Photo Essay on Glacier Lake Outburst Flood (GLOF) affected areas of Rangpo (Sikkim): 06Oct2023

Map showing IMD rainfall gauge stations along the Teesta valley as well as important places

Images of Chungthang dam under construction in April2013, when I visited North Sikkim. This dam was commissioned in Feb2017 and became known as the Sikkim-Urja power project. It was the largest (1200MW) hydro-electric dam in Darjeeling-Sikkim Himalayas and collapsed in the early hours of 04Oct2023 under a glacial lake outburst flood (GLOF) in South Lhonak glacier in North Sikkim.

I took these two images of Rangpo town two years apart, in October and from almost the same spot. The BEFORE and AFTER photos clearly show the devastation caused by the GLOF. The top photo shows IBM colony of Rangpo when it was a thriving market place and the lower image shows it as it was, after the GLOF which transformed it into a sand covered field.

Drone image of parts of IBM colony of Rangpo. Much of the shanty colony of tin homes were swept away by the Teesta river and the concrete structures buried under almost 15 feet of sand. The areas where the river never reached survived (Photo credit: Praveen)

IBM colony of Rangpo town. What was once a thriving market place with 500 - 800 shops, homes and smaller businesses is now buried under 10-15 feet of sand which Teesta river deposited during its brief but violent visit to this place.

An aluminum foil factory and a SUV lies partially buried at IBM market in Rangpo

A water tank on top of a double storeyed building juts out of the sea of sand at IBM while the building lies buried below. The whole area was a crowded market place as can be seen on the Google Earth image placed until it was transformed into a desert by the GLOF.
I cannot but marvel at the terrifying force of nature - to move and deposit almost 10-15 feet of sand everywhere the flood waters reached, in just a matter of hours - this has happened at Teesta bazar, Bardang, lower Mamring and here at IBM in Rangpo

Heavy construction material and equipment belonging to DRA construction company lie partly buried at IBM. The company (contractors of NHIDCL) had their offices and storage area here and other equipment are completely buried below the sand and cannot be seen. This area was also crowded with shanties and storage houses (godowns) made of corrugated tin sheets all of which were swept away. I spoke to a resident who also told me many, many vehicles had been taken away by the river when it invaded this premises.

The residents of this complex had a miraculous escape. Having come to know of the floods only after the first floor was engulfed by the waters, some twenty people were compelled to stay in the top floor of this building and wait for 13 hours until personnel of the Sikkim Fire Brigade rescued them.The ground floor and parts of the first floor are buried in sand.

Residents commence their recovery process by shoveling out sand from the first floor of their home even as the ground floor lies totally submerged in sand and flowers bloom on the terrace.

While heavier things were buried in the sand, the flood waters dumped tons of trash which floated and have to be cleaned up now.

GLOF refugees crowd around a place at Rangpo where relief material was being distributed. Immediately, we saw a lot of enthusiasm from the public while volunteering to distribute different types of relief material but bigger NGOs and agencies will have to move in to sustain this effort in the long term and rehabilitate these people who have lost every thing.
We visited a relief camp (of the several which are there) set up in a school at Rangpo where there were around a thousand GLOF victims.

Picking up the pieces. With everything gone, people living near the new bridge try and salvage what they can. (Photo credit: Praveen)

A long road to recovery. People who had walked away from their homes and the flood waters with only what they were wearing had returned to excavate their buried homes and dig out what ever little precious or usable things they could find.

Picking up the pieces.Women wash mud covered currency notes recovered from their lost homes at IBM in Rangpo.(Photo credit: Praveen)

A single hangar in a mud covered almirah is all that is left of the belongings of a victim at IBM colony, Rangpo (Photo credit: Praveen)

People who had lost everything especially valuable documents such as ID cards, bank papers and other important documents were foraging around in the still slushy, sand and mud for these items.

A GLOF victim ponders. I wonder what was going thru his mind as he was rummaging thru what was left of his home (Photo credit: Praveen)

Mud and slush marks on the building exterior and erosion on the opposite bank shows where the Teesta water level had reached during the GLOF on 04Oct2023. A wall of water almost 15 feet high smashed thru everything in its path - trees, bridges, infrastructure and roads.

The Indian army lost a number of soldiers on the night of the GLOF. Here excavators work to dig out their remains, equipment and material from a site near Bardang. Notice that even these large vehicles are almost totally inside a mound of sand which must be around 10 to 15 feet high.

Mr RN Pradhan and friends of Lower Mamring village.
This is another badly affected area in Rangpo. Though they managed to evacuate people from here on 04Oct2023 morning, they lost all their livestock to the flood waters as well as 8 to 9 tin shed homes here. There were a lot of trees next to the river bank which all got swept away.

