Monday, August 24, 2009

19Aug2009 : 189.2mm of rainfall and 3deaths

Case Study : Landslide situation around Kalimpong town (Aug2009)

“With rapid urbanization and a phenomenal growth of tourism, the Darjiling and Sikkim Himalayas have been experiencing an unprecedented rise in population since independence. Consequently, pressure on land is increasing with the gradual elimination of virgin forests. Unscientific and unplanned usages of land coupled with vulnerable geological structure and high rainfall have led to the establishment of vicious cycle of soil erosion and landslides. During or after every monsoon, landslides create havoc in the Darjiling-Sikkim Himalayas devastating human lives and properties.
As a result, the Darjiling-Sikkim Himalayas, one of the most densely populated tourist centers in such monsoon environments is on the verge of an environmental catastrophe so that just one concentrated shower of 50mm per hour could initiate landslides endangering innumerable local people and their properties”

- Subhas Ranjan Basu (University of Kolkata) and Sunil Kr De (University of Tripura)

1. Meteorological background.

While rainfall data for the months of May, June and July 2009 reveal that the district has had deficient rainfall, what is significant is that rainfall has been extremely erratic.
Thus, despite less precipitation, we have had major landslides this year coinciding with periods of intense, heavy rainfall:-

  • 24May-27May2009 - Cyclone Aila.
    Resulted in 27 deaths and major destruction in
    Darjeeling and Kurseong

  • 2July2009, 112mm of rain (in Kalimpong).
    Resulted in some deaths and a large number of landslides in Nimbong (Kalimpong sub-division).
  • 15Aug2009, 152mm of rain over 18hr period.
    Resulted in death and destruction in Kurseong and Kalimpong
  • 19Aug2009, 189.2mm of rainfall in Kalimpong.
    Resulted in major destruction in and around Kalimpong town and several deaths in Mirik,
    Kalimpong subdivision and Sikkim.

Historically speaking, most of the major landslides in Darjeeling district have occurred towards the end of the monsoons i.e. when the earth is saturated with water and the trigger for landslides is a burst of high intensity rainfall.
Thus, severe landslides occurred in the district in Sep1899, Oct1968 and Sep2007.
As such the urgent need for preparedness to deal with recurrence of such devastation during Aug-Oct 2009.

2. Landslide situation in areas surveyed after 19Aug2009.
Placed below is a report on the situation of the affected areas visited on 20/21/22Aug2009.

a) Chibo & Pashyor area.
A designated “sinking zone” for decades but which is densely populated now. As on date both these places remain isolated from Kalimpong town after road access and bridges were washed away on 19Aug09 by the many rivulets (jhoras) which plough through this area. Judging by the extent of damage, it is unlikely that these communication links can be restored quickly.
A large number of fast flowing jhoras/rivulets are the primary source of major landslides here though a contributory factor also may be the paddy cultivation in Chibo & Pashyor.

b) 7th Mile (Pachis Dhurey), 8th Mile (Shali Khop) area.
A number of houses at Pachis Dhurey are now vulnerable due to slopes which have been destabilized. In Shali khop, a large landslide became active in Sep2007 and has worsened this year after the heavy rains in Aug. The slide has decimated a road which connects several villages in the Nursery Gaon area of Shalikhop to the arterial road to Kalimpong town. The slide has also affected 3 fresh water sources which supply water to approx 100 houses in this neighbourhood.

c) Chota Bhalukhop area.
This is a densely populated zone lying below the sub-divisional Hospital and Macfarlane church complex. In Sep2007, there were major landslides (and two deaths) here caused by poor drainage. Despite having pointed this out, no work was done to change or improve the drainage over the last two years as such the torrential downpours in Aug09 resulted in numerous landslides in this area.
In view of the population density here, further landslides in this place could result in a large number of casualties.

d) Soureni village and Bara Bhalukhop area.
Rock falls at Soureni village originate at the crest of Deolo Hill. In view of the steepness of this place and size of rocks the only choice maybe to relocate this village in case of further landslides.
Bara Bhalukhop lies directly below Soureni and Tirpai and has several large landslides due to which a number of families have lost arable land. Comparatively, the population in this area is less than that in Chota Bhalukhop.

e) TV tower area and Tirpai.
The TV tower area (and Saipatri gaon) constitutes an old landslide area where there were a number of fatalities in the Oct1968 landslides.

