Assessing Coarse Sediment Connectivity of the River Avon, Devon: a Geomorphological Conceptual Model Based on Physical Catchment Characteristics

River managers have embraced integrated management approaches to improve river health, rehabilitate landscapes and create sustainable catchment practises. Geomorphic processes such as the routing of coarse sediment, impacts the connectivity of sediment throughout a river system which influences channel morphology and the availability of spawning sites. The geology, topography and land cover within the catchment ultimately determines the sources of coarse sediment and its potential to transfer throughout the catchment. A conceptual process-based framework was created based on physical catchment characteristics to predict the level of connectivity of sediment throughout the River Avon, Devon. A combination of modelling, GIS and fieldwork methods were used to determine the potential sediment sources, the influence of geology, topography and land cover on catchment processes and subsequently to calculate the bedload transport rates of coarse sediment within the catchment in order to evaluate connectivity within the catchment. The results showed that the erosion potential was greater in the middle and lower reaches of the Avon catchment as the geology is less resistant. The river banks were determined to be the main source of coarse sediment while the hillslopes were shown to be uninfluential due to dense vegetation cover. As a result, the channel was found to be the main transport mechanism for sediment connectivity. Using surveyed reaches to calculate bedload transport rates, the river network was shown to be partially connected throughout the catchment as only 12 of the 26 sites were capable of transporting appreciable loads of coarse sediment downstream at regular flows. This investigation created a framework capable of assessing coarse sediment connectivity within the Avon catchment. Although further validation is required, the model provides a foundation for further validation on rivers with similar catchment characteristics. If successful, the method would become a useful tool for catchment managers to improve spawning habitats for Atlantic salmon