The effects of sediment loading on morphology and flood risk in a lowland river system

Diffuse sources of sediment may have important implications for flood risk management (FRM), especially as catchment sediment yields are predicted to increase in future. UK legislation requires FRM to work with natural processes wherever possible, including accounting for sediments. However, the importance of wash-material load to FRM has been under researched and both a robust evidence-base and practical sediment models are needed to identify, prioritise and justify sediment-related catchment management. Research addressing these issues was centred on the River Tone, a sub-catchment of the Parrett, in which features excessive inputs of sediment in its upper catchment combined with high potential for deposition in its lower reaches. Links between sediment sources, water and sediment runoff, and downstream sediment sinks were established and the research examined the role played by sediment, especially wash-material load, within the fluvial system. The greatest sediment-related threats to the functioning of this lowland river stem from either: a protracted, major reduction in wash-material load; or a significant increase in bed-material load. Imbalance in the Tone fluvial-sediment system may not significantly affect flood risk directly, but has implications for FRM operations, maintenance and monitoring. Impacts on land quality result from soil loss. For example, ~2.5 million tonnes of soil has been eroded from the Parrett catchment since WWII. Water quality issues include delivery of phosphate and other pollutants into the river, and potentially more frequent dredging that remobilises contaminants. The thesis defines the key sediment-related components of sustainable, integrated catchment management and provides an improved evidence-base upon which to engage stakeholders. It tests and benchmarks sediment assessment tools including the Sediment Impact Assessment Model (SIAM). An approach to catchment-scale sediment assessment for lowland rivers is recommended, which involves a nested-approach using routinely collected and project-specific field data, stream power screening and SIAM.EThOS - Electronic Theses Online ServiceGBUnited Kingdo