The rivers flowing from Bhutan into India have changed dramatically in the last few years. Small Himalayan rivers like the Gaurang, Beki, Namlang, Daranga and many others which used to be well fed in the months of June and July now run dry. Even transboundary rivers originating in the sub-Himalayan areas such as the Sunkosh, Manas, Champabati, Aai and Dhanshiri are running shallow.

These changes are new, barely a decade old, and not well understood. They follow from repeated flash floods that have resulted in the dumping of a huge amount of sediment and silt. This has changed even the slope of the riverbeds, making them far less steep, slowing down the flow of river waters.

Glacial Lake Overflow Floods (GLOFs), cloud bursts and Landslide dam outburst flood (LSDOFs) have all resulted in flash floods. While flash floods are significantly different from normal floods in terms of cause, propagation, intensity, impacts, predictability and management they are generally not investigated as a separate class of events but are rather reported as a part of the overall seasonal floods situation. This means that these new activities are neither reported on, nor managed, in a manner that would best suit them.

Moreover the floods now carry massive sand deposits as the sharp hills have been eroded by the waters. It is suspected many mining and development activities like dam building may also be responsible for sand and stone deposition in the river beds.

Industry by the Kala river in Samdrup Jongkhar district, Bhutan

As Bhutan has become richer, and invested more in dam building and infrastructure this development has led to further erosion. The sediment resulting from these activities – mostly sand, boulders, pebbles and shingles – now choke the transboundary rivers. This type of sediment contains less organic nutrients, which negatively impacts agriculture in these regions. Sand deposits used to extend from 5 to 10 kilometres in to the southern plains as the rivers entered the state of Assam. Now, according to local people, this area has stretched to at least 20 kilometres downstream.

Anil Swargiary, a local farmer said, “Flash floods that become frequent in the last 10-15 years are responsible for this transformation. Every year flash floods erode the river bank in different directions and the river bed became shallow, wide and full of sand. Flash floods transformed vast stretches into deserts within the last two decades. In some areas sand deposition is as deep as 7 feet. Land along the river banks full of alluvium yielded rich harvests two decades back are now abandoned due to desertification.” In the past land that had been inundated by floods could be reclaimed in 3 to 5 years, but now in some cases no vegetation has arisen even after fifteen years.

As the river flow become less regular the people living downstream move away from the river into the forests, leading to deforestation and encroachment.

assam bhutan

Local people are becoming more dependent on the forests for firewood

A change in Himalayan river system has, therefore, now triggered changes in the population distribution, density, migration and occupations of the people that live beside them. The inhabitants of the India-Bhutan border are by and large poor, and depend heavily on the land and natural resources for their livelihoods.

Water flowing from Bhutan’s Himalayas sustains the lives and livelihoods of millions of people residing in plains of Assam and West Bengal. More than 80% of people in the region live near rivers to have water accessibility. Some 70% of the region’s population is food-energy deficient, a proportion almost as high as that in desert region. At the same time rice, the staple food in the region, requires huge amounts of both water and energy to grow. For many families collecting drinking water is an arduous task. Generally women walk half a kilometre or more to fetch water. On the other hand, with loss of livelihood, many young people have turned to the business of sand mining and stone crushing both legally and illegally.

According to Professor Abani Kumar Bhagwati, department of geography in Gauhati University, climate change and local deforestation are mostly to blame. “Deforestation wiped out natural barriers to check the materials that are carried by the rivers and flash floods and deposited in the wider river-beds in the plains. Apart from rising temperatures in the Hindu-Kush Himalayas as a whole, intense seasonal precipitation in the Bhutan Himalayan foothills triggers a variety of natural hazards,” he said.

The geomorphology of the rivers has also changed. The rivers have bhabar formations. These consist of alluvial sediments, but now they are mixed with boulders, pebbles, sand and silt. As the bhabar have changed they have caused erosion around the wider edges of the river, widening the rivers, and sometimes causing the rivers to flow out of their banks, cutting through the fertile fields and causing erosion in the plains.

The Daranagar river on the Indo Bhutan border

The Darangar river on the Indo Bhutan border

A combination of building activity in Bhutan, and changes in rainfall patterns are now making major changes to the land, having knock-on effects that few can fully foresee. Unfortunately because the effects are felt most by the poor, researchers and the policy community have paid little attention. It may be wise for researchers to start looking at these neglected areas before the changes become irreversible.

2 comments

  1. Before, the news stories from India always blamed the dams in Bhutan releasing water during heavy rain… when all dams in Bhutan are “run-of-the-river” and do not hold storage water… or uncontrolled logging..
    Now, its development activity in Bhutan causing flash floods? Why?

    Any studies on this? Are these locations not in the foot hills of Himalayas and in naturally occurring “alluvial fans” and flood plains?

    Observation will also tell you that most of the flash floods come out of valleys with hardly any development and large forest cover. Even within Bhutan, all the numerous flash floods come in areas valleys with hardly any settlements, but areas that seem to naturally channel excessive rain.

