Complementary experiments for hydraulic modeling of multi-box culverts

Culvert design must account for a large range of flow rates but most of the time culverts convey flows that are smaller than the design flow. Repeated high flows passing through the culverts lead to a gradual increase of the sediment deposits in the culvert vicinity, eventually resulting in reduced flow and sediment capacity. Sedimentation at culverts is quite an involved process due to the combined effect of flow non-uniformity and unsteadiness, as well as of the flow-sediment interaction. This paper reports results from a series of laboratory experiments aimed at understanding the hydro and morpho-dynamic changes occurring in the vicinity of a three-box culvert. For this purpose, velocity and turbulence characteristics upstream of the culvert were mapped globally and locally during the transition from an original flatbed to equilibrium sediment transport condition using contemporary acoustics, light detection and ranging, and image-based technologies. The experimental results reveal flow complexities not currently accounted for in the design of the multi-barrel culverts, but which can be detrimental for their long-term operation. Considerations on practical approaches to efficiently model the complexities were formulated. Key words: culvert, non-uniform flow, LSPIV, LiDAR, acoustic instrument. La conception des ponceaux doit tenir compte d'une grande plage de debits mais, la plupart du temps, les ponceaux font passer des debits qui sont inferieurs au debit prevu. Les debits eleves passant a repetition dans les ponceaux engendrent une augmentation graduelle du depot de sediments aux environs du ponceau, ce qui conduit eventuellement une capacite reduite de debit et de transport solide. La sedimentation aux ponceaux est un processus complexe en raison de l'effet combine de la non-uniformite et de l'instabilite du debit ainsi que de l'interaction debit-sediments. Le present article presente les resultats d'une serie d'experiences en laboratoire visant a comprendre les changements hydrodynamiques et morpho-dynamiques survenant aux environs d'un ponceau tricorps. A cette fin, les caracteristiques de vitesse et de turbulence a l'amont du ponceau ont ete cartographiees globalement et localement durant la transition d'un lit plat initial a une condition de transport a l'equilibre de sediments en utilisant l'acoustique contemporain, le LiDAR et les technologies basees sur les images. Les resultats experimentaux revelent des complexites de debits dont on ne tient pas presentement compte dans la conception de ponceaux multitubes, mais qui pourraient nuire a leur fonctionnement a long terme. Nous avons formule des recommandations concernant les approches pratiques afin de modeliser efficacement ces complexites. [Traduit par la Redaction] Mots-cles: ponceau, debit non uniforme, LSPIV, LiDAR, instrument acoustique.
1. Introduction Culverts are common hydraulic structures for secondary roads crossing small streams in the rural US Midwestern area. In this region, the sedimentation at culverts is a chronic problem [...]