Abstract:
Surface runoff and sediment loading areimmense problems that have threatened water resources
development in the Omo river basin.Deposition of sediment in reservoirs reduces the storage
capacity of the reservoir and they can cause serious problems concerning the operation and
stability of the dam.The objective of the study is to model runoff-sediment yield for upper Omo
Gibe III Catchment, characterizes the runoff from catchment and associated sediment yield, to
evaluate spatial distribution of sediment source areas, and identify hot spot areas, to assess the
impact of different catchment management interventions on runoff and sediment yield and
finally develop appropriate management options to control soil erosion and sedimentation
problems in Omo-Gibe III watershed by using SWAT model. Thus, an insight into surface
runoff /sedimentation mechanisms and mitigation methods plays an imperative role for the
sustainable water resources development in the region. This paper presents daily flow and
sediment yield simulations in the upper Omo-Gibe III under different Best Management Practice
(BMP) scenarios. Scenarios applied in this paper are (i)maintaining existing / baseline
conditions, (ii) introducing different width of filter strips, (iii) applying stone bunds (parallel
terraces) with different slope length, and (iv) reforestation. The Soil and Water Assessment Tool
(SWAT) was employed for modeling runoff and sediment yield in Upper Omo -Gibe III
watershed and used to identify soil erosion prone areas and assess the impact of BMPs on
sediment reduction. The model was calibrated and validated against measured flow and sediment
data. Both calibration and validation results showed good match between measured and
simulated flow and suspended sediment. For the existing conditions scenario, the model results
showed a satisfactory agreement between daily observed and simulated sediment concentrations
as indicated by Nash-Sutcliffe efficiency greater than 0.84. The simulation results showed that
applying filter strips, parallel terrace/stone bunds and reforestation scenarios reduced the current
sediment yields both at the sub basins and the basin outlets. However, a precise interpretation of
the quantitative results may not be appropriate because some physical processes are not well
represented in the SWAT model.
