Abstract
Gully erosion has many negative impacts on both cultivated and grazing lands in Ethiopian highlands. The present study was conducted in Chentale watershed, Ethiopia, to quantify the contribution of gully erosion, and to assess its temporal changes. Within the Chentale watershed, we selected a sub-watershed (104.6 ha) and nested gully catchment, and gauged for stream flow and sediment concentration data in 2015 and 2016. We measured gully dimensions before and after the onset of the rainy season in 2016 to determine soil loss due to gully erosion. The temporal changes of gully expansion were determined by digitizing gully plain area from Google earth images taken in 2005 and 2013. The results support that gullies were expanding at higher rate in recent years. Area covered by gullies in the watershed increased from 1.84 to 3.43 ha between 2005 and 2013, indicating that the proportion of the watershed covered by gullies was nearly doubled in the investigated period. The estimated soil loss from the main watershed and gullies catchment was 6 and 2 t ha−1 year−1 in 2015, and was 7 and 9 t ha−1 year−1 in 2016, respectively. The results support that gullies were the main contributors of soil erosion in the watershed, and that integrated soil and water conservation measures are required to reduce soil erosion.
Highlights
Soil erosion consists of a series of natural processes that move earth and rock material (Tebebu et al 2010), and the natural processes can be accelerated by human interventions
The results indicated that the area affected by gully erosion in the Chentale watershed increased from 1.84 to 3.48 ha in 8 years
This is translated to 89% increase during the study period and indicates that an area of about 0.2 ha year−1 or 0.19% of the watershed was affected by gully erosion annually
Summary
Soil erosion consists of a series of natural processes that move earth and rock material (Tebebu et al 2010), and the natural processes can be accelerated by human interventions. Soil erosion is a global problem and has both onsite and offsite effects. Soil erosion could deteriorate soil fertility and reduce agricultural productivity (Desta and Adugna 2012). Soil erosion has different forms including sheet, rill and gully erosion. Among the different forms of soil erosion, gully erosion resulted in permanent damages such as depreciation in land value, lowering of water table, dissection of agricultural and grazing lands (Lakew and Basin 2012), and requires more effort to control. Similar to other parts of the world, gully erosion in the highlands of Ethiopia is mainly attributed to excessive removal of vegetation and has led to reduce soil moisture in the agricultural lands and contributed to the reduction in crop yield (Descheemaeker et al 2006a, b; Nyssen et al 2002, 2004)
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