A probabilistic model of debris-flow delivery to stream channels, demonstrated for the Coast Range of Oregon, USA

Debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance. Identification of channels susceptible to debris-flow inputs of sediment and organic debris, and quantification of the likelihood and magnitude of those inputs, are key tasks for characterizing spatial and temporal patterns found in channel conditions and associated habitats in a river network. Widely available digital elevation and land-cover data (10-m DEMs and 25-m satellite imagery) offer the potential to assess debris-flow runout paths over regional extents. This paper presents a model for using these data to calculate empirical probabilities for debris-flow runout over DEM-determined flow paths and shows how these probabilities can be combined over all sources to estimate the potential for debris-flow delivery to stream reaches throughout entire channel networks. The model is calibrated and model predictions are compared to field-mapped debris-flow travel paths from study sites in the Coast Range of Oregon, USA. This model predicts debris-flow probability over channel-reach scales that can be aggregated to basin-scale measures of debris-flow potential. It offers unprecedented ability to characterize debris-flow effects over channel networks, providing a tool for risk assessment and for generating hypotheses that relate topographic and forest-cover controls on debris-flow runout to the types and abundance of channel habitats in a river basin.