Teesta River

• The Teesta River (or Tista) is a river in the Indian state of Sikkim. It is 309 kilometres (192 miles) long.
• Teesta River originates from the Tso Lhamo Lake at an elevation of about 5280 m in the North Sikkim district.
• The Teesta river starts at Pahunri glacier, and flows south through rapids in the Sikkim Himalaya. The river goes by the town of Rangpo.
• It is the right bank major tributary of the Brahmaputra river system. Like many other major Himalayan rivers of India, like the Ganga, Teesta is a glacier-fed river.
• It changes course southwards flowing into West Bengal, before joining the Brahmaputra River.
• In Bangladesh, the Teesta joins the Brahmaputra on its right bank, from where the river is known as the Yamuna. Then, it finally merges with the river Padma, which falls in the Bay of Bengal. 
• Historically, the Teesta river system was considered the major tributary of the Ganges. 
• The major portion or the greater part of the river basin lies in India and only 17% of it is in Bangladesh. 
• Teesta basin is home to around 30 million people, 2% in Sikkim, 27% in West Bengal; and 71% in northwest Bangladesh.
• Sikkim is mountainous with very low population density, whereas West Bengal has a mix of low hills and plains, and in Bangladesh, the terrain is almost flat. 
• There are two major large barrages on Teesta that diverts water for mainly irrigation purpose:
  • Gajoldobha in India
  • Duani in Bangladesh.

Major tributaries of Teesta river

• The tributaries on the eastern flank are shorter in the course but larger in number whereas the tributaries on the western flank are much longer with larger drainage areas, consequently contributing much more amount of discharge to the main Teesta river.
• The left bank tributaries originate from semi-permanent and much smaller snowfields as compared to right bank tributaries. Right-bank tributaries drain heavily glaciated areas with large snowfields. 
• Major Tributaries of Teesta River
  • Left-bank Tributaries: Lachung Chhu, Chakung Chhu, Dik Chhu, Rani Khola and Rangpo Chhu.
  • Right-bank Tributaries: Zemu Chhu, Rangyong Chhu and Rangit River.

Rainfall pattern

• The Teesta river is characterised by heavy rainfall and floods in the monsoon season. 
• In the north Sikkim region, due to steep slopes and uneven elevation, these extreme events lead to slope transformation, landslides, and erosion. 
• These events are responsible for the deposition of suspended sediments in the river channel. 
• The northern parts of Teesta river basins are dry and cold, whereas the southern and middle parts are hot, humid and wet.