Streamflow modelling is crucial for developing successful long-term management, soil conservation planning, and water resource management strategies. The current work attempts to develop a robust hydrological model that simulates streamflow with the slightest uncertainty in the calibration parameters. A physical-based and semi-distributed hydrological SWAT model was employed to assess the hydrological simulation of the Ouergha watershed. The monthly simulation of the SWAT model achieved in the time frame from 1990 to 2013 has been split into warm-up (1990–1996), calibration (1997–2005), and validation (2006-2013). The SUFI-2 algorithm's preliminary sensitivity and uncertainty analysis was done to calibrate the model using 11 hydrologic parameters. The model's performance and robustness findings are promising. To evaluate the model, the coefficient of determination (R2), Nash-Sutcliffe efficiency (NSE), and percent of bias (PBIAS) were utilized. The value of R2, NSE, and PBIAS ranged from 0.45–0.77, 0.6–0.89, and +12.72 to +21.89% during calibration and 0.51–0.85, 0.64–0.88, and +8.82 to +22.19% during validation period, respectively. A high correlation between the observed and simulated streamflow was recorded during the calibration and validation periods. More than 68% of the observation data are encompassed by the 95PPU across both the calibration and validation intervals, which is excellent in terms of the P-factor and R-factor uncertainty criterion. The projected streamflow matches the observed data well graphically. According to the total hydrological water balance study, 29% of precipitation is delivered to streamflow as runoff, whereas 54% of precipitation is lost through evapotranspiration. The recharge to the deep aquifers is 8%, whereas the lateral flow is 10%. The findings of this study will help as a roadmap for the anticipated water management activities for the basin since the management and planning of water resources require temporal and spatial information.