Investigating the shear and velocity profiles within the estuary of Shatt Al-Arab river, Southern Iraq

• Erosion and sedimentation occurred in Shatt Al-Arab River estuary. • Thalweg line shifted ∼50m due to erosion near the Iraqi border. • CFD showed higher velocity and shear stress than HEC-RAS 2D. • Both models showed good agreement with actual measurement data. Morphological changes, represented by erosion and sedimentation, are a natural phenomenon that occurs in most river estuaries, causing changes in waterways and affecting offshore structures. One of these estuaries is the Shatt Al-Arab River estuary, which is the main waterway for trade and a major outlet for oil exports, is suffering from these changes. Moreover, the Thalweg Line, which is the deepest point within the estuary, forms the international border between Iraq and Iran. This line is moving at some rate towards the Iraqi land. To understand the process of erosion and sedimentation within the Shatt Al-Arab River estuary, a hydraulic mathematical simulation by using both HEC RAS and ANSYS Software. The HEC RAS was used to simulate the flow within the last part of the Shatt Al-Arab River and to predict the hydraulic conditions at approximately two kilometers from the river mouth that will be used as an upstream boundary in ANSYS Software. ANSYS was used to obtain comprehensive fine details of Shear stress and velocity within the estuary as indicators to identify erosion and sedimentation zones. The results showed that the HEC RAS model has good agreement with the actual water level data, with an RMSE value of 0.09. While it was 0.07 when comparing the ANSYS results with experimental data. The results showed that the maximum deviation in the Thalweg Line occurred two kilometers toward the Iraqi land compared to the field survey of 1975. The mathematical results showed that the maximum shear stress and velocities were located right the Thalweg Line, causing it to move toward the Iraqi border. The average velocity in ANSYS Software was approximately 18% greater than in the two-dimensional HEC RAS, while the difference in shear stress was approximately 25%.