In Sep2007, this area again became active forcing the people to take shelter in a nearby unoccupied shopping complex.
On 19Aug2009, there were a number of small landslides in this area; more would have certainly followed had the rain continued. So in view of the dense population, the area needs to be watched in case of heavy rain. The western face of Tirpai bazaar too has been destabilized with cracks and landslides occurring at numerous places along the ridge.

f) East Main Road area.
Lying on the eastern face of the Kalimpong ridge, this area was earlier very stable. In 2009, a number of rivulets / jhoras charged by run-off from built up places in Durpin (army cantonment zone) have ploughed up portions of this area and a number of landslides have occurred, especially, directly below Durpin. 3 bridge/culverts in this area have been destroyed by the rains in Aug09 and the drinking water source of a number of houses in the East Main Road area have been affected.

g) Bong bustee area.
Lying directly below (f), it was again one of the most stable areas of Kalimpong. The same drains or jhoras which have caused problems in (f) have caused a number of new landslides in Aug2009 especially in the vicinity of Bong church and Animal Shelter.

h) Sindebung.
This comprises of fertile farmland in the underbelly of Kalimpong. A serious landslide situation has existed here for many decades with numerous jhoras/rivulets from the town and Dr Graham’s Homes area dissecting these farmlands. Much farmland has been lost to landslides in the past and in Aug2009; the already serious situation has only become worse.

i) Dr Graham’s Homes, Dalapchand and 14th Mile areas.
Though there were major landslides in these areas in Sep2007, in Aug2009, they were relatively stable.

3. Conclusion

  • Cause of landslides.
    The cause of landslides is the high intensity of rainfall coupled with poor drainage.
    Over the years there has been a vast increase in urban/built up areas which has led to extremely high volume surface runoff water. The jhoras /rivulets which are fed by this water are simply incapable of handling this huge overload of high velocity water since no jhora/river training (and other landslide preventive) work has been carried out in the district for decades; this is leading to soil erosion and landslides on an unprecedented scale.
    This is compounded by the fact that many of the over populated vulnerable slopes appear to be where unplanned (illegal) settlements have mushroomed and where there is virtually no drainage.
    Thus the causes are largely anthropogenic
  • Damage assessment.
    It is apparent that in Aug2009, barring the town itself, almost all areas in the vicinity of Kalimpong town suffered damage equal to or more than Darjeeling did during Cyclone Aila (except for the fact that there was no major loss of life).
  • Prognosis.
    The intense bursts of rainfall on 15 and 19Aug09 have led to outright damage in many areas or a condition where one or more concentrated showers on a similar scale will lead to landslides in many structurally weakened slopes resulting in large scale loss of life and property – such susceptible areas exist in virtually all the zones mentioned above.
    With the monsoons expected to last until 12Oct2009 (as per IMetD), the likelihood of such high intensity rainfall recurring is very real.
  • Possible solutions.
    a) Whereas, firefighting (preventive) engineering measures such as retaining wall construction, drainage correction, river/jhora training etc are being resorted to, the sheer magnitude of damage will not permit meaningful work to be undertaken in all the vulnerable areas in the time available (Aug-Oct 09).
    It is therefore necessary to empower the communities to deal with the situation as best they can, if and when heavy and concentrated burst of rainfall occurs. This can only be achieved by carrying out an intense awareness campaign amongst the affected people on community based disaster risk management (CBDRM).
    c) Whereas SaveTheHills has been engaged in raising awareness about landslide hazards in the district for the past two years, it is urgently requested that NIDM carry out crash courses on this aspect, in Kalimpong immediately.
  • A word of caution.
    Not withstanding this, it goes without saying that all agencies/ NGOs involved in post disaster relief should remain on high alert should there be intense rain in the month or more that monsoons will be active in this region.

Comment by Praful Rao
I visited all the above areas between 20-22Aug2009 and have met scores of desperate, anxious people who spend sleepless nights whenever it starts raining. Even though I have written the conclusions, the views are not mine alone but those I have gleaned from the many discussions I have had with ordinary people and experts.
Lastly, the entire report has been mailed to the National Disaster Management Authority and District Magistrate (Darjeeling) amongst many others.

1 comment:

HIMU said...

Govt. of West Bengal includes Darjeeling in DRMP (2nd Phase)from State's own budget head. As soon as it is possible, the programme will start.