How to destablize a hill in quicktime: Nursery Gaon landslides, (Kalimpong) 07Jul2020

I had visited Nursery Gaon along with GSI Geologist Debashish Bhattacharya in Dec 2012 and blogged about it. It lies below the 7/8th mile area of Kalimpong and several landslides there were active even then. Some picture posts of our visit in 2012 from the STH blog are below:

Subsequently on 01Jul2015, following heavy rainfall, a landslide occurred again at Nursery Gaon and an entire family perished. Their bodies could never be traced.

• I am very familiar with the area which lies on the western face of Kalimpong and as such is steep and mostly rocky. Compared to the eastern face, this region has sparse population but at the crest (the 8th mile area) there is a large urban build up with several prominent schools, flower nurseries and the road (State Highway -SH12) linking Kalimpong to Teesta bazar passes thru this region.

• Kalimpong has long needed a by pass road since the SH12 passes thru town and traffic snarls are increasingly becoming impossible esp when large military vehicles have to pass thru narrow areas. To obviate routing thru the congested town area, a by pass road circumventing the urban cluster was planned. This road which was to start at 7th mile, pass below the 8th mile area and terminate somewhere in Bhalukhop avoiding the entire town area.

• The by pass road was inaugurated in 2009 (to the best of my knowledge) and rather coincidentally my first record of a landslide in the region is also of Aug 2009.

• Since then I have visited the by pass area many times, to check the increasing areas of instability along the road.
• On 07Jul2020, following heavy rains, there were reports of landslides in the area. I visited the area on 10Jul2020 and this is my assessment:

Images from my survey in the area are place below:

Size of slide is approx 60m in length

The length of this subsidence is around 30-40m

RAINFALL ON 06Jul2020 : 109mm

Having talked to affected people of the area:
1. It is well known that roads interfere with the natural drainage of a mountain and therefore are a major cause of landslides. In the case of the above landslides, this is very evident. Whereas there was little instability in this region before 2009, the incidents of landslides have increased sharply over the years.
2. This was very evident even in 2012, when I visited the area and made a pointed remark that this area would be susceptible to slope failures due to poor drainage (see first slide).
3. Sure enough, on 01JUL2015 we had a fatal landslide in the area.
4. Unfortunately even after that, nothing has improved. Merely loading the area with more concrete, stone and sand is NOT the solution and perhaps the engineers will have to incorporate some innovative ideas on how to manage the water and improve drainage.
5. High time we think seriously about how to control the instability instead of how to make money from it.

Praful Rao
Kalimpong district
Darjeeling-Sikkim Himalaya

A pictoral record of the landslides of JUN 2020 in Darjeeling-Sikkim Himalaya

Shown above are the approx timelines when due to the more than normal rainfall in Jun2020, there were numerous landslides in the Darjeeling - Sikkim Himalayas and all occurred during periods of heavy rain. For example, in 6 days (17Jun-22Jun2020) Kalimpong received approx 78% of its monthly rainfall which is when all the landslides in Kalimpong took place.
More specifically:
a. Darjeeling and Kurseong area had landslides just as the SW monsoons entered the region on 12/13Jun 2020. Many of these landslides are documented here.
b. Kalimpong district which had almost no rain during this onset period, had intense rain on 17Jun which triggered a number of slides in the district.
c. Mangan (N Sikkim) and E Sikkim were the only places which had surplus rain over the winter months and continued to have very heavy rain towards June end and that triggered a number of landslides.
In order to maintain a record of the landslide events I am posting verified photos of some of them as submitted by HA members.

Kalimpong:

North Sikkim (Passingdang)

North Sikkim (District HQ: Mangan)27.4979° N, 88.5348° E

North Sikkim (Barfok)
27.509787°N, 88.437531°E

Debris Torrent as seen from across the Teesta from Mangan. No loss of lives, some houses evacuated.

