North-East India Rivers Profile (Brahmaputra Basin)

The profusion of rivers in the northeast India is simply unparalleled. There two major rivers Brahmaputra and Barak have been joined by tributaries in abundance – small and big, the bigger tributaries often surpassing some prime main stem rivers of other states of the country.

Interestingly, both Brahmaputra and Barak, after flowing through the length of the state, merges with other rivers at Bangladesh, to finally fall into the Bay of Bengal. On the other hands, both the rivers, notwithstanding their accompanying hydro disasters in the corresponding Brahmaputra valley and the Barak valley (also known as Surma valley) during monsoon, makes the floodplains fertile by the endowment of fine nutrient laden silt load.

Though, in the midst of the wilderness of the watersheds and pristine nature over large parts of the catchments, several tributaries flowing through urban and industrial stretches turned into causes of concern due to growing pollution and degradation of water quality. However, from qualitative aspects, futuristic scenario of the northeast rivers indicate their chance of survival as productive ecosystems because anthropogenic interventions has still not reached gargantuan proportion as in case of other important river systems of India such as the Ganges, and the Yamuna or rivers of the south like the Cauvery, the Krishna or the Mahanadi.

The Brahmaputra River System

ASSAM_Drainage_map1

Brahmaputra is a wealth of rivers – small and big. Northeast India with just five per cent of country‘s area has thirty per cent of the national water resource potential and its per capita water availability is 16,589 cubic meters as compared to the national figure of 2,208 cubic meters.

The Brahmaputra is known in different names along its course. Originating in the east of Kailash Mountain, it flows east of the Mansarovar lake along the Indus Tsangpo sutures known as Tsangpo. The river is known as the Brahmaputra along its traverse from Dibrugarh to Dhubri and as the Jamuna in the Bangladesh. It receives many tributaries all along its course of about 2800 km.

The total drainage area of the Brahmaputra river system from its origin to its mouth is 630000 km2, of which about a third,220000 km2, lie in Tibet. It drains an area of 200000 km2 in the Assam and the Bangladesh plains and 120000 km2 in the Himalaya. Only recently, in 2011 scientists from Chinese Academy of Sciences found that the origin of the Brahmaputra is the Angsi Glacier.

Mythology, Art and Culture

The name Brahmaputra finds its mention in Kalika Purana, a mythological text of Hinduism, which is believed to have been written around 10th Century A.D. (Dutta, 2001). The Santanu- Amogha-Parasurama myth finds place here and explains the origin of the river (Dutta, 2001).

The Tsangpo-Brahmaputra is considered sacred in India, Bhutan and Tibet by the population characterized by multiplicity of cultures. The literal meaning of its Tibetian name, Tsangpo, is the Purifier (Dutta 2001). In Hindu mythology, the river is considered to be sacred and thousands of people take a dip in Brahmaputra during the festival Ashok Astami.

Assamese folk songs, modern songs, Bihu songs are resplendent with river centric theme and is often linked to valour and glory of the Assamese people and also depicts the cultural mosaic of the valley. Reknown Bard of Assam Dr. Bhupen Hazarika wrote numerous poetry and songs centring rivers like the Brahmaputra, Kolong, Kopili, Digaru and many others.

In the field of fine arts, most of the landscape artists of Assam like Benu Mishra, Nilpaban Barua, have done vast numbers of paintings on river Brahmaputra and life on the river bank. Apart from numerous articles in Newspapers, Magazines and Academic Journals, a number of important books published on the Brahmaputra.

Physiography, Geomorphology and Climate

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The Brahmaputra valley separates the sub-Himalayan foothills from the Shillong plateau and the Patkai-Naga hill ranges. The Mizo hills and the Barail ranges die out towards the west and south west into the plains of Cachar, which is a part of Surma-Kusiyara valley.

The bank of the Brahmaputra, for the most part, is extremely unstable. Bank failures are rampant and are a result of frequently changing flows, coupled with the fragile geology of the river banks.

