Monday, July 20, 2009

Excerpts from "Landslides in Darjeeling Town"

Landslide is perhaps the most rampant environmental hazard threatening the Darjeeling town itself. During or after monsoon landslips create havoc in and around the Darjeeling township area. Numerous slips have occurred in the past however the intensity, cause and severity of the slide are being recorded since 1899.
Up to the first half of the present century there were certain regulations for the commercialization of the hill slopes, but since independence in a desperate attempt to acquire as much arable land as possible, extensive area under forest cover was gradually encroached upon. The ever increasing number of people haphazardly settled in a every bit of land available. During the British period it was made a rule that forest on the upper part of the hills should not be brought under ordinary commercial forest management. They had the notion of the ecological disaster that it would bring if these forests were denuded. But after independence, the demand for timber increased at an unprecedented rate and even the upper layer of the forest was not spared. Even after mass afforestation programme have been implemented a big gap remains between felling and replanting. It has been estimated that 70% of the cooking energy needs of the people is still being met by firewood. Needless and reckless obliteration of forests along with unscientific use of slopes especially in construction works coupled with geological, rainfall and slope characteristics have changed the scenario completely.
As a result Darjeeling one of the most densely populated tourist center in comparable environment exits on the verge of an environmental catastrophe as with just one concentrated shower of 50 mm/h would initiate numerous landslides endangering the lives and properties of the local inhabitants.
For a better understanding of the geographical distribution of landslip-prone areas in Darjeeling town, the following five categories of susceptibility zones have been identified:
Class I – Extremely high slip prone zone:
Almost after every torrential rain these tracts experience slips. They are mostly found on eastern lope of Jalapahar-Katapahar ridge it mainly covering the areas like Alubari, Munpari bustee, Toongsong, Pandam tea garden. Bhutia bustee and Hermitage, eastern lope of Lebong spur, it around Ging and Bannock - burn tea gardens and in small pockets on western slope of the Lebong spur i.e. Pattabong and Rangit tea gardens. It is also noticed a long western part of the town below Batasia.
Class II – Very high slip prone zone
These are the areas where slips occur for more than 5 times in 10 years. They are found along both the eastern and western slopes of the edge. i.e. upper Alubari, upper Toongsoong, along Tenzing Norge road, C.R. Das Road, eastern slope of Mall, below Raj Bhavan. It is also to be found on both sides of Lebong spur mainly in the tea gardens of Bannock-burn, Rangit and Pattabong. On the western slopes of the ridge it covers Rajbari bustee, Kagjhora, Victoria Falls, Dr. Zakir Hussain bustee, Dhobitala, around the jail, below the railway station, Lochanger, Haridashatta and Singamari.
Class III – High slip prone zone :
It covers the western spur of the town along the Hill Cart Road, Gandhi Road, Nimkidara, Police line, Marry Villa, Maypuri, Upper Kagjhora, below the convent cemetery, Dr. Zakir Hussain Raod, along the Birch Hill spur and the Lebong spur. Here landslips occur 2-5 times in ten years.
Class IV – Moderate to low slip prone zone :
In this zone landslips occur once or twice in last ten years. It is found mostly along the ridges of Jalapahar-Katapahar up to the Mall including the bazaar area and also along the Lebong spur including the Lebong cart road.
Class V – None to negligible:
It is found in pockets on the ridge tops of the Jalapahar Katapahar ridge, the Lebong ridge (Military Cantonment) and the Observatory hill and on the top of the Birch Hill ridge where slips occur rarely.

Water Management Scenario In Darjeeling Town:
Slope instability has a direct relationship to water supply in Darjeeling town. At present the town almost wholly depends on the supply of 182000 m3 of drinking water from 3 lakes of Senchal ridge. Taking the UN human water requirement standard of 0.076 m3 individual/ day the total demand for Darjeeling town has been estimated by the Municipality authority as 110 million gallons. Considering the present population of 10,7530 this demand will be much, more in the future, pointing to a perpetual crisis in water in Darjeeling town. There would not be any water crisis if the storage capacity could be enhanced by the construction at least five more reservoirs of the capacity of 38 thousands m3 each. But the Senchal ridge is hardly stable enough to stand such construction of reservoirs. At the most one more reservoirs can be constructed. So at present only 8 out of 26 jhoras feeding the Senchal lakes are kept alive during the monsoons and the rest cut off because there is no capacity to store. The Rockville reservoir at the centre of the town above the railway station was affected by landslip in 1950 and it was feared that the reservoir also might be damaged and it’s bursting might cause further damage. The area that slipped involved only the superficial layer of sandy clay and boulders originally resting at an angle 40 degrees, which is greater than the angle of repose for such materials. Lubrications further lowered the angle of repose and caused the slip.

Nearly 100 m length of the topmost water pipe line located on the eastern slope of Darjeeling – Jalapahar ridge was damaged during 1950 monsoon. Slips had damaged and twisted the pipe at various places causing temporary stoppage to water supply. The damages to pipes can be prevented burying them underground. This however would be costly and frequent inspection is not possible. However some protective measures should be provided to the pipelines in order to protect them against the impact of falling materials. In 1988 & 1993 landslides damaged water pipe lines in different parts of Darjeeling also. During tourist season when the population doubles itself, the water problem reaches its maximum these months (April to June and late September to November). The hotel bribes the municipal authorities to divert the maximum water to their establishments by tapping the pipelines. In such situations the local people the most badly affected lot. It is true that landslides affect the water supply in the Darjeeling town but for aggravating the problem it is man himself who is to be blamed. Depletion of forests and the increase in average run - off (about 2180, 86 mm at present) has helped in drying up of many local springs, which used to supply water to local people. The situation has deteriorated further in recent years. Villages have to walk a few kilometers in search of water during non-monsoon months and even the tourists living in moderate hotels have to pay five to ten for a bucket of water during peak tourist season in the month of May (2003 and 2004).
Conclusion: In view of the ever increasing problems of landslide in Darjeeling town man must be aware of the possible dangers that he is inviting due to the careless dealing with nature. It is true that one has to make room for the growing population and in this pursuit he has to utilize every piece of land available. But the precautions that have to be adopted should not be neglected. In the town the revetments are not properly maintained, the weep holes are choked and drains are dumped with garbage, restricting free drainage of water. Moreover, the present land use system should be properly evaluated. The construction of high-rise building should be stopped immediately. The people should be provided with some alternate sources of energy through construction of Mini hydel projects, utilizing the springs, which can be an option to prevent them from cutting down more trees. Above all it should be of utmost priority to develop mass awareness among both the local people and tourists so that they become aware of the possible dangers they are inviting by interfering with natural laws.

the above excerpt is from "Landslides in Darjeeling Town" by Dr Subhash Ranjan Basu, Professor of Geomorphology and Environmental Geography, Univ of Calcutta. (the full article is available here)

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