Hydraulics

Erosion and deposition processes are usually described using empirical formulations developed under steady uniform flow conditions that are not well adapted to fast transient flows. Consequently, significant variations exist among the predictions of the morphological evolution in rivers.

Based on laboratory experiment, we investigate the flow behaviour and the development of the velocity profile to better characterise the bed shear stress responsible for erosion and deposition processes. Digital imagery techniques such as PIV are used, allowing for a detailed measurement of the velocities, both in the water and in the moving sediment layers.

Experimental work and PIV measurements (PhD theses by Rui Aleixo 2011, Ilaria Fent 2018)

Discharge measurements in rivers rely on direct measurements of the velocity field, or on water-level measurements and stage-discharge relations. With the development of digital imagery and photogrammetry, it possible to obtain surface-velocity measurements in streams from aerial images acquired for example using a drone flying over the considered river-reach. The key challenge is then to transform these velocity measurements into discharge measurements. Research on these topics is performed both in the lab and on the field to solve the related issues.

Drone-based photogrammetry (PhD theses of Olivier Carlier 2019 and Adermus Joseph 2020)

Under extreme flow conditions, the riverbed is subject to significant morphological changes. While the simulation tools designed for pure hydrodynamic flows are nowadays quite reliable, there are still significant uncertainties when it comes to the prediction or erosion and deposition patterns. Different mathematical models exist, without any clear agreement in the scientific community about the best adapted approach, and many questions remain open as regards the closure equations for these models.

In our group, we have developed several finite-volume numerical simulation tools based on one- or two-layer models, both in one and two spatial dimensions.

Modelling the morphological evolution (PhD theses of Catherine Swartenbroeckx 2012, Sylvie Van Emelen 2014, Fabian Franzine 2017, Ilaria Fent 2018)

Dikes built along rivers or earthen dams are vulnerable structures in case of catastrophic flooding, as they can be completely eroded when overtopped. With the change in precipitation regimes observed worldwide following climate change, the risk of failure of such structures, initially aimed at protecting land and constructions, increases significantly. In our group, we develop both experimental tests and numerical simulations aimed at a better understanding of breaching processes for better simulations and predictions of the consequences of a failure.

Experiments by Sylvie Van Emelen (PhD thesis 2014)

Despite the development of the parallel computing, simulating a flood lasting several hours over a large urban area still requires a significant computational time. Porosity-based models rely on the analogy between a city and a porous medium: the buildings are the grains, and the streets constitute the pores. Using such an approach, it is possible to reproduce the effects of the buildings on the flow, e.g reduction of the storage capacity and of the flow propagation speed, using very coarse computational meshes.

In our group, we have participated to the pioneering developments of porosity-based models, together with Prof. Vincent Guinot from the University of Montpellier.

Results by Mirjana Velickovic (PhD thesis 2012)

Our group is very active in scientific cooperation research, through the RESCIF  network and through projects funded by ARES , related to floods and water distribution, in Haiti and in the Philippines.
In Haiti, we mainly collaborate with the Université d’Etat d’Haiti on flood-risk  related issues, which aver very important for the coutry, especially considering that their situation has not significantly improved 10 years after the terrible earthquake . Another project, in collaboration with the NGO Join for Water  concerns water distribution in rural areas in Haiti, through the development of a web-based application  for an improved management.
In the Philippines , activities are oriented towards water distribution, through better pumping wells, improvement of distributed water quality for an increase of public water consumption instead of bottled water, and improvement of the distribution network.

Hazard, vulnerability and risk maps for the Cavaillon city, Haiti (PhD thesis of Adermus Joseph 2020 )