wcm.02.2025.388.401

Understanding river flow and channel dynamics is crucial globally, especially under changing hydrological regimes driven by climate variability. In arid and semi-arid regions like Iraq, uncontrolled morphological changes in urban rivers, such as the Tigris in Baghdad, pose serious risks to infrastructure integrity, flood safety, and long-term hydraulic and ecological sustainability. This paper aims to investigate the impact of hydrological variability and sediment transport, driven by climatic fluctuations, on bed stability and channel morphology in the urban Tigris River. A one dimensional HEC-RAS model was prepared, calibrated and validated over 48.6 km of Tigris River within Baghdad Governorate. Six flow cases, for the years 1992, 2005, and 2001, were simulated under normal and controlled downstream boundary conditions (water surface elevation) using Quasi-Unsteady flow. For these cases, the sediment transport within this reach were simulated suing the Ackers–White and Toffaleti equations with field grain-size data to compute the changes in riverbed. The calibrated model with R2, RMSE, and NSE of 0.84, 0.30 m, and 0.83, was excellently validated with R2, RMSE, and NSE of 0.82, 0.39 m, and 0.81, respectively. Changes in the invert of river bed across all cases ranged from a minimum of −4.43 m with maximum flow with a downstream boundary condition of water surface fixed at 32 m.a.m.s.l (BCFS32) (Case 4) to a maximum of +4.48 m with minimum flow with BCFS32 (Case 6). Under normal flow downstream boundary conditions (BCNF), bed changes ranged between −3.83 m for maximum flow (Case 3) and +2.42 m for minimum flow (Case 5). The average invert changes were +0.23 m with average flow and BCNF (Case1) to +0.014 m with average flow and BCFS32 (Case 2), −0.27 m with Case 3, +0.44 m Case 4, +0.17 m with Case 5, and −0.03 m with Case 6. Erosion peaked at station 22+000, while peak deposition was observed at station 36+000. Flow velocities ranged from 0.12 m/s to 1.53 m/s (Cases 3 and 4), with average velocities 0.87 m/s 0.39 m/s, 1.09 m/s, 0.85 m/s, 0.67 m/s, and 0.26 m/s for the cases 1 to 6, respectively. Annual sediment deposition rates reached 7 cm/year in depositional zones, including up to 5 cm/year near intake structures. Downstream hydraulic controls are critical for maintaining channel stability and sediment balance, directly influencing the resilience of riverine infrastructure and flood safety in urban environments. Adopt adaptive sediment management strategies supported by real-time monitoring technologies to ensure hydraulic infrastructure sustainability under future climate-induced flow variability and sediment supply changes.