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Kathmandu: Many big and important revelations have been made in the preliminary report of Nepalese scientists regarding the horrific devastation that occurred in Bhotekoshi-Trishuli corridor in Nepal on 26th August. According to the Nepal Environment Society (NES) report, this devastating flood was not caused by ordinary heavy rains or cloudburst, but was caused by the avalanche of large chunks of snow, rocks and debris in the high Himalayas.

According to the study, a large portion of snow, rocks and debris fell from a height of about 5,200 meters in the Langtang-Lirung area of ​​Rasuwa and reached the Lhende river. After this, the strong flow of water and debris reached Bhotekoshi and then Trishuli river, which engulfed many cities and villages of northern and central Nepal and caused huge devastation.

According to officials, the death toll in this sudden flood has increased to 903 and the bodies are still being recovered.

Is it important for you to know this?

The importance of this report is not limited to just knowing how the flood occurred in Nepal. Rather, we also have to tell you that floods in hilly areas do not always occur due to rain.

Events such as glaciers, icy rocks, landslides and sudden blocking of rivers can also cause devastating floods in a very short period of time. In such a situation, understanding the flood risk based only on rainfall data may not be completely sufficient.

The impact of Himalayan disasters like Nepal can also reach the mountainous and plain areas of India. Therefore such studies may be necessary for early warning systems, river monitoring, disaster management and flood prediction.

The flood of debris started from a height of 5,200 meters

According to the study, huge chunks of snow and rocks started falling from the northern part of Langtang-Lirung at around 8:37 am on Wednesday.

The debris, which came down the steep slope from a height of about 5,200 metres, reached the Lhende River at a height of about 2,930 metres. After this the flow of the river moved towards Bhotekoshi and then Trishuli. Wherever this flood reached, scenes of devastation were seen everywhere.

Analysis of satellite images has shown major geographical changes in an area of ​​about 10 square kilometers. There are indications of breaking and separation of a part of the glacier spread over an area of ​​about 0.56 square kilometres.

22 kilometer journey in just seven minutes

The report revealed that this huge flow of snow, rocks and debris covered a distance of about 22 kilometers and reached Rasuwagadhi in a little more than seven minutes.

Its estimated average speed was 46.3 meters per second i.e. about 167 kilometers per hour.

Between Rasuwagadhi and Betravati, its speed reduced to about 73 kilometers per hour and further downstream it dropped to about 22 kilometers per hour. Although the flow slowed down, the flow continued to carry with it large quantities of rock, sediment and soil.

Why did the water level of the river decrease before the flood?

Another important clue emerged in the study. The river level and flow had reduced in Rasuwagadhi and Syafraubesi areas several hours before the flood occurred.

A drop in the average water level was recorded in Rasuwagadhi between 5 am and 8 am. At Syafrubesi, the river flow started decreasing at around seven o'clock.

According to scientists, such changes are important clues for further investigation and can help in finding out whether the flow of the river in the upper reaches was disrupted for some time.

The report rejected the fear of GLOF

The study said that based on the available evidence, this disaster was not a Glacial Lake Outburst Flood (GLOF), i.e. a flood caused by the sudden burst of a glacial lake.

In addition to satellite images, researchers analyzed hydrological and meteorological data, terrain characteristics, and changes in elevation and slope in the river system. The report found no evidence of GLOF.

However, experts say field investigations are still needed to determine the exact geological process, the role of melting snow and whether the river flow was disrupted for some time.

Questions raised on the claim of heavy rain

The study said there was no evidence of exceptionally heavy rainfall in the upper catchment that day.

This weakens the notion that the disaster was caused only by excessive rain or cloudburst. Scientists are now looking at sudden slides of ice, rocks and debris as the main causes of the disaster.

Huge loss to power projects too

The devastation caused by floods has also affected Nepal's energy sector. According to preliminary data from Nepal Electricity Authority, 13 hydropower projects and one solar project have been affected.

Due to this, about 431 MW power generation capacity is currently out of the system.

Its impact is not limited to just power companies. If power generation capacity is affected, pressure on power supply, industry, business and essential services at the local level may also increase.

Initial estimate of loss of three lakh crore Nepali rupees

Citing the preliminary assessment of the government, research has estimated the economic loss to be around three lakh crore Nepali rupees.

However, detailed assessment of the damage caused in various areas is still underway. Therefore the final economic loss may be different.

What will happen next?

According to scientists, now detailed investigation at the field level is necessary. It will be important to find out what was the exact cause of the ice and rocks slipping, how much the melted snow contributed to the flow and whether the course of the river was temporarily blocked at any place.

The answers to these questions can help in creating a system for better monitoring of floods and landslides in the Himalayan regions in future and issuing timely warnings.