Bathurst JC

Bovolo CI

Research on landslide incidence has tended to focus on threshold relationships and has only recently started to look into predicting the location, timing and magnitude of landslide events as a function of climate and geomorphology. In addition, only a few studies consider the post landslide effects of erosion or downstream sediment transport in rivers and most models are limited to areas of a few square kilometres or less. The SHETRAN landslide model is a physically based system which can predictively examine shallow landslide and debris flow incidence on a spatially distributed basis, at the scale of a catchment ( &lt; 500 km$^{2}$), as a function of land use and climate. As part of the European Commission LESSLOSS project (GOCE-CT-2003- 505448), SHETRAN was used to quantify the severity of landslide events and their sediment yield as a function of rainfall return period (RP). In addition, the timings and locations of landslide and debris flow occurrence were simulated in response to rainfall patterns of different combinations of intensity and duration. The study focussed on two areas, Valsassina 180 km$^{2}$ (Southern Italian Alps), and Ijuez 45 km$^{2}$ (central Spanish Pyrenees). The results show that the number of simulated landslides increases much more rapidly for increases of RP from 2 to 5 years, than for increases of RP beyond 10 years. This is in agreement with recent observations in New Zealand. A high intensity, single peak rainfall event produced similar number of landslides as a constant low intensity rainfall event of the same duration. Where rainfall increased to a peak at the end of the event, fewer landslides were produced, whilst the least number of landslides were produced where rainfall decreased from a peak at the start of the event. In general, landslides occur at the peak of the rainfall event or at the time of maximum soil saturation but vary according to rainfall distribution and magnitude patterns. Graphs of the number of landslides as a function of rainfall event intensity and duration are given as a series of curves which can be compared with existing thresholds and show the severity of the event in terms of the number of landslides for a given rainfall condition

Modelling the timing and location of shallow landslides and debris flows using the SHETRAN model.

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