Chalk streams are among the most unique and ecologically valuable freshwater environments on the planet, with several flowing right through Affinity Water’s region. Fed by underground chalk aquifers, these clear, cool rivers provide a vital habitat for a rich variety of wildlife. But over time, human interventions, including dredging, straightening, and modifying banks, have significantly altered their natural processes. Combined with the increasing impacts of climate change, including more frequent droughts and floods, many of these rare rivers are now under threat.
The River Colne is a clear example. It’s currently failing to meet Good Ecological Status as defined under the Water Framework Directive. In response, a river restoration project was launched to address the physical changes (known as morphological issues) that have made the river less resilient and less supportive of biodiversity.
The primary goal of the project was to restore the river’s natural chalk stream characteristics, enhancing its ability to manage high flows and support local wildlife. By working with nature rather than against it, the project aimed to improve flood resilience and re-establish diverse habitats. A key challenge was the historical dredging of the river, which disconnected it from its floodplain and removed much of the natural structure of the riverbed. To reverse this, the project team assessed the importance of reconnecting the floodplain, allowing water to overflow during heavy rainfall with the goal of helping reduce flood risk in nearby built-up areas.
The restoration also involved the installation of berms, shallow ledges built along the river’s edge that slow the flow of water and create variety in depth and speed. This makes the river more dynamic and suitable for species such as brown trout, kingfishers, and aquatic plants. Thinking about nature, the team assessed tree hinging as another technique, where trees are carefully felled and laid into the river to create natural obstacles and shelter for fish. In addition to tree hinging implementation, backwaters, (quiet off-channel areas), were created to offer refuge for fish during fast flows and support biodiversity by providing still water habitats.
Planning for the project began in October 2023, with detailed designs completed by summer 2024. Following approval of a Flood Risk Activity Permit (FRAP) from the Environment Agency in September 2024. This busy first year of planning meant that boots were on the ground to begin work in late October and the project was completed in November 2024. Initial reviews by Melissa Ahmet (Project Manager) have seen early signs of success of the restoration, with her commenting that “It’s great to see improved chalk stream processes already taking place in the river. Where the berms and tree hinging have been introduced, there’s already a faster, cleaner flow, and clean gravels are beginning to appear. Fish have been spotted in the new backwater areas, which is a very encouraging sign.”
This project is just one example of how targeted, nature-based solutions (Nbs) can breathe new life into precious ecosystems. By restoring the River Colne, we’re helping to ensure that this rare chalk stream can continue to support both wildlife and local communities for generations to come.