Abstract
Mass movement in Sri Lanka is mainly triggered by heavy rainfall. International literature is rich of works defining rainfall intensity-duration models to identify the rainfall threshold for various types of Mass movement. However, studies have not focused to establish a relationship between intensity and duration of rainfall in Sri Lanka. Therefore, this study focused to establish rainfall intensity-duration models to identify the rainfall threshold for mass movements in Badulla district in Sri Lanka, where forty four (44) rainfall events that resulted in same number of landslides during the last three decades were considered. Results indicate the rainfall threshold relationship fits to the log linear model of the exponential function, I = α·D-β. The constructed I-D curve revealed that short duration ( 54 mm/h) in rainfall events can potentially trigger the landslide. However, long-duration (>8 h) and low-intensity (<25 mm/h) in rainfall events may also trigger mass movements in Badulla. As per the results, most mass movements occur during northeast monsoons and inter-monsoons. In general, higher mean rainfall intensities trigger the debris flows, while long-duration rainfall events can trigger both landslides and debris flow. When compared to Sri Lankan mass movements triggering threshold intensities are fairly higher than the global threshold values. It confirms that within Badulla, mass movements are triggered by very high intense and/or long duration rainfalls events only. Further, time series analysis of the rainfall events shows an upward trend of extreme rainfall events, which increased landslide occurring frequency in last six (6) years.
Highlights
Landslide acts on natural and engineered slopes in steep topography [1] [2]
This study focused to establish rainfall intensity-duration models to identify the rainfall threshold for mass movements in Badulla district in Sri Lanka, where forty four (44) rainfall events that resulted in same number of landslides during the last three decades were considered
The I-D threshold for mass movements is identified on an I-D plot as the minimum rainfall for which a landslide could occur (Chen, 2015)
Summary
Landslide (mass movements) acts on natural and engineered slopes in steep topography [1] [2]. Various methods have been proposed in the literature to predict rainfall conditions that are expected to trigger mass movements [5] [12] [13]. These studies have been focused on rainfall parameters such as rainfall intensity, duration, cumulative rainfall, and antecedent rainfall [12]. Relationships between rainfall intensity and duration are the most common estimate of rainfall thresholds for landslides [14] [15] [16]. Different types of empirical rainfall thresholds for possible initiation of landslides are proposed in the literature. Most of the similar studies in the Indian subcontinent have established intensity-duration (ID) thresholds, thresholds based on the total event rainfall, and rainfall event-duration thresholds [18]
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