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29 July 2016

Watercourses and Problems Associated with Fine Sediments

The excessive sedimentation of watercourses is a national problem that affects many of the UK’s rivers. The release and transport of sediment and particulate matter in rivers is a natural and important process, part of the biochemical cycle critical to ecological functioning and habitat diversity. However, the amount of fine sediment entering rivers has increased dramatically over the last century resulting in poor water quality that threatens the integrity of aquatic ecosystems and the services they provide.

This issue was the theme of the recent British Hydrological Society Meeting held at Loughborough University entitled ‘Hydroecology and fine sediment conundrum: quantifying, mitigating and managing the issues.’ Talks and posters presentations were given by representatives from universities and statutory agencies that covering a wide range of associated issues.

The problem lies within the wider landscape where intensive farming, particularly arable farming, has accelerated the rate of soil erosion, and poor agricultural practices are responsible for the largest sediment-source apportionment. The loss of the valuable soil resource is in itself a major problem and a number of the presentations examined research underway to identify soil mobilisation processes and improving methods of soil management.

Siltation can have a detrimental impact on macroinvertebrates, fish, macrophytes, diatoms and threatened species such as the freshwater pearl mussel and white-clawed crayfish. For example, fine sediment that fills the interstitial space between gravels limits the oxygen exchange capacity and reduces fish embryo survival, which can pose a threat to the economic viability of fisheries. Excessive sedimentation also reduces channel storage capacity and increases flood risk and dredging costs.

Fine River Sediment

PAA contributed to the meeting with a poster presentation that described the remediation measures adopted to remove metal-laden mining tailings from Stoke Brook, a tributary to the River Derwent in the Peak District National Park. A mining lagoon failure sent a torrent of potentially toxic sediments into these watercourses that support important salmonid and coarse fisheries and an important breeding population of brook lamprey. PAA worked closely with specialist restoration practitioners, statutory agencies and local interest groups to devise a remediation approach that involved the commission of bespoke equipment and introduction of novel techniques to minimise intrusive and damaging operations.

Download a digital copy of our Stoke Brook Remediation Poster.