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Analysis of long-term gully dynamics in different agro-ecology settings
- Yibeltal, Mesenbet, Tsunekawa, Atsushi, Haregeweyn, Nigussie, Adgo, Enyew, Meshesha, Derege Tsegaye, Aklog, Dagnachew, Masunaga, Tsugiyuki, Tsubo, Mitsuru, Billi, Paolo, Vanmaercke, Matthias, Ebabu, Kindiye, Dessie, Mekete, Sultan, Dagnenet, Liyew, Mulatu
- Catena 2019 v.179 pp. 160-174
- aerial photography, agroecology, basins, computer software, cultivation area, geographic information systems, gully erosion, human settlements, image interpretation, land degradation, land use, landscape position, ravines, remote sensing, soil, surveys, water conservation, watersheds, Ethiopia
- 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.