Modelling the dynamics of soil redistribution induced by sheet erosion using the Universal Soil Loss Equation and cellular automata.

摘要

As a landscape changes, so do the flows of matter that run across it. These flows modify the landscape and can thereby alter their own course in a feedback mechanism. This study focuses on one instance of this process: medium-term background soil redistribution induced by sheet erosion. Previous studies that have modelled this phenomenon have either focused exclusively on a feedback loop, or have not included it at all. We incorporate all relevant soil-environmental variables, including a feedback loop, into a single model. A unique feature of the proposed model is in the handling of the fluvial sediment flux (q_s), which may be determined from the Universal Soil Loss Equation (USLE). The USLE itself does not explicitly incorporate a feedback loop, but can readily be made to incorporate it by calculating a new, spatially distributed value for q_s at each time step in response to topographical changes. Hence, the objective of this study was to develop a soil redistribution model that considers q_s as being both spatially distributed and temporally dynamic. Rainfall erosivity was derived from mean annual precipitation, vegetation cover from satellite imagery, and slope characteristics from a DEM; in addition, soil erodibility values were derived from legacy soil survey data. The developed model was tested on Bowen Island, British Columbia, Canada at a 25 m spatial resolution. Soil redistribution simulations were made for 100 years, where 95% of the soil depth change was between a 3.01 cm loss and a 2.40 cm accumulation. The model was tested in order to assess the effects of different flow routing algorithms, resolutions, and soil deposition regimes on soil redistribution. Incorporating a feedback loop into the model yielded a disproportionate effect on soil redistribution; hence, small changes in the model state resulted in effects that are several orders of magnitude larger than the original change.