The River Teesta said to be the lifeline of the Indian state of Sikkim, flows for almost the entire length of the state, carving out verdant Himalayan temperate and tropical river valleys. The emerald coloured river then forms the border between Sikkim and West Bengal before joining the Brahmaputra as a tributary in Bangladesh.Course:
The river originates from Cho Lhamu Lake at an elevation of 5,330 m (17,500 feet) above sea level in the mighty Himalayas. This lake lies to the north of the Donkia Pass near Shetschen, where the summit of the pass is about eight kilometres north-east of Darjeeling as the crow flies.
The Teesta River is then fed by rivulets which arise in the Thangu, Yumthang and Donkia-La ranges. The river then flows past the town of Rangpo where it forms the border between Sikkim and West Bengal up to Teesta Bazaar. At Teesta Suspension Bridge, which joins Kalimpong with Darjeeling, the river is met by its main tributary, the Rangeet River. At this point, it changes course southwards flowing entirely into West Bengal. The river hits the plains at Sevoke, where it is spanned by the Coronation Bridge which links the north east states to the rest of India. The river then courses its way to Jalpaiguri and then to Rangpur District of Bangladesh, before finally merging with the mighty Brahmaputra at Fulcherry (in Bangladesh).
Geography:Through its course, river has carved out ravines and gorges in Sikkim meandering through the hills with the hill station 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 the towns of Rangpo and Lohapul, 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 an innocuous looking river, the underlying current is very strong. In 1915, G.P. Robertson, the then Municipal Engineer of Darjeeling, while surveying the river, drowned after losing control of the boat in the turbulence. The boat then struck a partially hidden boulder and was sucked in by a whirlpool, leaving no trace of the occupants.
During the monsoons this humble river distends its banks; both in size and turbulence. Landslides in this region often dam up parts of the river in this season.
Great changes have taken place in the course of some of the rivers in Bengal and the adjoining areas, during the period since 1500 AD. Although positive evidence is lacking, similar changes can be assumed in the remoter past. The Teesta is one of the rivers that has changed over the years. .
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 and corrupted 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 near Jafarganj. In the destructive floods of 1787, the Teesta forsook its old channel and rushing south-east it joined the Brahmaputra.
Rennel 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 is 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.
Proposed Dams:India has proposed a huge 31 Billion Dollar series of Dams within the Teesta river that will lead to 50,000 MW within the next 10 years. With some of the largest sediment loads, the creation of a resivoir will lead to only increased pressure on an active fault area. There are concerns that the creation of these dams may lead to river induced seismicity.
Climate and tectonics of Tista river:
Tista river has preserved good imprints of climatic and tectonics along its valley and catchments.The significant fluvial landscape of the Tista river has been described by few workers e.g Archarya, Mukhopadhyay,Malay Mukul,Ingocha Meetei Lukram etc.International papers published about Tista river can be counted within fingers.Recent paper of Mr.Ingocha Meetei Lukram suggested that climate change, particularly on a millennial to multi-millennial scale, during late Quaternary had strong system-wide influence on sediment production, transport and deposition in the Tista (Teesta) river system (Meetei et al., 2007) The interrelationship between climate, erosion, deposition and tectonic activities is not properly understood to date. However, it appears that major alluviation and incision events could be ascribed to the factors associated with climatic processes such as strengthening or weakening of monsoonal precipitation and related fluvial discharge. Tectonic activity affects sediment fluxes and is responsible for the insetting of younger terraces/fanlobes into the older terraces/fanlobes. During seismic events, landslide activity along the slopes of river valleys influences sediment delivery into the valleys, causing the effects of tectonics to be intricately coupled with that of climate (Meetei et al. 2007). The terraces and floodplains, valley-side slopes and landslide slopes, alluvial cones of different generations, kettle shaped depressions, sickle shaped ranges, leveled plains, undulating plains and deeply-dissected valleys, glacial and periglacial deposits are some of the geomorphological features observed in the Teesta river basin in Sikkim (Mukhopadhayay, 1982). Three prominent knick points have been observed along the Teesta river profiles which correspond to the zones of tectonic discontinuities, the important ones being the MCT and MBT (e.g. Seeber and Gornitz, 1983). From the recent studies of Mukul 2000,Mukul et al.,2007, it is proved that the southern part of the frontal wedge near foothill zone is tectonically active along with the formation of NKT,SKT and MFT structures within the sub Himalaya in Tista basin.
Kosi:
The Kosi (Kausiki), which now flows through the north-eastern Bihar and joins the Ganges at a point much higher up than Rajmahal, originally ran eastward and fell into the Brahmaputra. The channel of the Kosi, therefore, must have been steadily shifting towards the west, right across the whole breadth of North Bengal. There was a time when the Kosi and the Mahananda joined the Karatoya and formed a sort of ethnic boundary between people living south of it and the Kochs and Kiratas living north of the river
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