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Land Assessment Using Digital Terrain Modelling: a Case Study from the Hilly Regions of Tankabati Union of Bandarban Sadar Upazila.

Md. Shahid Ullah
BBS-UNFPA Project, Bangladesh Bureau of Statistics, Agargaon, Dhaka-1207, Bangladesh.

M. J. Uddin
Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

Dr. Syed Fazle Elahi
Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

A study was conducted in landuse assessment using digital elevation modelling for the Tankabati Union of Bandarban Sadar Upazila under the hilly regions of Bangladesh. A digital contour map was used to calculate the slope class gradients for the study area making use of Triangulated Irregular Network (TIN). Slope class map prepared based on steepness making polygon coverage using ARC/TIN. The areas were estimated from the contour based digital landform map. From this account of land types, the potential land use had been assigned depending on the slope gradients. The medium high hill and low hill covers the highest area and would be suitable for fuel wood, fodder, timber plants and some fruit trees. High hill areas of this study area is suitable for growing tree crops and the valleys for dryland kharif crops.

Keywords: Landuse assessment, Digital terrain modelling, Hilly region, Bandarban

Location: Tankabati union, Bandarban Sadar Upazila, Bandarban district, Bangladesh

Start Date:

End Date:

Program Area: Socio-economic and Policy

Non-commodity: GIS

Objectives:

The study was conducted in land use assessment using digital elevation modelling for the hilly part of the Tankabati union of Bandarban Sadar Upazila of Bandarban district.

Methodology:

A small area variable terrain had been taken for this study on the basis of topography, data availability and accessibility. For terrain modelling and analytical purpose Digital Terrain Modelling (DTM) provides an appropriate tool (Tor Bernhardsen 1992). A study was undertaken in land use planning using DTM for the hilly areas of Bangladesh. Tankabati Union had been selected as a case study in assessing landuse using DTM. Tankabati Union is situated in the southern part of Bandarban Upazila, Bandarban, Bangladesh. It is located between 22°05' and 21°55' N and between 92°10' and 92°19' E at an elevation from 15 to 1000 m above MSL. The rocks of this area are made up of consolidated sandstone and Shale's of Tertiary age, which have been subjected to folding, faulting, tilting and dissection. These ridge crests are at heights 300 - 1000 m above MSL. The medium and low hills are at heights of 150-300 m and <150 m above MSL, respectively. These are formed mainly over unconsolidated sandstone of late Tertiary age (Brammer 1997). From the toposheets, 1978 contour lines above 30 m altitude and with 25 m vertical intervals were digitized on the basis of altitude, the boundaries of Different types of hills files. The slope class map is prepared based on steepness making digital landform maps based on contour polygon coverage using ARC/TIN. Toposheets generated by Survey of Bangladesh was used to digitize the contour lines in ARC/INFO 7.2 UNIX version. These contour lines were converted to TIN using the slope criteria using. These TIN were converted to ARC/INFO coverage as polygon. Here the slope criteria was placed and calculated the slope gradient for the study area. Using collected data a contour map from elevation data was created and then using TIN, it was determined the slope classes of the area. Data sources for a DTM consist of observation about terrain elevation and additional information about phenomena that significantly influence the shape of terrain surface i.e. structural features such as drainage pattern, ridges and the surface of discontinuity. The collected data was structured in a way that it can be used for any subsequent terrain modelling operation. So far two structures was identified as data structure; rectangular grid and TIN. it was taken TIN and DEM as an appropriate structure. TIN is able to reflect adequately the variable density of data points and the roughness of terrain. A TIN represents the terrain surface as set of interconnected triangular facet. Three vertices x, y coordinate (geographic location) and the z coordinate (elevation) values would be encoded. TIN or an area model is an average of triangular areas with their corners stationed at selected points of great importance, for which the elevations are known (Burrough 1993). The inclination of the terrain is assumed to be constant within each triangle. The area of the triangles may vary, with the smallest representing those areas in which the terrain varies the most. The resultant model is TIN.

Source of Information: J. Asiat. Soc. Bangladesh, Sci., 33(2): 147-151, December 2007

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Funding Source:

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Achievement/Findings:

The steep slopes severely limit possibilities for agricultural development (FAO 1983). Broadly speaking, the safe upper slope limit for cultivating tree crops is to be 40 per cent and for field crops 5 per cent. However, these limits can be extended or reduced depending on soil depth and texture and the degree of soil protection provided by individual crops and the way they are managed (Brammer 1997). Slope class is an important indicator of crop production planning in the sloping land of Bangladesh. The steep slopes severely limit possibilities for agricultural development. From this account of land types, the potential land use has been assigned depending on the slope gradients. The medium high hill and low hill covers the highest area and would be suitable for fuel wood, fodder, timber plants and some fruit trees. High hill areas of this study area is suitable for growing tree crops and the valleys for dryland kharif crops.

Knowledge Management: Journal