Soil piping or tunnel erosion (tunnelling) has been increasingly
recognised as a significant hillslope process in a wide range of climatic
regions. Piping refers to the hydraulic removal of subsurface soil,
causing the formation of underground channels in a natural landscape
(Boucher, 1990). Gully development, mass movements and topsoil
collapse can be significant secondary consequences of pipe enlargement,
inducing high soil losses (Bocco, 1991; Faulkner, 2006).
Comparison of an inventory of 560 collapsed pipes observed in the
Flemish Ardennes (Belgium; study area of 236 km²) with the soil and
lithological map revealed that zones with soil profiles developed on
loess covering homogeneous massive clays (Tertiary, Aalbeke Member)
were most prone to piping (Verachtert et al., 2010). Furthermore,
97% of the parcels with collapsed pipes are found under pasture.
However, the frequency analysis by Verachtert et al. (2010) only
qualitatively described the factors controlling the spatial occurrence of collapsed pipes in the study area and did not allow us to make
accurate quantitative predictions for spatial occurrence. There is
therefore a need to develop a quantitative approach giving the
susceptibility to piping at each location in the study area. This will be a
first step towards adjusting local management measures to reduce the
potential of soil collapse at a certain site.