An Engineer’s Perspective – Landslide Management in the Darjeeling Hills

From: http://www.savethehills.blogspot.com

HOLISTIC APPROACH TO LANDSLIDE MANAGEMENT AND MITIGATION IN THE HILL AREAS OF DARJEELING AND SIKKIM HIMALAYAS.

– Er. Upendra Mani Pradhan
B.Sc., B.Tech(Hons.), M.Tech(R.P.), A.I.T.P.(India)

Kalimpong.

Landslides may rightly be called the “Tsunami of the Hills”! It is, therefore, very encouraging to note that a Landslide Hazard Workshop is being hosted on 21st. November, 2008 at Darjeeling with the eminent Geographer and Landslide Expert, Prof. Leszek Starkel of Poland attending as the Chief Guest.

NEED FOR A HOLISTIC APPROACH :

Over 40 years of experience in Urban and Rural Planning has taught me that a simplistic approach, of building a wall here and a drain there, will not solve the problems of landslides in the hills. Numerous inter-connected factors come into play, requiring a deeper study of cause and effect that will finally lead us to a more Holistic Approach. A few points for interaction during the Workshop are given below :

1. BANNING OF POLYBAGS BY IMPOSING FINES :

This has been tried out by several municipalities from time to time, but the duration of success is barely a couple of months, after which the polybags reappear! The main objection being most of the marketing of goods are done in modern, attractive, polythene packages, which the municipalities cannot control. It is said that polythene and plastic bottles take as many as 400-700 years to just begin to breakdown in a land-fill – and they constitute millions of tons in garbage heaps of urban areas! Why not recycle this environmentally degrading waste material of global nuisance value into long-lasting attractive coloured modular-sized bricks for the ever growing building industry? Are the Tatas, Birlas, Mittals and Ambanis listening?? They can get their raw materials free of cost !

2. “JHORAS” (HILL STREAMS) – WORTH WORSHIPPING! :

It is often believed that ‘Jhoras’ are the main cause for landslides in the hills. This is far from the truth. In fact, ‘Jhoras’ form part of the natural drainage system and are meant to be Nature’s ‘safety valves’ to quickly and safely carry away rainfall runoff from large hilly catchment areas, to the rivers and seas in the plain areas below, without causing any damages along the way. ‘Jhoras’ carry water and so maintain natural vegetation like trees, shrubs, grasses along their sides to prevent toe erosion. But Man, in his infinite wisdom, cuts down such trees and shrubs; indiscriminately throws waste-matter into them; removes stone boulders, cobbles and sand; blocks the ‘jhoras’ and constructs buildings on them, thereby violating all the unwritten environmental laws of Nature! Mother Nature revolts and retaliates through landslides!

Another reason is that our hill areas are bombarded with heavy rainfall during the monsoon (2000mm to 3000mm per annum). In the natural scheme of things, this precipitation partly permeates into the soil through open ground and partly flows as surface runoff and finds its way to the ‘jhoras’. But with intense urbanization in our towns, almost all open ground surfaces have been built upon or paved by roads, courtyards and footpaths, thereby all the rainfall now flows as surface runoff and enters the ‘jhoras’ with great velocity, far exceeding their normal carrying capacity. This results in toe erosion of the ‘jhoras’ which is the precursor to a landslide.

From the above it can be seen that our forefathers were no fools! They set up ‘Devi-Sthans’ (Place of worshipping Goddess) amidst ‘jhoras’for the simple reason that our ‘jhoras’ must be faithfully conserved as they have a vital role to play in our lives. ‘Jhora’ water can also be diverted into farm lands for irrigation purposes. However, in the hills, it is better not to use this water for surface-irrigating paddy crops, because stagnant water kept in the fields over a long stretch of time, may cause landslides. From careful observation, it can also be found that the percolated water through porous soil, normally finds its way back into the ‘jhoras’ at a lower point below – this is naturally filtered water, which is used by village folk for drinking purposes. Our ‘jhoras’ are sacred entities – let us spread awareness and restore them back to their pristene glory, through planned Conservation.

3. URBANIZATION PARADOX IN THE HILLS – NOWHERE TO GO, BUT UPWARDS! :

About a week ago, Newspapers carried bold headlines about the demolition drive taken up by Darjeeling Municipality, to knock down two of the eight storied building constructed illegally within the Municipal area. A photograph of Darjeeling Town also accompanied this news. What pained me most was the depressing photograph of the so called “Queen of Hill Stations” – virtually in Rags, with sub-standard, un-aesthetic, tall buildings piled one-on-top-of-the-other!

