Landslides on Imphal-Dimapur National Highway

Dr N Irabanta Singh *

andslide and Pathetic condition of Imphal-Jiribam Highway in May 2016 :: Pix - Rajeshwor Yumnam

Introduction :

The first investigation on landslides on Dimapur- Manipur road was made by the Geological Survey of India (V.P. Sondhi, Unpubl. Rep. Strategic. Br. 1941). Another preliminary geological investigation of landslides along Dimapur- Mao section was also reported in Ind. Geol. Assoc. Bull. 21:199-205 ( Anand, R. 1988). Landslides and road instability along NH-29 between Kohima and Chumukedema (both in Nagaland) was also reported on Proc. Intl. Conf. Dis. Mangt., Guwahati, 556-568 (Bhattacharjee et al.,1998).

The Central Road Research Institute (CRRI) had also commented on weak zones along the same highway between Chumkedma (Nagaland) and Maram (Manipur) (2000a). The Geotechnical investigations of land instability along National Highway between Kohima (Nagaland) and Senapati (Manipur) were already available( Thong et al., 2006a).

Further, the report on the effect of landslides on environment between Kohima and Chakhambama (both in Kohima district) Nagaland was also available (T.P. Khale. M.Sc. Env.Sc. Thesis, TGOUN, 2014). In the article, the writer wish to suggest certain mitigation measures for landslides in this route and also correction for sustainable development of the environment.

Causes of landslides :

It could be natural but most of the time it is man-made and also due to the negligence on the part of its inhabitants. It could also be due to unplanned road construction, presence of shales, tectonism, steep slope, loose top soil, intense rainfall and high moisture content, quarrying, improper drainage, less vegetation cover, anthropogenic activities like Jhum cultivation, terrace cultivation, deforestation, forest fire and blocking natural waterways.

Effects on environment :

Landslides causes air pollution from the quarries. It also effects water quality and aquatic life, it destructs habitat, it reduces arable land. Water is affected by landslides whereas water also causes landslides (hydrological effect). Land slides also reduces forest cover. As we know trees play a major role in the carbon cycle.

They convert the carbon dioxide in the air to Oxygen through the process of photosynthesis. Hence, we can call trees as natural regulators of Carbon dioxide. Emission of green house gases have increased many fold from vehicles plying on this natural highways, factories and other installations. Landslides also have escalated the situation. Emission of Carbon dioxide and other gases from vehicle passing through this national highway (NH) is a major concern.

Effects on time consumption and expenditure :

The distance from Imphal to Dimapur is 220 km only. But the time require for reaching Dimapur or from Dimapur to Imphal by Winger service is 8 to 9 hours. It will be more if one travels by bus. Whereas by personal vehicle (Car, Bolero, etc.) it requires 6 to 7 hours to reach Dimapur or Imphal. There is a place known as Lalmati (red soil), few kilometer after crossing Kohima Town. Landslides in this area is a perennial type.

It is more during the raining season. As such additional time is wasted in road diversion or waiting road clearance by Border Road Organization (BRO). On the top of it, additional expenditure fare (Rs 700-/ or more) is charged by the Wingger Services. For the private vehicles (Car, Jeepsy, Van, Bolero etc.) also require more fuel to pass through this landslide prone areas. Physically too, one is really exhausted to travel through this 220 km long national highway.

Discussion :

Landslides are inevitable in young mountain chains that are being uplifted (Petley and Reid, 1999). The major landslides have occurred due to combination of thick deposits of unconsolidated materials on steep slopes and adverse lithological, hydrological and anthropogenic conditions (Kumar et al,1995; Cruden and Varnes,1996).

Various factors including bedlock, surfacial deposits, slope, vegetation, rainfall, human activity and ancient landslide deposits are responsible for landslides (Brabb et al,1972; Nelson and Brabb,1972; Nelson et al,1976). Landslides would occur at the top of a slope as soon as the driving forces exceed the resisting forces. The safety factor for a slope is the ratio of the sum of resisting forces that act to prevent failure to the sum of the driving forces that end to cause failure (Piteau and Peckover, 1989).

The landslides occurs in narrowly fissured clays as soon as the shear stresses exceed the average shear strength of the material. Hydrogeology, water flow through fissures, human activity, high intensity rainfall etc. are responsible for landslides. In India, the majority of landslides incidents fall in the category of rainfall induced landslides (CRRI,2000a).

The landslides in Imphal-Dimapur highway (NH- 02 upto Mao, NH-29 Jakhama to Dimapur) are mostly in the Nagaland region. As on now, the National Highway No.29 from Dimapur to Kohima is under SARDP-NE Phase “A” four lane, was allotted to ECI Engineering and construction company Ltd. and Matyas-Gayatri company under the supervision of the National Highways and Infrastructure Development Corporation (NHIDCL).

The street of NH-29 Between Patkai bridge to Phiphema which is around 30 kms was allotted to ECI Engineering and Construction Company Ltd, which in turn had sublet to work to the contractors belonging to the Nagaland constructors and suppliers union (NCSU).

But unfortunately, Dimapur-Kohima NH-29 four lane road project has encountered a road-block in the form of suspected “taxation” demands from a Naga political group, just months after it began its first phase of road cutting. According to reports (The Morung Express, Saturday, June 17,2017) earth cutting of the NH-29 between Phiphema and Patkai bridge came to an abruptly halt since Thursday (15 June,2017) after some youth appeared on the scene and ordered the earth cutting to be immediately stopped. Let us hope time will bring a solution for the good so that the project is completed successfully.

Mitigation measures :

It should include proper afforestation, slope stabilization, proper drainage, to grow more grass cover, proper retaining wall building, culvert construction, etc. Further, alternative to Jhum cultivation should be taken up by the government for improving quality of life of those villages living in these landslide prone areas of the national highway.

Conclusion :

Dust from the quarries, landslides, heavy vehicular traffic, etc. effects the air quality, water quality and aquatic life. Reduction of habitat leading to reduction in the number of flora and fauna and also reduction in cultivated land, hydrological effect and loss in forest cover. The four lane Dimapur- Kohima highway Project for Nagaland if executed successfully, landslides problem in the area will be solved. Time to travel through this route will also be lessened.