The Nepal Weekly | June 29, 2021
Landslides and flash floods triggered by heavy rain across Nepal last week killed some 21 people including one Indian and two Chinese workers at a Melamchi Drinking Water Project, while around 25 people were missing. This was the report issued on Friday.
Heavy rain since Tuesday (June 15, 2021) have damaged roads, destroyed bridges, washed away fish farms and livestock, and wrecked homes in Helambu region of Sindhupalchok district. Due to high magnitude flood in the Melamchi river, hundreds of people have been forced to move to temporary shelters, including schools, sheds and tents.
The area was covered by sand, soil and debris brought by flash flood. The debris of the landslide around 30 km from Melamchi was blocked and later suddenly pushed strongly by river water. Arriving at Melamchi the debris within a while covered the settlement where some could not flee. It claimed many lives. Some are missing and a number of houses swept and so many houses stood sand and debris covered two stories under the sand.
The flood had destroyed the Melamchi Drinking Water Project at Melamchi. The dam of the project has been damaged by the flood. The drinking water project was closed for checks and repairs after supplying 170 million of water per day to the Kathmandu Valley through a 27 km tunnel. The project was closed the same day after serving two and a half month. If that was in regular operation, the project might have witness ever extensive damage. The flood also had destroyed many bridges and road sections as well.
Some experts are saying that the preparedness to tackle possible natural disasters in the country is very poor. The available resources and systems are proved to be too weak to safe people and properties.
Similar disasters took place in the past should have been taken as lessons for preparation and alert. The experts say that the Melamchi river flood is similar as of Seti river flood in Kaski district took place on May 05, 2012. The experts Shreekamal Dwivedi, Yojana Neupane and Dr Jeffrey Kargel many others who conducted research and studies of Seti river flood had also warned that similar disaster may take place in other similar geographies in Nepal.
According to their studies, in late April and early May 2012, what was usually a roaring Seti river in North-western Nepal had slowed to a trickle. The milky-white turbid water had turned blue and clear. And then suddenly on May 5, 2012, the flooded river laden with slurry of sediment, rock, and water surged through the Seti valley in the Kaski district, obliterating dozens of homes and sweeping 72 people to their deaths. The floods waters were upto 30 m high at places. It reminded of the sequence of events leading to Tsunami. Questions swirled about where the water had come from and how it arrived with so little warning and that too in a non-monsoon season.
The high intensity floods in May 2012 came in waves, and the first wave alone had around a quarter of a million cubic meters of water in just a few minutes. There were about 27 waves in all over the next hours, according to eyewitnesses, so several million cubic meters of water flowed overall. As Dwivedi et al note, “The huge mass of debris along with ice chunks rushed down the river as a debris flow for 20 kilometres downstream at Kharapani in just 28 minutes (almost 12 meters/second). The flood arrived at Kharapani, where most of casualties occurred, at 9:38 AM and reached the dam of the Seti irrigation system at 10:35 AM… The high-water level at the dam weir at Pokhara was 2.15 meters. The discharge estimation based on the water mark revealed the peak as 935 m3/s (B. Poudel, personal communication). The eye-witnesses in Kharapani area reported huge ice blocks floating in the flood. They felt vibrating ground and heard very loud sound similar to flying of several helicopter together. The smell of the flood water was muddy… Kharapani was a popular spot for picnic and natural hot spring bath… Most of the causalities occurred in this area as the warning message from the Pokhara Airport tower could not reach this area”.
However, the series of event started weeks before the flood with a series of rockfalls that sent debris tumbling into the SetiRiver, backing water up in the extremely deep and narrow gorge. The last of these landslides occurred just a week or so before the flood. The situation grew dire on May 5, 2012, when an unusually powerful ice avalanche and rockfall tumbled down a vertical cliff on a ridge just south of Annapurna IV Mountain peak. The total drop from the Annapurna IV ridgeline to the bed of the Seti below Pokhara is about 6,100 meters (20,000 feet) spread over a distance of only 40 kilometers. The distance between the landslide dam and sight of worst floods was about 29 km.
Warning: More such events could occur
The scientists involved in research and studies on the Seti flood of may 2012 had mentioned that the southern slopes of Annapurna range have been experiencing avalanche-triggered high intensity floods also in the past. On August 15, 2003, the Madi River had experienced an unprecedented flash flood which destroyed the recently built rural road and triggered many landslides along its course and killed 5 people. The same processes that triggered the spring 2012 rockfalls and avalanche are still at work. “The only question is whether future events will be as destructive or whether people in the Seti River Valley will have absorbed the lessons of 2012 and found ways to move their homes out of the flood plain.” India should not forget that we are downstream country in Seti basin and what happens there will flow down here too. A detailed investigation of the circumstances of the disaster on May 5th, especially the possible influence of global warming on the trigger of the disaster, and a reliable forecast of a potential recurrence of similar events or of even much greater scope, are urgently required. For this, the thorough understanding of the conditions, triggers and mechanisms of the huge flows in the past to compare it with the recent flood is indispensable as well. (The Nepal Weekly)