Abstract

Soil erosion is the most challenging and continuous environmental problems resulting in both on-site and off-site effects in the world particularly in Ethiopia. Karesa watershed is one of the most erosion-prone watersheds which received little soil conservation attention. This study was conducted to estimate average annual soil loss rate using Geographic Information System and Universal Soil Loss Equation Model adapted to Ethiopian condition. The following datasets were obtained from different sources for estimating annual soil loss such as 15 years mean annual rainfall data for estimating erosivity factor, digital soil map for estimating soil erodibility factor, 30 m × 30 m resolution Digital Elevation Model for estimating slope length and slope steepness (LS) factor, Landsat6ETM+ images with 30 m × 30 m resolution for detecting vegetation cover and conservation practice factor. The result reveals that 42,413.72 ton per year soil loss from 9939 ha entire watershed or 4.27 tons per hectare per year average annual soil loss rate was observed. The mean annual soil loss rate was classified into four erosion severity classes as very less, less, moderate and high. The result also implies that 94.4% (9383.07 ha) of the watershed areas contributes 81.13% of the total soil loss which were observed from two slope classes (0-15% and 15-30%) and categorized under very less to less soil loss (0-6.25 tons ha-1yr-1). On the other hand, moderate to high soil loss (6.25-25 tons ha-1yr-1) was obtained on slope classes of >30% which covers 555.93 ha (5.6%) of the watershed areas and contributes 18.82% of the total soil loss indicating the maximum share of slope mainly due to cultivation of marginal land,intensive cultivation, poor vegetation cover during critical rainfall period. Moreover, about 2,184.93 ha of the watershed area requires integrated soil and water conservation measures.

Key words: Conservation priority, soil erosion, Universal Soil Loss Equation Model (USLE), geographic information system (GIS), Karesa watershed

Abbreviation

DEM, Digital Elevation Model; EEPCo, Ethiopian Electric Power Corporation; ENMA, Ethiopian National Meteorology Agency; ETM+, Enhanced Thematic Mapper plus; FAO, Food and Agricultural Organization; GIS, Geographical Information System; GPS, Global Positioning System; IDW, Inverse Distance Weight; LS, Slope Length and Steepness; LULC, Land Use Land Cover; RS, Remote Sensing; SCRP, Soil Conservation Research Project; SLM, Sustainable Land Management; SNNPR, Southern Nations Nationalities and People’s Region; SLT, Soil Loss Tolerance; USLE, Universal Soil Loss Equation; WGS, World Geodetic System.