Morphology of Tigris River within Baghdad City

Abstract. Changes in the morphology of the River Tigris within Baghdad City are very noticeable in recent years. The number of islands is increasing with time despite the fact that huge amount of sediments are trapped in reservoirs upstream Baghdad City. The debris of destroyed bridges in the wars of 1991 and 2003 had enhanced the development of these islands. As a consequence the ability of the river had been reduced to pass flood waves. This fact caused partial flooding of parts of Baghdad City. Cross sections of the River Tigris were surveyed in three occasions (1976, 1991 and 2008). The last survey conducted in 2008 by Ministry of Water Resources covered 49 km of the river from Al-Muthana Bridge to its confluence with Diyala River at 250 m intervals. The data was used to predict the maximum flood capacity for the river using one-dimensional hydraulic model for steady flow "HEC-RAS". Calibration was carried out for the model using field measurements for water levels along the last 15 km from its reach and the last 10 yr observations at Sarai Baghdad station. The average discharge of the river in Baghdad had been calculated for the past ten years. This value was introduced in the model. Then different scenarios were applied by increasing the discharge in order to find out the critical discharge that can cause inundation. The procedure continued to detect the areas that had been inundated and the water level was recorded. The model showed a significant reduction in the current river capacity in comparison with what the river had used to hold during floods of 1971 and 1988. The three surveys conducted on the same reach of the River Tigris indicated that the capacity of the river to pass water had been decreased. In addition the changes in the morphology of the river cross sections were very clear.