The Teesta River originates from Teesta Khangtse Glacier, west of Pahunri (or Teesta Kangse) glacier above 5,400 m (17,700 ft), and flows southward through gorges and rapids in the Sikkim Himalaya.[3]
After this point, Teesta river changes its course southwards flowing into West Bengal and some more tributaries like Relli River, Riyang river, Geil Khola etc joins. Than the river hits the plains at Sevoke, 22 km (14 mi) northeast of Siliguri, where it is spanned by the Coronation Bridge and Sevoke Railway Bridge linking the northeast states to the rest of India. After crossing Sevoke, the river is fed by some small tributaries like Chel Khola, Neora Khola, Leesh Khola etc, and than reaches Gajoldoba where there is Teesta Barrage. The river then flows through Jalpaiguri, where Jalpaiguri Teesta Bridge links Northeastern States. The river flows further down through Mekhliganj and HaldibariinCooch Behar district, where it is spanned by Joyee Setu, the longest roadway bridge of West Bengal with length 3.8 kilometres.
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 and the city of Siliguri at the foothills of Himalaya. Variegated vegetation can be seen along this route. At lower elevations, tropicaldeciduous 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.
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 monsoon, Teesta river distends its banks; both in size and turbulence. Landslides in this region often dam up parts of the river in this season. It has also caused severe flooding, multiple times during monsoon in Bangladesh.[6][7]
In the past, the Teesta flowed south from Jalpaiguri in three channels: the Punarbhaba, Atrai and Karatoya Rivers. The Teesta changed course as a result of the flooding of 1787, turning southeast to become part of the Brahmaputra.[8]
Hydel project on the Dikchu, a tributary of Teesta
The Teesta Barrage is a major irrigation project in Bangladesh, in Lalmonirhat District. Construction started 1979 and was completed in 1997–98.[9]
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.[10]
The successfully completed major projects and dams of Teesta River System are as follows:
Dikchu River Hydroelectric Power Project: Output: 96 MW on Dikchu River, tributary of River Teesta, Location - Dikchu, Gangtok district, Sikkim. Constructed by- Sneha Kinetic Power Projects Pvt. Ltd.[23][24]
Disputes over the appropriate allocation and development of the water resources of the river have remained a subject of conflict between India and Bangladesh for almost 35 years, with several bilateral agreements and rounds of talks failing to produce results.[26][27][28]
Negotiations have been going on since 1983.[29][30][31] In 1983, a temporary solution had been worked out— Bangladesh would get 36%, India would get 39% while the rest of the water remained unallocated.[30] Both countries signed a water sharing treaty in 1996 which would look into water sharing between the two countries in general following the Ganges water dispute.[30] The water sharing remains a challenge.[30]
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.[10]
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.[3][32][33]
^ abcMullick, M. R. A.; Babel, M. S. & Perret, S. R. (2011). "Discharge‐based economic valuation of irrigation water: Evidence from the Teesta River, Bangladesh". Irrigation and Drainage. 60 (4): 481−492. doi:10.1002/ird.597.
^ abMeetei, L. I.; Pattanayak, S. K.; Bhaskar, A.; Pandit, M. K.; Tandon, S. K. (2007). "Climatic imprints in Quaternary valley fill deposits of the middle Teesta valley, Sikkim Himalaya". Quaternary International. 159 (1): 32–46. Bibcode:2007QuInt.159...32M. doi:10.1016/j.quaint.2006.08.018.
^Chaudhuri, Samita; Chaudhuri, Utpal (2015). And the Teesta Flows... Niyogi Books. p. 188. ISBN978-93-83098-70-5.
^"Teesta-V D01535". India Water Resources Information System. National Remote Sensing Centre. Government of India. Archived from the original on 18 October 2014. Retrieved 15 June 2014.
^Mukul, Malay (2000). "The geometry and kinematics of the Main Boundary Thrust and related neotectonics in the Darjiling Himalayan fold-and-thrust belt, West Bengal, India". Journal of Structural Geology. 22 (9): 1261–1283. Bibcode:2000JSG....22.1261M. doi:10.1016/S0191-8141(00)00032-8.
^Mukul, Malay; Jaiswal, M.; Singhvi, A. K. (November 2007). "Timing of recent out-of-sequence active deformation in the frontal Himalayan wedge: Insights from the Darjiling sub-Himalaya, India". Geology. 35 (11). The Geological Society of America: 999–1002. Bibcode:2007Geo....35..999M. doi:10.1130/G23869A.1.
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