Pots and pans at what used to be a home of a villager - Lower Mamring at Rangpo (Photo credit: Praveen)

Bedroom of a home at Lower Mamring on 06Oct2023. The whole area was covered with slushy sand/mud and walking was still difficult despite 48 hours of dry weather.

Locals at Mamring told us that the river had changed its course and was flowing much closer to their village now and also what was all too evident, that the due to siltation the Teesta was flowing at a higher level than earlier.

Slush and sand at Lower Mamring village.Locals informed us that there was a high tension power pylon or tower at this spot which also got swept away by the GLOF. Incidentally, the entire Rangpo town did not have any power from early morning on 04Oct2023 till 08Oct2023, perhaps due to pylons getting damaged or washed away or the damage to the hydro-electric power stations at Chunthang and Dikchu dams.

GLOFs will continue to occur more frequently and with the Himalayan rivers becoming pockmarked with more dams of all shapes and sizes, this is an all important event for us.
Some things worked:
  * The rudimentary alarm system of alerting people with loud hailers and sirens worked even at 2 -3 am and when it was raining heavily. Most people from the low lying areas were successfully evacuated in time - even tho the death toll may continue to rise as we unearth more bodies from under 10-15 feet of sand.
This evacuation also worked in North Sikkim where reaction time was much less.
  * Reaction from civil society and the government has been swift in delivering relief to victims but since almost all the affected people have lost everything including ID papers etc, rehabilitation needs to be sustained and long term. Maybe this will be a challenge, especially after the initial enthusiasm wears off and people get busy with the Dasain (puja) festivities
Somethings did not work:
  * Early warning for GLOF event was not there and if it was there it did not work.
  * Information about North Sikkim continues to be sketchy. There was no news whatsoever about survivors or casualties from the Sikim Urja dam after parts of it collapsed.
  * SANDRP has a lengthy article here
 An observation & a question mark?
Observation
 * The speed at which the GLOF advanced on 04Oct2023 morning was astonishing and its sheer size doesn't give anyone a second chance.
 * The only remedy maybe a reliable early warning system and an alert community. Regular drills in low lying population centers must be incorporated.
 Question mark
 *The GLOF and the dam burst resulted in the Teesta river carrying unimaginable volumes of water at high velocities with tons of debris such as tree trunks, boulders, motor vehicles, infrastructure pieces (such as the 14 bridges which collapsed).
Much of debris continuously and repeatedly impacted and collided with the downstream dams and bridges on the Teesta river. Will these structures be checked for safety?

 

My thanks firstly to my young friend Raghunath at Rangpo who spent the whole day with us, taking us to relief camps and other affected areas.
Thanks to the many victims for talking to us despite having endured such a catastrophic loss.
Thanks to Praveen bhai too with whom STH has done really good work in the past. We will  continue to work together to throw more light on disaster issues - so that people become more aware.

Praful Rao
Kalimpong district
Darjeeling- Sikkim Himalaya
savethehills@gmail.com
9475033744

 

 

Was there a cloud burst in Sikkim on 03Oct2023?

The media is howling about a cloud burst that occurred in North Sikkim around the 03Oct2023 and which triggered the GLOF (Glacial Lake Outburst Flood) at South Lhonak lake, which led to the terrifying devastation in Sikkim and Kalimpong district on 04Oct 2023.

To get to the truth of the matter let us first see what is a cloud burst:
As per IMD
'If 100mm rainfall is received at a station in one hour, the rain event is termed as cloud burst.'

Placed below is a map and the rainfall data of North Sikkim (and Gangtok) and of Darjeeling and Kalimpong for the period 01Oct to 04Oct2023.

What is apparent is that Darjeeling and Kalimpong received far more rain than North Sikkim during this period and to support this are placed the Infra Red cloud images of 03Oct2023. Sikkim

It is highly unlikely that the type of clouding seen in the vicinity of Lhonak glacier would trigger a cloud burst since such high intensity rain is normally associated with convective clouding and cumulonimbus (CB) clouds which generate a distinct white signature in IR satellite images.
What are cumulonimbus (CB) clouds and how do they appear on IR satellite images?

How CB clouds appear on satellite imagery

There is no doubt that a GLOF did occur at South Lhonak glacier on 03/04Oct2023 between midnight and around 1am on 04Oct2023 - satellite imagery and reports from people at Lachen confirm this.
However, the widely held belief that a cloudburst triggered the GLOF is probably incorrect and maybe ascribed to media loosely calling any 'heavy rain' event a 'cloud burst' just as many issues these days are conveniently labelled under the banner 'climate change' without any verification.

