Applicability of relative weights derived for Nuwara Eliya and Badulla regions to the areas with different terrain and climatological characteristics

Abstract

Landslides affect the life and economy of Sri Lanka frequently. The National Building Research Organisation (NBRO), Sri Lanka, has identified factors (i) bedrock geology, (ii) hydrology and drainage, (iii) surface overburden, (iv) slope angle range, (v) land use, and (vi) land forms as the major causative factors of Sri Lankan landslides. As these factors contribute in different degrees to initiate a landslide, they have been assigned subjective severity levels based on the characteristics of studied landslides. The numerical evaluation system, presently used by NBRO to assess the overall landslide hazard of a given site, has been derived through studying 1,076 landslides in Nuwara Eliya and Badulla districts. As NBRO has extended its landslide hazard mapping programme into other districts, verification of the applicability of weights derived through Nuwara Eliya-Badulla study to the other districts with different terrain and climatological characteristics has become a timely requirement. The researchers have selected the districts of Galle, Kalutara and Kegalle for this verification. Galle and Kalutara districts have gentler terrains than those in Nuwara Eliya and Kegalle which have similar rugged terrains. The Galle, Kalutara and Kegalle districts have higher soil moisture content than those in Nuwara Eliya and Badulla. The geology of all districts belong to the highland series, with differences in rock constituents and the structure. Similar to Nuwara Eliya, tea plantation is the major land use in Galle and Kegalle districts. The land use in Kalutara, is rapidly changing from rubber plantation to other commercial crops. All these regions have a recorded history of landsliding. These highlands are becoming rapidly populated and inappropriate land use practices also have contributed to the increasing frequency of landslides. Therefore, accurate mapping of landslide potential is essential for ensuring the safety of the people and to delineate the suitable land for development.