This paper investigated the rate of gully formation and development, and its impacts on land competition and crop yield reduction in the Genbo Wonz Watershed, north-west highlands of Ethiopia. Geometrical gully dimension measurements, field observations and satellite imagery assessment have been performed selecting 22 gullies. As a result, road construction and design problems of soil and water conservation practices (SWCPs) were found to be important causes of gully formation and development. The total volume of soil loss from 22 gullies in three decades was ~340, 957 t, changing ~10 ha agricultural land to unproductive land. The annual rate of gully erosion was found to be ~62 t ha-1 with an average gully density of 16.4 m ha-1. Gully erosion also results in loss of 24 t yr-1 Teff grain yield (Eragrostis teff, E. abysainica) and 14 t yr-1 animals forage. To arrest the problem, proper design of SWCPs within farmlands, appropriate runoff discharge mechanisms along roads and controlled grazing systems within the grazing lands ought to be executed.
Blue Nile basin is one of the hotspots of soil erosion areas in Ethiopia. However, there impact of land use changes on soil erosion is poorly understood in the Tagaw areas. Hence, the objective of the study was to assess the impact of land use land cover changes on soil erosion over the last 31 years. Rainfall, soil, satellite images and topographic data were acquired from field survey and secondary sources. Land use change analysis was conducted using supervised classification based on four different satellite images. In addition, Revised Universal Soil Loss model was used to estimate soil erosion. The study shows the watershed was predominantly covered by farm land (22%), bare land (17.8%), built up (22%), grassland (9.7%), marshland (8.8%), shrub land (12.4%) and forest (6.7%) in 2016. Moreover, the mean annual soil losses of the watershed were 19.3, 22.93 and 26 tons/ha/yr for the 1995, 2006 and 2016 respectively. The total soil losses varied from 0.06-503.56, 0.11-516.67, and 0.00-543.5 tons/ha/yr. for the year 1995, 2006 and 2016 respectively. The highest soil loss was found for bare land. The RUSLE model further showed that the highest soil erosion occurred in 2016 whereas the lowest soil erosion was occurred in 1995. Most of the land use changes (36%) occurred on farmland (36.1%), shrub land (-52.4%), built up (50.9%), and bare land areas (31.6%) due to rapid population growth and inappropriate farming practices. To conclude, there is a significant impact of land use land cover change on soil erosion in Tagaw watershed.