Landslide Hazard Zonation/Susceptibility Map

The Landslide Hazard Zonation (LHZ) map of Guwahati city is generated by integrating various thematic parameters using Analytical Hierarchal Process (AHP) depending on their role in causing slope instability. Thematic maps are generated using RS and GIS techniques, field surveys and from collateral data representing geo-environmental parameters of the study area. However, like most of the current hazard maps this map is also aims to predict where failures are most likely to occur without any clear indication of when they are likely to take place hence ideally this map can defined as landslide susceptibility maps.

The LHZ map is generated on the assumption that the factors which caused slope-failure in a region are the same as those which will generate landslides in the future (Carrara et al., 1996). The map thus generated is divided into five classes, namely, Very Low Hazard Zone (VLHZ), Low Hazard Zone (LHZ), Moderate Hazard Zone (MHZ), High Hazard Zone (HHZ) and Very High Hazard Zone (VHHZ). Validation of the hazard maps with respect to reported landslide events shows good correlation with respect to actual landslide occurrences. The model as well as the results can be further validated with respect to future new landslide location as and when reported. The landslide occurrence maps have three classes, such as active landslides(as surveyed during 2010 to 2012), old dormant landslides(as reported before 2010) which can reactivate, potential areas of future landslides. LHZ map is generated based on the database prepared from satellite images acquired during 2009-2011. Therefore, the hazard zonation map indicates landslide susceptibility based on the prevailing ground condition during 2011. Any subsequent landslide in the predicted high hazard classes, therefore, validates the result.

Briefly, the slope failure problem in the Guwahati city has resulted due to interactions of different causes such as geological, structural, physiographical and hydrological etc. Beside these, the quantity, duration and kind of precipitation have also been considered as direct mechanical cause along with alarming unscientific anthropogenic activities.

Correlation with seismic activities could not be established for reported landslide. However, an earthquake with magnitudes greater than 4.0 can trigger landslide on very susceptible slopes and an earthquake with magnitudes greater than 6.0 can trigger wide spread landslide specially of rock slide/fall once reaching critical acceleration.