Identifying Erosion Hot Spot Areas and Evaluation of Best Management Practices in the Toba Watershed, Ethiopia

Abstract

Ethiopian highlands have been increasingly exposed to the risk of soil erosion and evaluations of how various management practices can reduce the risk of soil erosion are still limited. Here, the calibrated and validated Soil and Water Assessment Tool (SWAT) is used to estimate soil loss rates, identify erosion hotspot areas and evaluate effective best management practices (BMP) to curb the risk of soil erosion. The annual sediment yield (SY) in Toba watershed varies from 0.09 t ha-1 yr-1 to 44.8 t ha-1 yr-1 with an average SY of 22.7 t ha-1 yr-1. Cultivated lands on steep slopes are the sources of extensive soil loss rate, whereas areas with good vegetation cover have low SY. The increased population pressure, increased cultivation of steep slope and uncontrolled grazing are the causes of high SY in the watershed. 17 sub-basins with SY higher than the tolerable erosion of Ethiopia (2-18 t ha-1 yr-1) are considered for the application of BMP scenarios. Implementing all BMPs could reduce the extent of SY but with varying degrees and combination of the BMPs are more pronounced and desirable. Reforestation with vegetative strips was the most effective management (87.8% reduction) followed by soil/stone bund with vegetative strips (83.7% reduction). These findings are important to ensure sustainable land management and promote sustainable agricultural production in a rapidly changing agricultural watershed. In general, the result highlights the need for regional developments and cooperation to urge for strong BMPs strategies for the rapid land and water resources degradation.

Erosion Risk Assessment for Prioritization of Conservation Measures in the Watershed of Genale Dawa-3 Hydropower Dam, Ethiopia

“…The corresponding mean annual sediment yield contribution of each subbasin is shown in Table 9. The estimated sediment yield in the Genale Dawa-3 dam watershed was consistent with that of other studies done in other basins in Ethiopia, including the studies by [30] in the Finchaa catchment [33], in the Awata watershed [36], in the Bilate watershed [37], in the Megech reservoir catchment [38], in the Welmel watershed, and [39] in the Toba watershed in Ethiopia.…”

Effectiveness of physical soil and water conservation measures under simulated and observed dataset in Ethiopia: Meta‐analysis

“… Grass stripe : grass with conservation value planted within a 1‐m width along a contour and across the slope to create a vegetative ridge (Betela, 2015). Reforestation : converting degraded cropland to forestland (Betela, 2015; Dibaba & Ebsa, 2022). Grassed waterway : a grass‐covered way of water.…”

“…Consequently, several studies have used the SWAT model to evaluate the effectiveness of SWC structures to recommend best practices for implementation and further scaling‐up. Accordingly, simulation results revealed a maximum of 81.30% of soil loss reduction effectiveness was reported by soil/stone bund (Demissie et al, 2013) and 69.3% (Dibaba & Ebsa, 2022). Stone/soil bund effectiveness shows high variability (28.10%), with a minimum effectiveness of 30.50% in the Gedeb watershed (Gashaw et al, 2021).…”

“…Because of those reasons, the simulation approach is used by many disciplines. In particular, from the SWC perspective, employed to estimate and compare the erosion impact, examine the trend, make accessible the inaccessible area (large area), extrapolate the monitoring data, and recommend suitable and best measures for the area by evaluating their effectiveness (Admas et al, 2022; Dibaba & Ebsa, 2022). For instance, many SWC scholars have used the SWAT model owing to its strong calibration and validation system, free accessibility, and compatibility with the ArcGIS environment.…”

“…Besides, utilized to simulate erosion hot spot areas, recommend suitable SWC measures, and evaluate their effectiveness at a time when they can access the required data, which is used as input for model calibration and validation (Gashaw et al, 2021). Stone bund, soil/stone bund, grass strip, terracing, reforestation, strip cropping, contour farming, and zero tillage (conservation farming) are the most common measures in which their effectiveness was simulated using the SWAT model in the lowland, mid‐highland, and highland agroecological zones of Ethiopia, and have shown 5.40%–93% effectiveness (Amdihun et al, 2014; Dibaba & Ebsa, 2022).…”