Abstract:
Soil erosion presents a significant challenge in Ethiopia. In response, Ethiopia has
undertaken ongoing watershed development campaigns. Scholars are actively engaged in
estimating erosion rates, identifying hotspot areas, and assessing the effectiveness of
implemented and potential soil and water conservation measures to reduce erosion. This
study contributes to these efforts by focusing on tolerable soil loss estimation, identifying
erosion hotspot areas, and exploring best Soil Conservation practices (BSCPs) to reduce
erosion rates to/ or below tolerable soil loss limits (TSLLs). To achieve these objectives,40
composite soil samples were collected from the study watershed and subjected to laboratory
analysis to determine the soil texture, bulk density, pH and organic carbon (OC) content
indicators for assessing the TSLL and predicting soil and water assessment tool (SWAT)
database parameters. The SWAT model, coupled with the SWAT Calibration and
Uncertainty Procedures (SWAT-CUP), was utilized for simulation, sensitivity analysis,
calibration, and validation using streamflow and sediment yield data. The calibrated SWAT
model was used to assess soil erosion hotspot areas and evaluated the effectiveness of the
selected BSCPs: soil and/or stone bund (SSB), grass strip (GT), reforestation (RF), soil
and/or stone bund and grass strip (SSB and GT) and soil and/or stone bund and reforestation
(SSB and RF). The results revealed that 49.33%, 32.49%, 13.87%, and 4.31% of the area
exhibited TSLL values of 12.5, 10.0, 7.5, and 5 t ha-1yr-1, respectively, with 22.9% of the area
showing soil loss rates below the TSLL. Furthermore, varying degrees of erosion above the
TSLL were observed, with sub watershed SW-12 experiencing the highest erosion rate (47
tha-1yr-1) and sub watershed SW-2 experiencing the lowest (7.8 t ha-1yr-1). Among the
evaluated BSCPs, SSB + RF demonstrated the greatest erosion reduction effectiveness at
76.6%, followed by SSB + GT, SSB, RF, and GT, with erosion reduction effectiveness values
of 61.7%, 60.0%, 43.3%, and 13.9%, respectively. Based on these findings, SSB + RF is
recommended for erosion reduction to or below the TSLL, with implementation priority
given to sub watersheds SW-12, SW-10, SW-3, SW-2, and SW-5, which are ranked in
descending order of erosion rate severity. During implementation, emphasis should be
placed on reforestation of plant species of high ecological importance.
