Wood is a vital component of healthy rivers, providing habitats for a wide range of creatures. Birds, including kingfishers, use wood and fallen trees in rivers as perches, fish use it as shelter to hide in (fish live in trees!), some dragonfly species lay their eggs in wood and a wide range of invertebrates shelter and feed on it. In short, wood creates a complex and dynamic habitat that is essential in maintaining a diverse aquatic ecosystem.
As well as providing physical habitat wood also changes the flow and hydrology of the river, areas of faster and slower flows are created. Faster river flows clean the channel bed, washing away layers of silt to reveal clean gravels that are a vital fish spawning habitat. Slower flowing deeper areas of waters catch sediment, allowing in-channel vegetation to establish. Wood also adds an element of friction to rivers which holds back river flow, reconnecting the river to its floodplain, creating wetland habitats, reducing flood risk downstream, and forming fish habitats during summer low flows.
If wood is as amazing as we say then why are we so used to seeing rivers without any in-channel wood or trees? Despite its importance wood is now absent from many Norfolk rivers. Naturally, bank top trees would fall into rivers, but, we have cleared many riverbank trees to develop on the floodplain whilst also actively removing fallen trees from rivers to prevent localised flooding and to tidy up “messy” areas. This has resulted in the misconception that wood does not belong in rivers.
However, research has shown that installing large wood deflectors or felling whole trees into rivers is one of the most simple and effective river restoration techniques, encouraging natural processes and increases in a range of wildlife. Norfolk Rivers Ecology and Norfolk Rivers Trust have worked on a number of projects across Norfolk installing large wood deflectors to create habitat.