The Kosi’s sorrow, and scopeExploring Nepal’s largest river during a destructive monsoon
- Three decades after it was first proposed, a 26.5km tunnel starts supplying water from Melamchi to Kathmandu.
- A deadly flood on the Melamchi-Indrawati in Sindhupalchok on 16 June kills at least 27 people, and destroys infrastructure.
- The much-delayed 465MW Upper Tama Kosi hydropower plant starts feeding electricity to the national grid.
- SJVN says it has completed half the work on the 900MW Arun III project and the Investment Board awarded it another contract to develop the 679MW Lower Arun as well.
- Work has begun on the Sunkosi-Marin Diversion, to channel water to the Bagmati Basin and irrigate much of Province 2.
All five events have one thing in common: they are all on the trans-boundary Kosi Basin that drains 75,000 sq km of territory in China, Nepal and India.
Last week, I was standing on the Pati Bhanjyang ridgeline at the northeastern rim of Kathmandu Valley. Pour a glass of water on one side, and it flows westwards into the Gandaki River Basin. On the other side the streams drain into the Melamchi, which meets the Indrawati, then the Bhote Kosi to become the Sun Kosi that flows 200km eastward until it merges with the Arun and Tamor to form the Sapta Kosi.
At that point, the river makes a tight turn south to tumble into the Kosi megafan in the Tarai and Bihar to finally to join the Ganga at Kursela. The Kosi, in fact, is the largest tributary of the Ganges, bigger than the Gandaki, Karnali, Jamuna, and even bigger than the Ganga itself as it debouches into the plains at Haridwar.
The Kosi’s origin in Nepal is near Kathmandu. But it largest tributary, the Arun, originates in Tibet where it is called the Phung Chu, makes a mighty arc in Tibet and cuts through the Himalaya between Mt Makalu and Mt Kangchenjunga to meet its siblings Sun Kosi and Tamor at Tribeni.
Geologists say rivers like the Arun that slice through the Himalaya are older than the mountains, and cut their way through as the terrain rose over millions of years with the collision of the India and Eurasian tectonic plates.
The Kosi watershed therefore drains an enormous vertical landscape stretching from Mt Xixapangma which lies just 80km on the other side of the Himalaya in China, both sides of Mt Gauri Shankar (Chomo Tseringma), Mt Everest and Mt Makalu, as well as the western slopes of Kangchenjunga. Six of the world’s 13 peaks above 8,000m are therefore a part of the Kosi catchment.
These mountains block the monsoons, and in eastern Nepal their southern slopes get more than 3,000mm of rain a year, weathering them down relentlessly, making the sedimentation load of the Kosi the heaviest for any river in the world.
The topography of this mighty river has shaped Nepal’s history and culture, and can determine the country’s future prosperity as well. But only if we respect its geology, hydrology and the climate of its basin.
Watershed expert Madhukar Upadhyay says, “We have not even begun to understand the hydrological and geological specificities of our mountains and rivers and yet are rushing headlong into ever-larger infrastructure development. Nepalis will still be here 500 years from now, what kind of country and landscape are we leaving behind for them?”
Last month, landslides blocked the Melamchi-Indrawati, unleashing a deadly debris flow that destroyed infrastructure, homes and livelihoods. It imperilled the Melamchi project, and its tunnel supplying water to Kathmandu was saved only because the gates were closed for maintenance just hours before the onrush.
This week, the Upper Tama Kosi project started generating electricity, that will provide one-third of Nepal’s total power demand. But there was a scare just days before the inauguration: China informed Nepal that a massive landslide had blocked the river upstream, threatening the Rs55 billion project. Fortunately, the river found its way around the blockage. The near escapes of the Melamchi and Upper Tama Kosi sites make us take Upadhyay’s warnings seriously.
Other flash floods this year in Manang, Kaski and Lamjung also showed that while our rivers hold great promise, we ignore the risk to settlements and major infrastructure along their banks. Our engineering methods have been inherited from the West, and do not account for cloudbursts and extreme Himalayan weather events. All these risks have been exacerbated by climate change.
In Melamchi, the power of the flood last month is evident in the steel hulk of the Indrawati Bridge that lies crumpled in the muddy river 100m downstream amidst room-sized boulders. The new sand bank is 25m thick, indicating the flood’s maximum height.
It is not clear what happened, for a bishyari or two (bursting of a landslide-damming of the river) would not be enough to generate such a massive debris flow. Some speculate there may have been centuries-old glacial deposits which suddenly got released through a combination of earthquake weakening and heavy rain.
We also saw that Melamchi Bazar had expanded into the river’s flood plain, with buildings in place of rice paddies, which added to the loss of life and property. Less than a month after the disaster excavators and tipper trucks are already on the Indrawati river bed, scooping up sand and boulders to feed Kathmandu Valley’s voracious appetite for construction material.
It is the Kosi’s Melamchi tributary that augments Kathmandu’s water supply, while the sand and boulders from the Indrawati, Sun Kosi, Bhote Kosi and Rosi fulfil the Valley’s demand for sand and aggregates.
While earthquakes, floods and landslides are seen as ‘natural disasters’, and indeed they are to some extent, they become ‘man-made’ calamities with unregulated sand-mining of rivers, quarrying on steep slopes, and haphazard road-building.
The highway along the Indrawati is crowded with sand-laden tipper trucks bound for Kathmandu. Downstream towards the Kosi Barrage along the BP Highway, the road follows the river past the site where a part of the Sun Kosi is to be channeled through a 13km tunnel to irrigate farmlands in the Tarai of Province 2. A similar inter-basin diversion scheme on the Kali Gandaki is now pitting Gandaki vs Lumbini Province, and the central government.
We finally get to the new bridge across the Sapta Kosi at Chhatara, connecting Udayapur and Sunsari districts. This is exactly the point where, after its epic journey from the Tibetan Plateau and between the highest mountains in the world, this great river fans out into the plains.
North of the bridge is the site of the proposed mammoth Kosi High Dam. The 300m high dam will create a reservoir submerging huge tracts of the Sun Kosi, Arun and Tamor Valleys in a kind of ‘trishul’. India needs the dam for flood control, and to facilitate inland navigation by storing monsoon water and discharging it in the dry season. But there are many questions regarding the proposed mega project.
To begin with, the high silt load means that a future Kosi Reservoir would soon fill up with sediment. There are alternatives to dams: people in the Kosi plains have learnt to live with annual floods which deposit valuable soil nutrients, and diverting water through earlier river channels would ease flood impact.
The village of Hanuman Nagar had to be relocated because of the barrage, and 60 years later some of its families and those further upstream have still not got compensated. The barrage also destroyed an important wetland, and migratory birds now alight in Kosi Tappu Wildlife Reserve instead.
Extending the reserve further north and south could increase the habitat of endangered arna, wild elephants and freshwater dolphins, encourage ecotourism, and provide income to villagers whose grandparents had to move.
The 60-year-old embankments that jacket the Kosi upstream and downstream from the Barrage have created the potential for a massive future disaster, an inland tsunami. Because of the river’s heavy silt content, the Kosi now flows on a deck 3-4m above the surrounding land. In 2008, the Kosi breached the eastern embankment at Kusaha, causing destruction downstream in Sunsari and Bihar. And that was when the river was not even in spate.
With extreme weather caused by climate change, or a confluence of cloud-bursts in the mountain catchment, a record-breaking flood in future could cause an engorged Kosi to bypass the barrage altogether and unleash a catastrophic flood downstream.
The Kosi Barrage was meant to be a temporary solution, and the Kosi High Dam was always in the minds of the Indian authorities. There is a need for transparent and independent study by water experts, social scientists and technocrats to study the pros and cons of the Kosi High Dam.
Siltation, seismicity, adaptation and mitigation, all need to be factored in with projected future climate impact. Meanwhile, across the world, ecologists are warning that the price to pay for large dams is too great because of the destruction of river ecosystems.
A massive rockfill dam on a seismically active zone, the geopolitical implications as well as the social and environmental costs may outweigh the planned benefits. To make up for the mistake of the Kosi Barrage, we may be making an even greater blunder with the Kosi High Dam.