in a lack of diversity in water depth and as a result, a absence of varied habitat types (pools and riffles) which are crucial for the existence of various species. Thirdly, a lack of woody debris means there is nothing to catch the excess of sediment which is an issue in many rivers, as it settles on riverbed gravels smothering fish eggs and invertebrates.
One technique which promotes in-stream habitat diversity is the installation of ‘brushwood mattresses’ and ‘flow deflectors’. These structures are positioned within the channel to pinch the channel and accumulate with sediment, creating flow diversity. Diverse flow conditions begin to erode and deposit materials in various sequences, promoting the formation of pools and riffles.
The structures are constructed using natural materials; by coppicing trees on the river banks and securing limbs into the river bed at the correct angle into the flow. The space behind the tree limb extending into the channel and the river bank is packed with brushwood and secured in place. These structures help to re-meander the profile of the river and provide a diverse range of habitat. Over time, the structures will accumulate sediment and eventually vegetate to become part of the riverbank.
Trees in rivers were previously only seen as an issue which cause blockages, but are now recognised as a conservation tool that can help increase population numbers of many different species, including aquatic invertebrates, fish and birds and mammals.
Many people like the look and sounds of weirs in rivers, but did you know that they are detrimental to river ecology? See the diagram below to learn more about these impacts:
Where possible, BART builds plans to remove weirs and other artificial structures to reinstate the natural flows of the river channel. Where it is not feasible to physically remove weirs, BART builds plans to install fish passes (such as ‘fish ladders’) so that migratory fish such as sea trout and salmon can make it upstream to breed.
