The Mighty Teesta River: Lifeline of Sikkim and Beyond

Teesta river

The Teesta river is an important river in the Indian states of Sikkim and West Bengal. Teesta river originates from Teesta Khangse glacier in Sikkim and flows through the state in a north-south direction for around 175 km before entering West Bengal.

Hereby, the UCN Team offers a comprehensive analysis, giving you key information and insights about Teesta river alongwith Teesta river maps.

The Teesta river basin has a total catchment area of 12,159 sq km, out of which 6,930 sq km lies in Sikkim state. The river and its numerous tributaries comprise the major drainage system in the state of Sikkim. Some of the major tributaries of Teesta river mentioned are – Lachung Chu, Chakung Chhu, Rangpo Chhu, Rangit river etc.

Considering the enormous river flow and steep gradient, Teesta river holds great potential for hydroelectric power generation. Teesta river sees a massive drop of around 3,300 m in elevation over its 175 km course through Sikkim, making it an ideal site for hydropower projects.

Physical Characteristics

Origin and Course

The Teesta river originates from the Teesta Khangse glacier located at an elevation of 5,280 m in the North Sikkim district. The glacier lies at the base of the Pauhunri peak (7,056 m).

The Teesta river then flows through the entire state of Sikkim in a north-south direction for around 175 km before entering the plains of West Bengal. Then finally merging into the Brahmaputra river in Bangladesh

Major tributaries

The Teesta river basin includes several important tributaries draining into it from both banks.

Left bank Tributaries of Teesta

Some of the key left bank tributaries of Teesta river in Sikkim are:

• Lachung Chu
• Chakung Chhu
• Dik Chhu
• Rani Khola
• Rangpo Chhu

Right bank Tributaries of Teesta

The major right bank tributaries of the Teesta river are:

• Zemu Chhu
• Rangyong Chhu
• Rangit River

These tributaries further have their own complex drainage system and several small streams draining into them.

Basin Characteristics

The Teesta river basin covers a total catchment area of 12,159 sq km as per the documents. Out of this, around 6,930 sq km lies in Sikkim state.

The basin includes several glaciers and snowfields which are important water sources for the river. As per the glacier atlas survey data, there are:

• 84 glaciers spread over a total area of 440 sq km in the Teesta basin in Sikkim
• 197 snowfields covering an area of 251 sq km

These glaciers and snowfields play a key role in feeding the Teesta river and maintaining year-round water flows. They store massive amounts of frozen water, which melts in the summer months and monsoon season and feeds into the Teesta river and its tributaries. For example, the total water equivalent estimated to be stored in the form of ice and snow is around 145 cubic km for the Teesta basin.

Therefore, the presence of extensive glaciers and snow-capped peaks makes the Teesta basin hydrologically very important in this region.

Climate and Hydrology

The Teesta river basin in Sikkim experiences a heavy monsoon rainfall regime, which accounts for most of its annual discharge.

The average annual rainfall over Sikkim is around 2,534 mm. Specifically, during monsoon the basin receives very heavy rainfall, with July recording 480 mm on average for the state.

In terms of river discharge, Teesta is a perennial river with substantial flows even in the lean winter months. At its lower reaches near the Sikkim-West Bengal border, the average annual runoff in Teesta is estimated to be 11,500 million cubic meters.

Therefore, the tropical monsoon climate, as well as glacial meltwater contribute enormously to the Teesta river flows. The rainfall peak coincides with summer melting season, which further augments river discharge during monsoon months.

Biodiversity and Threats

The Teesta river basin supports rich aquatic biodiversity owing to its unique location spanning different bio-geographic zones across plains and mountains.

Some key species mentioned are snow trout and golden mahseer. These coldwater fish species form important capture fisheries in the river.

However, this unique riverine ecology faces several threats:

• Hydropower projects along the river have impacts on river connectivity, water flows and sediment transport. Large dams can hamper fish migration and breeding.
• Deforestation in the watershed region leads to increased soil erosion and siltation, affecting habitats.
• Climate change is projected to alter monsoon rainfall and glacial meltwater patterns, which can severely impact the river hydrology and dependent biodiversity in the long term.

Therefore, maintaining adequate environmental flows and preserving key ecosystems is crucial for sustaining the biodiversity of Teesta river basin. The rich biodiversity also has important cultural, economic and aesthetic values for local communities.

Utilization

The most important utilization of the Teesta river is for hydropower generation. The Teesta river sees an enormous drop of 3,300 m in elevation from its origin in Sikkim till the plains. This makes its hydroelectric potential one of the best among Indian rivers.

Several major hydropower projects have been developed along the Teesta river and its tributaries, like Teesta-VI ( Power project is a 500 MW run-of-river project under construction in Sikkim). Many more projects are planned, with a total installed capacity of over 5,000 MW anticipated just within Sikkim state over the coming decade.

Besides hydropower, Teesta river water is also utilized for public water supply to major towns in Sikkim such as Gangtok, Singtam, Rangpo etc. The projected future water demand for domestic use in various urban centres in Teesta basin, amounts to over 35 million litres per day.

Other significant uses of Teesta resources are:

• Irrigation
• Inland fisheries
• Tourism and recreation
• Biodiversity conservation

Thus the Teesta river basin serves a multitude of environmental, economic and socio-cultural needs of the region. However, an integrated approach is required for sustainable management of Teesta’s resources.

Issues and Concerns

Some significant issues and concerns regarding the Teesta river are:

• Water sharing dispute between India and Bangladesh – The downstream riparian conditions of Bangladesh depend heavily on the Teesta river flows received from the Indian stretch. However, India and Bangladesh have a longstanding conflict over sharing of Teesta waters, which also impacts diplomatic relations. Achieving an amenable bilateral solution is challenging.
• Biodiversity impacts of developmental activities – As described earlier, rich aquatic and terrestrial biodiversity in the basin faces threats from activities like hydropower development. Maintaining adequate environmental flows and implementing impact mitigation measures remains a concern.
• Sedimentation – Deforestation and land use changes are accelerating soil erosion and sediment fluxes in the Teesta river. Increased sediment deposition downstream is impacting river morphology, bank erosion and flooding events.
• Floods – Flash floods and changing flood regimes associated with climate change pose a rising risk to riparian communities. Effective early warning systems, risk-informed planning and disaster management capacities need strengthening.

Balancing Teesta’s development with ecological sustainability concerns involves reconciling the needs and interests of various stakeholders in the basin as well as regional politics. Ongoing research and advocacy regarding these issues is vital.

Final Thoughts

In the UCN team’s careful evaluation, the Teesta river basin is clearly of immense ecological, social and economic importance in the region. From its origin as a glacier-fed stream to its vast floodplains, the Teesta river ecosystem influences various communities through its provisioning of water, energy, fisheries and livelihood sources.

However, increasing developmental pressures pose substantial risks of degrading the very resource base that local livelihoods depend upon. Habitat loss threatens unique aquatic biota, while floods and erosion continue to challenge riverside inhabitants. Conflicting inter-state water interests further confound basin management.

Truly adopting the principles of Integrated River Basin Management can pave the path for equitable and sustainable solutions. This includes public participation, scientific considerations of environmental flows, cooperative institutions for fair water allocation and robust regional impact assessment frameworks for planned interventions in the basin.

By safeguarding the incredible biodiversity and rich water endowment of the Teesta, the shared natural heritage of the region can continue benefitting communities into a just future.