Identifying and Determining Hydraulic Inspection Indicators Affecting the Vulnerability of River Bridges

River bridges are subject to destruction due to their interaction with water and hydraulic factors. In the first step, identifying the vulnerability indicators of river bridges from a hydraulic perspective for hydraulic inspection is essential in the maintenance process of these structures. In this regard, a comprehensive checklist for hydraulic assessment of bridges was prepared and the required information was collected and the checklists were completed during field visits to river bridges in four provinces of Gilan, Isfahan, West Azerbaijan and Lorestan. The findings of this research show that scouring around bridge piers and abutments is a major hydraulic threat that, when faced with strong currents and floods caused by heavy rainfall, reduces the stability of bridge structures and poses the risk of their destruction in the long term. Environmental factors such as poor vegetation around bridges and excessive removal of materials from riverbeds reduce the bed's resistance to strong currents and increase the vulnerability of foundations to scour. River obstructions, including debris, large logs, and other suspended objects, can change the flow path and increase its speed, which puts additional pressure on bridge structures and causes physical damage to them. In assessing the overall condition of the bridges, the results showed that among the five bridges studied, the Isfahan Railway Bridge was in a more unfavorable condition overall and was affected by hydraulic phenomena such as scour, and needed to be reviewed and preventive measures taken to maintain their safety and efficiency. Also, the Rudbar Arch Bridge was in a more favorable condition than the other bridges in most indicators.