Abstract
In this paper a rainfall threshold and a Bayesian probability model are presented for the landslide occurrence of shallow landslides in Ha Giang city and the surroundings, Vietnam. The model requires the data on daily rainfall combined with the actual dates of landslide occurrences. Careful study on the database is a prerequisite for the paper. For this reason, selecting the input data was carried out carefully to ensure the reliable results of the study. The daily rainfall data covering a time span of 57 years was collected from a unique rain gauge station of National Centre for Hydro-meteorological Forecasting of Vietnam (from 1957 to 2013) and a landslide database with some landslides (37 of total of 245 landslides) that containing dates of occurrence, was prepared from historical records for the period 1989 to 2013. Rainfall thresholds were generated for the study area based on the relationship between daily and antecedent rainfall of the landslide events. The results shows that 3-day antecedent rainfall (with the rainfall threshold was established: RT = 40.8 − 0.201R3ad) gives the best fit for the existing landslides in the landslide database. The Bayesian probability model for one-dimensional case was established based on 26 landslides for the period 1989 to 2009, daily rainfall data with the same time and the values of probability varies from 0.03 to 0.44. Next, the Bayesian probability model for two-dimensional case was generated based on 11 landslides, rainfall intensity and duration in three months (May, June and July) of 2013 and the values of probability ranges from 0.08 to 0.67, and computed values of conditional landslide probability P(A|B) from two-dimensional case of Bayesian approach are clearly controlled by rainfall intensity > 40 mm with rainfall duration > 0.3 day.
Highlights
Landslide occurs every where on over the world, especially in the small and medium river basin, along traffic road, mountain foot area in the mountainous areas in the countries under the influence of climate and storms.Landslide studies have been carried out from very long time ago until now
The Bayesian probability model for two-dimensional case was generated based on 11 landslides, rainfall intensity and duration in three months (May, June and July) of 2013 and the values of probability ranges from 0.08 to 0.67, and computed values of conditional landslide probability P(A|B) from two-dimensional case of Bayesian approach are clearly controlled by rainfall intensity > 40 mm with rainfall duration > 0.3 day
Landslide triggering is significantly controlled by an empirical minimum rainfall threshold: RT = 40.8 − 0.201R3ad
Summary
Landslide occurs every where on over the world, especially in the small and medium river basin, along traffic road, mountain foot area in the mountainous areas in the countries under the influence of climate and storms.Landslide studies have been carried out from very long time ago until now. The early studies about the rainfall intensities and duration associated with shallow landslides and debris flows were carried out by Caine [1] He and some scientists who published their previous studies supposed that the effect of rainfall in producing shallow (less than 2 or 3 meters deep) landslide and debris flow activity is an obvious one, though one that is difficult to define precisely. This difficulty arises because rainfall only influences slope stability indirectly, through its effect on pore water conditions in the slope material and because its influence requires an interaction with other characteristics of the waste mantle
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