Culvert Design for Flood Routing Considering Sediment Transport,

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Current flood routing methodologies do not consider sediment bed-load transport through the culverts or pipelines of road crossings. Many practitioners either ignore the transport of sediment through a culvert or assume that sediment is transported in suspension with little effect on the flow capacity of the culverts. However, sand and gravel sized sediment is transported through a culvert as bed-load and not as a homogeneous suspension. Bed-load transport of sediment can reduce effective flow areas, reduce flow capacity, increase energy loss, increase upstream flow depths, and cause flow regime changes with bed forms. The presence of bed-load is a major contributor of culverts plugging with sediment. This study investigates the bed-load transport of sediment through culverts and the methodology for studying the transport phenomena in a laboratory. This paper discusses the preliminary test results of 6.50 mm Dm sized sediment transported as bed-load through a 30.20 cm diameter culvert. The tests were successful in demonstrating and determining incipient motion criteria, bed form regimes, energy loss, and transport rates under a variety of flow rates and three bed elevations. The study has also demonstrated that several of the sediment bed-load transport methods used for channel flow can be applied to transport in a culvert. Testing so far has been focused on fully pressurized culverts with tailwater control. From the preliminary test results, a design procedure and an example are presented for sizing culverts for bed-load sediment transport. Results from the example demonstrate the need for sediment transport and bed form regime considerations in the design of culvert systems where flood flows deliver sediments to and through culvert inlets.

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