Kosi, with its seven tributaries known as Saptkosi, drains the eastern part of Nepal and parts of Tibet. Some of the headstreams emerge beyond the Nepalese border in Tibet. Approximately 50 kms north of Indo-Nepal border, the Kosi is joined by its seven tributaries and breaks southwards through the Shivalik Hills at the narrow Barahkshetra gorge. The river then flows on the plains of northern Bihar on its way to Ganga meandering through a course of approximately 700 kms. Originating from the glaciers of Tibet and Nepal, the river is exceptionally turbulent because of the steep gradient flow in Nepal. It has the history of changing its course every 50 to 100 years. The main cause of Kosi changing its course is exactly the steepness and the consequent heavy silt it carries along with its swirling water. The river carries approximately 700 lakh tones of silt every year, which is almost five times the sediment load of any other river in Bihar.