Modelling of sediment yield using the soil and water assessment tool (SWAT) model: A case study of the Chanchaga Watersheds, Nigeria

Abstract

Water erosion poses a threat to agricultural land and water resources and leads to land degradation with river/reservoir sedimentation. Against this backdrop, the soil and water assessment tool (SWAT) model was used to assess the effects of Ridging Across the Slope (RAcS) and Ridge Along the Slope (RAlS) on sediment yield in the Chanchaga basin. The multiple slopes were integrated into SWAT and modified soil textural class in each sub- basin. Observed sediment yield was used to calibrate and validated using SUFI2 for one year each. Nash–Sutcliffe efficiency (NSE) and coefficient of determination (R 2 ), PBIAS, P- factor and R-factor for monthly sediment yield in RAcS were 0.77 0.7, 4.5, 0.75 and 1.24 in the calibration. The validated models were 0.56, 0.56, 4.0, 0.92, and 0.61 at the Koropa sub-basin. Similar results were found for sediment yield in RAlS during calibration, but the PBIAS was -2.8. The corresponding values are 0.56, 0.60, 22.4, 0.75 and 0.44 for validation. In the Shatta sub-basin, RAcS was confirmed by NSE and R 2 (0.61 and 0.64) during calibra- tion. Also, the PBIAS, P and R-factors have values of 16.6, 0.75, and 2.21, respectively. The equivalent values were 0.74, 0.75, 13.0, 0.67 and 1.32 during validation. The same results got for sediment yield- RAlS. During calibration, the values of the PBIAS and R-factor were -15.3 and 3.78. The corresponding values for validation include 1.3 and 3.62. The NSE’s im- ply that model validations were satisfactory. Runoffcurve number (CN2), soil water storage capacity (SOL_ AWC), and erosion (USLE) are the most sensitive parameters for predicting sediment yield. RAlS is unsuitable as they produced values of 20.32 t/ha/yr in the Koropa and Shatta sub-basins. RAcS is effectual for lessening sediment loads, particularly on very gentle slopes. Designing sediment traps and installation will lessen sediment yield along slope ridging in rivers.