The team at BART have been busy undertaking in-stream habitat restoration on the River Marden near Calne. This work, made possible through funding from Calne Without Parish Council (CWPC), aims to diversify water flow and habitat conditions by creating several woody berms with the help of local volunteers. This project will help achieve the strategic objectives of the CWPC Climate Emergency Working Group which aims to restore and reconnect habitats in the Marden Valley catchment to enhance the area’s aquatic and terrestrial biodiversity.
This section of the upper Marden has suffered from a lack of flow diversity and over-siltation resulting in a poor invertebrate and aquatic plant community present in this stretch. Slow-flowing straightened sections of the river create a uniform flow pattern across the channel width, reducing the microhabitats present and resulting in silt deposition that smothers gravel bed habitats which are essential for many invertebrates and spawning fish.
Working with contractors, BART staff and volunteers collected woody branches and brash from trees on site. In doing so, helping open up sections of the canopy to maintain a roughly 40:60 light to shade ratio for the stream, encouraging greater aquatic plant colonisation. At specified points along the river identified by BART, staff alongside volunteers secured aged chestnut stakes into the riverbed and packed the collected woody material to create wedge shaped structures jutting out into the river channel. These structures are called woody berms. The berms were secured using twine and designed to overtop in high flow conditions.
Creating woody berms helps add complexity to rivers, helping restore natural processes by creating areas of faster and slower flows, increasing flow diversity and create areas of scour and deposition. This process enhances the physical diversity of the river by encouraging it to “re-wiggle”, in doing so increasing the microhabitats found in both the river cross section and downstream profile with benefits for a variety of species and communities. By increasing flow diversity in the newly narrowed channel, our berms will help expose gravel habitat essential for trout spawning. Over time the berms will in-fill with silt and bankside vegetation will colonise helping to stabilise the structure and blur the divide between the natural bank and our berms.
We would like to thank Sprays Farm for the permission to undertake this important restoration work and Calne Without Parish Council for funding the project. A huge thank you also goes out to the volunteers who came out to help and make this work possible!