C. D. Singh’s research while affiliated with Geological Survey of India and other places

This paper compares the findings of macrolevel landslide hazard zonation carried out along the highway from Bhalukpong to Bomdila, West Kameng district, Arunachal Pradesh following GSI and BIS guidelines. The map resulted from the GSI guideline shows that 69.31% of the faceted area falls under the Low Hazard Zone (LHZ) while 17.69%, 7.31%, 5.03% and 0.65% of the area are in Moderate Hazard Zone (MHZ), High Hazard Zone (HHZ), Very Low Hazard Zone (VLHZ) and Very High Hazard Zone (VHHZ) respectively. Correlation between the landslide incidences and different hazard zones reveals that maximum failure percentage is in VHHZ and it is followed by HHZ, MHZ and LHZ. The second map resulting from BIS guideline reveals that 45.77% of the faceted area falls under MHZ while 41.39%, 11.52% and 1.29% of the area are in HHZ, LHZ and VHHZ respectively. Not a single facet falls in VLHZ.With regard to failure percentage VHHZ experiences 50%, while that of HHZ, MMH and LHZ is roughly 11.5% each. In the study area, the landslide hazard zonation map resulting from GSI guideline broadly conforms to field condition. It may be due to the fact that the study area is along the road corridor where slope cutting and landslides are very common and GSI guideline considers both the slope cutting and landslide parameters, while it is not so in the case of BIS guidelines. However, a final conclusion can be drawn after carrying out such studies in different geological settings.

Landslides may be caused either by natural process or human activity or combination of both. In many cases, modifications in hill slopes are carried out with or without proper slope stability analysis, even though the consequences are well known. In other cases, stable slopes are converted into unstable slopes by the people residing in the area by artificial modification/alterations of the hill slope without basic knowledge of hill slope management. Such cases are very common in the hilly terrain including northeast India and they have caused loss of many lives even though the size of such landslide are very small. The present paper describes four examples from different parts of the northeast India where the terraced hill slopes that remained stable for an appreciable length of time have been converted to unstable slopes.

National Highway-39 is the only lifeline of the state of Manipur. The sector between Karong and Mao is highly landslide prone and frequently blocked the NH-39. The area is represented by Disang and Barail Groups of rock. Considering the importance of NH-39, landslide susceptibility zonation studies along NH-39 between Karong and Mao were carried out following GSI guideline, a modified form of BIS (1998). Landslide susceptibility zonation map reveals that 57% of the facets belong to low susceptible zone. It is followed by moderate susceptible zone (33%), high susceptible zone (9%) and very low susceptible zone (1%). All the facets of high susceptible zone are concentrated along the road section of NH-39, especially Maram-Mao sector. The landslide susceptibility zonation map gives an overall picture of the stability condition of the hill slopes so it can be used as a base map for planning any developmental scheme or maintenance of the existing one.