Nepal flash flood raises concern over possible water surge in Bangladesh

A sudden and severe flash flood along the Tibet-Nepal border has triggered concerns over a possible rise in water levels across the Ganga-Padma basin in Bangladesh, according to weather and climate researcher Mostafa Kamal Palash. 

In a Facebook post on Thursday, Palash, a weather and climate researcher at Canada’s University of Saskatchewan, said floodwaters generated along the Tibet-Nepal border are moving downstream through the Bhote Koshi and Trishuli rivers into the Narayani-Gandak river system and toward India’s Bihar state.

India’s Central Water Commission (CWC) has already issued a warning over a possible sudden rise in water levels downstream of the Gandak River. 

The Bihar government has also opened all 36 gates of the Gandak Barrage at Valmikinagar and is closely monitoring the situation.

The additional flow from the Gandak is expected to move through Bihar before joining the Ganga near the Hajipur-Sonepur area. It will then travel eastward with the main flow of the Ganga, cross the Farakka Barrage and enter Bangladesh’s Ganga system before eventually joining the Jamuna and contributing to the Padma’s flow.

However, the exact timing of when the floodwater from Nepal could reach Bangladesh cannot yet be reliably determined from current observations, Palash said.

He noted that the intensity of a mountain flash flood generally weakens as the water travels downstream. The CWC has also indicated that the flood surge is likely to lose strength before reaching downstream areas.

Meanwhile, water levels at several monitoring stations along the Ganga in Bihar are already above danger levels. Authorities therefore need to closely monitor downstream conditions after the additional flow from Nepal enters the Ganga.

The projected route of the floodwater is: Valmikinagar - Gandak - Hajipur/Sonepur - Ganga - eastern Bihar - Farakka - Bangladesh.

People living along Bangladesh’s Ganga-Padma river system, particularly those in char areas, have been advised not to panic but to remain vigilant and closely monitor changes in river water levels over the next several days.