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 (<2 h) and high-intensity (>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.
Groundwater flow and accumulation within a landslide mainly govern its movement along the slip surface. Thus, a comprehensive understanding of the subsurface flow regime would be imperative in mapping the landslide body. Geoelectrical resistivity can be used to detect the significant changes in the ground caused by water flow and accumulation. A systematic vertical electrical sounding (VES) at selected locations would provide preliminary information on the subsurface nature of the landslide that can guide future surveys including 2-D electrical resistivity traversing. A VES survey using Schlumberger electrode configuration was carried out at the creep-type landslide that occurs on the southwestern part of the
A sufficient knowledge on prehistoric culture and habitat of earliest Homo sapiens (Balangoda man) is available in Batadomba-lena cave, a noticeable rock shelter in lowland rainforest of southwestern Sri Lanka goes upto Pleistocene and Holocene eras. Late Pleistocene inhabitants of Batadombalena cave’s foraged for a broad spectrum of plant and mainly arboreal animal resources such as, monkeys, squirrels and rainforest snails etc. Archaeo-faunal evidence would help to describe the prehistoric man eating behavior as well as availability of nature pre-historic flora, fauna and environmental status. The family Acavidae is very sensitive to climatic variations, hence used as a bio-indicator to describe the variations of paleo-climatic nature. This study examined the morphological features of 20 samples of Acavidae family (living/fossil samples of Acavus superbus, and sub fossil samples of Oligospira waltoni) collected from soils by digger method in 2005 and compared with 20 samples from the same area at presently available. The shell characters of snails such as, height, width, diameter of mouth, thickness of lip, and angular of axis were measured and subjected to multivariate analysis to understand how climatic variability and nature of paleo-diet contribute survival of Acavidae species. Results showed that Acavus superbus living species had large shell characteristics than the sub fossils. Results of similar study in the same climatic status in 2000 showed that the shell measurements of Acavus superbus are relatively larger than both living and sub fossils in Batadobalena cave. Ordination diagram derived from species shell characteristics showed that Acavus superbus living species grouped as scattered /diffuse clusters, while sub fossil species grouped as a single cluster at the center of the ordination diagram. It is imply a trend of speciation /diversification of Acavus species from Pleistocene era to date. Multivariate analyses prove that, a strong positive correlation of species characteristics, such as height (r = 0.62), thickness of lip (r = 0.544) and angular of axis (r = 0.744), and a strong negative relationship (r = 0.832) for shell width for the species were observed. Our results are useful to compare with other fossil snails to see whether the climate change influence for changing body size. In conclusion, palaeo-environment, and present environment variation has been occurred in minimum way without much changes to observed Acavidae species compositions present and past.
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