A technical assessment by Nepal’s Flood Forecasting Division has outlined how Wednesday’s devastating Bhotekoshi flood travelled from Tibet through the Bhotekoshi and Trishuli rivers before reaching the Narayani in roughly 10 hours. A magnitude 4.4 earthquake was recorded at 8:37am, while the Syabrubesi water-level monitoring station stopped transmitting data at 8:50am after recording a river level of 1.62 metres. Authorities received information at 9:05am that a major flood had entered the Bhotekoshi from the Tibetan side and began issuing warnings. Between 9:15am and 9:16am, more than 600,000 SMS alerts were sent to residents in high-risk areas of Rasuwa, Nuwakot, Dhading and Chitwan. The Betrawati monitoring station also stopped transmitting at 9:20am. As the surge moved downstream, the Phurke station exceeded its danger level by 11:26am, and 17 minutes later the flood swept away the Phurke bridge and other structures. By 1pm, the flood had passed Muglin, prompting further evacuation warnings for communities as far as Devghat. The Kalikhola station recorded a peak water level of 12.3 metres at 2:14pm, while the flood reached the Narayani-Devghat area around 3:20pm. Water levels at Devghat peaked at 6.57 metres at 4pm before falling to about 4 metres by 6:30pm. The assessment estimates the flood carried an additional 20 million cubic metres of water, while disruptions to monitoring stations complicated efforts to track its movement. Despite the data losses, authorities continued issuing alerts as the surge advanced along the river corridors.
