Quantifying small scale spatial variability in diffusive erosion and deposition

Hillslope and catchment evolution will be the cumulative product of short and long-term processes that operate and dominate over different hillslope length scales. In this study, erosion and deposition pattern rates generated over short lengths scales (0.1–3 m) are examined using erosion pins over 14 years for a field site in northern Australia. The pins consisted of two sets of nine pins located on a catchment divide. Over the 14 years, there was considerable variability in erosion and deposition with both sites being depositional (~7 mm of deposition). The sites, separated by several hundred metres both had very similar erosion and deposition patterns. Annual erosion and deposition patterns were modelled using a computer-based Landscape Evolution Model (SSSPAM) that models both fluvial and diffusive erosion. Model results found that SSSPAM was unable to predict the erosion and deposition rate and patterns using a Digital Elevation Model (DEM) for the site. However, when the DEM was modified at each annual time step to capture short length scale random particle movement, SSSPAM predicted both erosion and deposition variability as well as the field measured deposition. This is the first time that a hillslope diffusion model has been evaluated for erosion produced by rainfall. The model results demonstrate that the commonly used equation for diffusion when calibrated for the site performs well.