Predicting the flow in the floodplains with evolving land occupations during extreme flood events (FlowRes ANR project)

Abstract

Abstract. Flood hazards (flow depth and velocity) must be accurately assessed in high-risk areas during extreme flood events. However, the prediction of the very high flows is not an easy task due to the lack of field data and to the strong link between flow resistance and the land occupation of the floodplain. Confinement and inhomogeneity in lateral and longitudinal directions of hydraulic roughness strongly vary with return period T. The physical processes are complex, some still largely unexplored, and the assumptions linked to numerical modelling cannot be validated without field data. The FlowRes project (2015)(2016)(2017)(2018), funded by the French National Research Agency (ANR), aims at improving the flood hazard assessment in floodplains in: 1) investigating in laboratory the hydrodynamic structure associated with extreme flood flows for various land occupations and flow discharge magnitudes; 2) assessing if the existing numerical modelling practices used for T ~ 100 years are still valid for extreme events with T > 1000 years, relying on the experimental data and on one field case. This paper reports some results obtained during the first year of the project.

Drag on a Square-Cylinder Array Placed in the Mixing Layer of a Compound Channel

“…The experimental array is composed of nine square cylinders with width d = 0.045 m. It was placed at the interface between the main-channel and the flood plain, forming a grid orthogonal to the channel axis, as depicted in Figure 3. The distance d 0 between two consecutive cylinders was kept equal to 0.10 m. Spacing and sizing were chosen so as to align with those of the experiments carried out in the context of FlowRes ANR, a project oriented to the investigation of compound-channel flows with transition in bed roughness, described in [39]. The tests were run under uniform-flow conditions in the compound channel.…”

An Optimized and Scalable Algorithm for the Fast Convergence of Steady 1-D Open-Channel Flows

“…The numerical resolution of this set of non-conservative equations has been shown to provide accurate results in many practical cases, including in the presence of discontinuities [22,23]. Assuming a steady flow, temporal derivatives vanish in Equation (1). Since solving the first equation is straightforward, the discharge distribution is known on the entire domain for a given distribution of q l .…”

“…Channelized flows can be simulated using 1-D, 2-D or 3-D models depending on the level of flow detail that is required [1]. Results from hydrodynamic numerical models are used in multiple domains including flood risk analysis [2] or real-time control of river facilities [3], for instance.…”