Landslide at NHPC Stage V 510 MW Dam at Dikchu, East Sikkim

Landslip on Dhotrey- Maneybhanjang road (22Jun2020?)

Rimbick- Lodhoma landslide (28Jun2020)
at Chota Hatta, Kankeybong.

Breaches on NH55 (Siliguri to Darjeeling) near Pagla Jhora (Kurseong)
30Jun2020

My sincere thanks to all those who have volunteered their time and effort in 'HAZARDS ALERTS' (Whats App group)  and elsewhere to provide the information and photographs for the above record.

Praful Rao
Kalimpong district
Darjeeling Sikkim Himalaya

Rainfall data of some towns in the Darjeeling-Sikkim Himalaya: Jun2020

Jun 2020 turned out to be a WET month for the Darjeeling-Sikkim Himalayas, in fact for Kurseong at least, the wettest June in the last 5 years

What is very apparent from the data below is that most of the precipitation occurred - in intense bursts. See image of STH AWS panel of 17Jun recording a transient rainfall intensity of 106.7mm per hour at Kalimpong and it is this type of intense rainfall which triggers landslides.

Towards the latter half of the months, RED & Amber warnings for heavy rainfall became the norm rather than the exception in SHWB (SubHimalayan W Bengal) and Sikkim.

The rainfall of Jun2020 resulted in numerous landslides in Darjeeling and Kalimpong districts as well as many in North Sikkim. STH will try and document as many as possible in this blog.

My thanks to Ms Shreya Gurung for her help

Praful Rao
Kalimpong district
Darjeeling- Sikkim Himalaya

The landslides of Darjeeling town (13Jun2020) - human factor also a trigger?

The SW monsoons finally arrived over the Darjeeling - Sikkim Himalaya on 12Jun2020.
Darjeeling town, received 105mm of rain over a approx 36 hour period, most of it coming down on 12Jun in intense bursts. Between 11-13Jun, Kurseong clocked an astounding 299 mm of rain and this not unusual since our experience shows that Kurseong certainly receives some of the heaviest rainfall in the region.
Six of the landslides which took place within the Municipal Limits of Darjeeling are shown in the map:-

Coordinates of these landslides and two others which are known to have taken place at Kurseong and Mungpoo are given below:-

Images of the landslides at Mungpoo and Sivitar T.E, Kurseong are placed below:-

Rainfall data of 2020 for our region is placed below:-

From the rainfall data it is very evident that, except for Gangtok ie East and North Sikkim, the whole region has been deficient in rainfall not only in 2020 but from the end of the monsoon season in 2019. As such I wonder how 6 landslips (small landslides) were triggered by the first burst of heavy rain (109mm) in Darjeeling town?
It is not abnormal to receive 100mm of rain over a 24hr period during the monsoons, what is abnormal is that this rain coming after a prolonged dry period caused so many landslips in Darjeeling town.
Each of those slope failures were capable of taking human life and our experience over the years has been that it is these small landslides in an urban setting which cause most of the fatal landslides. Saying so, I am painfully reminded of a fatal landslide barely 5 mins walk from my home in Jun2010, at Tirpai Kalimpong when it rained only 45mm overnight. It snuffed out the lives of a young mother and her 2 school going children.
In saying so, I must point out that occurring in densely populated urban settings, the trigger for the  landslide always has a human component and in most cases it boils down to managing our drainage system well. The high volumes of surface runoff from the intense rain in our towns must be drained away quickly and safely - otherwise they are bound to do mischief.

Praful Rao,
Kalimpong district
Darjeeling-Sikkim Himalaya

Rainfall data of some towns in Darjeeling - Sikkim Himalaya - May2020

The major weather event of May2020 was of course Super Cyclone 'Amphan' (see above). Much more on the storm is covered in earlier posts.

Rainfall data of Sikkim is from IMD Sikkim.

Grateful thanks to Shreya for helping out.

Praful Rao,
Kalimpong district,
Darjeeling - Sikkim Himalaya