Search

© 2019 The Author(s) Gully erosion is one of the main causes of land degradation, particularly in the drought-prone regions of Ethiopia. This study assessed spatio-temporal changes of gully length and density in watershed pairs in Guder, Aba Gerima, and Dibatie sites, which are representative highland, midland, and lowland agro-ecologies in the Upper Blue Nile basin of Ethiopia. Aerial photographs (1957, 1982) and very high resolution satellite images (QuickBird, IKONOS, Worldview-2, SPOT-7, and Pleiades) of the six watersheds, along with field survey results, were used in the analyses. The aerial photographs were scanned and orthorectified using ENVI 4.3 image analysis software, and gullies were mapped by visual image interpretation in the ArcGIS environment. Rates of increase in gully length in Guder (36.9 m yr −1 ) and Aba Gerima (33.6 m yr −1 ) were almost double the rate in Dibatie (17.8 m yr −1 ) from 1957 to 2016 or 2017, and over the same period, gully density similarly increased by 5.9, 5.4, and 3.7 m ha −1 in Guder, Aba Gerima, and Dibatie, respectively. The higher rates in Guder and Aba Gerima reflect the long history of cultivation and human settlement in those sites, whereas agricultural activity became widespread in Dibatie only after implementation of the national resettlement program in the 1980s. Moreover, although gully density tended to increase over time in all six watersheds, in the three watersheds (one in each paired watershed) where soil and water conservation measures had been introduced, the rate of increase was lower than in those where no such measures were implemented. In addition, gully distribution was linked to land use and landscape position; gully density was higher in cultivated areas and where slope gradients were gentle. The results of this study indicate that careful site-specific identification of factors controlling gully initiation and development is crucial so that appropriate management strategies can be developed for these three sites and for other areas with similar agro-ecologies in the Upper Blue Nile basin. ispartof: CATENA vol:179 pages:160-174 status: published

In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5tha-1yr-1 and a gross soil loss of ca. 473Mtyr-1, of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score=1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (>30tha-1yr-1) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (>15tha-1yr-1), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basin's land resources and possibly open up prospects for cooperation in the Eastern Nile region. publisher: Elsevier articletitle: Comprehensive assessment of soil erosion risk for better land use planning in river basins: Case study of the Upper Blue Nile River journaltitle: Science of The Total Environment articlelink: http://dx.doi.org/10.1016/j.scitotenv.2016.09.019 content_type: article copyright: © 2016 The Authors. Published by Elsevier B.V. ispartof: Science of the Total Environment vol:574 pages:95-108 ispartof: location:Netherlands status: published