The same is true for Kurseong and Kalimpong Towns. In Sikkim, Gangtok, Ramphu, Namchi, Singtam and the other towns are doing no better, Mirik is a relatively new lake-town, but its overall development and upkeep leaves much to be desired. We claim that Tourism is one of our main economic planks – but once they arrive, the tourists experience a sense of deprivation and despair. There is no planning involved in all these towns and there is a great shortage of greenery, parks and playgrounds, public utilities and facilities and other infrastructure necessary to qualify as a Tourist Town. The enthusiastic tourists surely deserve a better deal!

Darjeeling and Kurseong Towns are now super saturated – all private lands have been built upon and many available public lands have been encroached and also built upon – not sparing ‘jhora’ lands! Both these towns are surrounded by tea gardens and forests, and there is no further scope for horizontal expansion in areas of low gradient. The only possibility is to go upwards, which explains why illegal construction of buildings 5-8 stories (i.e. 60 feet) high are taking place at random. Needless to say that tall concrete buildings exert excessive pressure on the land, heightening the possibility of landslides. Since land has become a very scarce commodity, Illegal constructions are now mushrooming on lands that have a natural gradient of 50 degrees or more. Exceeding the “Angle of Repose” of soil, is a direct invitation to landslides! Foolish but daring people are also building houses on the surface of old landslides, many of which have been washed away during monsoon rains. We don’t seem to learn from our past mistakes! It is distressing to note that all three Towns are sitting on time bombs – Kurseong atop the infamous Ambootia Landslide (supposed to be the biggest in Asia!); Darjeeling atop the Aloobari-Toongsoong and Jail Landslides, and Kalimpong atop the Sindebong, Bhalukhop-Alaichikhop Landslides! A disaster of unimaginable magnitude is waiting to happen anytime!!

Before India’s independence, the British never allowed any construction in the hills to exceed 2 stories, and most of the structures at that time were neat little cottages, made of wood and other light-weight materials. Now, the maximum height of buildings allowed by the Darjeeling Hill Municipal Building Bye-laws is 11.5 meters ( 38 feet) or 4 stories, assuming that room height of 8.5 feet to 9.0 feet will be sufficient for the cold climate of Darjeeling hills. This figure was arrived at during an Expert Committee meeting held at Calcutta (in which I was also a Member). The Darjeeling Municipality has now raised this to 13.5 meters!

Kalimpong and Mirik are better situated, as the Municipal areas are surrounded by large tracts of Khasmahal farm-lands. Sikkim Towns also have restricted space for horizontal expansion, as a result of which heavy RCC high-rise buildings are fast coming up everywhere, giving nightmares to everyone – especially during the rainy season!

The only solution to this problem is to follow Gandhiji’s “Back to the Village” policy and prepare and implement Balanced Regional Growth Plans for the entire hill areas, interspaced with ideally located and well planned Satellite Townships

4. SOIL CONSERVATION POSSIBILITIES – ROADS VERSUS ROPEWAYS :

It has been found that bamboo groves near human settlements in the hills can be dangerous. As bamboo has very shallow roots, the entire grove, having dense interlocked root system, tends to slide down as a solid mass, thereby threatening to cause big landslide damages. Some fast growing native trees with deep root system were also tried out to conserve soil on landsides. However in a few years time, the trees became very tall , big and weighty and finally the trees themselves were responsible for causing fresh landslides. What should perhaps be done is to go in for light shrubs and grasses (e.g. Vitever) with deep root system. An inventory should be made of suitable plants by the Soil Conservation and Forest Departments for immediate testing and application at landslide sites and along both sides of ‘jhoras’. Stunting of suitable deep-rooted trees to reduce their weight may also help. ‘Soil Nailing Techniques’ also sound good – but need to be thoroughly investigated for applicability in the our hills.

It is seen that major road alignments, cutting across our hills, are responsible for triggering the maximum number of landslides during monsoon period. While extensive road connectivity is undoubtedly very important, taking a road upto a certain major focal point in the rural area and then connecting this centre with other secondary villages by ropeways, for movement of both passengers and goods, could be a viable alternative for economic development of the hills, Ropeways need minimum land for putting up their towers and, therefore, cause least damages to the hill sides. While constructing roads, use of blasting technology should be avoided as much as possible, as there is risk of sliding owing to vibrations under the soil. If geological formations permit, we can also think of constructing a series of tunnels (as they have in Pune), which will also reduce travel lengths considerably.

