Soil Erosion Assessment Using The Rusle Model And Gis Techniques: A Case Of Laga Haya Watershed, Eastern Wollega, Western Ethiopia.

Abstract

Soil erosion is one of the critical problems in Ethiopia. It is estimated that the country loses 1.9 to 7.8 billion tons of soil in a year and this cost the country lose to about one billion in Ethiopia birr. The rate of soil loss can be estimated and erosion hotspots can be identified by using revised Universal soil loss equation (RUSLE) model and GIS Techniques. This study was carried out with the main objective of quantifying the rate of annual soil loss and identification of soil erosion risk (erosion hotspots) area through prioritizing Sub-watersheds in the Laga Haya watershed. Rainfall data, Soil data, Landsat image and digital elevation model data were collected and then processed to generate RUSLE input factors. RUSLE parameters were analyzed and overlain using raster calculator in spatial analyst tools in ARCGIS 10.5 environment to estimate annual erosion rates and map erosion risk areas in the Laga Haya watershed. The result showed that the total annual soil losses ZDV DERXW WRQ \HDU DQG LWV UDQJHV from 0.00 ton ha/year in plain areas to 150.917 ton/ha/year by the rate of 23 ton/ha/year which was steep slope areas of Laga Haya watershed. The annual soil loss was classified in to Very low, low, moderate, high and very high severity classes. The vulnerability of soil erosion severity classes in the study area indicated that 3.28% fall under high to very high soil erosion risk class. Steep slope with poor vegetation cover experienced with high soil erosion. To identify erosion hotspots in the Laga Haya watershed the five sub-watersheds were prioritized for soil and water conservation. The study finding revealed that soil erosion was high and very high in the northern and northeastern part of the watershed and the sub-ZDWHUVKHGV ³$´ DQG ³%´ QHHGV XUJHQW conservation since it has higher rate soil loss, which is 23 t ha/yr and 15.2 ton/ha/yr, and the remaining sub ZDWHUVKHGV FRXOG EH FRQVHUYHG DFFRUGLQJ WR WKH RUGHU RI LWV SULRULWL]DWLRQ ZKLFK LV 6XE -ZDWHUVKHG ³&´ ³'´ DQG VXE -ZDWHUVKHG ´(´ UHVSHFWLYHO\ . Vegetation cover (C factor) and topography (LS factor) have a significant effect on soil erosion in the watershed from the five soil erosion factors. Implementation of Immediate soil and water conservation practices are needed where areas its annual soil loss above 10 ton ha-1 year -1 .therefore, the local experts and administrative bodies uses this information to prepare plan for prioritized sub-watersheds and area fallen under very high and high severity classes to conserve and monitor the degraded land resources.