In this research the hydraulic characteristic of seventy seven cross sections along 21 km of Tigris River at Mosul city were studied. These cross sections were surveyed and their bed and water surface elevations were measured.
The river at the studied reach have a different morphology and includes three different shapes (meander part braided part and straight part). The results of the study showed that the river at study reach has an average water surface slope equal of 4.7*10-4. The straight part of the river reach has uniform and regular hydraulic characteristic compared to other river parts. The river have wide cross sections, the values of T/D varies between 50-1500 and due to reduction in discharge there was a great reduction in flow depth and the river was receded and river reach was narrowed than before . The deepest part was extended beside the right bank from upstream of Ninevah Bridge to downstream of Al-Horriya Bridge. Application of HEC-RAS Model showed that the model can simulate the hydraulic characteristics of river under different flow condition. Data obtained from the model was used to find empirical relations between (average velocity, average depth, cross section area, Top width and discharge with the stage.

Key Words: Tigris River, Mosul City, Hydraulic Characteristics, HEC-RAS Model.