Understaing the interaction of sediments, habitats and watercourse management
The Environment Agency invests significant resource in managing sediments in rivers and channels. An improved understanding of sediment processes and the impact of capital and maintenance works would enable more effective targeting of resources and a reduction in environmental impacts. HR Wallingford led a team of organisations that considered how sediments, habitats and the management of a watercourses interact, in the context of delivering flood risk management that is both cost effective and provides significant environmental benefits.
Sediment erosion, transport and deposition are important in forming habitat diversity in rivers and thereby influencing biodiversity. Sediments are the building blocks of discrete habitats such as bars, which, depending on their character, are subsequently colonised by different species. In general, the more natural and varied a river or channel, the higher the ecological value.
However, sediment deposits and vegetative debris along with growth of vegetation also act to increase the chance of flooding through their influence on channel roughness and blockage potential, reducing conveyance and associated in-river water levels and hence flood risk. The effects of these activities on the natural environment must be understood to ensure that protecting people and property from flooding can be achieved whilst also delivering the greatest possible environmental benefits. This project looked at five field sites selected to represent different channel types and sediment management interventions across a broad geographical range of particular relevance to flood risk management. Field data were supplemented by desk studies of historical and contemporary watercourse management at the study sites.
A typology for watercourses in England and Wales was developed so that the results could be readily applied to similar watercourses which form part of a flood risk management system. The typology brings together watercourses that (morphologically) behave in a similar way and that might reasonably be expected to respond to sediment management activities in a similar way. The typology can be used by Environment Agency staff planning to undertake sediment removal or other sediment-related activities to manage and reduce flood risk.
We examined the impacts of capital works and maintenance on sediments and habitats by considering a range of case study rivers.