Calibration and validation of SWAT model using stream flow and sediment load for Mojo watershed, Ethiopia

The main aim of this study was to setup and evaluate the applicability of physically based soil and water assessment tool (SWAT) model with ArcGIS version 9.3 in assessing the runoff and sediment load from Mojo watershed having a total area of 2017.21 km² situated in central Oromia Regional state, Ethiopia. In this study for stream flow simulation parameters involving surface runoff (CN₂.mgt) and ground water (ALPHA_BNK.rte) are found the most sensitive parameter and the parameters representing channel process (SPCON.bsn, SPEXP.bsn &ADJ_PKP.bsn), geomorphology (SLSUBBSN.hru) and surface runoff (CN2.mgt, & HRU_SLP.hru), were found more sensitive for sediment load simulation. There are a good agreement between the observed and simulated discharge, which was verified using both graphical technique and quantitative statistics. The value of R ² = 0.75, NSE = 0.76, RSR = 0.49 and PBIAS = 10.9 obtained during calibration and R ² value 0.71, NSE value 0.70, RSR value 0.59 and PBIAS 9.5 obtained during validation as well as the uniformly scatter points along the 1:1 line during calibration and validation justify that the model is good in simulating runoff from Mojo watershed. For sediment load the computed statistical indicators R ² = 0.77, NSE = 0.76, RSR = 0.49 and PBIAS = 48.70 were obtained during calibration and during validation the computed statistical indicators were found 0.67 for R ², 0.65 for NSE, 0.59 for RSR and 50.5 for PBIAS. From the calibration and validation result, it can be concluded that the calibrated parameter values of SWAT model can be used for hydrologic simulation of the un-gauged watershed that is having the similar agro-climatic condition.