Simulating two-phase debris flows in HEC-RAS at Hummingbird Creek, British Columbia, Canada

Abstract

Debris flows are typically modelled as a single homogeneous surge due to lack of data to support more complex model development and due to lack of time and funding for the practitioner and the communities they aim to support. Coarse debris flows are typically characterized by a coarse front, followed by a muddy slurry, that is then followed by a hyperconcentrated flow phase with lesser sediment concentrations. Presented herein is the modelling for a debris flow hazard assessment for Hummingbird Creek, British Columbia, Canada. Model calibration best matched the observed debris flow deposit when the coarse front and hyperconcentrated flow were modelled separately in two phases allowing for separate flow rheologies to be used for the front and the tail of the debris flow, and allowing for deposition between phases. Further research is needed to understand when simulation of two-phase flow may be most representative, particularly when no calibration data is available.