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    SOIL LOSS RISK ASSESSMENT UNDER CLIMATE CHANGE AND MANAGEMENT PRACTICES: A CASE OF NERI WATERSHED, OMO-GIBE BASIN, SOUTHWESTERN ETHIOPIA
    (Hawassa University, 2019-10-22) ABEBE HEGANO HEMACHO
    Soil erosion is one of the biggest global environmental problems resulting in both on-site and off site effects. Climate change is expected to affect soil erosion based on a variety of factors, including a direct impact on soil loss by increasing precipitation amounts and erosive power. Neri watershed was chosen for this study. The objective of study is to assess soil loss risk under climate change and anticipated management practices. Revised Universal Soil Loss Equation model was applied by integrating bio physical and remote sensing data. Model parameters were computed from available data. Three Representative concentration Pathway scenarios (RCP2.6, RCP4.5 and RCP8.5) and management practices considered for estimation of annual soil loss rates. The resultant annual soil loss map under baseline condition shows the mean and total of 9.955t/ha/yr- 1 and 0.46m t/yr respectively. Estimates suggest that out of the total (46546 ha), about 32.7% % of the total area exceeded the tolerable limit and 67.3%% of the total area were below tolerable rate. The future soil loss rates are higher than the baseline period if no management actions are taken. Under no- management action scenario, the predicted the incremental rate of soil loss from (21.95%) for RCP8.5 (2051-2080) followed by 4.57% RCP4.5 (2021-2050) to insignificant decline (-0.75%) for RCP2.6 (2021-2050) compared to baseline period whereas, the other two predicted reduction. Moreover, inclusion of comprehensive management may result much higher reduction in soil loss over baseline and future condition of no action. The maximum reduction by 41.2% of its soil loss due to climate change is predicted RCP8.5 (2051-2080). The resultant soil loss map of baseline period was used in prioritization of intervention areas based on soil loss tolerance. Among eleven (11) sub-watersheds, eight and ten administrative kebeles out of nineteen are above the tolerable limit. However, watershed as planning unit, taking the proportion of soil loss to area, seven sub watersheds were identified as areas of intervention. To ensure sustainable resource use, management practice like contour cropping system complimented with terraces in agricultural fields and with giving special attention through strong policy measures to climate change, erosion minimization in non-agricultural land use classes were needed. Finaly, the study indicates a need for further study to understand the land suitability that consider the climate change
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    ESTIMATION OF SOIL EROSION AND SEDIMENT YIELD OF GEFFERSA RESERVOIR WATERSHED
    (Hawassa University, 2021-07-10) KANAOL MERERA ABDISA
    Sedimentation is an important parameter to measure the life of a reservoir. It depends on sediment yield and sediment yield depends on soil erosion. This study has been conducted in Geffersa reservoir watershed in the upper Awash River basin of Ethiopia. The objective of the study is to estimate potential soil erosion, sediment yield from the watershed and identify hotspot areas for proper planning using Arc GIS and RUSLE adopted to Ethiopian condition. The revised universal soil loss equation (RUSLE) was integrated with Geographic Information System (GIS) to model the spatial patterns in soil erosion in the watershed. All the parameters of the model (erosivity, erodibility, steepness, land use land cover, and supportive practice factors) were used in ArcGIS to create a soil erosion map. The annual soil loss of the watershed range from 0 to 728.48 ton/ha/year. The average annual soil loss value was found to be 23.6 ton/ha/year and has been classified into five erosion severities classes as very slight, slight, moderate, severe, and very severe to identify erosion hotspot area. Based on those results, 772.73 ha & 606.34 ha of the watershed were felt under severe and very severely vulnerable to soil erosion. The estimated Sediment yield delivered to the outlet was found ranges 0 to 78 ton/ha/year. The average annual sediment yield from the entire watershed is 5.3 ton/ha/year. If the same rate of sedimentation continues, the total storage volume will be filled up in 394 years. Out of the available reservoir sedimentation management strategies, watershed management is the best technique to minimize the sediment yield and its flow into the reservoir.