    Of, course, there is increased risk from changing climate and rain patterns and increased run off from development, but the real dangers of development comes from people settling and building in floodplains and disaster prone areas of a natural “alluvial flood pan”.

  2. Hydropower development in Bhutan has gained considerable ground as a sector capable of
    contributing to the development of the country through the export of power. Some of the
    major hydropower projects in the region are the Tala, the Kurichu, the Basochu, the
    Punatsangchu, and the Mangdechu. The Sankosh project – the biggest in Bhutan – is the only
    multipurpose project. However, these developmental activities are often impacted by natural hazards which are common in this region due to its geography. Owing to Himalayan tectonic movements, Bhutan is prone to natural hazards including landslides. Caused by seismicity and high precipitation, landslides at times lead to the damming of steep narrow valleys of the high rugged mountains of Bhutan, as these valleys are blocked by relatively less material. The breaching of such landslide-dams can cause serious hazards.
    In 2004, the artificial landslide-dammed Tsatichu lake (which was formed 30 km upstream of
    the Kurichu Hydel Project in Bhutan) burst, and water from the reservoir flowed into two
    tributaries of the Brahmaputra – the Manas and the Beki – spelling disaster for the people
    downstream. The Kurichu Hydropower Corporation authorities opened the reservoir gates to
    avoid major destruction to the dam and other casualties. A significant amount of Manas’s landmass and forest cover has already been washed away following excess water release from Kurichu dam.While there is demand for a dialogue with Bhutan to resolve the issue amiably, the Bhutan foreign ministry has clarified through an official statement that
    the Kurichu Hydropower Project is a run-of the-river scheme, not a storage scheme. Small diversion dams like Kurichu, according to the ministry, are constructed solely for the purpose of generating electricity and do not store water. While not denying the landslide dam breakage and consequent flooding of downstream villages in July 2004, government sources reiterated that water levels in dams like Tala, Chukha, and Kurichu were normally kept below the full reservoir level to provide some cushion against a sudden rise in the inflow of water.
    Bhutan’s officials also denied that the 2007 monsoon flood in Assam was caused by excess
    water in dams in Bhutan, as the Central Water Commission of India had reported.
    The managing director of the Druk Green Power Corporation, D. Rinzin, clarified that the
    waters discharged through the dams of all the hydropower projects in Bhutan are normal
    discharges from the rivers, and reiterated that in the event of any flushing of the silt and logs
    that may accumulate behind the dams, and consequent opening of the reservoir gate, prior
    permission from the Central Water Commission of the Indian government is mandatory.
    According to Rinzin, the storage capacity of the Kurichu dam is equivalent to about four
    hours of peaking generation, and as such, release from a reservoir of such limited capacity
    will have minimal impact on the overall natural river discharge.
    But, the high point of the conflict was the raging flood due to the Kurichu landslide dam
    breakage, which caused extensive inundation, widespread devastation to standing crops,
    homestead, life and property, disruption of road and rail communication, public utilities,
    water supply installations, irrigation structures and flood control structures downstream. The
    Manas biosphere reserve was also affected. Highways were inundated and bridges collapsed.
    This was an instance of how water allowed to pass through a reservoir can lead to severe destruction in downstream areas. The Central Water Commission is a key Indian institution and is fully involved in the construction of the Kurichu project. The government of India and that of Bhutan have established a Joint Expert Team on Flood Forecasting and Flood Warning, which meets twice a year. According to a decision in the first meeting of the JGE, a Joint Technical Team (JTT) on Flood Management between the two countries was constituted which held its first meeting in April 2005 and submitted its report in January 2006. The JGE reconstituted the JTT with the Chief Engineer, CWC, Shillong as its India team leader. The firstmeeting of the reconstituted JTT was held in Bhutan on 13-16 September, 2010.
    It is feared a breach in the newly blocked Wabrachu lake or Tsatichu lake may
    once again generate such flood waves downstream. So the need of the hour is to reduce the
    huge volumes of debris and loose material flow deposited downstream of the Tsatichu
    confluence, which may lead to another breach in the near future.
    When conflict situations arise due to water infrastructure issues, authentic and effective
    participation is necessary in an appropriate timeframe when decisions about the project and
    mitigation of its impacts can be influenced. While initiating dialogue for water conflict
    resolution issues like the Kurichu dam initiated flash flood, the voices of those directly
    affected need to be heard, comprehended, and necessary action initiated to counter negative impacts. To allay fear of the destructive impacts of dams being built in Bhutan, study teams need to dispatched to the dam site to gather first hand information so that a correct evaluation can be made about the need for intervention and a dialogue towards finding solutions.
    Ref: http://www.indiawaterportal.org/sites/indiawaterportal.org/files/kurichu.pdf
    http://www.ercindia.org/…/Aaranyak%20concern-dams%20&%20WHS%20in

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.