Sediment availability on burned hillslopes

Authors

  • Petter Nyman,

    Corresponding author
    1. Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria, Australia
    2. Bushfire Cooperative Research Centre, East Melbourne, Victoria, Australia
    3. eWater Cooperative Research Centre, University of Melbourne, Parkville, Victoria, Australia
    • Corresponding author: P. Nyman, Department of Forest and Ecosystem Science, Melbourne School of Land and Environment, University of Melbourne, 221 Bouverie St, Parkville, Vic 3010, Australia. (nymanp@unimelb.edu.au)

    Search for more papers by this author
  • Gary J. Sheridan,

    1. Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria, Australia
    2. Bushfire Cooperative Research Centre, East Melbourne, Victoria, Australia
    3. eWater Cooperative Research Centre, University of Melbourne, Parkville, Victoria, Australia
    Search for more papers by this author
  • John A. Moody,

    1. U.S. Geological Survey, Boulder, Colorado, USA
    Search for more papers by this author
  • Hugh G. Smith,

    1. School of Environmental Sciences, University of Liverpool, Liverpool, UK
    Search for more papers by this author
  • Philip J. Noske,

    1. Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria, Australia
    Search for more papers by this author
  • Patrick N. J. Lane

    1. Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria, Australia
    2. Bushfire Cooperative Research Centre, East Melbourne, Victoria, Australia
    Search for more papers by this author

Abstract

[1] Erodibility describes the inherent resistance of soil to erosion. Hillslope erosion models typically consider erodibility to be constant with depth. This may not be the case after wildfire because erodibility is partly determined by the availability of noncohesive soil and ash at the surface. This study quantifies erodibility of burned soils using methods that explicitly capture variations in soil properties with depth. Flume experiments on intact cores from three sites in western United States showed that erodibility of fire-affected soil was highest at the soil surface and declined exponentially within the top 20 mm of the soil profile, with root density and soil depth accounting for 62% of the variation. Variation in erodibility with depth resulted in transient sediment flux during erosion experiments on bounded field plots. Material that contributed to transient flux was conceptualized as a layer of noncohesive material of variable depth (dnc). This depth was related to shear strength measurements and sampled spatially to obtain the probability distribution of noncohesive material as a function of depth below the surface. After wildfire in southeast Australia, the initial dnc ranged from 7.5 to 9.1 mm, which equated to 97–117 Mg ha−1 of noncohesive material. The depth decreased exponentially with time since wildfire to 0.4 mm (or < 5 Mg ha−1) after 3 years of recovery. The results are organized into a framework for modeling fire effects on erodibility as a function of the production and depletion of the noncohesive layer overlying a cohesive layer.

Ancillary