A spatio-temporal framework for modelling shallow landslides along mountainous transport corridors

Rainfall-induced shallow landslides affect transport infrastructure by reducing serviceability and increasing road maintenance costs. These impacts are likely to become more severe with climate change. The aim of this research was to develop a framework to assess the spatio-temporal stability of slopes along transport corridors for decision support. The developed approach couples daily soil water balance with a widely used physically-based model: Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability (TRIGRS). Performance of the framework was evaluated along the Mukamira – Kabaya national road that crosses a rugged topography in Nyabihu, Northwestern Rwanda. Spatio-temporal analyses conducted on landslide inventory in the road corridor indicated that the road has been susceptible to shallow landslides originating both from roadcuts and elsewhere in the road corridor.  The observed temporal increase in landslides density in the corridor underscores an escalating threat to the road. Consequently, incorporating temporal variability of landslide predictors into future projection can assist to better understand prospective landslide activity in the road corridor, and the subsequent impact on the road. Applying a water balance model as input into TRIGRS provides a more realistic temporal assessment of initial soil moisture conditions and, in turn, a more relevant evaluation of triggering rainfall magnitudes. Using historic weather data, the framework showed capabilities of tracking variations of stability conditions of the roadside and forecasting the road sections that could potentially become blocked by road cut shallow instabilities. The framework highlights road sections exposed to distinct hazards, e.g. debris slides or debris flows paths. For landslide risk assessment, using historical data it was possible to link observed landslide occurrences to soil moisture and triggering rainfall conditions. It was also possible to estimate probable mobilised volumes of debris to be deposited on the road. In addition, the framework enabled evaluation of deteriorated shear strength of road cut materials on future projections of stability. For existing roads, the framework provides an important contribution to enable road asset managers to develop effective and economic maintenance plans. For the development of new roads, this framework can assist with the optimisation of alignment and cutslope morphology.