Winter season flash flood in Rishiganga–Dhauliganga valley of Uttarakhand Himalaya on February 7, 2021 caused major devastation, particularly around the hydropower projects at Rini and Tapoban in Chamoli district. Geomorphic changes brought forth by the flash flood created a lake on Rishiganga river that has been the focus of post-disaster investigations.
Most institutions including Geological Survey of India (GSI), Defence Geoinformatics Research Establishment (DGRE) and National Remote Sensing Centre (NRSC), as also the Joint Study Team organized by National Disaster Management Authority (NDMA) perceived this lake to be a major threat for the downstream areas. So grave was the concern of some that they even advised blowing off the barrier outright. Most, however suggested continuous monitoring together with an effective early warning apparatus.
Nothing concrete could however be put in place even after 07 months of the incidence.
The state has no doubt resorted to aerial reconnaissance of the lake from time to time to assess the threat. But then, it is doubtful if there actually exists technology or expertise to assess the threat remotely, sitting in a helicopter.
Regular monitoring of the lake level and discharge has so far not been initiated. Moreover, none around – not even ones busy assessing the risk posed by the lake – seems to be sure of exact volume of the impounded water as the dimensions of the lake still elude the researchers. At the same time no warning system has so far been put in place.
In such a situation one can only thank the nature for averting collapse of the landslide barrier, and saving the downstream habitations from yet another catastrophe.
This is however not the first such incidence in the region. Floods are common to all river systems, and in the Himalayan region these have often been caused by heavy localized precipitation termed cloudburst, as also by the breach of landslide dammed lakes that is commonly referred as landslide lake outburst flood (LLOF).
So rather than putting forth alibis – accessibility, rugged terrain, weather conditions, telecom connectivity and the like – should we not review previous incidences, and learn lessons for prompt and positive action?
1893 – The Gohna Tal
On September 6, 1893 a massive landslide occurred in the catchment of Birahi Ganga, a tributary of Alaknanda river that meets it at Birahi. This brought down around 500 crore cu m (5000 million ton) debris from 900 m high valley flank, and blocked the course of Birahi Ganga forming a lake, Gohna Tal – 150 m deep, 3 km long, and 600 m wide.
Discharge of Alaknanda river got reduced by the blockade of Birahi Ganga on September 6, 1893. Apprehending some geomorphic upheaval in the upstream region, District Surveyor T.H. Holland was sent for field investigations along with one Army personnel. After field investigations T.H. Holland reported Gohna Tal having come into existence in the Birahi Ganga valley, and apprehended devastation in the downstream areas due to its breach in future.
Partial breach of Gohna Tal on August 25, 1894 caused major loss of property and infrastructure around Chamoli, Srinagar, Devprayag and downstream areas. This flood is amongst the earliest recorded disaster incidences in Uttarakhand Himalaya, and is known for continuous monitoring and data transmission, timely warning generation and dissemination, and precautionary measures that successfully averted loss of human lives.
1893-94 – Monitoring and assessment
Based on the reported dimensions of the landslide dam and available topographic details of the area, Army engineers assessed the quantity of water likely to be impounded. Together with this the threat posed to the downstream habitations by the breach of the landslide dam and subsequent sudden release of water was also assessed. In view of the seriousness of the threat it was decided to monitor Gohna Tal on a continuous basis so as to have a warning of the likely flood.
A telegraph line was accordingly laid between Gohna Tal and the downstream towns; Chamoli, Srinagar, and Haridwar, so as to communicate the discharge and water level data together with warning message. It is important to note that the first long distance telegraph link between Agra and Kolkata was established only in 1884, and this was the first telegraph line to be laid in the region.
Instead of T.H. Holland and Lt. Crookshank some scholars give credit of survey and monitoring related to this incidence to Superintendent Engineer Pulford and District Surveyor Pandit Hari Krishan Pant. Purpose out here is however not to verify individual details.
1894 – Disaster averted
Based on discharge and lake level data sent regularly by Lt. Crookshank Army engineers assessed that the lake would breach on August 24, 1894.
Eight suspension bridges on Alaknanda river between Chamoli and Haridwar were thereafter dismantled, and placed at safe locations so as to protect them from being washed away in the anticipated flood.
Together with this warning of the possible flood situation was disseminated all along the Alaknanda river by employing drummers, and the habitations on the lower reaches were evacuated.
Water actually began to trickle over the dam one day later on August 25, 1894, and partial collapse of the dam took place around midnight. Approximately 2832 lakh cu m water thus surged downstream. The flood lasted until the morning of August 26, 1894, and caused major loss of property and infrastructure around Chamoli, Srinagar and Devprayag. Loss of human lives in this incidence was however limited to one due to the precautionary measures put in place.
It is important to note that measures related to the survey, monitoring, data transmission, warning generation and precautionary action were all undertaken under severe constraints of access, communication and resource mobilisation.
1970 – The final breach
Gohna Tal remained in existence even after the breach of August 25, 1894, and the final breach of the lake took place on July 20, 1970 and devastated the Alaknanda valley.
A roadside settlement Belakuchi, between Pipalkoti and Helang was washed off in this flood along with a convoy of 30 buses. Around 400 pilgrims en route to Badrinath were however saved due to the alertness of a Police constable who guided them to safety on the uphill side.
Besides this 13 bridges were swept away in this incidence, and around 10 km stretch of the Ganga Canal in Haridwar was clogged with sediment and uprooted trees. Lower portion of Srinagar town was completely destroyed by this flood.
No warning could be generated for this incidence, as the monitoring of the lake was not continued after 1894.
This article aims at highlighting some significant facts related to August 1894 LLOF of the Alaknanda valley –
(i) Reduced discharge of Alaknanda river was taken note of, and reasons thereof were quickly investigated,
(ii) The risk posed by likely release of impounded water was perceived, and taken seriously,
(iii) Decision was quickly taken to monitor the situation continuously,
(iv) Resources were mobilised, and a dedicated telegraph line was put in place for data transmission,
(v) Timing of the breach was successfully assessed,
(vi) Warning was timely generated, and effectively disseminated,
(vii) Preventive measures were quickly implemented, and
(viii) Loss of life was averted.
Prompt and planned action, and successful delivery by the British Raj in 1893-94 should envy present day disaster managers who despite being armed with state of art surveying, monitoring and communication technology and gadgets, besides immense resources and authority have not been able to put in place a reliable monitoring and warning system for the landslide dammed lake that came into existence on the Rishiganga river on February 7, 2021.
If not anything else, review of August 1894 LLOF of the Alaknanda valley should result in a truthful introspection to identify and eliminate procedural bottlenecks, and facilitate prompt and positive decision making in times to come.