Soil armouring and weathering: toward catchment-scale computational modelling

Abstract Hillslope surface armouring and weathering processes have been largely ignored in geomorphic and hydrological models due to their complexity and the uncertainty associated with them. However, their importance in a wide range of spatial processes is well recognised. An armouring and weathering computer model (ARMOUR) has previously been used to successfully simulate the effect of these processes on erosion and soil grading at a hillslope scale. In order to apply such a model across larger and more complex environments we used a Markov process conceptualisation to reduce the complexity of ARMOUR's numerics. This new armouring-weathering model (named MrARM) is now capable of large-scale two- dimensional simulations. In this paper we describe the calibration and evaluation of MrARM as well as the results of multiple hillslope-scale simulations for varying weathering rates. The MrARM armounng component was calibrated against ARMOUR results, while its weathering component was validated against recently published laboratory results. A parametric study was conducted to evaluate model predictions under various conditions. The results described here demonstrate that the modelling approach used is effective and that the simulation of the armouring and weathering processes corresponds well with previous experience with ARMOUR and with generally accepted field understanding.