Application of HEC-RAS Software for Steady and Unsteady Hydraulic Simulation of Al-Musayyab Canals

The Al-Musayyab Canal, a vital irrigation infrastructure in the Babil Governorate of Iraq, serves numerous cultivated areas.However, it has faced frequent flooding in recent years due to increased flow rates and changes in land use.This study aims to define the hydraulic characteristics of the 49.5 km-long Al-Musayyab Canal, which extends from the head regulator at Al-Musayyab City to Jabla City and includes 13 branches that distribute water to agricultural areas.To simulate both steady and unsteady flow conditions, HEC-RAS version 6.3 software was used, incorporating 175 cross-sections distributed along the canal.Calibration and verification with flow rates ranging from 25 to 45 m /s revealed that the optimal Manning roughness coefficient is 0.025, which minimizes the error ratio between observed and calculated water surface elevations for both steady and unsteady states.Various scenarios with gate openings ranging from quarter to fully open were simulated.The results indicated that, for the steady flow model, the water surface elevation ranged from 26.32 to 31.78 meters, and velocities ranged from 0.2 to 0.98 meters per second.For the unsteady flow condition, these values ranged from 26.58 to 33.12 meters and 0.22 to 0.89 meters per second, respectively.Risk areas were identified between stations 6750 and 24750 km, which require either cross-section training or embankment heightening to enhance the canal's discharge capacity and mitigate flooding during high flow rates.