Bridge Rail Rating Curves and Submergence Characteristics

Abstract

This paper describes a three-parameter model used for determining the hydraulic performance of bridge rails during extreme flood events as well as two submergence models. Typically the geometry of the bridge rails is not considered when conducting floodplain analysis. The use of certain bridge rails with large height or minimal open space may adversely impact the surrounding floodplain. Therefore, a mathematical model used to characterize the hydraulic performance of bridge rails has been developed in order to understand how different bridge rail systems may impact a floodplain. Physical modeling experiments are conducted in order to determine rating curves for various rail geometries that describe the upstream specific energy as a function of the flow rate passing over the rail. In addition, the effects of the submergence of bridge rails by an increase in downstream water surface elevation are also evaluated, as well as the submergence effects of two bridge rails in series. Two different mathematical models are used to approximate and characterize the effects of rail submergence.