Bridge scour is a complicated phenomenon that involves interactions between the soil and the water during the contraction of the bridge and the nearby structures. The top cause of bridge failures in the USA is scour, thus studies in this field are relevant. This study presents a comparison between four approaches to estimating scour in bridges in which different methods to compute the approach velocity at the bridge piers were used. These approaches used the hydraulic models WSPRO, HEC-RAS 1D steady flow, HEC-RAS 2D unsteady flow, and HEC-RAS 2D employing a hole-in-the-mesh approach. In all cases, scour depths were computed using HEC-18 equations. These four methods were applied to a Coffee County Road 606 bridge over the Little Double Bridges Creek in Alabama. This bridge has a USGS stream gauge station that is currently operational, which has enabled other efforts to perform hydrological calibration of the watershed using HEC-HMS. Two different river flood scenarios were modeled, the first being a hypothetical hyetograph representing tropical Storm Alberto (July 1994) and the second, a much milder event recorded in March of 2022. Some significant differences in the velocities, and consequently in the estimated scour depths, were obtained with each one of the considered methods. This study complements other efforts to estimate and measure real-time scours on Alabama bridges.