So if a cloudburst did not trigger the GLOF, just what did?

That is a question which has still not been answered.

Praful Rao
Kalimpong district
Darjeeling-Sikkim Himalaya
savethehills@gmail.com
9475033744

GLOF in North Sikkim triggers flashfloods down stream

We have had incessant rain in our region for the past 24hrs or so and as always STH has tracked the cloud movements and put updates in our WhatsApp group 'HAZARD ALERTS 1 & 2' with a view to provide some rudimentary early warning to the community.

Perhaps it is this incessant rainfall, due to a circulation over Jharkhand, which triggered the GLOF in South Lhonak glacier in North Sikkim. A very technical study has been done and is available here
The abstract from the article is reproduced below:

The Teesta basin in Sikkim Himalaya hosts numerous glacial lakes in the high altitude glacierized region, including one of the largest and the fastest-growing South Lhonak Lake. While these lakes are mainly located in remote and unsettled mountain valleys, far-reaching glacial lake outburst floods (GLOFs) may claim lives and damage assets up to tens of kilometers downstream. Therefore, evaluating GLOF hazard associated with current and potential future glacier-retreat-driven changes is of high importance. In this work, we assess the future GLOF hazard of the South Lhonak Lake by integrating glacier and hydrodynamic modeling to calculate the lake's future volume and hydraulic GLOF characteristics and impacts along the valley. We identify the increased susceptibility of the lake to potential avalanche impacts as the lake grows in the future. Here we model six avalanche scenarios of varying magnitudes to evaluate the impact-wave generated in the lake and overtopping flow at the dam. Avalanche simulations indicate that the frontal moraine is susceptible to overtopping. The overtopping flow hydraulics is evaluated along the channel assuming no erosion of the moraine. Further, we consider three lake-breach scenarios to model GLOFs originating from the lake, flow propagation, and its downstream impacts. The uncertainty in the breach parameters including breach width and time of failure are calculated to estimate the upper and the lower hydraulic limits of potential future GLOF events. Further, the uncertainty in the flow hydraulics was evaluated using dynamic flood routing of six GLOFs that originate from the lake. Hydrodynamic GLOF modeling resulted in a predicted peak discharge of 4311 m³s⁻¹, 8000 m³s⁻¹, and 12,487 m³s⁻¹ for breach depths of 20 m, 30 m, and 40 m respectively. The large-potential scenario suggests that maximum flow depth and flow velocity at Chungthang, a town proximally located to a major hydropower station built-in 2015, could reach up to 25–30 m and 6–9 m s⁻¹, respectively. Mapping infrastructure exposed to GLOFs in the Teesta valley shows that many settlements and assets located along the river channel at Chungthang are potentially exposed to future GLOFs, indicating the need to conduct a full environmental impact assessment and potentially undertake GLOF risk mitigation measures.

I was up at 2.20am after being notified of the GLOF by a friend. I spoke to several people in Sikkim to verify the information but it was difficult to get thru and rather embarrassing to disturb a person at that time.

After becoming reasonably sure of the event, I alerted the NDMA control room at 3.33am with a request to verify the information from SSDMA. (Sikkim State Disaster Management Authority).

I was surprised at the speed at which the flood waters advanced. Luckily, most people in the low lying areas made it to higher ground, despite the non-stop rainfall and darkness. Approximate timeline of the flooding (based on information given to me this morning by a friend when the event was unfolding) is given below:

Casualties and damage:

