Land Degradation Mapping and Erosion Estimate in Gado Subwatershed Using Remote Sensing and Geographical Information System

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Addis Ababa Universty


Land degradation is exhibited in different forms of which soil erosion is dominantly affecting the livelihood of many people who are dependent on natural resources in particular on griculture. In this respect, a land degradation study was conducted in Gado subwatershed, which covers 500 km2. The site is located in North Shewa Zone, Amhara region of longitude 39 0 28’31E -39 0 44’ 24 E and latitude 9 0 41’`3N - 9 0 54’ 49 N. Satellite images, thematic maps and relevant data were acquired, organized, analyzed and produced information for decision making. Supervised classification was undertaken on Enhanced Thematic Mapper (ETM+) and land use/land cover of the area was developed. Land use/land cover map revealed, degraded land (150 km2), plantation (18.60 km2), scrub land (62 km2), cultivated land (180.4 km2), grassland (8.7km2), and marginal lands (91.8 km2). Land classification contingency matrix developed and evaluated for the accuracy to be more than 85%, and histogram of the classification was also evaluated. Land degradation map of the study area was extracted from the land use map. It was also attempted to estimate depth of streams/gullies in the subwatershed by analyzing contour lines and it revealed that depth of channel increases as elevation decreases, and the relationship is polynomial. Rate of soil erosion was estimated using Universal Soil Loss Equation (USLE) and the maximum erosion rate identified for the subwatershed was more than 171 t/ha/year with average rate of 22 t/ha/year. Erosion rate was related to drainage network. On areas of high concentration of streams similarly high erosion rate was noticed. Erosion rate identified was beyond soil formation rate of 2 t/ha/year. Abay Basin Master Plan Study stated North shewa zone erosion rate between 51-100 ton/ha/year and classified under area that cannot tolerate further soil loss which the subwatershed is also located. The subwatershed is under severe threat and the community livelihood as a consequence Key words: Degradation, Erosion, Remote sensing and GIS, Sub-watershed, USLE



Degradation, Erosion, Remote sensing and GIS, Sub-watershed, USLE