The Brahmaputra River of South Asia is the fourth largest river in the world, in the aspect of annual discharge. The lower Brahmaputra River basin is prone to catastrophic flooding with major social, economic, and public health consequences. There is relatively little rainfall and snowfall information for the watershed, and the system is poorly understood hydrologically. Using a combination of available remotely sensed and gauge information, this study evaluates snow cover, rainfall and monsoon period discharge for a 14-yr time period during 1986-99.
The interannual rainfall variability is low and is a weak predictor of monsoon discharge volumes in the Brahmaputra basin. Strong evidence is found, however, that maximum spring snow cover in the upper Brahmaputra basin is a good forecaster of the monsoon flood volume. Despite the temporal and spatial limitations of the data, this study`s analysis demonstrates the potential for developing an empirical tool for predicting large flood events that may happen as an annual early window for justifying flood damages in the lower Brahmaputra basin, which is home to around 300 million people.
As the river Brahmaputra enters Arunachal Pradesh, it is called Siang and makes a very rapid flow from its original elevation in Tibet, and finally comes out in the plains, where it is called the Dihang River. This river flows for about 35 km and is joined by two other major rivers: Dibang and Lohit. From this point of convergence, the river becomes very wide and is called Brahmaputra. It is joined in Sonitpur District by the Jia Bhoreli and called the Kameng River where it flows from Arunachal Pradesh and then flows through the entire expanse of Assam. In Assam the river is at times as wide as 10 km.
Between Dibrugarh and Lakhimpur districts the river divides into two different channels---the northern Kherxhutia channel and the southern Brahmaputra channel. The two channels again join about 100 km downstream forming the Majuli island. At Guwahati near the ancient pilgrimage site of Hajo, the Brahmaputra flows through the rocks of the Shillong Plateau, and is at its narrowest at 1 km bank-to-bank. Because the Brahmaputra is the narrowest at this point the Battle of Saraighat was fought here. The first rail-cum-road bridge across the Brahmaputra was opened to public in April 1962 at Saraighat.
The old Sanskrit name for the river is Lauhitya, however the local name in Assam is Luit. The native inhabitants or the Bodos called the river Bhullam-buthur that means `making a gurgling sound`. This name was later Sanskritized into Brahmaputra.
The Brahmaputra is less polluted river in India, if compared to other rivers. The main problem related to this river is petroleum-refining units, which contribute most of the industrial pollution load into the basin and other medium and small industries. The main problem facing the river basin is that of regular flooding. Floods have been occurring more often in recent years with deforestation, and other human activities being the major causes.
The main rivers in the Brahmaputra basin are Brahmaputra River, Lohit River, Burhidihing River, Dihing River, Kameng River, Manas River, Sankosh, Yamuna, Teesta River, Rangeet River, Lachen River, Lachung River, Darla River and Jaldhaka River.
