OVERALL FEATURES OF MULTIPLE LAND-SLIDES ALONG TRISHULI RIVER TRIGGERED BY THE 2015 GORKHA EARTHQUAKE, NEPAL

Abstract

 We adopt a depth-integrated particle method to analyze overall features of multiple landslides along Trishuli River, Nepal, which area was devastated by the Gorkha Earthquake, April 25, 2015. Considering the difficulty in obtaining material properties of weathered matters of metamorphic rock accumulated along gorges on valley walls, the number of material parameters used in this evaluation procedure is limited as small as possible; the initial failure slope angle, i_f, Manning coefficient, n, for the flowing soil-water mixture, the angle of repose, i_d, at which the mixture on its depositional area stops spreading, and the rain concentration, RC, an index to describe rain-water collectivity of gulleys. We applied the procedure to our target area along the canyon of Trishuli River, Nepal. The result from this study indicates that weathered matters remaining on 41-degree slopes or steeper are in the critical equilibrium, and can be detached at any time. However, even debris deposits on gentler slopes such as the one in Ramche show creeping movements, and we need to keep a vigilant eye on these slopes.