Modelling the erosional susceptibility of landslide catchments in thick loess: Chinese variations on a theme by Jan de Ploey

In his 1990 paper (Catena, 17: 175–183), Jan de Ploey proposed a system whereby catchments are viewed as functional units in which geomorphic work results from the combined effects of water erosion and mass movements. His measure of erosional susceptibility of catchments, ES, introduced the gravitational potential in addition to the kinetic energy of the eroding agents. This modelling of the erosional susceptibility of catchments in terms of energy was being used to explore time-dependent variations of ES when Jan de Ploey died. Also at this time, he extended an invitation to the present authors to test and extend his model using our data base on the landslide-dominated catchments in the thick loess country of north-central China. aper presents a series of new equations expressing variations in ES using a data base for over 200 landslides in the loess-covered mountainous terrain (relative relief up to 1500 m) of the Lanzhou region of eastern Gansu Province. These equations express the loss of potential energy of the landslide mass in relation to the relative relief and the pressure energy input in the form of rainfall. These indices of erosional susceptibility can be used to analyse the differences in response, from one catchment to another and through time, between the characteristics of vegetation cover including land use, hydrology, geomechanical behaviour, and mechanisms of movement on slopes. certain assumptions on percentage area of catchments affected by mass movement and long-term mean annual precipitation in the Lanzhou region, the Es equation suggests an estimate for non-clayey materials of about 10−4 m−2/s−2, which is a significantly higher susceptibility value than the mean worldwide value for non clayey materials obtained by De Ploey.