Practical Evaluation of Scour at Bridge Piers Along River Banks: A Case Study of the Tigris River in Baghdad, Iraq

Scour near the banks of a river, particularly at the piers of bridges, is one of the most important components of hydraulic engineering because it plays a significant role in the stability and durability of bridges. This paper performs a complete investigation, utilizing an HEC-RAS-based hydraulic (Hydrologic Engineering Center’s River Analysis System) to evaluate the scour risk in the beds and banks at the Abu Nuwas Bridge piers on the Tigris River in Baghdad, Iraq. Studies that looked at different hydraulic factors, like flow rate, sediment transport, and the shape of the riverbed, were used in the evaluation to guess and model the possible scour depths of existing structures. Calibration (Manning’s n) and model validation were performed with measured discharges of 700 and 425 m3/s, respectively. In the calibration, the n value of 0.03 for the overflow banks and 0.023 for the main channel gives an acceptable performance with R2=0.84, RMS=0.3m, and NSE=0.83. In comparison, the model was valid with R2=0.82, RMS=0.39m, and NSE=0.81. These values are considered acceptable for modelling large rivers like the Tigris River. The research results showed that the risks of scouring under the cladding on the banks, even a small depth of scour, can lead to the collapse of both banks and the stone cladding versus scouring at the bottom of the bed. The study results indicated that the depth of the scour ranged from 0.0 to 2.8 m, with the greatest scour observed at Piers D30 and D148. Further, these results help improve our knowledge of the scour phenomenon and make specific contributions to the design and management of bridges near riverbanks.