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Durham University

Department of Geography

Departmental Research Projects

Microscale Modelling of Debris Flow Super Elevation

A research project of the Department of Geography.

Background

Debris flow are common destructive mass movements in mountain environments and understanding the velocities of these flows is important for hazard assessment. The velocity of debris flows can be estimated retrospectively using the superelevation approach. This method assumes the velocity of the flow can be predicted from the channel geometry and superelevation of the deposits flow. This approach has been universally applied to a wide range of geophysical granular flows with little consideration of the physical principles underpinning the theory.

Aims

The aim of this study was to develop a simple laboratory model to study small-scale debris flows in curved channels.

Methods & Objectives

This study uses small-scale physical modelling of debris flows based on dimensional analysis and principles of dynamic similarity. The approach builds on Davies, T.R. (1994) ‘Dynamically similar small-scale debris flow models’. Model characteristics:

  • Interstitial fluid slurry: a solution of 8g per litre of wall paper paste in water (kinematic viscosity ~ 0.005 Pa-s at 22°C)
  • Coarse grained solids: coal slack of 1 - 11.4mm size and density of 1.4g cm3
  • Mass used - 5 litre volume of dry sediment
  • Model scale is approximately 1:20
  • Channel slope15°
  • Channel shape - 200mm wide semicircular section - straight and curved (Rc = 0.163)
  • Discharge rates: 0.125, 0.286, 0.410 l s-1
  • For practical purposes getting the fluid viscosity right is the key

Results & Outputs

The primary outcome was the design of a working model to simulate microscale debris flows in the laboratory. Preliminary results provide guidance for further refinements of this approach. These include:

  • Better characterisation of rheology of debris flow mixtures
  • Configure channel to allow out of channel deposition
  • Real-time DEM models of flows
  • Higher resolution video capture and velcoimetry (particle tracking)
  • Testing of a range of channel shapes (RC values)
  • Redesign of channel configuration to avoid end of flume drawdown and acceleration

Staff

From the Department of Geography