Sensitivity of Water Surface Elevation Level in the Tigris River within Baghdad city to the Changes in the Value of Mannings Roughness Coefficient

Evaluating the factors affecting the flow properties of the Tigris River is one of the important studies due to the importance of this river to the city of Baghdad. One of the most important factors affecting the properties of the flow is the Manning's roughness coefficient (n). Precise estimation of the value of this parameter for natural rivers is a challenge due to the large number of factors affecting it. This study demonstrates the impact of the changes in the value of this parameter on water surface elevations of Tigris River within Baghdad city. To understand how the changes in this parameter affects the water surface elevations, different scenarios of Manning's n and discharge values were adopted. The range values for Manning coefficient and discharges were (0.025, 0.03, 0.035, 0.04, 0.045) and (500, 1000, 1500, 2000, 2500, 3000 m3sec-1) respectively. The program HEC-RAS version 4.1 was used in this study and the case of steady ?uniform flow was assumed to run it. The results show clearly the effect of changing Manning's n on water surface elevations also It had been seen that the value of n equal to 0.025 and to some degree 0.03 is the most safe and suitable value for Tigris river within Baghdad depending on the adopted flow values in the study.