The interaction between armouring and particle weathering for eroding landscapes

Abstract

The interaction between particle weathering and surface armouring and its effect on erosion has been investigated. The effect of soil armouring is to decrease sediment transport with time by preferentially stripping away fine particles. On the other hand the effect of weathering, which breaks down the particles in the armour, is generally believed to increase erosion. By extending an existing armouring model, ARMOUR, and using a variety of published weathering mechanisms this interaction has been explored. The model predicts that while this is generally true, in some cases erosion can be decreased by weathering. When the particles generated by weathering were approximately of equal diameter, erosion increased while armouring decreased. When weathering produced very fine particles by spalling, erosion increased and armouring also increased. When weathering produced a range of particles from fine to coarse, the armour layer broke down and erosion decreased relative to the no-weathering case. This latter decrease in erosion was due to the high entrainment of coarser transportable materials from the bed decreasing the sediment transport capacity of the flow. In these studies clear regimes could be identified where erosion was limited by either the energy of the flow alone (i.e. 'transport-limited'), or the rate of weathering ('weathering-limited'); however, for some mechanisms there was an interaction between the two, which we called 'weathering/ transport limited'. Copyright © 2006 John Wiley & Sons, Ltd.