Three-Dimensional Morphodynamic Modelling of Tigris River in Baghdad

Abstract

Bathymetric and land surveys were conducted for the northern Tigris River reach (18 km length) in Baghdad, producing 180 cross sections. A river bed topography map was constructed from these cross sections. The velocity profiles and the water discharges were measured using ADCP (Acoustic Doppler Current Profiler) at 16 cross sections, where intensive number of sediment samples was collected to determine riverbed characteristics and sediment transport rate. The three-dimensional morphodynamic model (SSIIM (simulation of sediment movements in water intakes with multiblock option)) was used to simulate the velocity field and the water surface profile along the river reach. The model was calibrated for the water levels, the velocity profiles and the sediment concentration profiles using different combinations of parameters and algorithms. The calibration and the validation results showed good agreement with field measurements, and the model was used to predict the future changes in river hydro-morphology for a period of 14 months. The results of the future predictions showed the Tigris River which behaved like an under-fit river, increases in depositions on the shallow part of the cross section having lower velocity, and the river deepens the incised route to fit its current hydrologic condition leaving the former wide section as a floodplain for the newer river. The net deposition/erosion rate was 67.44 kg/s in average and the total deposition quantity was 2.12 million ton annually. An expansion in the size of current islands was predicted. An indication of the potential threats of the river banks' collapse and the bridge piers' instability was given by high erosion along the thalweg line.