Applying the HEC-RAS Model to the Investigation of the Tigris River's Impact from a Proposed Bridge North of the Al Kut Barrage

This study investigates the hydraulic impacts of constructing a planned bridge north of Al Kut Barrage on the Tigris River using the HEC-RAS v6.6 model. The research assesses how the proposed bridge affects river behavior under three discharge scenarios (500, 1050, and 3000 m³/s) by comparing conditions with and without the bridge. The analysis focused on key hydraulic parameters including bridge scour, backwater effect, and velocity profiles. Field and laboratory data, combined with geometric and hydrological inputs, were used to calibrate the model. Results indicate that scour depth increases significantly with discharge, reaching up to 7.87 m at piers and 5.90 m at abutments under peak flow. However, the backwater effect remained negligible, with only a 1 cm rise detected during the highest flow scenario due to the minimal obstruction (4.36%) posed by the bridge. Similarly, no significant changes in upstream and downstream velocity profiles were observed. These findings demonstrate that while localized scour presents a notable risk, the overall impact on river hydraulics remains limited due to the bridge's optimized design.