Teesta River

Teesta and Rangeet Confluence

The Teesta River originates from the Pahunri (or Teesta Kangse) glacier above 7,068 metres (23,189 ft), and flows southward through gorges and rapids in the Sikkim Himalaya.[2]

It is fed by rivulets arising in the Thangu, Yumthang and Donkha mountain ranges. The river then flows past the town of Rangpo where the Rangpo River joins, and where it forms the border between Sikkim and West Bengal up to Teesta Bazaar. Just before the Teesta Bridge, where the roads from Kalimpong and Darjeeling join, the river is met by its main tributary, the Rangeet River.[3]

Teesta River Bridge Inscription

At this point, it changes course southwards flowing into West Bengal. The river hits the plains at Sevoke, 22 kilometres (14 mi) northeast of Siliguri, where it is spanned by the Coronation Bridge linking the northeast states to the rest of India. The river then goes merging up with the Brahmaputra River after it bifurcates the city of Jalpaiguri and flows just touching Cooch Behar district at Mekhliganj and moves to Fulchori in Bangladesh.[4]

Through its course, the Teesta river has carved out ravines and gorges in Sikkim meandering through the hills with the hill station of Kalimpong lying just off the river. Variegated vegetation can be seen along this route. At lower elevations, tropical deciduous trees and shrubs cover the surrounding hills; alpine vegetation is seen at the upper altitudes. The river is flanked by white sand which is used by the construction industry in the region. Large boulders in and around the waters make it ideal for rafting enthusiasts.

Between Rangpo town and the railway bridge (popularly called Lohapul or iron bridge) on it as it enters the plains at Sevoke, the Teesta flows with a very strong current, ideal for white river rafting. Towns like Teesta Bazaar and Melli have facilities for group rafting. Though the river looks innocuous, the underlying current is very strong. In 1915, G.P. Robertson, the then Municipal Engineer of Darjeeling, drowned after losing control of the boat in the turbulence while surveying the river. The boat struck a partially hidden boulder and was sucked in by a whirlpool, leaving no trace of the occupants.

During the monsoons, Teesta river distends its banks; both in size and turbulence. Landslides in this region often dam up parts of the river in this season.

James Rennell's 1776 map shows an earlier flow of the Teesta meeting the Ganges in three channels before a devastating flood in 1787 changed its course

Great changes have taken place in the course of some of the rivers in Bengal and the adjoining areas, during the period since 1500 CE. Although positive evidence is lacking, similar changes can be assumed in the remoter past. The Teesta River is one of the rivers that has changed over the years.[5]

The Teesta earlier ran due south from Jalpaiguri in three channels, namely, the Karatoya to the east, the Punarbhaba in the west and the Atrai in the centre. The three channels possibly gave the name to the river as Trisrota "possessed of three streams" which has been shortened to Teesta. Of these three, the Punarbhaba joined the Mahananda. The Atrai passing through a vast marshy area known as Chalan Beel joined the Karatoya and the united stream joined the Padma (Ganges) near Jafarganj. In the destructive floods of 1787, the Teesta river forsook its old channel and rushing south-east it joined the Brahmaputra.[5] James Rennell made a survey between 1764 and 1777 and his maps are one of the earliest authentic maps of Bengal in existence. In these maps Teesta is shown as flowing through North Bengal in several branches—Punarbhaba, Atrai, Karatoya, etc. All these streams combined lower down with the Mahananda, now the westernmost river in North Bengal, and taking the name of Hoorsagar finally discharged into the Ganges at Jafarganj, near modern Goalundo. The Hoorsagar river still in existence, being the combined outfall of the Baral, a spill channel of the Ganges, the Atrai, the Jamuna or Jamuneswari (not the main Jamuna through which the Brahmaputra now flows), and the Karatoya, but instead of falling into the Ganges, it falls into the main Jamuna, a few miles above its confluence with the Padma at Goalundo.[6]

British Engineering - Teesta Suspension Bridge in Sikkim (1894)

Coronation Bridge across Teesta in West Bengal.

India has an estimated total hydroelectric power potential of 84 GW (at 60% load factor). Of this, Sikkim's potential share is 2.9%, or about 4.29 GW. As of 2010, 13.9% (594 MW) of Sikkim's potential had been implemented and was under operation, 44.8% is under implementation (1919 MW), and another 41.3% (1773 MW) is yet to be examined from environment and engineering design perspective.[7]

The successfully completed major projects and dams are:

1. Teesta -V dam, the largest project so far, was completed in 2007 on Teesta in Dikchu, East Sikkim district. Its height is 87 metres (285 ft) and its length is 176 metres (577 ft). It generates 510 MW hydroelectric power and assists flood control.[8]
2. Rangit III hydroelectric project was completed in 2000 on Greater Rangit River which is a tributary of Teesta River. The catchment area of Rangit III dam is 979 square kilometres (378 sq mi) and the dam is 47 metres (154 ft) high. The project has 60 MW generation capacity, and is already online.[9]

The other three completed projects are significantly smaller and minor—Lower Lagyap, Upper Rongni Chhu and Mayang Chhu projects.[7]

Teesta Barrage on the river Teesta, Bangladesh.

The Teesta Barrage is a major irrigation project in Bangladesh, in Lalmonirhat District.[10] Construction started 1979 and was completed in 1997–98.[10]

Disputes over the appropriate allocation and development of the water resources of the river have remained a subject of conflict for almost 35 years, with several bilateral agreements and rounds of talks failing to produce results.[11][12][13][14]

Teesta river area is in the seismically active Zone-V and has experienced micro-seismic activity. According to India's Ministry of Environment & Forests, the Teesta river dam projects have been approved with the requirement that they adopt suitable seismic coefficient in the design for the dam, tunnel, surge shaft and power house. The projects are cascaded over the length of the river, do not store large amounts water, have small reservoirs, and therefore the projects are expected to have very low risk from the reservoir induced seismicity in the area.[7]

The Teesta river has preserved good imprints of climatic and tectonics along its valleys and catchments. The interrelationship between climate, erosion, deposition and tectonic activities is not properly understood to date. These are being studied.[2][15][16]

View of the Teesta river from Teesta Bridge of Bangladesh on March 2019. Downstream.

• Tista River at GEOnet Names Server
• Mesbah-us-Saleheen (2012), "Tista River", in Sirajul Islam and Ahmed A. Jamal (ed.), Banglapedia: National Encyclopedia of Bangladesh (Second ed.), Asiatic Society of Bangladesh