The Brahmaputra valley is characterized by humid sub-tropical climate with four distinct climatic seasons, pre-monsoon, monsoon, post-monsoon and winter. The region is influenced by the southwest monsoon, which accounts for 90% of the annual precipitation in the range between 2500 and 3200 mm causing severe flooding during the rainy season.  Northern and southern part of the valley has comparatively less rainfall.

Major tributaries and sub-tributaries of the Brahmaputra Basin

Originating from Kailash ranges of the Himalayas at an elevation of about 5150m, river Brahmaputra flows through Tibet (China), India and Bangladesh for about 2900m and joins the Ganga. The river receives a number of tributaries at the north and south banks, in the catchment area within India. The major tributaries and sub tributaries of the Brahmaputra are as follows:

Brahmputra 7

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Wetlands in Brahmaputra Basin

 

The floodplains of the Brahmaputra and Barak rivers is dotted with a large number of wetlands, numbering more than 3,500, covering an area of around 1,01,232 ha.(Singh et al., 2013), which have great significance as unique habitats for exquisite varieties of flora and fauna and also as natural flood water retention rservoirs. These wetlands, home to a variety of fishes and other aquatic fauna, also act as ideal natural habitat for both domestic and migratory birds. The lake-like water bodies are locally known as beels, while the swampy areas are variously called as Jolah, Pitoni, Doloni, Doba, Hola, Khal etc. 

Major human settlements and structures

The characteristic features of the braided river is numerous amount of big and small sandbars known locally as “Char”, separated by several distributary channels, these char areas are of different sizes and permanency. Away from the core, and with the river bed becoming shallower, flood havoc is extensive, making permanent settlement impossible. Fringe char areas are prone to high rate of erosion and thus less frequented by settlers (Singh et a).

Structural interventions for flood protection

Assam has 3 % of total population & less than 1% land mass of India whereas it has 9 % of the total flood prone area of the country. The data shows it has suffered extreme damage due to flood annually both to humans and its rich biodiversity owning to its topographical & climatic setting. In this approach physical structures are envisaged to prevent the flood waters from reaching potential damage regions. The main structural measures undertaken so far in the Brahmaputra basin are as follows.

  1. Embankments, Floodwalls, Flood levees
  2. Dams and Reservoirs
  3. Natural Detention Basin
  4. Channel Improvement
  5. Drainage Improvement
  6. Diversion of flood water
  7. Catchment area treatment/ afforestation
  8. Anti-erosion works

The sediment load is significant for the rivers of the region (Mahanta et al.,2004) leading to high turbidity values. Sediment load in rivers raises the channel bed and thus leads to flood during monsoon, exhibiting a particular water quality profile.

Sediment load in the Brahmaputra Basin

The sediment flux of the Brahmaputra River system is consistently estimated to be higher than that of the Ganga River system. This is despite the fact that the Brahmaputra River drains a shorter arc of the Himalaya than that of the Ganga. The monsoon climate generates higher runoff for the Brahmaputra than for the Ganga. Tectonic uplift may be more active in the eastern side than on the western side of the Himalaya. Nevertheless, little is known about erosion in the eastern Himalaya and it is difficult to analyse the origin of the difference between the two Himalayan basins (Singh and Lanord, 2002).

Pollution of Rivers in Brahmaputra Basin

Studies (Mahanta et al, ) revealed that there is serious threat to some rivers of Brahmaputra basin from pollution due to the rapid industrialization and urbanization. The high monsoonal flow to the rivers of the basin is very significant in diluting the pollutant almost throughout the year, whereas river water quality scenarios become critical for most of the tributaries in the dry season, particularly in urban areas. Although the rivers have not been worst impacted by pollution so far, rivers flowing through urban areas are highly threatened.  Urban centers of the region are lacking in proper waste disposal, sewage or storm water management systems. Besides, watershed degradation due to the growing urbanization has led to increase in yield of non-point pollutants like sediment into the rivers.

Brahmaputra 10.png

Conflicts over Rivers

The management challenges have emerged and loomed large, especially because of the lack of the ecosystems perspective. While interlinking of rivers have been thought without considering the ecosystem concerns, hydropower projects and other forms of anthropogenic interventions in upper reaches of the sub-basin are also devoid of the same.

