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Title: Evaluation of Land Degradation and Soil Erosion Hazard Assessment Using GIS and USLE Model in Ketar Catchment
???metadata.dc.contributor.*???: Dr. Dagnachew Legesse
Addisu, Dereje
Keywords: Ketar;DEM;GIS;Land degradation;Soil loss (erosion);USLE
Issue Date: Jul-2005
Publisher: Addis Ababa University
Abstract: Land degradation and soil erosion are major problems of Ethiopian highlands. It is estimated that 1.5 billion tones of soil is being eroded every year in Ethiopia. In some parts of the highlands the erosion rate reaches up to 300 t/ha/yr, which is beyond tolerable condition. This study is intended to assess the spatial distribution of soil erosion risk in Ketar catchment, part of Ziway–Shala basin using GIS and the Universal Soil Loss Equation (USLE). In addition to this, the distribution of gullies and population in each weredas, and livestock data in the zone were compared with the resulting soil erosion map. A set of the six factors necessary for the USLE model were studied and generated. These include Rainfall Erosivity factor (R), Soil Erodibility factor (K), Slope Gradient factor (S), Slope Length factor (L), Crop and Management factor (C) and Conservation Practice factor (P). Each parameter, which consists of a set of logically related geographic features and attributes, is used as input data for the model analysis. The analysis of 4 years mean annual rainfall of 9 metrological stations give the Rfactor. K-factor was assigned for the soil types in the area obtained from the soil map of ETHIOGIS data sets and other soil map of the area. Digital Elevation Model (DEM), derived from topographic contours, was used to generate the slope map and, from the slope map S-factor and L-factor were generated. Land use/land cover, extracted from Landsat ETM+ with field checking, was used to determine the C-factor and P-factor values. Each of the above analyzed USLE factors, were rasterized to create six grid layers. Multiplication overlay on these six layers produces the resultant soil erosion (loss) map; each cell of the input grid layers has equal area (100m x 100m). The USLE model calculation applied on the six input grid maps gave values of the soil erosion (loss) map in t/ha/yr. Values of the out put map were again grouped in to 6 erosion classes of < 4.71, 4.71-9.42, 9.42-28.56, 28.56- 51.83,51.83-98.94 and > 98.94 t/ha/yr. High erosion classes concentrate in area where the slope gradient and length factors are high. The resulting map also showed that 96.81% of the area has a soil erosion rate of less than 9.42 t/ha/yr, which is less than the rate of soil formation. This value shows that much of the area is currently in tolerable condition. The field checking of the study area revealed that gully formation is in early stage. To evaluate the effects of population and livestock growth on the rate of erosion, both data were checked relative to the erosion map, woreda and zone levels respectively. The result confirmed that both data are increasing, which have great impact on the rate of soil erosion. So some measures and strategies should be designed to reduce their effects on the soil erosion rate. Finally, this study showed that, the effectiveness of the application of GIS and remote sensing in modeling soil erosion.
Appears in Collections:Thesis - Earth Sciences

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