Debris flow triggering by impulsive loading: mechanical modelling and case studies

A mechanism is proposed by which debris flows can be triggered through impulsive loading. Momentum transferred from hillslope failures to steep stream bed materials may be sufficient to initiate a debris flow where one may not otherwise occur. An important parameter in the momentum transfer is the planimetric angle between the slide path axis and the stream channel axis. Preliminary stability equations for both drained and undrained loading are developed from formulae commonly used to assess stream channel stability. Case studies from two basins in the southern Coast Mountains of British Columbia are used to illustrate the mechanisms.