S.Vasantha Kumar
GIS Engineer
Centre for Disaster Mitigation and Management,
Email: [email protected]
N.Raja
GIS Engineer
Centre for Disaster Mitigation and Management
G. Prasad Babu
Geological Specialist
Centre for Disaster Mitigation and Management
In hilly regions, landslides constitute one of the major hazards that cause losses to lives and property. Landslide analysis is a complex analysis, involving multiple of factors and it needs to be studied systematically in order to locate the areas prone for landslides. The topographic & morphometric features play an important role in deciding the areas prone to landslide. In this paper an attempt has been made to derive the topographic features such as slope, aspect, various convexities and curvatures and morphometric features such as peak, ridge, pass, plane, channel and pit for Mettupalayam-Udhagamandalam ghat section of length 54 Kilometers. The 1: 50000 scale Survey of India toposheets were used to derive contours of 20m intervals. The digitized vector contour was then converted to Digital Elevation Model (DEM) using the topographic functions of ENVI 4.3. The pixel size of output DEM was set no smaller than the contour interval in an attempt to reduce interpolation artifacts. The DEM was then used to derive topographic features such as slope, aspect, and various convexities and curvatures. All of the parameters are calculated by fitting a quadratic surface to the digital elevation data for the entered kernel size and taking the appropriate derivatives. The profile convexity measures the rate of change of the slope along the profile. The plan convexity measures the rate of change of the aspect along the plan. The longitudinal curvature and cross-sectional curvature are also measures of the surface curvature orthogonally in the down slope and across slope directions. Also the minimum and maximum overall surface curvatures are calculated.
Finally an output image that classifies each pixel into one of the following terrain types or morphometric features: peak, ridge, pass, plane, channel, or pit was generated. The slope and curvature of the surface determines the morphometric feature. For example, a sloping surface that is concave in the cross-sectional direction is a channel. A sloping surface that is convex in the cross-sectional direction is a ridge. Peaks have a convex cross-section and convex longitudinal curvature while pits have concave curvatures. These derived products if viewed in 3D surface view will be useful in enhancing the preparation of hazard zonation maps and would pave way for effective decision making for various development and regulatory activities in the mountaneous regions.
