Evacuation of earthquake-triggered landslide sediment by rivers in the Nepalese Himalaya: insights from Gorkha 2015

Abstract

This loan was part of an ongoing effort by our team and collaborators (funded by two GCRF grants, one NERC grant and NERC PhD studentships) to understand the influence of sediment transport from mountains to basins on flooding risk for the populations living in the Indo-Gangetic Plain. In particular, the Gorkha earthquake has caused widespread landsliding, therefore contributing large amounts of sediment to the river system. This loan was part of Emma Graf’s PhD project, which is aiming to constrain the timescales of sediment transport from source areas (landslides in mountains) to sedimentary basins (Indo-Gangetic Plain). Emma's project combines numerical modelling with field surveys to better understand (1) how and how rapidly sediment from landslides is incorporated into the river sediment load, (2) how the characteristics of this sediment evolve downstream (grain size, gravel fraction), and (3) how quickly the "slugs" of sediment are moving downstream. The observables include topographic evolution of landslide deposits, grain size characterization of landslide and gravel bar deposits, and evidence of change in channel geometry, including river bed elevation and cross-section form (as a result of deposition or erosion).