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Assessment of Resources in Hilly Areas from Semi-detailed Soil Survey Information Applying GIS Techniques

AHM Kamrul Habib Khan
System Analyst (incharge).
Retired as Director, SRDI, Dhaka

Moqbul Hossain
SSO
PSO and PD (SMFS) SRDI

Dilara Hasan
SO
GIS unit, SRDI.

Abstract/ Executive Summary:

In development planning of mountainous areas, information on location of particular landform and specifically, slope characteristics is needed. This information is usually not shown on semi-detailed soil survey maps that show landform and soils. Under each landform, description of soils and slope classes is usually provided. Available soil and landform maps (1:50,000) and topographical maps (1:25,000) are used as base materials which are digitized to produce contour based landform and slope class maps in the same scale. In contour based landform maps high hills, medium high hills, low hills and valleys are clearly differentiated. The slope class map shows the special patterns of slope steepness. It also shows the land features in greater detail. Other features such as areas susceptible to different degrees of soil erosion/landslides, land use, soil cover etc can be shown more reliably in the contour based digitized map. Overestimation of areas with gentle slopes can be avoided if the contour intervals are reduced. In countries where resources are a constraint, GIS could be used successfully to extract RSS/semi-detailed survey data and to analyze and prepare digitized resourceful maps, which are more useful to planners and policy makers.

Keywords: Contour, Slope, Soil, Hill, Digitized maps, GIS

Location: Banderban

Start Date:

End Date:

Program Area: Resource Development and Management

Non-commodity: GIS

Objectives:

To asses resources of semi-detailed information, analyze and use this information applying GIS techniques as a case study.

Methodology:

Reconnaissance and semi-detailed soil survey of Tankabari union were cacarried out in 1968 and 1988, respectively. Most of the soils developed on very steep to steep slopes over Surma-Tipum rocks are shallow, excessively to moderately well drained, sandy loam to silty clay loam/clay and light brown to dark brown colour. On the other hand, most of the soils developed on very steep to steep slopes over unconsolidated sandy Dupitila rocks are are deep, excessively to moderately well drained, sandy loam to silty clay loam, dark brown to red. In the study soil and landform maps (1:50,000) and topographic maps (1:25,000) are used as base materials. Soil and landform map of Tankabati union under Banderban thana is digitized and reproduced at 1:25,000 and 1:120,000 scale. From the toposheet information contour lines above 30m altitude and with 15m vertical intervals are digitized. On the basis of altitude the boundaries of different types of hills and valleys are delineated on the map and the areas are calculated. After conversion of the scale from 1:50,000 to 1:25,000 the digitized soil and landform map is superimposed on the contour map and reproduced at 1: 100,000 scale. The calculated areas of each landform from semi-detailed survey and information and from landform map are prepared from contour data. The digitized contour map is used to calculate the slope making use of TIN (triangular irregular network). The slope class map is prepared based on steepness making polygon coverage using TINARC command with percentage of slope option at 1:25,000 scale and is reproduced at 1:100,000 scale. A part of map is reproduced to display the features in details at 1:10,000 scale.

Source of Information: SRDI 2001. Soil Resources in Bangladesh: Assessment and Utilization. Proceedings of the annual workshop on soil resources. 14-15 February, 2001. SRDI, Dhaka.

Article Link (Online Journal):

Funding Source:

1. Government

Budget: 250,000 (approx)

Total Budget (Tk.) : 250,000 (approx)

Achievement/Findings:

Digital landform maps based on contours are more informative than soil and landform map. Under each mapping unit, 2-3 landforms are mapped in association. The lack of location of a particular landform limits the practical uses if the map. In contour based landform map, the position of particular landforms, e.g., high hill or medium high hill and the distribution patterns are easily recognizable. Thus the area of interest can be studied more reliably than would be possible with the soil and landform map alone. A comparison of areas estimated from semi-detailed soil survey information and those calculated from contour based digitized landform map reveals that the latter is more accurate and realistic than the former. The biggest advantage of the digitized map is that the location and the area of land within each slope class are delineated. Now it is possible to locate the area of hills with different percentages. It is possible to correct the areas with identified soils and land uses, and areas with risk of soil erosion/landslides. It is also possible to suggest remedial measures necessary for sloping land agriculture. If it is desirable to assess the resources of the area under study in more details, the map scale can be enlarged according to the user requirement. For the purpose of planning crop production and other use of sloping land, slope class maps may also provide a better basis. The success of presentation of all features on the map and its perfection depends on the accuracy of the contour map and the quality of imagery. GIS and RS may be used for improvement of semi-detailed soil survey information and make the map a more useful tool for future soil survey and land use planning of the hilly areas.

Knowledge Management: Journal, Report/Proceedings