Little Avon River Restoration Update

Bristol Avon Rivers Trust – Nick Wilson 

October 2023 

 

Introduction 

Bristol Avon Rivers Trust (BART) have been busy undertaking in-stream habitat restoration on the Little Avon, Damery. The work, funded by South Gloucestershire Council as part of their Climate and Nature Emergency Action Plan, used nature-based solutions to increase biodiversity by creating 16 woody berms with the help of Berkeley Estate Fishing Syndicate and local volunteers. 

Issues 

The Little Avon is currently rated moderate ecologically under the Water Framework Directive (WFD). Increased housing development and climate change impacts has resulted in lower flows and reduced water levels, limiting the ecological health of the river. This is exacerbated by historic management practices which have led to section of the river being straightened and overwide, reducing biodiversity further. 

There is also a lack of in-stream habitat. No wood in the river and a lack of aquatic plants due to overshading has led to a featureless channel that provides little in the way of food or cover for fish and other freshwater species (figure 1). 

 Figure 1: Overshaded, straightened section of the Little Avon providing poor quality habitat for wildlife. 

Action 

To address these issues BART developed a river restoration project to improve a 1km stretch of the Little Avon by installing 16 woody debris berms. This project was delivered over 5 days in late September with help from the Berkeley Estate Fishing Syndicate. 

BART staff with a local contractor selectively coppiced hazel and alder alongside the riverbank to provide material to create the woody debris berms (figure 2). At specified points along the river identified by BART, volunteers supervised by BART created the woody debris berms by packing the collected woody material to create wedge shaped structures jutting out into the river channel. 

Figure 2: The Hazel stand in figure 1 being coppieced to allow light into the channel and provide material to create woody debris berms. 

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 (figure 3). 

Benefits of complex woody debris: 

• Increase flow variability – Using appropriately positioned woody material in the channel will allow processes such as bed scour to clean sediment from the gravels. The woody material will also act as sediment traps, to help remove sediments from the system. It will also narrow the channel during summer low flows increasing the rivers resilience to groundwater abstraction and climate change. 
• Increase marginal vegetation – The use of woody debris features installed along the channel margins will create a more gradual change from in-stream to terrestrial habitat, providing more suitable habitat for colonisation from marginal plants such as yellow flag iris (Iris pseudacorus) and water mint (Mentha aquatica). This will in turn create improved habitat for species such as water vole (Arvicola amphibius) as well as a range of invertebrate species that provide an essential food source for freshwater fish. 

• Selectively reduce canopy cover to enable more light to get to the channel. This will in turn encourage the growth of in-channel macrophytes such as Ranunculus (water crowfoot) species, which is an important species for flow variability, oxygenation and the lifecycles of several key invertebrates. 

Figure 3: BART staff and volunteers from Berkeley Estate Fishing Syndicate creating woody debris berms. 

BART would like to extend thanks to Tortworth Estate, and other local landowners for their permission to undertake this important restoration work. We would also like to thank Berkeley Estate Fishing Syndicate for their incredible assistance delivering the project, and South Gloucestershire Council for funding the project. Also many thanks to Louise Bidwell for supplying the Drone video.