Exploring colluvial channel agency in mountain sediment routing and erosion

Mountain sediment routing systems have been shown to preserve a valuable record of how climate and tectonics can influence earth surface processes and the topographic form of landscapes. Catchment drainage density and the efficacy of hillslope-channel sediment transport (namely through landslides and rockfalls) is shown to regulate mountain erosion and the response time of landscapes to external perturbations. The role of colluvial channels/gullies in the mountain sediment routing system is largely overlooked, despite recent research in upland deglaciated landscapes highlighting the significance of these upland channels in storing and transporting sediment via debris flow processes. This preliminary work, at the proof-of-concept stage, looks to (1) include and then reflect upon the contribution of these ephemeral channels to catchment drainage densities, and then (2) reexplore the links between catchment drainage density and erosion. The Blue Ridge Mountains of Central Appalachia, USA is an ideal location for this initial investigation as the range is unglaciated, tectonically inactive, and has a relatively uniform lithology and climate. High resolution LiDAR data and satellite imagery was used to map the channel network of 24 catchments in the Blue Ridge Mountains. Cosmogenic nuclide erosion rates for these catchments were then evaluated against their drainage densities. Initial results suggest that while drainage density likely influences the erosion rates recorded in Central Appalachia, the role of colluvial channels within this is complex. These findings have raised some important questions about the controls of colluvial channel sediment flux, morphology and distribution in mountain areas.