Debris Flow

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  • Created by: nicola
  • Created on: 12-04-11 18:36

A combination of boulders, wood and water

Changing climate has caused increase in debris flow - increases in rainfall seen = such increased frequencies make it hard to protect against all flows

Flows can be.....

  • ...on slopes - material becomes unstable and flows downhill and along gullies
  • ....or in channels -  mainly water charged triggered by heavy rainfall and flow down a pre-existing channel

Can also be referred to as a mudslide -

  • triggered by intense rainfall or snowmelt and travels as a viscous fluid
  • Can flow fast or slow depending on water capacity

Process can be divided into three stages:

  • INITIATION - needs an angle/ slope gradient of more 25 degrees
  • TRANSPORTATION - needs a gradient of more than 15 degrees
  • DEPOSITION - needs a gradient of less than 15 degrees

Can form fans of material or levees on the side of flow channels - seds are usually coarse grained therefore deposits are poorly to very poorly stratified

May occur rapidly with little to no warning - usually occurs in areas such as Japan, USA and China (mountainous areas) = have a similar distribution to landslides

Mitigation

Can be wither passive or active:

  • PASSIVE - no direct engineering as not trying to control the hazard. When one hazard has been identified the area is cleared and avoided
  • ACTIVE - engineering required once the hazard has been identified e.g. ring nets

Preventative structures need to consider:

  • Frequency
  • Max discharge and flow depth
  • Size of debris
  • Likely flow paths
  • Elevation of the slope
  • Magnitude of the event
  • Impact 

Not all…

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