Avalanche creates two new water bodies in Nepal; experts urge caution
HYDERABAD: An avalanche in Nepal’s Langtang Lirung mountain range has altered local drainage patterns and created two new water bodies, satellite imagery analysed by the National Remote Sensing Centre (NRSC) shows.
The NRSC analysed high-resolution imagery captured by ISRO’s Cartosat-3 satellite during its morning pass on August 28. It compared the imagery with pre-event PlanetScope images captured on August 25, a day before the avalanche struck Rasuwa district.
Two impoundments cover nearly 30 hectares
The avalanche, along with the movement of ice, rock and debris, disrupted natural drainage channels and led to water accumulation at two locations.
One water body is near the glacier and the ice-rock avalanche zone. The other has formed near a river confluence downstream.
The larger impoundment covers an estimated 19 hectares. It stretches about 623 metres in length and 450 metres at its widest point.
The second water body covers around 11 hectares. It is more elongated, extending nearly 944.6 metres along the valley and measuring about 236 metres at its widest point.
Together, the two impoundments cover nearly 30 hectares.
Satellite imagery indicates that the larger water body has formed in a broad depression created by the disturbed terrain. The second has developed along an existing drainage channel.
The pattern suggests that avalanche debris has obstructed or altered water flow at more than one location.
Experts call for continued monitoring of water bodies
The newly formed impoundments are currently small and do not pose an immediate threat, according to the assessment. However, experts have stressed the need for continued monitoring as conditions in steep Himalayan terrain can change rapidly.
Accumulations of ice, rock and debris can temporarily block natural drainage systems and allow water to build up behind unstable barriers. Changes can occur depending on inflows, weather conditions and erosion.
The NRSC said the August 28 Cartosat-3 imagery provides a baseline for future assessments. Subsequent satellite observations can be compared with the current measurements of 19 hectares and 11 hectares to determine whether the impoundments are expanding, stabilising or draining.
Any sharp increase in the spread of water, erosion of debris barriers or sudden release of stored water could have implications for downstream areas.
The August 25 pre-event imagery, although partly obscured by cloud cover, provides the closest available satellite reference for assessing changes in the landscape following the avalanche.