However, the concerns raised by India about the hydropower project in the Tibetan boundary does not hold much ground from the ecological, social, and economic standpoint, as there is neither much water flow, nor much sediment load in the upper reaches of the basin to really affect the downstream economy.

Climate change impacts in the Brahmaputra Basin

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The effect of climate change on the Brahmaputra basin is expected to be strong due to three major reasons i.e. Influence of snow and ice melt on stream flow, increased monsoon rain intensity, increase in sea level rise hampering the drainage of rivers. Bolch et al., (2010) found that the glaciers in this area have been retreating at a rate of around 10 m/year for the period 1976 to 2009.  A study by (Mahanta et.al, 2014) infers a gradual increase of temperature in the Brahmaputra basin. The increase of temperature ranges from 0°C to 4.5°C by 2050 & from 0°C to 6°C. The average increase of monthly temperature ranges from 1.3°C to 2.4°C by 2050 & 2°C to 4.5°C by 2100, with the increase more in dry and winter months than in monsoon.

Conclusion

From qualitative aspects, futuristic scenario of the northeast rivers indicate their chance of survival as productive ecosystems because anthropogenic interventions has still not reached gargantuan proportion as in case of other important river systems of India such as the Ganges, and the Yamuna or rivers of the south like the Cauvery, the Krishna or the Mahanadi.

Although flood has negative implications to public life and property, ironically annual flooding also acts as a cleansing mechanism by taking all the physical and chemical contaminants of the entire Brahmaputra floodplain, starting a new cycle every year. Most of the solid, municipal and industrial wastes actually get diluted and diffused by the heavy monsoonal surge in the river.

Evaluating the status of a large unique alluvial river like Brahmaputra with respect to hydrology, morphology, water quality and biodiversity is almost of impossible proportion – particularly when future scenarios due to enhanced pollution load compounded by less understood phenomenon like climate change impact is considered.

Brahmputra 2

The role of annual seasonal flooding in terms of rejuvenating the grassland ecology and supply of particulate nutrients to the floodplain is undeniable and needs to be continued. Yet, unusually high flood and lack of adequate treatment during dry season are two extreme annual challenges. The condition of urban tributaries receiving municipal pollution load is inexplicable.

While some rivers of the northeast are severely polluted, most rivers have moderate or low pollution mainly due to their rejuvenated life every year during monsoon season. However, there are rivers on the verge of extinction which is the cause of greater concern. It is an entirely different story for rivers which are flowing through intensively urbanized areas like Guwahati, Jorhat, Aizawl. There are concerns about some relatively smaller but highly polluted rivers flowing through densely populated region which are facing death as a pristine ecosystem or some of the rivers can be described as dead rivers.

Examples of highly polluted rivers which are mainly flowing through the urban areas are the Bharalu in Guwahati city, the Bhogdoi in Jorhat, Kolong in Nagaon, Imphal River through Imphal, and Tlawng River through Aizawl. These rivers have been observed to be having very poor quality of water, full of sludge even during the rainy season. Although contaminants in the rivers are diluted during rain and flooding, but as soon as the monsoon is over, they become extremely polluted once more as the rivers mostly drain city and urban drainage. So a greater focus of the polluted northeast rivers pertains to those urban rivers which not only have been deprived from natural fresh water flow from upstream, but they have essentially turned into urban drainages.

These dying rivers needs special attention, strong policy intervention as well as stringent measures for their restoration as well as conservation keeping in mind future urban population increase, industrial effluents and solid waste dumping. These rivers needs initiatives of greater dimensions like structural measures to treat waste water, to develop river front and to maintain both freshwater flow and quality. The threatened rivers obviously cannot be restored in their entirety in a short span but at least should be maintained in reasonably good health so that it should not become a perpetual source of disease burden to the people living on the bank of the rivers. It can only be hoped that adequate steps not long before are taken to ensure sustainable health of these precious entities of our constantly changing landscapes and society.

A report by Dr. Chandan Mahanta 

Notes:-  

 

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