Nepal lost several critical hydrological monitoring stations during the catastrophic Bhote Koshi-Trishuli flood on 26 August 2025, severely undermining real-time river surveillance as an extreme flood wave tore downstream at unprecedented speed, according to a government assessment. The loss has left the Bhote Koshi and Trishuli river corridors without an adequate flood-warning system at a time of heightened seasonal risk.

Stations Destroyed or Disabled

The Assessment Report II, prepared by the Centre of Hydrology and Water Resources Research (CHWRR) under Nepal's Water and Energy Commission Secretariat, confirmed that the flood was severe enough to destroy or disable several key monitoring stations along the Bhote Koshi-Trishuli corridor. The affected sites included stations at Rasuwagadhi, Syaphru Besi, Betrawati, and Phurke Khola in Malekhu — all strategically located along the flood-hit river system.

At Rasuwagadhi (Timure), data transmission ceased at 8:40 a.m. with the final recorded water level at 3.8 metres, after which the station was washed away. At Syaphru Besi, transmission stopped at 8:50 a.m. when the last reading stood at 1.62 metres before the station was swept away. The Betrawati station on the Trishuli River went offline at 9:20 a.m. after recording 3.55 metres, and the Phurke Khola station at Malekhu in Dhading district was destroyed at 11:43 a.m. after water levels exceeded the danger threshold — taking an associated bridge with it.

Flood Wave Speed: A Monitoring Nightmare

The assessment underscores why conventional monitoring struggled: the flood wave travelled approximately 22 km from its source to the Rasuwagadhi border in roughly seven minutes, at an average speed of about 188 km per hour. This extraordinarily rapid propagation left virtually no warning lead time for downstream communities or operators.

Sauharda Joshi, a hydrologist at Nepal's Department of Hydrology and Meteorology and one of the officials who prepared the report, said the stations 'were unable to capture the exact flood levels because the massive flood washed them away on 26 August.' He attributed the destruction to the 'massive flood that flowed at too high a velocity.' The report described the losses as highlighting 'the extreme nature of the flood event.'

A Dangerous Monitoring Gap

With the stations gone, Nepal is currently operating without a functional flood-warning network on both the Bhote Koshi and Trishuli rivers, Joshi said. 'The immediate risk is that we are without a flood-warning system in the Bhote Koshi and Trishuli,' he noted. The Bhote Koshi is a transboundary river shared between Nepal and China, adding a cross-border dimension to the monitoring challenge.

As an interim measure, Nepal has installed a CCTV camera at Timure, Rasuwagadhi for visual river monitoring. Authorities have also initiated the process of installing flood-monitoring systems at Betrawati and Phurke Khola, with locations identified following field visits, according to Joshi.

Long-Term Fix Under Discussion

Officials are currently deliberating a dual-station model — one monitoring system installed along the riverbank and a second at a higher elevation — so that if a bank-level station is damaged, the elevated station can continue transmitting flood data. Joshi acknowledged, however, that there are 'currently not enough flood-monitoring systems in place following the latest disaster.'

The destruction of Nepal's monitoring network raises urgent questions about infrastructure resilience in the face of increasingly extreme Himalayan flood events. With monsoon season ongoing and the affected corridors still vulnerable, the timeline for restoring a robust early-warning system will be closely watched by disaster management authorities and downstream communities alike.