The Gilgel Gibe catchment in SW Ethiopia is one of the areas in East Africa affected by landslides. To better understand the patterns and the causal factors of these landslides, all landslides in a small study area (14 km²) in the hilly parts of the Gilgel Gibe catchment were mapped and analyzed. In total, 60 landslides were mapped. These landslides caused a displacement of 1 million m³ slope material, which corresponds to a mean displaced volume of 50 ton ha-1 y-1 in the last 20 years. Moreover many landslides deliver directly sediment to the rivers and hence increase the sediment load in the rivers. This soil loss to the rivers was estimated at 11 ton ha-1 y-1 during the same period. High annual rainfall (ca. 2000 mm y-1), lithological and pedological properties and to a lesser extent steep (> 16°) slopes turn the area into an inherent unstable situation and can be indicated as preconditions for the landslides in the study area. Distance to rivers is significantly the most important precondition, as slopes near rivers are less stable than slopes This article is published as: N. Broothaerts, E. Kissi, J. Poesen, A. Van Rompaey, K. Getahun, E. Van Ranst, J. Diels (2012) Spatial patterns, causes and consequences of landslides in the Gilgel Gibe catchment, SW Ethiopia. Catena, 97, 127-136. 2 further away from the rivers. This is mainly caused by river incision and bank erosion which often occur in the area and which can be attributed to increased runoff due to deforestation over the past 20 years. Therefore recent deforestation caused more shallow landslides but also indirectly more deep-seated landslides close to the rivers. Heavy rainfall is indicated as the main triggering factor for almost all landslides.

Purpose -Visible and near-infrared (Vis-NIR) reflectance measurements may be an alternative technique to identify suspended sediment sources in streams of headwater catchments. In this study, we examined if Vis-NIR reflectance measurements are capable of estimating sediment source contribution to sediment yield and compared this technique with the chemical technique.Materials and methods -Two headwater catchments in Ethiopia, Unta (2052 ha) and Desera (1657 ha), were both analyzed with the same techniques in order to find differences and agreements. The first technique used (Vis-NIR) spectral analysis as a fingerprint, using a partial least squares regression model. A second technique was a quantitative composite fingerprinting technique using chemical analysis of soil and suspended sediment samples. As a comparison, the partial least squares model was also used on the chemical data. In the period of August until September 2009, 30 soil samples of 3 different land uses (landslides, cropland and grazing land) and 21 suspended sediment samples at the catchment outlet were collected. Soil samples were all sieved to <63 µm. Chemical analyses consisted of total element concentration, percentage carbon, percentage nitrogen, atom percentage 15 N and δ 13 C. Reflectance measurements were taken on dried soil samples with a spectrometer.Results and discussion -Both techniques were not able to predict the contributions of the three land use types. They could only distinguish between landslide and top soil material. The agreements between the results of both techniques were significant for the Unta catchment (R 2 =0.80) but not for the Desera catchment (R 2 =0.39). The uncertainty of the technique using Vis-NIR reflectance measurements was slightly higher than with the chemical technique. Both techniques revealed that top soil erosion played an important role during storm runoff discharges. Using the partial least squares model for the chemical data revealed that uncertainty can differ a lot when using other statistical techniques.Conclusions -The quantitative composite fingerprinting technique using spectral signatures from both soil and suspended sediment samples was able to quantify the contribution of two source materials (landslides and top soil). It provided a faster and more cost effective alternative to the classical procedure.

Background: Soil erosion is one of the major causes for food insecurity, and environmental degradation in Ethiopia. To reduce erosion effects, soil and water conservation practices have been promoted at farm level and watershed scale-executed via mass-community mobilization program. In Lemo district, little information is available on suitability of soil conservation practices implemented through this program. The aim of this study was to assess technical fitness of physical soil conservation structures implemented via mass-community mobilization, its effect on soil properties, and extent of farmers participation in soil conservation practices. Field observation and physical structure component measurments were used to assess the technical fitness. Whereas, composite soil samples were collected from steep, moderate and gentle slope classes to evaluate the effects of conservation practices on soil properties. Structured questionnaire was used to assess the farmers participation in soil conservation. Results: As compared to nationally established specification of graded soil bund for areas similar with Lemo district, technical errors were found in bund spacing and vertical interval. The studied soil properties were not significantly (P > .05) influenced with sample distance from soil bund. But, soil moisture content, bulk density, clay, reaction, electrical conductivity, organic carbon, total nitrogen and cation exchange capacity were significantly (P < .05) affected with slope gradient. These properties become better as the slope gradient decrease. Among the study household heads, only 59.69% were participated in soil conservation activities. Land holding size, cropland slope, contacts with extension agents and training opportunity were significantly (P < .05) contributes for farmers' participation in soil conservation activities. Conclusions: To ensure the sustainability of watershed management practices and minimize observed technical faults on conservation structures continued technical supports, trainings, and follow-ups are required in the study area.

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Despite their restriction, smallholder farmers have been continuing growing Eucalyptus globulus in the cultivated land in the central highland of Ethiopia. Literature has shown controversial issues against E. globulus. Therefore, the objective of the study was to investigate the compatibility of E. globulus in the smallholder farmers’ land use system. Soil samples were collected from five different land uses and analysed for selected physical and chemical properties. The socioeconomic contribution of E. globulus was collected through household surveys from 110 households. Analysis of soil showed that organic carbon (OC), total nitrogen (TN) and cation exchange capacity (CEC) were significantly higher (P<0.05) under E. globulus compared to the cultivated land. The survey results also showed that the largest proportion (58%) of households was interested in growing E. globulus because of its multiple uses. About 83% of households responded that E. globulus help them to attain food security through increasing the purchasing power of smallholder farmers to buy agricultural inputs and food. This study has substantiated the role of E. globulus in the land use system of smallholder farmers. Most of the soil fertility indicators were better under E. globulus. The present finding reveals that E. globulus degrade the soil seemingly difficult to generalise. Growing E. globulus must be promoted under appealing land use to enhance smallholder farmers’ livelihoods. Removing E. globulus from the land use system may jeopardise the food security situation of many households.