The GBM River Basin System

The Gangas, Brahmaputra, Meghna, which is the acronym for GBM, river basin system is a popular concept of water resource management in the southeast Asia subcontinental area. 

The GBM is a transboundary river system spanning five countries: Bangladesh, Bhutan, China, India and Nepal. [1] 

The GBM basin covers an area of 174.5 million hectares, across parts of the four Eastern Himalayan countries of Bangladesh and India (all three rivers), Bhutan (the Brahmaputra), Nepal (the Ganges), and the Tibet Autonomous Region (TAR) of China (the Brahmaputra and Ganges). [2]

With an average run-off of around 1,200 km³, it constitutes the third-largest hydrological region in the world. [3]

The Ganga basin has around 1,087,000 sq. km. whereas the Brahmaputra basin possesses 552,000 sq. km. and the Meghna basin holds approximately 82,000 sq. km. simultaneously. The GBM basin is home to approximately 700 million people, comprising over 10% of the world’s population. [2]

The drainage basin inside Bangladesh is only about 7% of the total drainage basin and the rest 93% is from the outside of Bangladesh.

The annual average sediment discharge is more or less in the range of 1.2 to 1.7 billion tons.

References:

1. BRIDGE in the Ganges-Brahmaputra-Meghna river basins (BRIDGE GBM) | IUCN

2. (1) (PDF) Why Eastern Himalayan countries should cooperate in transboundary water resource management (researchgate.net)

3. Ahmad, Q. K., Biswas, A. K., Rangachari, R. & Sainju, M. M. (eds) (2001). Ganga-Brahmaputra-Meghna Region: A Framework for Sustainable Development. The University Press Ltd, Dhaka.