Abstract. Shatt Al-Arab River was the most important tide river in Iraq, it suffered from neglect and lack of maintenance in the past decades. The river embankment is constantly exposed to erosion processes due to several factors, one of the most important of these factors is the movement of water currents due to the tidal energy coming from the Arabian Gulf. In this study, one dimension unsteady-state model was implemented to study river flood capacity simulation by using HEC-RAS (5.0.7) software in Shatt Al Arab River and its tributaries. The data included flow rate, water level records were collected daily from 2018 to 2020 at different stations along the mentioned river and its feeders, additionally, the considered flood discharge data was taken. These records were taken as boundary conditions for calibration and verification of the model, Furthermore, it used for operation Scenarios. The calibration result shows a good agreement between observed and predicted records with minimum root mean square error (RMSE) was equal to 0.128 with suitable Roughness coefficient value 0.029. The study conclusions indicate that Shatt Al Arb river banks for the southern part were unsafe against the flood in the spring tide case. Furthermore, the maximum safe discharge was estimated about 850 m3/s.
