Modelling post-wildfire debris flows

Summary

This project will build upon emerging soil and fire science understanding to examine methods to model the formation of water repellent layers and subsequent debris flow and motion numerically. Such knowledge will greatly improve our ability to identify at-risk areas prior to fires taking place. 

Project background

Debris flows after wildfires arise due to changes in the hydrologic function of the underlying soil. In the extreme heat, water storage in the organic litter layer is lost (accompanying Figure a), deep infiltration decreases and water concentrates in the topsoil (Figure d). The key driver in this mechanism is the formation of a water repellent soil layer: heating the soil to 175–280°C for durations of 5–20 min volatises the surface organic layer, which then infiltrates the soil. Volatised organic matter cools and recondenses at shallow soil depths (1-5 cm), rendering the soil water repellent (Figure c). This leads to water runoff on sloped surfaces and subsequent debris flow. This effect is compounded by atrophy of the below-ground biomass due to soil heating, with the consequent loss of its stabilising biomechanical properties.

This project will combine environmental, geotechnical and fire engineering to examine the factors driving debris flow initiation and to reproduce the key mechanisms under laboratory conditions. Soil samples will be exposed to radiant heating to examine heat migration through a soil body and organic matter volatisation. Thermal exposures will be defined by measurements of heat flux to a substrate during laboratory flame spread studies. Flow initiation and propagation will be modelling using the Discrete Element method, building upon observed and derived material behaviour from the laboratory setting.

Research questions

What are the material conditions driving the thermal gradient?

How do volatised organic molecules travel through the soil?

What rate of infiltration is needed to initiate flow and can we extract the environmental and topological conditions?

Can Discrete Element modelling be used to capture the salient mechanical processes and predict the initiation of a debris flow?

Methodology

Year 1: Review interdisciplinary literature, analyse soil samples and develop the full experimental programme

Year 2: Commence experimental testing and numerical modelling using the Discrete Element Method (DEM)

Year 3: Formalise modelling efforts and prepare written materials

Training

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills.

For further information and to apply: https://www.ed.ac.uk/e4-dtp/how-to-apply/our-projects?item=801 

Closing Date: 

Thursday, January 9, 2020

Principal Supervisor: 

Assistant Supervisor: 

Eligibility: 

Minimum entry qualification - an Honours degree at 2:1 or above (or International equivalent) in a relevant science or engineering discipline, supported by an MSc Degree. Further information on English language requirements for EU/Overseas applicants.

Master's Degree in an Engineering or Geosciences discipline with a focus on soils and/or fire dynamics.

 

Funding: 

 

E4 DTP Studentships

E4 DTP studentships are fully-funded for a minimum of 3.5 years. They include:

  • Stipend based on RCUK minima (currently £15,009 for 2019/2020)

  • Fees (Home/EU Fees)
  • Research Costs (Standard Research Costs plus, depending on the projects requirements, Additional Research Costs can also be allocated)

The stipend can be extended to up to another 5 months through our two optional schemes, subject to the approval of the Management Board.

Informal Enquiries: