Hydropower on thin ice
Under the October sun, workers rest on boulders by the banks of the Rolwaling Khola. They are building what they already know may not last: a temporary bridge between the villages of Dongang and Thanding directly downstream from the Tso Rolpa glacial lake.
Tso Rolpa used to be a debris-covered glacier with a few ponds 30 years ago. Since then it has steadily expanded into a lake 3.2km long and 100m deep dammed by a fragile moraine perched precariously above the Tama Kosi valley.
The bridge is just a few long logs lashed together, anchored to giant boulders on both sides of the roaring rapids. Until a more permanent trail bridge is built, the community will have to rely on these makeshift crossings that are swept away every monsoon and have to be rebuilt.
Janmu Sherpa, a grandmother who ran one of Dongang’s only two lodges, was swept away when the Dorji Phungmo glacial lake up the valley burst in June last year. Her body was never found. She had told a Nepali Times reporter in 2020: “No one knows when the lakes will burst, let fate decide.”
Tanka Raj Rai is a climbing guide and has watched the lake grow over the years. This year he is leading two French trekkers to Yalung Ri Base Camp and over the Tashi Lapcha Pass to the Khumbu.
“Tso Rolpa has become much bigger than the first time I saw it,” Rai tells us. “And the pass will be more dangerous in future because of frequent avalanches and rock falls. The mountains, lake and rivers will continue to exist, but human beings may not unless we change course.”
Tso Rolpa’s water level was reduced by 3m in in 2000 by building a sluice gate and spillway, but researchers say that as the lake continues to expand, a further drawdown of 11.5m will be needed to lower the risk of it bursting during a future earthquake, or if an avalanche falls into it. If that happens, it would be catastrophic for the settlements, hydropower plants, highways and airports down the Tama Kosi valley.
Just over the Tashi Lapcha Pass on the other side is Thame village, which has been battered repeatedly since 1985 when the Dig Tso glacial lake burst, destroying a hydropower plant and the trekking trail to Everest Base Camp. Two other lakes burst in August last year and the debris flow swept away half the houses in Thame.
The National Adaptation Plan (2021–2050) warns that in the next five years most districts in Kosi, Madhes, Bagmati, and Gandaki Provinces will face high to very high climate risk. The Tarai will experience more floods and heatwaves, while mountain regions will see extreme weather and glacial lake outburst floods — the risk compounded by earthquakes.
Tso Rolpa, which lies directly below Mt Gauri Shankar ((7,181m) in the Rolwaling, is scenic — the lake’s surface simmers in the sunlight and snow-capped peaks tower on all sides. This time of year, the moraine overlooking the lake becomes a popular selfie spot for trekkers.
Yet, the raw beauty of the mountains distracts from the fact that the lake is a ticking time bomb as the glacier recedes and shrinks. This presents a clear and present danger for hydropower plants downstream in Dolakha and beyond the confluence of the Tama Kosi with the Sun Kosi.
LOOMING THREAT
Nepal generates 3,500MW of hydropower, but the country’s energy future is threatened because most of the plants depend on water from melting Himalayan ice. And as the glaciers are replaced by lakes, they face additional risk of them bursting.
This looming threat is most real with Tso Rolpa, which feeds the Rolwaling Khola that joins the Tama Kosi just above the power house of the 456MW Upper Tamakoshi Hydropower Project that came into operation in 2021 at a cost of $450 million
Tso Rolpa is one of Nepal’s largest and most unstable glacial lakes, and if it bursts it could obliterate the plant’s structures. The power house was destroyed in 2023 by a rockfall that killed four engineers, but is now back in operation after expensive repairs.
Dolakha district has prospered from the construction of over a dozen hydropower plants that could generate up to one-fourth of Nepal’s total generation capacity. Even more hydropower schemes are under construction or planned.
Nepal's Energy Development Roadmap and Action Plan 2025 aims to increase generation capacity to 28,000MW in the next ten years to create potential for economic growth, job creation, and 15,000MW for export. Investments totalling $46.5 billion will be needed to meet the ambitious target, but factoring in climate risk would make it even more challenging to achieve. The sector has also been plagued by corruption and bureaucratic delays caused by outdated Environment Impact Assessments and local opposition.
For districts like Dolakha, the opportunities come with hazards as demonstrated by almost annual floods and landslides. But these recent disasters could be dwarfed by potential future glacial lake outbursts due to climate breakdown.
Here in Dongang, the problem needs a more immediate solution as workers finish hammering together this year’s post-monsoon bridge over the Rolwaling Khola. The budget from the provincial government for a permanent suspension bridge is delayed because of the GenZ unrest, says Ward 9 Chair Imgeli Sherpa.
The community is building more than a bridge between two villages — it is suspended between resilience and risk, and the hope that its fragile foundations will hold as the rivers rise and glaciers melt.