Applying Mobile Boundary Models at Gravel-Bedded Stream Crossings

Mark C. Browning, Hydraulics Engineer, FHWA

This presentation will discuss using mobile boundary models (i.e., BRI-STARS, HEC-6) to compute bridge backwater curves at gravel-bedded stream crossings. Using a case study from the Pacific Northwest, the presentation will compare the bridge backwater results of fixed boundary models (i.e., HEC-2, HECRAS) to those of mobile boundary models. This topic will include a discussion on sediment and hydrologic data requirements and operational/physical modeling parameters such as time steps, stream tubes, and sediment transport formulas, active layer thicknesses, and boundary conditions. The presentation will also include expected reductions in bridge backwater values based upon computed bridge contraction scour.