Invited Speaker: Basanta Raj Adhikari
Title: Importance of landslide Early Warning System for the sustainable risk reduction in the Nepal Himalaya
Basanta Raj Adhikari is an engineering geologist at the Department of Civil Engineering, Pulchowk Campus, Institute of Engineering, Tribhuvan University Nepal, also affiliated with the Institute for Disaster Management and Reconstruction, Sichuan University-Hong Kong Polytechnic University, Chengdu, China. He has done his PhD in Earth Science from the University of Vienna, Austria. His research interests are climate change, hill-slope movement and human interaction, Himalayan sediment flux generation, community-based disaster risk reduction for different kinds of natural disasters e.g. landslide, flood, earthquake. He has published more than a dozen research papers in both national and international journals and received various recognitions for his work in the field of earth science.
Abstract
Nepali Himalayas are one of the seismically active mountain belts in the world with several kilometres of relief and very prone to catastrophic mass failure. The collision between Indian and Eurasian plates resulted in numerous tectonic faults and highly deformed rocks which are responsible for triggering many earthquakes of different scales. High grade of rock weathering and subsequent torrential rainfall is directly related to increasing the numerous geo-hazard problems i.e., landslides, debris flow, and floods, etc. The Mw 7.8 Gorkha Earthquake-2015 has ruptured a 150-km long section of the Himalayan décollement and triggered more than 19332 co-seismic landslides in central Nepal. These landslides are carrying a large volume of sediment to the rivers and deposited in valleys and foothill of the Himalaya. Several catastrophic valley infills are quite interesting in the Himalayas and urgently needed for gauging and predicting the recovery times of seismically perturbed mountain landscapes. In this context, outstanding research on Pokhara valley has suggested that this valley was formed due to catastrophic events in ~100, 1255 and 1344 C.E based on radiocarbon dates from peat beds, plant microfossils and humic silt in fine-grained tributary sediment. Moreover, mountains slopes are unstable due to reoccurring earthquakes and intense rainfalls. E.g., a high-intensity rainstorm (540 mm in 24 hours) in July 1993 hit central Nepal and 52 houses were destroyed and 62 persons were killed by debris flow and deposited 5.1 million m3 sediment volume in the Kulekhani Reservoir.
Gorkha Earthquake-2015 has shattered rock mass forming cracks and these phenomena can represent a major part of the overall disaster with an impact that can last for years before restoring to background condition. These landslides can be done with the help of both structural and non-structural measures to reduce the impact of geo-hazard in this region. The research on community-based landslide risk reduction has clearly shown that small scale intervention can be a fruitful solution for low-income countries like Nepal, however, structural measures are not always sufficiently effective due to the ain and unpredictable geological as well as meteorological conditions. In such conditions, non-structural measures such as Landslide Early Warning Systems (LEWS) is piloted by increasing community awareness and monitoring system. Based on landslide susceptibility map, topography and need of the community, LEWS system has been piloted in one of the major landslides triggered by the earthquake in the Nepali Himalayas to understand the surface dynamics and relations between rainfalls with surface movement. The locally developed Flash Flood Early Warning System will be useful for prediction of flood and can significantly reduce the destruction of life and property.