Spatial Patterns of Disconnectivity Explain Catchment‐Scale Sediment Dynamics and Transfer Efficiencies

Abstract

While connectivity studies are becoming common in the Earth sciences, disconnectivity has received much less attention. Sediment storage is the direct result of sediment disconnectivity and can provide concrete evidence of the spatial patterns of disconnectivity at the catchment‐scale. In this study, we explore the catchment‐scale sediment dynamics of the Tahoma Creek watershed, a high‐gradient glacio‐volcanic landscape, within a sediment budget framework and identify and map sources of disconnectivity to determine whether they explain the spatial patterns and estimated efficiencies of sediment transfers. We found that up to 80% of the total eroded sediment is sourced from the proglacial zone. The proglacial zone is characterized by high connectivity resulting from frequent debris flows and floods, and rapidly responds to changing conditions. Down valley, however, sources of disconnectivity become increasingly more prevalent, the hillslopes become decoupled from the channel, and a majority of the eroded sediment is redeposited with as little as ∼15% reaching the outlet. The spatial distribution of sources of disconnectivity and their upslope affected areas explains, to a large degree, catchment‐scale sediment dynamics and sediment transfer efficiencies and is in close agreement with quantitative connectivity estimates. We find that steep, glaciated watersheds are predominantly disconnected over human timescales and suggest that disconnectivity is the dominant state of landscapes over most timescales of interest. Mapping sources of disconnectivity provides a straightforward and concrete approach to estimating system disconnectivity and can increase confidence when paired with quantitative indices.