Estimation of soil loss rate using the USLE model for Agewmariayam Watershed, northern Ethiopia

Abstract

Background Soil erosion and nutrient depletion threaten food security and the sustainability of agricultural production in sub-Saharan Africa. Estimating soil loss and identifying hotspot areas support combating soil degradation. The aim of this paper is to estimate the soil loss rate and identify hotspot areas using USLE model in the Agewmariam watershed, northern Ethiopia. Methods Rainfall erosivity factor was determined from annual rainfall, soil erodibility factor from soil data, slope length and gradient factor were generated from DEM, cover factor and conservation practice factor obtained from land use cover map. Finally, the parameters were integrated with ArcGIS tools to estimate soil loss rates of the study watershed. Results Mean annual soil loss rates were estimated to be between 0 and 897 t ha−1 year−1 on flatter and steeper slopes, respectively. The total annual soil loss was 51,403.13 tons from the watershed and the annual soil loss rate of the study area was 25 t ha−1 year−1. More than 33% of the study areas were above tolerable soil loss rate (11 t ha−1 year−1). The spatial risk categorization rate was 67.2% severe (> 51 t ha−1 year−1), 5.4% very high (31–50 t ha−1 year−1), 5.8% high (19–30 t ha−1 year−1), 3.2% moderate (12–18 t ha−1 year−1) and 18.3% slight (0–11 t ha−1 year−1). Conclusion The results showed that the severity of erosion occurred on the steep slope cultivation, absence of conservation measures, and sparse nature of the vegetation cover. This area required immediate action of soil and water conservation which accounts for about 33.5% of the total watershed.

Estimating Landscape Vulnerability to Soil Erosion by RUSLE Model Using GIS and Remote Sensing: A Case of Zariema watershed, Northern Ethiopia

“…The slope ranges from 0 to 584%. High erosion rates on steep slopes were also reported in other similar studies such as in Agewmariam watershed where the slope ranged between 0 to greater than 50% [21]. So, high soil loss was observed in high slope areas and sloppy cultivated land.…”

“…The mean annual soil loss rate projected for total watershed of 2239.33 Sq. Km area was 16.09 ton ha -1 yr -1 which is equivalent to other findings by Hurni [22] for the highland of Ethiopia (20 ton ha -1 yr -1 ); by Amsalu and Mengaw (2014) [5] for the JabiTehinan watershed in the Northwestern Highlands (30.4 ton ha -1 yr -1 ); by Ayalew and Selassie (2015) [9] for the Guang watershed in the Northwestern Ethiopia (24.95 ton ha -1 yr -1 ); by L. Tamene et al (2017) [38] for the Laelaywukro catchment in the Northern Highlands (20.8 ton ha -1 yr -1 ); by Gashaw et al (2017) [18] for the Geleda Watershed in the Northwestern Ethiopia (23.7 ton ha -1 yr -1 ) and by Girmay et al (2020) [21] for the Agewmariam watershed in the Northern Highlands (25 ton ha -1 yr -1 ). Considering the tolerance limit of 10 t ha -1 yr -1 , the total area with a soil erosion risk higher than the soil loss tolerance was 31.41% of the watershed area which 703.33 Sq.…”

“…However, for the study area of Zariema watershed, there were no conservation measures, as data were lacking on permanent management practice and there were no management practices it is preferable to use the P-factor suggested by Wischmeier & Smith (1978) [42]. This method has also been employed in the highlands of Ethiopia by other researchers [21,28,39]. This method categorizes land covers into cultivated land, shrub land, and other land.…”

“…The annual soil loss rate ranges between <11 ton ha -1 yr -1 to >51 ton ha -1 yr -1 (Figure 8 and Table 5). The estimated soil loss rate was divided into five severity class, which were adapted from [18,21] like low (0 -11 ton ha -1 yr -1 ), moderate (12 -18 ton ha -1 yr -1 ), high (19 -30 ton ha -1 yr -1 ), very high (31 -50 ton ha -1 yr -1 ), sever (>50 ton ha -1 yr -1 ).…”

“…These incidents resulted in harsh land degradation problems in the highlands of Ethiopia [7]. The worldwide annual rate of soil erosion from cultivated land ranges from 22 to 100 ton ha -1 and declines in crop yield as much as 15-30% annually [21,29]. According to Morgan RP [29], soil erosion costs the US economy between US$30 billion and US$44 billion annually related to on-site which is the price of crop yield and crop land loss and offsite such as contamination and sedimentation of downstream water resources development and sources are affected by soil erosion.…”