Maintaining adequate ground cover is the ‘golden’ rule to reduce soil erosion. Leaf litter or similar absorbs the kinetic energy of rain drops as they hit the soil surface. This reduces soil surface disturbance and prevents aggregate breakdown that can lead to the formation of a surface seal.  Under some conditions however, in particular on steep slopes, adequate ground cover may not protect the soil from erosion even if the soil hydraulic conductivity exceeds rainfall intensity.  The mechanism that can lead to runoff and then erosion may be due to the formation of concentrated flow. 

Consider a thought experiment: our soil surface has a saturated hydraulic conductivity of 30 mm/h and we have a rainfall intensity of 20 mm/h: we should not get runoff!  Now 50% of the soil is covered and hence, only 50% of the soil surface can take in water.  This means that the hydraulic conductivity of the uncovered soil must be at least 40 mm/h to prevent runoff (i.e. 20 mm/h from the rainfall plus 20 mm/h that enters the soil as runoff from the groundcover).  Therefore we would have runoff as the hydraulic conductivity is only 30 mm/h.  Of course, this thought experiment does not apply to the real word, but the principle is still valid.

This project aims to assess the impact of groundcover on the formation of concentrated flow.  The experimental plan would assess the effect of soil hydraulic conductivity, slope and ground cover type and quantity on runoff and erosion.  The project will be conducted at the Erosion Processes Laboratory at the St Lucia  campus and can be supplemented in-situ using our field rainfall simulator and infiltrometer equipment.

The results will have implications on recommended management practices of sloping soil to prevent soil erosion.

Project members

Dr Gunnar Kirchhof

Principal Research Fellow & Senior Lecturer
School of Agriculture and Food Sciences