Kathmandu, August 27
The Flood Forecasting Division has released a detailed technical report on the devastating floods that swept through the Bhotekoshi, Trishuli and Narayani rivers on Wednesday.
According to the report, a lake formed after the river was blocked in Tibet burst, sending a massive surge of water through the Bhotekoshi in Rasuwa and downstream along the Trishuli and Narayani river corridors.
The flood swept away four automatic hydrological monitoring stations along the river system. A preliminary technical assessment estimates that around 20 million cubic metres of additional water passed through the Devghat area alone during the flood.
Earthquake recorded before flood
The Department of Mines and Geology recorded a 4.4-magnitude earthquake at 8:37am on Wednesday. Shortly afterwards, a massive flood entered the Bhotekoshi from the Tibet side.
The Flood Forecasting Division said it began sending continuous alerts and SMS warnings to people living along the riverbanks and in vulnerable settlements after receiving information about the flood.
In coordination with Nepal Telecom and Ncell, a total of 679,295 early-warning SMS messages were sent to residents in vulnerable areas of Rasuwa, Nuwakot, Dhading and Chitwan.
The messages included 435,635 SMS sent through Nepal Telecom and 243,660 through Ncell.
The report said the timely dissemination of the warnings helped many people save their lives.
Flood’s journey from Bhotekoshi to Devghat
The report provides the following timeline of the flood:
- 8:37am: A 4.4-magnitude earthquake was recorded by the Department of Mines and Geology.
- 8:50am: Data transmission stopped from the Bhotekoshi-Syafrubesi hydrological station. Its last recorded water level at 8:40am was 1.62 metres, against a warning level of 6 metres and danger level of 7 metres.
- 9:00am: Information about a major flood entering the Bhotekoshi from Tibet was received from the District Administration Office, Rasuwa, and staff at the Betrabati hydrological station.
- 9:15–9:16am: The first early-warning messages were issued for communities along the Trishuli corridor up to Muglin, with 679,295 SMS messages sent.
- 9:20am: The Betrawati hydrological station stopped transmitting data. Its last recorded water level was 3.55 metres, against a warning level of 4.1 metres and danger level of 5 metres.
- 10:28am: The flood was reported to have reached the Galchhi area of Dhading. Further SMS alerts were sent to people along the Prithvi Highway, Muglin–Narayangadh road section and Trishuli river corridor.
- 11:26am: Water level at the Fhurke Khola (Malekhu) hydrological station crossed the warning level.
- 11:43am: The water level at the Fhurke (Malekhu) station crossed the danger level. Shortly afterwards, the station and the bridge were swept away by the flood.
- 11:50am: The flood reached the Malekhu Bazaar area.
- 1:00pm: The flood passed Muglin.
- 1:35pm: Authorities again warned that the lake formed by the river blockage in China had not fully drained and that the risk remained.
- 2:14pm: Water level at the Kalikhola hydrological station crossed the danger level of 12.1 metres and reached a peak of 12.3 metres.
- 3:20pm: The flood reached the Narayani-Devghat area.
- 4:00pm: Water level at the Devghat hydrological station peaked at 6.57 metres before beginning to recede.
- 6:30pm: The water level at Devghat returned to around 4 metres, considered normal.
Four hydrological stations destroyed
The intensity of the flood destroyed four hydrological monitoring stations operated under the Centre for Water Resources and Hydrology.
The affected stations were the Rasuwa Bhotekoshi station, Rasuwa Syafrubesi station, Nuwakot Betrabati station and Dhading Malekhu (Fhurke) station.
The stations were swept away along with bridges, making it impossible to obtain direct water-level data from those locations, according to the report.
A technical assessment showed that approximately 20 million cubic metres of additional floodwater passed through the Devghat station during the event.
The division has mapped the area from the Rasuwagadhi border point to the Nepal-India border into very high-, high- and medium-risk zones and issued instructions to maintain heightened vigilance.
