Gully Erosion and Effectiveness of Its Treatment Measures, Upper Abay Basin, in the Northwest Highlands of Ethiopia

Abstract

In Ethiopia, gully erosion is a priority problem and identifying solution is a main concern for governmental and non-governmental organizations. The investigation of gully erosion and effectiveness of treatment practices is vital for the decision making. Therefore, this research was conducted with the objectives of assessing gully erosion and evaluating the impacts of gully treatment practices on gully erosion control and to address the research question: What are the major causes of gully formation and development in the watershed? How much soil was lost as a result of gully erosion? Are the implemented gulley treatment practices effective? Field measurement from four selected experimental gullies was conducted, (i) gully treated with physical practices, (ii) gully treated with biological/vegetative practices, (iii) gully treated with biophysical practices, and (iv) gully without any treatment as a control. Interview and focus group discussion, transect walk, soil sampling, satellite imagery, and field measurements were used for data collection. Statistical Package for Social Science (SPSS), Excel, Arc GIS, and Google Earth Software were used for data analysis. The result shows that the major causes of gully formation and development in the order of importance were local footpaths, surface runoff, free grazing, poor agricultural practices, and absence of proper waterway. Due to gully erosion, ~3.66 ha of land and ~55,198 t of soil were lost from the four identified gullies. The long-term gully erosion rate was found to be 15 t ha−1 yr−1. Large amount of sediment was trapped by the gully treatment measures and help to reduce downstream sedimentation of water bodies. The integration of physical and biological (biophysical) practices was found to be more effective than individual practices. Land loss due to gully erosion also played a vital negative role on farmers’ income in addition to the social influence by damaging roads, causing cattle deaths and flooding. In general, in Timet watershed, in the upper Blue Nile (Abay) basin of Ethiopia, there is high rate of gully erosion causing downstream reservoirs sedimentation, and biophysical gully treatment measures were found to be more effective in reducing gully erosion and downstream sedimentation.