Waterway transitions at US bridges

Stream and river management projects are implemented to improve water quality, stream function, aquatic habitat and aesthetics, and provide mitigation for road construction. In contrast, bridge maintenance activities are undertaken to convey water, sediment and debris beneath bridges at high flows. Road crossings can have a significant influence on local hydraulics and sediment transport, resulting in an altered flow pattern that can cause backwater, increased erosion, debris and sediment deposition and channel instability. Thus, managing rivers and streams that include one or more road crossings requires some knowledge of the flow hydraulics over a range of flows in order to create a smooth, stable transition through the bridge opening. In-stream structures, such as vanes and weirs, can help to transition flow, sediment and debris through a bridge opening. The use of these in-stream structures at road crossings, and scenarios for planning projects where road crossings intercept the project reach, are presented.