Investigating the Effect of Different Roughness on Velocity Pattern at a Reach of Shatt-Al-Arab

Shatt al-Arab River is the only international navigational river in Iraq, extending from the city of Qurna to its mouth in the Arabian Gulf at the city of Al-Fao within the governorate of Basrah for a length of approximately 204 km. Its width ranges from 400 m to 2000 m and its depth ranges from 8 m to 20 m. Since many years Shatt al-Arab River suffer from scouring at the right side (Iraqi side), that is led to displace the borders between Iraq and Iran (Al- Thalweg Line) towards Iraqi territory and thus led to loss of Iraqi land to Iran. Reducing flow velocity along the Iraqi side can led to reducing or preventing erosion in the right bank. Increasing the riverbed roughness will reduce the velocity of flow and then reducing the erosion. This principle was adopted in this study. In this research, a reach of Shatt Al-Arab with a length of 2.5 km located at 34 km northern Fao city was selected to represent the study area. A small area at the upstream of the reach mentioned earlier (700 m length) was selected and called strip in order to change the bed roughness for three different heights. This scenario was simulated with full scale (prototype scale) to investigate the effect of increasing the bed roughness on the velocity pattern at river cross sections and along the reach. The simulation done by using 3D numerical modeling CFD solver (ANSYS fluent 19). For each allocated area, as increasing the roughness height (ks), the longitudinal velocity (v) decreased at the right side by about 10% to 70% and increased by about 5% to 260% at left side along the river reach.