Kosi

Kosi, also spelled Koshi, is a major river in the eastern South Asia region, running through Nepal and India. It is part of the Ganges river system and plays a significant role in the hydrology and agriculture of the eastern Gangetic plains. In Nepal the river system is often referred to as Sapta Koshi, the Seven Rivers, reflecting its in-country tributaries.

Course and characteristics: The Kosi rises in the Himalayas and is formed by the convergence of several major tributaries in Nepal. It flows southeast across eastern Nepal, then crosses into India, passing through the Bihar plains before joining the Ganges in northern India. The river carries a heavy sediment load from the mountains, which continually shapes its dynamic floodplain and its channels.

Flooding and management: The Kosi is one of the most flood-prone rivers in the region, with annual floods causing loss of life and widespread damage in both Nepal and Bihar. To regulate flow and support irrigation, flood-control works and a barrage system have been developed on the river, with various upgrades over time. Despite engineering efforts, the Kosi remains susceptible to seasonal and monsoon-driven flooding, and channel shifts can disrupt local communities.

Ecology and economy: The Kosi basin supports substantial agricultural activity, including crops such as rice, maize, and pulses, aided by the nutrient-rich sediments deposited by the river. The floodplains sustain fisheries and provide livelihoods for many communities. The river’s ecology is linked to monsoon patterns, seasonal flows, and sediment dynamics, making water management an ongoing concern for residents along its course.

Names and significance: The river is a defining geographic feature in eastern Nepal and Bihar, shaping settlement, culture, and regional development.