Modelling the location of shallow landslides and their effects on landscape dynamics in large watersheds: An application for Northern New Zealand

In this study we propose a model to assess the location of shallow landslides and their impact on landscape development within a timeframe of years to decades. Processes that need to be incorporated in the model are reviewed then followed by the proposed modelling framework. The capabilities of the model are explored through an application for a forested 17 km2 study catchment in Northern New Zealand for which digital elevation data are available with a grid resolution of 25 × 25 m. The model predicts the spatial pattern of landslide susceptibility within the simulated catchment and subsequently applies a spatial algorithm for the redistribution of failed material by effectively changing the corresponding digital elevation data after each timestep on the basis of a scenario of triggering rainfall events, relative landslide hazard and trajectories with runout criteria for failed slope material. The resulting model will form a landslide module within the dynamic landscape evolution model LAPSUS. The model forms a spatially explicit method to address the effects of shallow landslide erosion and sedimentation because digital elevation data are adapted between timesteps and on- and off-site effects over the years can be simulated in this way. By visualization of the modelling results in a GIS environment, the shifting pattern of upslope and downslope (in) stability, triggering of new landslides and the resulting slope retreat by soil material redistribution due to former mass movements can be simulated and assessed.