Spatial variability of suspended sediment yield in a gravel-bed river across four orders of magnitude of catchment area

• Specific sediment yield not related to catchment area in Eden
• Dominant sediment input mechanisms varied across catchment.
• Specific sediment yields higher in lowland sub-catchments
• Process domain concept used to explain sediment yield spatial variability

The spatial variation in suspended sediment yield in the River Eden, Cumbria, UK, is quantified and examined from a process-based perspective to challenge existing models for scale dependency in sediment yield. Field measurements were used to quantify suspended sediment yields for 14 sub-catchments within a total catchment area of nearly 1400 km2, including nine catchments defining a nested basin system starting from 1 km2. A novel catchment characterisation system was developed, in which broad-scale landscape characteristics were quantified using existing datasets, types of sediment supply feature were identified in a field survey and their distribution across the catchment was quantified using a survey of air photographs. Specific suspended sediment yield was found not to be related to catchment area. The main fine sediment input was from the riparian zone, where many sediment sources were discrete areas of erosion such as sites with livestock poaching and streamside scars. Connectivity of the rest of the catchment was low. The dominant types of source in an area were related to its topographic, geologic and land use characteristics. Specific suspended sediment yields were higher in lowland sub-catchments where the higher land use intensity and greater extent of superficial sediment deposits resulted in higher erosion susceptibility. Two ‘process domains’ were identified: lowland and upland. It is suggested that these provide a simple concept for explaining spatial variability in sediment yields as a function of easily measurable catchment properties.