SOIL EROSION RISK ASSESSMENT TO PRIORITIZE MANAGEMENT OPTIONS IN MIDHAGDU WATERSHED WESTERN HARARGHE HIGHLAND, EASTERN ETHIOPIA

Abstract

Soil erosion is being detected as a risk to humnan survival by diminishing food and water availability of the planet Earth in the 21st century. Assesment and management of this resource is becoming extremely important. This study aimed to investigate Soil Erosion Risk and Prioritize Management Options in Midhagdu Watershed of Western Hararghe Highlands, Eastern Ethiopia. Satellite data, SRTM DEM, Land sat 8 OLI with 30m resolution, rainfall and soil data were used to generate all soil erosion risk factor maps and integrated to generate a composite map of soil loss for the watershed. The RUSLE model in combination with remote sensing and GIS techniques was used to identify the five thematic maps as an input to estimate mean annual soil loss. The results of the spatial distribution of soil erosion risk factors indicated that rainfall erosivity, soil erodibility, slope length and steepness, cover management and anthropogenic soil erosion control practices values ranged from 41.365 to 43.793MJ mm ha−1 yr −1 , 0.26 to 0.31t ha−1MJ−1 mm −1 , 0 to 220.512, 0.21 to 0.87and 0.11 to 1 respectively. And the most powerful factor that influences soil erosion risk is topography followed by anthropogenic soil erosion control practices. The results of the study showed that the annual soil loss rate in the watershed ranged from 0 in gentle slopes to 1504 t ha-1yr-1 at the steepest slope of the watershed with a mean annual soil loss of 48.5 t ha-1 yr -1 at Midhagdu watershed level.The soil loss map was categorized into five soil loss numerical ranges and soil loss risk nominal scales: low, moderate, high, very high and extremely high using Ethiopian highland maximum soil loss threshold level 18 t ha-1 y -1 .The model output revealed that 52.24% of Midhagdu watershed fell in low to moderat soil erosion risk levels and 47.76% fell under high to extremely high soil erosion risk levels.The soil loss risk levels identified at 28 micro watersheds showed that twelve micro watersheds rated as first, eleven micro watersheds as second and three micro watersheds as third priority for soil erosion risk management options implementation. Out of 28 micro watersheds 26 fell above Ethiopian highland maximum soil loss threshold levels. Therefore, the study result indicated that Midhagdu watershed needs immediate intervention for better soil erosion risk management options planning and implementations by considering identified soil erosion risk areas and priority classes to control soil erosion risk below the national threshold level.