Evaluation of shallow landslide-triggering scenarios through a physically based approach: a case study from Bulathsinhala area, Sri Lanka

Abstract

Transient Rainfall Infiltration and Grid-based Regional Slope-stability analysis (TRIGRS) is a regional, physically based stability model which could be applied to predict shallow landslides. It is important to evaluate the accuracy of TRIGRS for the prediction of landslide locations using actual events before use the TRIGRS model for further applications. This study presents the application of TRIGRS for Bulathsinhala area, Kaluthara in south western part of Sri Lanka where the number of shallow landslides occurred on 26th May 2017 and many of those events transitioned into damaging and killing debris flows. A back analysis of that landslide event was executed to authenticate the model by using different methods and techniques for the definition of the input parameters. Reliability of the model was evaluated through comparison with the 2017 landslide inventory in the particular area and it was revealed that most of the actual landslides were occurred in the predicted area (FS<1) of the model. In order to quantify the effectiveness of the model, an index was proposed in the study called LRclass (landslide ratio for each predicted FS class). The obtained values of the LRclass index realize the trustworthiness of the model which indicates the considerably higher value (60%) for the lowest stability class. With this particular manner, the output of the study could be used to implement more reliable land use management and development plans and resettlement procedures. Further the TRIGRS model is advantageous for susceptibility mapping and landslide flow path analysis, particularly when linked with various advanced applications using GIS spatial functions.