Complex Drivers of Interdecadal Variation in Clastic Sediment Yield from a Forested Mountain Basin: The Role of Hydroclimate, Land Use and Geomorphic Connectivity.

Abstract:

The variation in fluvial sediment yield can be viewed as a signal of geomorphic change within the upstream basin. Such changes represent landscape’s response to natural or anthropogenic drivers. However, the relationship between the geomorphic signal recorded at the basin’s outlet and its drivers may be complex, depending on how the mobilized material is transferred between the hillslopes and the valley floor and through the channel network.

This research examines the links between interdecadal sediment yield variability and its drivers, including hydroclimate and land use, in the context of sediment sources and geomorphic connectivity within the routing system. The study was carried out in a forested, mountainous basin in NE Washington, USA. A combination of ground surveys and historical aerial imagery was used to study sediment yield based on delta growth. Climatic and hydrometric records and land use databases were used to reconstruct the history and spatial pattern of key disturbances and a simple routing approach was adopted to account for geomorphic connectivity.

Our results reveal a wide range of interdecadal variability in sediment yield from the study basin. This variability can only be reasonably explained when hydroclimate as well as the timing, magnitude, and spatial configuration (connectivity) of sediment sources associated with land use are considered jointly. Taken together, our findings provide insight into the landscape system behavior and its sensitivity to natural and anthropogenic disturbances. Such understanding is crucial for river management, including ecological restoration and hazard assessment, especially in light of the ongoing rapid environmental change.