Assessing the Need for Floodplain Culverts Based on Geomorphology

Project summary:

Minnesota roadways intersect rivers and streams in hundreds of thousands of locations across the state, often in culverts--an economical way to pass water underneath roadways. Floodplains adjacent to rivers and streams carry water, sediment, nutrients, and aquatic organisms during high flows. For streams with wide floodplains, placing a single crossing on the main channel forces floodplain flow to concentrate, potentially causing scour near culverts and leading to excess sedimentation as flood flows recede. These processes can lead to structure damage, maintenance costs, and impacts to aquatic organism passage (AOP). The installation of off-channel, or floodplain culverts, is a potential solution to maintain connectivity of floodplain flows and sediment transport and to improve resiliency of stream crossings. However, the installation of floodplain crossings has upfront costs and there is limited information on the design and placement of floodplain culverts. Therefore, the objectives of this project are to 1) examine how floodplain culverts can aid in passing flood flows and maintaining sediment transport processes, 2) determine where floodplain culverts have the most benefit and should be considered, and 3) identify and quantify the potential benefits of floodplain culverts as a function of site characteristics and culvert design. Researchers will do this with a combination of small- and field-scale laboratory studies, case studies, and a survey of culvert maintenance needs and costs.