Context: Amid the Bihar elections, the Prime Minister of India will inaugurate the historic Kosi Rail Mahasetu.

About the project

• The dedication of the Kosi Rail Mahasetu is a watershed moment in the history of Bihar and the entire region connecting to the North East. 
• In 1887, a meter gauge link was built in between Nirmali and Bhaptiahi (Saraigarh). During the heavy flood and severe Indo Nepal earthquake in 1934, the rail link was washed away and thereafter due to meandering nature of river Kosi no attempt was made to restore this Rail link for long period. 
• The Kosi Mega Bridge line project was sanctioned by Government of India during 2003-04. The Kosi Rail Mahasetu is 1.9 KM long and its construction cost is Rs. 516 Crore. This bridge is of strategic importance along the India-Nepal border. 
• The dedication of this project will fulfil the 86 year old dream and the long wait of the people of the region. 
• It will also enhance the accessibility as well as the nation's capability to transport Army and military-related equipment and materials from the northern part of India to northeastern parts of India.

About Kosi River 

• The Kosi river consists of seven streams namely Sut Kosi, Tamba Kosi, Talkha, Doodh Kosi, Botia Kosi, Arun and Tamber and is popularly known as Saptkaushiki. 
• These streams flow through eastern Nepal which is known as the Sapt Kaushik region. 
• The sources of seven streams of the Kosi are located in snow covered areas which also receive heavy rainfall. 
• Consequently, huge volume of water flows with tremendous speed. 
• Seven streams mingle with each other to form three streams named the Tumar, Arun and Sun Kosi. 
• They unite at Triveni north of the Mahabharata Range to form the Kosi. 
• The river enters the Tarai of Nepal after cutting a narrow gorge in the Mahabharata Range. 
• The joins the Ganga near Kursela in Katihar district of Bihar.
• Soon after debouching onto the plain the river becomes sluggish. 
• Large scale deposition of eroded material takes place in the plain region. 
• The river channel is braided and it shifts its course frequently. This has resulted in frequent devastating floods and has converted large tracts of cultivable land into waste land in Bihar. Thus the river is often termed as the ‘Sorrow of Bihar’. 
• In order to tame this river, a barrage was constructed in 1965 near Hanuman Nagar in Nepal. 
• Embankments for flood control have been constructed as a joint venture of India and Nepal.