Of late, increase of vehicle population in the hills, is simply maddening! As a result, vehicles are forced to move at crawling speed and searching for suitable space to park the car becomes an impossible and frustrating task! Better to introduce and encourage a system of mass transportation by mini-buses.

5. FOREST LANDS AND WASTE LANDS :

In the beginning of British Rule around 1836 – it is said that the entire hill areas of Darjeeling and Sikkim were dense forests, with no sign of urbanization as we know it today. Forests were clear-felled in a big way in and around Darjeeling. Huge migration of labour took place from Nepal, Bhutan and Sikkim and tea plantations were laid by the British. Human settlements, therefore, took place in Forest lands. In 1975, it is learnt that the total forest area in the hill region was 1141 sq. km. distributed over the 3 forest divisions of Darjeeling, Kurseong and Kalimpong. Reserved Forests covered 1113 sq.km, Protected forests 9 sq.km and unclassified State forests 29 sq.km. Out o the total 1141 sq.km., only 466 sq.km. were available for economic exploitation by the State of West Bengal. It is a known fact that the Forest Department zealously guards its property and quite rightly so, otherwise by now everything would have been reduced to barren hills. Transfer of forest lands is normally not allowed except in very rare cases when equivalent land must be handed back to the forest department by the transferee, together with cost of re-plantation. This is a wonderful system to preserve our ecology and bio-diversity.

Not much is known about “Waste lands”, but one can presume that they belong to a category of land, which has not been put to any use so far! It is high time that thorough geological studies and mapping of Waste lands are carried out immediately and appropriate steps taken to put them to good use. First and foremost, we need to identify a number of large (say 5 sq.km. – 15 sq.kms. each ) suitable, physio-geographically stable areas for setting up Planned Satellite / New Townships in the region. Do we have a local qualified Hill Geologist amongst us?

6. LAND RECLAMATION IN THE HILLS – FOR OUR LANDSLIDE-FREE, FUTURE TOWNS AND CITIES :

For centuries in Human history, valuable lands in the plains have been reclaimed from the sea or marshes, on which planned cities and other infrastructure have been developed (e.g. Holland where 40% of land is below the sea level ; Salt Lake City in USA; Salt Lake in Kolkata; Queen’s Necklace in Mumbai). I feel that huge tracts of stable, valuable lands can also be reclaimed in the hill areas for setting up our future towns and cities.

It is observed that the most stable lands in the hills are found on hill tops and spurs. The Main Road strip of Kalimpong is located on a spur, where landslides are not known to have occurred at all. This is because drainage ‘jhoras’ are situated at quite a distance away. The catchment area on top being small, flow of water in these ‘jhoras’ is also minimal and therefore their erosion capacity is practically nil. Suppose we find a number of hillocks (preferably waste lands), adjacent to each other and having natural slopes of low gradient – then we will discover that they are separated from each other by shallow valleys at a formative stage. If we draw a cross section of the hillocks, we will see cross sectional lines having low gradient and representing less stable top soils of varying thicknesses and characteristics, below which there will be more stable soils and rocks. The thickness of the top soil can be anything between 3 feet to 10 feet or more. The idea is to bulldoze the entire topsoil and create large terraced surfaces made up of stabilized rocks. The excavated topsoil/rocks can be used to fill up the shallow valleys and fully compacted. This way we will be able to create extensive stable ground surfaces on rocky, freshly created terraced ground levels, on which we can plan out our NEW TOWNS AND CITIES! Of course, all infrastructure like roads, footpaths, multi-storied car parking, water supply, drainage, sewerage, telecommunication, public facilities and utilities etc. must be in place. Water harvesting from roof-tops, Solar Energy for heating and lighting etc. must also be part and parcel of the Project. All this may sound utopian, but this is not beyond the realm of possibility! The most attractive part of this Project is that it will be LANDSLIDE-FREE, as the unstable layers of soil on top will have been removed!! TO ACHIEVE THIS DREAM, WE WILL HAVE TO THINK BOLDLY AND DO THINGS DIFFERENTLY!! This is only a theoretical concept. WHERE IS OUR GEOLOGIST ?

OUR TOWNS ARE FAST TURNING INTO UNMANAGEABLE, UNHEALTHY SLUMS, AND IF WE DON’T TAKE PROMPT POSITIVE ACTION NOW, THEN WE HUMAN BEINGS OURSELVES WILL HAVE TO FACE THE REAL DANGER OF BEING ENLISTED UNDER THE “ENDANGERED SPECIES”!

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