Sediment dynamics and connectivity drive the river hazards in the Kosi basin in the central Himalaya

WEBINAR SERIES ON GEOSCIENCE FOR SUSTAINABLE DEVELOPMENT (EPISODE NO 10)

Date: October 04 (Sunday), 2020
Time: 17:00 NPT (+5:45 GMT)

Welcome to the 10th episode of the Webinar series on GeoScience for Sustainable Development: " Sediment dynamics and connectivity drive the river hazards in the Kosi basin in the central Himalaya" this Sunday (October 04, 2020, 17:00 NPT (+5:45 GMT))

Register here

Presenter: Prof. Dr. Rajiv Sinha, Department of Earth Science, Indian Institute of Technology, Kanpur, India

Moderator: Asst. Prof. Dr. Basanta Raj Adhikari

Sediment dynamics and connectivity drive the river hazards in the Kosi basin in central Himalaya

The geomorphic and climatic settings strongly influence the hydrology and sediment transport characteristics of a large river system. The upper Kosi basin in Central Himalaya covers an area of 52731 km2 draining through Tibet and Nepal. The rainfall in the upper Kosi basin has large regional and temporal variations due to considerable orographic contrast with a basin average value at the mountain exit (Chatara) of 898 mm/yr. Seven major tributaries namely, the Indrawati, Bhote Kosi, Tama Kosi, Dudh Kosi, Sun Kosi, Arun, and Tamor join at different points and the combined annual water and sediment discharge at Chatara are measured as 1546 m3/s and 101 Mt respectively before it debouches into the plains of north Bihar, India. Such high sediment fluxes in the Kosi basin have been considered as the central problem influencing multiple hazards such as river dynamics, bank instability, and floods, particularly in the alluvial parts of the basin. Further, the model, efficiency, and scale of sediment transfer in a catchment are controlled by the degree of linkages between the different landscape components (i.e. sediment connectivity). The northern Tibetan part of the Kosi basin is poorly connected and transport very little sediments. The well-connected western parts of the Kosi constituting ~34% of the basin area contribute ~40% of the total sediment load at Chatara. This is in contrast to moderately-connected eastern and central parts with 8% and 56% of the basin area which bring in ~16% and 44% of total sediment flux respectively. These fluxes assume significance because the Kosi is a transport-limited system, and therefore, several reaches of the basin, particularly in the alluvial part, are characterized as highly aggrading leading to frequent avulsion and extensive flooding. It is argued that the spatial analysis and cross-correlation of hydrology and sediment connectivity are essential in order to develop effective sediment management strategies and to mitigate the associated hazards in large river basins where systematic field investigations are not feasible.