Sikkim State Disaster Management Report
Gangtok, October 4 (IPR): The Glacial Lake Outburst Flood (GLOF) in portions of Lhonak Lake, Mangan District, which caused the rise of water levels with very high velocities downstream along the Teesta River Basin in the early hours of October 4, 2023, has caused severe damage in Mangan, Gangtok, Pakyong, and Namchi Districts.
The lake outburst in portions of Lhonak Lake in North Sikkim caused a rise in water levels with very high velocities near about 15m/sec, crossed the CWC Melli site measuring 227 m, near about 3m above Danger Level, at 0600 am.
According to the Central Water Commission (CWC), the flood occurred at midnight on October 3, 2023. Simultaneous flood forecasts for both India and Bangladesh were made at 0600 hrs and 1400 hrs. The river Teesta is flowing below the warning level at CWC Domohani FF Station. The water level at 0600 hrs is 84.83m and is expected to cross its warning level within 6 hours.
Similarly, around 1 a.m. on October 4, 2023, the major flooding of the Teesta River was reported from Chunthang. Likewise, by 2:30 pm, the flood had reached the lowlying areas of the remaining districts, causing serious destruction to public properties and public infrastructure. The communication network under Mangan District surrounding Chungthang and its pheriphery has been affected. Districts sprung into action and immediately initiated the evacuation of the people from the lowlying areas.
Further, the SDRF team from the State Home Guard and Civil Defence, Gangtok, and NDRF Pakyong has already been deployed in the affected areas.
As per  the report received from the SSDMA, the following damages have been reported from the districts:
(i) Mangan District: Chungthang cut off due to the Toong Bridge collapse. Phidang Bridge collapsed. Four pucca houses at Phidang were washed away. Two houses at Dikchu were washed away. Houses along the river line are in danger, and two GREF labourers are reported missing at Sangkhalang, as per information received from GREF sources and one person missing from Phidang.
The GREF Crusher Plant and Old Police Barrack have been washed away at Toong, and four people have been reported missing.
Forest Guest House and two units of government quarters at Sangkhalang has been swept away.
(ii) Gangtok: Four injured have been taken to Singtam Hospital. 25 people have been rescued by SDRF, more rescue is underway.
(iii) Namchi district: LD Kazi Bridge washed away. Indreni Bridge washed away. A relief camp was set up at Namphing Sai Mandir. As of now, 500 people have been kept in the relief camps, and permanent relief has been set up at  Pranami Mandir.
(iv) Pakyong district: Two minor injuries, one dead in West Bengal, and one person is under observation at Rangpo PHC. 23 army personnel have been missing and one person has been rescued at Bardang.

SSDMA

Fatalities/Missing
Known missing thus far are 23 army soldiers who were presumably swept away from their barracks at Bardang near Singtam by massive 15-20' waves of the Teesta river.
20 civilians are also reported missing.

Damages
Proper estimation of the damages in Sikkim and W Bengal may take some time. However, the major damage are as follows:

1. Sikkim Urja Dam at Chungtang, a 1200 MW Teesta Stage III Hydro Power plant was partly swept away by the GLOF resulting is huge release of water.

2. Indreni bridge at Singtam (30km from Gangtok) and another bridge at Baluatar were swept away. Several other bridges have also been washed away.

3. Control room of NHPC Stage V Dam at Dikchu has been damaged.

4. NH10 and communication lines all over Sikkim and Kalimpong district in W Bengal have been severely damaged at many places. Road towards Darjeeling from Kalimpong is severely damaged at Teesta bazar.

5. Three districts in Sikkim including Mangan (north Sikkim), Pakyong and Gangtok (east Sikkim) were severely affected. Mangan was the worst hit.

Will update this continuously over the next few days as more information is available

Incredible photos (includes drone imagery) by STH photo/videographer Praveen Chhetri of the GLOF devastation at Teesta bazaar (taken in the morning on 04Oct2023)

Why at Teesta Bazaar only and not in Sikkim?
Because there is no road access anywhere - National Highway10 (NH10) towards Siliguri is damaged and eroded, as is the highway to Gangtok. The road to Darjeeling from Teesta has been 'eaten away' by the floods this morning

As I write at 8.pm on 04Oct2023, it continues to rain in Kalimpong, Darjeeling, Kurseong and I am sure in many places in Sikkim for almost 36hrs now, at varying intensities.
Hope things get better tomorrow.

Praful Rao
Kalimpong district
Darjeeling - Sikkim Himalaya
savethehills@gmail.com
9475033744

Rainfall data of September 2023 of some towns in the Darjeeling - Sikkim Himalaya

Technically the 'SW Monsoon season' in the country is deemed over on 30September, with October ushering in the 'Post Monsoon season'.

A number of low pressure areas formed in the Bay of Bengal in Sep2023, some being remnants of storms in the Pacific which intensified in the warm waters of the Bay. These systems undoubtedly impacted the rainfall pattern over our region.

The district-wise rainfall distribution for the period 01Jun to 27Sep2023  for Sikkim and Sub-Himalayan West Bengal (SHWB) ie for approx the entire monsoon season is given below:

See below a media report on rainfall during the monsoon season in the country:

September 2023 rainfall

The map below clearly indicates that in Sep2023, the hills towns of Darjeeling, Kalimpong districts and those in Sikkim received less rain than the towns in the plains and the really heavy rain was reserved for the foothills of Kalimpong and the Dooars plains.

Landslides
Landslides did occur in Sep2023; the most important one which occurred on NH10, at Sethi Jhora on 23Sep2023 has been covered in the previous blog. Information on other landslides will be posted as updates to this blog.

Praful Rao
Kalimpong district
Darjeeling-Sikkim Himalaya
savethehills@gmail.com
9475033744