Variable hydrograph inputs for a numerical debris-flow runout model

Natural Hazards and Earth System Sciences, Vol. 22 (2022)

Keywords
Authors
  • A. Mitchell
  • Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, V6T 1Z4, Canada
  • A. Mitchell
  • BGC Engineering Inc., Vancouver, V6Z 0C8, Canada
  • S. Zubrycky
  • BGC Engineering Inc., Vancouver, V6Z 0C8, Canada
  • S. McDougall
  • Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, V6T 1Z4, Canada
  • J. Aaron
  • Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903 Birmensdorf, Switzerland
  • M. Jacquemart
  • Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903 Birmensdorf, Switzerland
  • M. Jacquemart
  • Laboratory of Hydraulics, Hydrology and Glaciology (VAW), Department of Civil, Environmental and Geomatic Engineering, ETH Zurich, 8049 Zurich, Switzerland
  • J. Hübl
  • Institute for Alpine Natural Hazards, University of Natural Resources and Life Sciences, 1190 Vienna, Austria
  • R. Kaitna
  • Institute for Alpine Natural Hazards, University of Natural Resources and Life Sciences, 1190 Vienna, Austria
  • C. Graf
  • Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903 Birmensdorf, Switzerland

Abstract

Debris flows affect people and infrastructure around the world, and as a result, many numerical models and modelling approaches have been developed to simulate their impacts. Observations from instrumented debris-flow channels show that variability in inflow depth, velocity, and discharge in real debris flows is much higher than what is typically used in numerical simulations. However, the effect of this natural variability on numerical model outputs is not well known. In this study, we examine the effects of using complex inflow time series within a single-phase runout model utilizing a Voellmy flow-resistance model. The interactions between model topography and flow resistance were studied first using a simple triangular hydrograph, which showed that simulated discharges change because of local slopes and Voellmy parameters. Next, more complex inflows were tested using time series based on 24 real debris-flow hydrographs initiated from three locations. We described a simple method to scale inflow hydrographs by defining a target event volume and maximum allowable peak discharge. The results showed a large variation in simulated flow depths and velocities arising from the variable inflow. The effects of variable-inflow conditions were demonstrated in simulations of two case histories of real debris flows, where the variation in inflow leads to significant variations in the simulation outputs. The real debris-flow hydrographs were used to provide an indication of the range of impacts that may result from the natural variability in inflow conditions. These results demonstrate that variation in inflow conditions can lead to reasonable estimates of the potential variation in impacts.

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