Contribution to the modeling of the hydraulic effect of floating debris accumulation at bridges (en ce compris une introduction à la méthodologie de la recherche)

Abstract

This master thesis contributes to the numerical modelling of the hydraulic effects engendered by floating debris accumulations at bridges. To overcome the limitations of current empirical and analytical approaches, which often neglect anthropogenic debris and are difficult to integrate into computational tools, this study evaluates a vertical contraction model developed by the HECE department of the University of Li`ege. This approach was implemented in the WOLF2D software and tested across three configurations: a straight channel, a channel with floodplains, and a real-case application (the Vesdre River in Verviers). The first configuration allowed for benchmarking the model against an experimental database and quantifying the model’s accuracy. The results demonstrate that the method is globally conservative, predominantly overestimating water level rises, while the rare underestimated cases present a mean discrepancy of 15%. In the model integrating floodplains, the simulations served to optimize the deployment of future laboratory instrumentation, identifying downstream confluence zones as strategic locations due to high velocity gradients. Finally, to guarantee the repeatability of future laboratory tests aiming to account for floodplains during this clogging process, debris densities must be controlled. This requirement drove the research for a protective method for the debris used, aiming to stabilize density evolution during the tests in order to increase test repeatability. Ultimately , the application of this modeling to the Vesdre River clearly highlights the impact of these debris, which significantly increase water depths in Verviers. This real-case application reinforces the suggestion to integrate debris into future flood risk maps, given their demonstrated impact during the 2021 flood events in Verviers.