Abstract

The annual water flow in Brahmaputra river is 537.2 km³ and the Brahmaputra basin has an area of 194.4 thousand km². The annual sediment yield from the Brahmaputra basin constitutes, 438.7 million tones of soil and 506, 81, 376, 18.2, 11.4, 45.8 and 34.9 thousand tones of N, P, K, Mn, Zn, Ca and Mg, respectively. The sediment yield from different states of the basin varies from 2126 to 2572 t km^-2, with a mean value of 2257 t km^-2. Both, the river and the streams/tributaries form an excellent sink for the sediments as 25.2% of the soil and 21.8% of the nutrient load gets deposited here. Only 51.4% of the soil and 57.6% of nutrients from the sediments are carried out of the basin towards sea, while rest is deposited in different sinks within the basin itself. The huge sediment load in the runoff to the river channel, results in an annual deposition of 9.5 mm sediment thickness on the river bed, thereby reducing its intake capacity and causing floods in the basin. About 72370 km² area in the basin has degraded with irreversible damage at some places, 31830 km² area in the basin is prone to floods while 3609 km² land gets flooded every year. All these processes have caused land and environmental degradation and ecological imbalance in the Brahmaputra basin. The prevalence of shifting cultivation has further aggravated the problem of soil erosion as it involves deforestation and the people are socio-culturally attached with the practice. The ground and surface water have been polluted due to the use of agricultural chemicals in the basin catchments.

Keywords: Sediment yield, Brahmaputra basin, socio-economic, environmental, implications