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Gully Erosion Rates and Analysis of Determining Factors: A Case Study from the Semi‐arid Main Ethiopian Rift Valley

Mukai, Shiro
Land degradation & development 2017 v.28 no.2 pp. 602-615
aerial photography, case studies, drainage, gully erosion, highlands, land use, photogrammetry, rain, soil texture, topography, vegetation cover, watersheds
The assessment of temporal interactions between environmental change (land use, vegetation cover) and gully erosion is one of the important challenges in gully erosion research. In this study, the combination of photogrammetric techniques using small‐scale aerial photographs and analysis based on volume–length relationships was used to: (i) estimate the erosion rate of gully networks in the semi‐arid main Ethiopian Rift Valley and (ii) determine variables that significantly influence the gully erosion rate at three periods (1957, 1972 and 2005) and establish their correlation with the volume of the gully networks in each period. The area‐specific gully erosion rate (gully erosion rate per unit area) from 1957 to 2005 of the gully networks in 12 study catchments was 16·2 Mg ha⁻¹ y⁻¹, a finding in accord with results from other case studies in the East African highlands. Over the three periods of 1957, 1972 and 2005, it was found that: (i) catchment topography and gully morphological variables strongly correlate with the total volume of gully networks; (ii) rainfall, soil texture and slope gradient variables strongly correlate with both the area‐specific volume of the gully networks and drainage density; and (iii) land use/cover in each period plays a minor role in controlling the total volume and the area‐specific volume of the gully networks and drainage density, but when the land use/cover is expressed in temporal variables, it strongly correlates with the rates of gully erosion. Copyright © 2016 John Wiley & Sons, Ltd.