Understanding the accuracy of common methods for estimating peak discharge is essential because hydraulic structures are designed based on these discharges. The Wadi Marwani basin in Jeddah, Saudi Arabia was selected as the study area for this investigation. The catchment area of the Wadi Marwani is 2875km², and the total length is 99km. To recommend the most accurate method for estimating peak discharges, four methods were applied to the measured peak discharges in 2-, 5-, 10-, 25-, 50- and 100-year return periods. These methods were: the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS), the probabilistic rational method (PRM), the modified Talbot method (MTM), and regional flood frequency analysis (RFFA) regression equations. The hydrologic and morphometric parameters of each method differed in accuracy for estimating peak discharges. The root mean square error (RMSE) was used to measure the accuracy of the four methods. The RMSE values of peak discharges estimated by the PRM, HEC-HMS, MTM, and RFFA ranged from 0.019 to 0.038, 0.029 to 0.112, 0.068 to 0.198, and 0.007 to 0.205, respectively. The MTM and RFFA equations displayed much higher errors. The results of this study are consistent with the most comprehensive analyses of measured and modeled peak discharge in northern Jeddah in western Saudi Arabia.