Erosion of the river bank and river beds can have a big impact on the health of the river and its inhabitants. Despite silt particles being tiny, what we can’t always see with the naked eye is causing untold damage. While some silt in water is normal and healthy, large quantities of silt find their way into our water every year, negatively impacting water quality. This pollution, known as siltation results from erosion and land disturbing human activities, such as agriculture and construction.
As a Trust, we are particularly motivated by a need to protect freshwater pearl mussels for example. These are a highly endangered species who have taken residence in the North Tyne and can only be found in very few parts of the country due to specific needs. Freshwater pearl mussels need clean gravel in order to survive and breed. As they open and close to feed, contaminated water is taken in which poisons the mussels. Stagnant water too poses a big threat to this species, as silt clogs and blocks gaps in gravel a lack of oxygen suffocates freshwater pearl mussel eggs leading to a decline in numbers.
It’s not just mussels that need our help from erosion siltation across the catchment and beyond, salmon and trout rely on clean, oxygenated, fast flowing water too. A rapid accumulation of sediment has detrimental effects on salmon’s life cycle given that the survival of eggs is dependent on a well-supplied oxygenated water. Too much fine sediment in spawning beds leads to suffocation of eggs.
With this in mind, our goal is to stop silt getting into the Tyne rivers and improve habitat where the silt has contaminated the water. Our interventions have included the repair of riverbanks and footpaths in the catchment, introducing fine sediment traps and cleaning gravels as part of an experimental method.
‘Green engineering’ such as a log jam matrix as used in a project on the River Derwent utilised our hydromorphological expertise to design a solution that matched the natural surroundings of the location but crucially withstood extremely challenging flow conditions experienced at the site. This involved the use of larch posts to create a log jam matrix to robustly protect the riverbank and absorb river energy. It was also agreed that the riverbank would be reprofiled, protected using biodegradeable coir matting and seeded with native grass species. Projects like this can be carried out safely, efficiently and with no environmental harm.
[insert photo of Derwent case study intervention]
Works to slow, and ideally eradicate the problem of erosion siltation are ongoing as part of our mission to protect the Tyne rivers. Many of our interventions use natural materials that provide a robust and long-term solution to the problem. Measuring success is important, returning to sites years-on, such as a footpath restoration project in the South Tyne has withstood some major flood events. By now vegetation has become established, ensuring it blends in with the local environment and provides the long term robustness required.
Going back to protected species like freshwater pearl mussels, geomorphological survey and assessment techniques continue to be used, along with Fine Sediment Fingerprinting to understand exactly where the major sources of fine sediment are. When we understand the major sources of fine sediment in the Tyne, we’ll be able to plan the interventions that will have the greatest environmental benefit. All these interventions will involve nature-based solutions such as tree planting, wetland creation and peatland restoration. This work will prevent sediments entering the river, providing a boost for wildlife while capturing carbon, reducing flooding, and improving the river for everyone to enjoy.