The Mountains’ Shifting Soils

A new project brings together researchers from China, India, and Nepal to study sediment dynamics in the Koshi basin

Despite their height, the Himalayas are some of the youngest mountains in the world. This brings with it an element of fragility because many of the mountains’ formations have yet to permanently settle. Because of this, the Himalayas are highly vulnerable to erosion, and each year in the Koshi basin monsoon rains wash as much as 135 million tonnes of sediment into the rivers. These rivers, bulging with seasonal glacier and snow melt and rain, rush down to the Gangetic Plains, carrying loads of sediment along with them. The sediment is deposited on the plains’ flat riverbeds, and, over time, these riverbeds begin to rise. This prompts rivers to divert and meander to find new, easier paths, which can be dangerous for nearby communities. Over the past 220 years, the Koshi River has moved approximately 115 kilometres westward. In its wake, it has eroded farmlands, washed away crops, and displaced many people who live on the densely-populated plains surrounding it.

The aim is that the project will not only break new ground of our understanding of erosion and sedimentation processes in the Koshi basin, but also set an example of regional science collaboration on environmental challenges.

In order to better understand the Himalayas’ transboundary geomorphological processes, the Koshi Basin Programme has started an integrated, basin-wide study looking at the causes of land degradation and the impacts of erosion and sediment in relation to water related hazards. The study, which began in 2014 and will continue until 2017, brings together cross-border expertise from the three Koshi basin countries. Using GIS technology, land modelling, and statistics, the Institute of Geographic Sciences and Natural Resource Research, which is part of the Chinese Academy of Sciences, is conducting research on land use and land cover change to understand the relationship between environmental factors and erosion. Researchers from the Indian Institute of Technology-Kanpur are using a landscape evolution model to understand the movement of sediment and its overall relationship with the basin’s rivers, and Nepal’s Department of Hydrology and Meteorology is collecting data from five sediment stations in the upper section of the Koshi basin to analyse erosion processes. The aim is that the project will not only expand the understanding of erosion and sedimentation processes in the Koshi basin, but also set an example of regional science collaboration on environmental challenges.

While the research is still in the early stages, some advancements have already been made. Researchers working on land use have produced a series of maps and an accompanying paper that details soil loss over 20 years, and have marked out conservation priority areas on which to focus future management. These areas are mostly in the hilly and mountainous regions of Nepal and the Tibet Autonomous Region of China.

Taken together, the project’s goal is to create transboundary knowledge around erosion and sediment dynamics in the Koshi basin that will help in designing sustainable management and hazard mitigation plans in the future. Proper management requires an understanding of where sediment comes from and how it is distributed on a basin-wide level. With this knowledge, planners can design stable water channels and dams, promote smart soil conservation practices, and encourage irrigation schemes that lessen erosion and help the region to avoid future disasters.