Sediment Yield Modeling Using SWAT Model: The Case of Arjo Didessa Catchment
Creators: name: Tamiru Geleta Kenate
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2019
Subjects: Arjo Didessa Catchment, Soil Erosion, Sediment Yield, Sediment Rating Curve, Trap Efficiency, ArcGIS-Arc SWAT Model, SWAT-CUP, SUFI2.

description: Soil erosion is a major watershed problem in many developing countries like Ethiopia in general and in the Arjo Didessa Catchment in particular. The consequences of soil erosion have an enormous effect in causing loss of soil fertility, loss of productivity, and environmental degradation and desertification. In addition, water pollution, reservoir sedimentation and modification of river morphology are the prominent problems. Didessa River is the largest tributary of the Blue Nile River in terms of volume of water, contributing roughly 16.5% of the total flow of the Blue Nile which consists Wama, Dabana and Anger river major tributaries and multiple minor tributaries. The Arjo Didessa Catchment, the study area is located in the upstream part of Didessa Catchment that covers drainage area of around 9,981.0 sqkm. The maximum and minimum temperature varies between 21-37 0C and 8-17 0C respectively and the mean annual rainfall ranges between 1509mm and 2322mm. For the study, a physical-based, semi-distributed hydrological model, SWAT model was applied to simulate hydrological response (streamflow and sediment yield) of Arjo Didessa catchment using 17 years hydrological and 30 years meteorological data. The simulated streamflow and sediment yield results were utilized to analyse seasonal variability of streamflow, erosion vulnerable areas and spatial variability of sediment yield to the catchment. The sediment rating curve was developed that average annual sediment yield was estimated at around 74.4t/ha. The capability of SWAT model was measured through sensitivity analysis, calibration and validation. The model calibration and validation were done using 10 years (1992-2001) and 7 years (2002-2008) periods average monthly observed data respectively. The model evaluation statistical fit values between measured and simulated streamflow and sediment yield were in the acceptable ranges. Hence, the NSE and R2 values obtained were greater than 0.70 and PBIAS in the ranges of ±4.0 and ±10.0 during calibration and validation for average monthly streamflow and sediment yield. Therefore, the result indicated that SWAT model is performed well and estimated result of average annual streamflow and sediment yield of the catchment shows slightly over estimated and results were around 106.1m3/s and 72.6t/ha respectively in which the sediment yield result is within the range of NBCBN-RE study. Brune’s method was applied for the estimation of sediment trap efficiency of the Arjo-Didessa Reservoir and given as 96%; but adopted 100% assuming all incoming sediment deposits within the reservoir. According to the empirical area reduction method, useful life of the reservoir has been examined and shows as it works for around 100 years at the reservoir trap efficiency of 100% and average deposit density adopted 1.12t/m3. Finally, the model analyzed sediment yield distribution and differentiated the sub catchments to erosion vulnerable areas that helps different stakeholders to plan and implement appropriate soil and water conservation measures such as changing land use/crop diversification, reforestation, check dams, bank stabilization, terraces, etc. for the reduction of sediment yield of the catchment and sedimentation rate of the reservoir.