HR: 1330h
AN: H42C-1096    [PDF]
TI: Wildfire Disturbance and Sediment Transfers over Millennial Time Scales: A Numerical Modelling Study
AU: * Martin, Y
EM: ymartin@ucalgary.ca
AF: Department of Geography, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4 Canada
AB: Wildfire may lead to accelerated soil erosion, debris flow and shallow landsliding activity in the years following disturbance. This study focuses on coastal drainage basins in British Columbia over millennial time scales, for which accelerated rates of shallow landsliding following wildfire may be of particular significance. An algorithm for wildfire occurrence, based on lake and sediment charcoal studies undertaken in coastal British Columbia and western Washington over millennial time scales (for example, Gavin et al., 2003), is incorporated into a numerical model of sediment routing over these same time scales. A stochastic rule set for wildfire frequency, based on a Weibull distribution of fire return intervals, assigns years of fire occurrence in the model. In terms of location, south-facing aspects are assigned a 25 times greater susceptibility to wildfire than north-facing aspects. As a first-order approximation, it is supposed that loss of tree root strength resulting from stand-replacing wildfires is comparable in its effects to clearcut logging. Therefore, documentation of increased shallow landslide activity associated with logging is used to adjust landsliding transport equations for the years following wildfire disturbance. Thereafter, landsliding rates are returned to pre-disturbance values. Fire return intervals, particularly those on north-facing aspects, can be relatively long in coastal British Columbia when compared to return intervals typically found in drier mountain ranges. This study investigates the degree to which wildfire disturbance affects sediment routing and delivery to channels over millennial time scales in coastal British Columbia. Sensitivity to model parameters is evaluated. Further investigations of wildfire effects on geomorphic process operation will lead to improved understanding of natural disturbance regimes to which ecosystems adjust over both the short and long term. Such information can be used to evaluate possible landscape and ecosystem responses to human disturbances, such as logging and prescribed burns. Reference: Gavin, D. Brubaker, L. and Lertzman, K. 2003. An 1800-year record of the spatial and temporal distribution of fire from the west coast of Vancouver Island, Canada. Canadian Journal of Forest Research 33, 573-586.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting