Limnology report on the Teesta River

by Rohan Nath

Introduction 

In India, Teesta is one of the major rivers that originate from Himalayan glaciers along with  Brahmaputra, Ganga, Jhelum, and Sutlej (Fig. 1). More than 1.3 billion people living  downstream depends upon the major rivers system of the Himalayan glaciers for water. The  Teesta River originates at an elevation of 5033-m from the Tso Lhamo Lake in North Sikkim. Khangse glacier, Pahunri glacier and Chho Lhamo Lake are also considered as the source of  the Teesta River.

Fig. 1. Teesta Basin and its streams with local points. Image Source: Goyal, M. K., &  Goswami, U. P. (2018). Teesta river and its ecosystem. In The Indian Rivers (pp. 537- 551). Springer, Singapore.

Geography 

Snow and glaciers cover the upper portion of the catchment area of Teesta River and the  lower portion is covered with forest. Canyons and narrow valley in Sikkim and highlands of  Kalimpong is a result of the Teesta River flow. The vegetation cover changes with elevation,  from tropical deciduous vegetation in the lower elevation zone to alpine vegetation in the  high elevation zone. The Teesta basin in Sikkim is divided into five geo-eco-climatic zones  based upon the geo-morphological ecological and climatic regimes (Table 1). 

Table 1. 

Sl. No. Zone Elevation
1. Sub-tropic zone Up to a 1000-m elevation
2. Warm temperate zone Between 1000 and 2000 m
3. Cold temperate zone Between 2000 and 2500 m
4. Cold zone Between 2500 and 4000 m 
5. Frigid zone Above 4000 m 

Hydro-climatology 

Heavy rainfall and floods dominate the Teesta River basin in the monsoon season. It can lead  to landslides, slope transformation, and erosion which deposits suspended sediment in the  river channel. The huge variation in the elevation from 8598 to 213 m within 100 km is the  primary reason for an abrupt change in the climate. The Teesta River basin has an average  annual rainfall ranging from 2000 to 5000 mm. The rainfall varies throughout the seasons  (Table 2). 

Table 2. 

Season Rainfall
Winter 0.7%
Summer 13.6%
Monsoon 80.2%
Post-monsoon 5.5%

Slope variation 

The Teesta Basin slope profile varies from 8598 m to 213 m (Fig. 2). 

Characteristics of soil 

The diversity of soil type is large in the Teesta basin (Fig. 3). In the hilly terrain, random  construction, extensive deforestation, random use of land, slope cultivation and improper  drainage system are the common issues. To save the natural resources in mountainous  regions, it is crucial to practice water and soil conservation. 

Fig. 2. The variation in slope in the Teesta Basin. Image Source: Goyal, M. K., &  Goswami, U. P. (2018). Teesta river and its ecosystem. In The Indian Rivers (pp. 537- 551). Springer, Singapore.

Socio-economic and environmental characteristics 

Large infrastructure projects like a dam and/or hydro-power projects help in the economic  development but affect the environment and the socio-economic values for downstream  communities. Few favourable/unfavourable effects are: 

i. The construction changes land use and increases soil erosion.

ii. The disposed construction material degrades the water quality. 

iii. The hydrologic regime, siltation and sedimentation are disturbed.

iv. Indiscriminate fishing and migrant fish species increase the pressure on aquatic  ecology. 

v. The power generation increases employment and revenue.

Fig. 3. The soil characteristics of Teesta Basin. Image Source: Goyal, M. K., & Goswami,  U. P. (2018). Teesta river and its ecosystem. In The Indian Rivers (pp. 537-551). Springer,  Singapore.

Natural hazards 

Natural hazards like landslides, floods, glacial lake outburst floods, and drought are most  likely due to climate change and global warming. Sikkim is prone to earthquakes and  landslides and hence is the most vulnerable zone for natural hazards. Numerous landslides in  Sikkim Himalaya affect the river morphology and hydrology.  

Many waterbodies and glacial lakes in the Sikkim Himalayas are vulnerable to outburst. This  can change the hydrology and geomorphology of the river system. 

Conclusion 

The Teesta River originates with a high altitude of 5033m and forms the right-bank tributary  of the Brahmaputra River. Due to the high altitude, it has a high hydroelectric power  production potential. Six hydroelectric projects are proposed in the Teesta River with the  Teesta stage II hydropower project being the largest power generation project in Sikkim (Table 3). Hence, understanding the hydrological process and water resources management  and planning are important. 

Table 3. 

S. No. Name of project Capacity (MW)
1. Teesta Hydro-electric Project Stage-I 280
2. Teesta Hydro-electric Project Stage-II 480
3. Teesta Hydro-electric Project Stage-III 1200
4. Teesta Hydro-electric Project Stage-IV 495
5. Teesta Hydro-electric Project Stage-V 510
6. Teesta Hydro-electric Project Stage-VI 440

Reference 

1. Goyal, M. K., & Goswami, U. P. (2018). Teesta river and its ecosystem. In The Indian  Rivers (pp. 537-551). Springer, Singapore.

Published by LakesOfIndia

Lakes of India is an E.F.I initiative aimed at sensitizing the larger public on freshwater habitats across the country. A blog platform where one can read about lakes across India. You can become a guest blogger to write about a lake in your hometown and initiate an action to protect that lake.

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