Evaluation of Scour Depth around Bridge Piers with HEC-RAS (Case study: Bridge of Simineh Rood, Miandoab, Iran)

In the present study, the scour depth around bridge piers of Simineh Rood Miandoab was investigated through HEC-RAS model using with two of CSU and Froehlich method (two methods of HEC-RAS software) for the discharge with a different return period. For this purpose, first, using a field data, a hydraulic model of the river range, where the bridge is located was created in the software medium. Then for discharges with the return period of 5 to 1000 years, the change in flow discharge for scouring around the middle and lateral sides piers of the bridge was investigated. The results showed that with increasing the discharge (increasing the flow velocity), the flow interference are increased and the amount of scouring in the middle of the piers is reduced relative to the sides. Moreover, for the discharge with a return period of 5 to 40 years, no scouring is observed in the bridge sides. Whereas for the discharge with a return period of 50 to 1000 years, the scouring around the the bridge sides increases significantly. For different return periods, in both CSU and Frohlich methods, pier number 7 has the highest scour and pier number 1 has the lowest value. The Frohlich method is not as sensitive as the CSU in calculating the scour depth compared with increase discharge, and approximately 20% are different in calculating the scour depth. Such difference could be attributed to the applying the pier shape coefficient, the bed conditions, as well as the coefficient of sediment particles in the CSU method.