At the European and national level, in the field of turbulent free-surface flows on complex bottoms, the experimental and metrological expertise of the H2O group has been clearly identified and recognized in the European project Hydralab+  (2015-2019, https://hydralab.eu/) and the ANR Flowres (2015-2018, https://flowres.irstea.fr/en/).

In particular, the development of innovative optical techniques around PIV (stereoscopic multi-planar and/or scanned) or umbroscopy (integrated PTV at channel scale) now allows a rigorous change of scale from local 3D measurements to a vertical 1D description (Saint-Venant equations), giving access to all relevant components of the local flow. This expertise also includes the joint use of acoustic techniques, which are mostly used in other European laboratories or in situ studies.

Multi-plane PIV measurements in a canopy of regular prisms. (a) Reynolds tensor in the central vertical plane through the center of the prisms. (b) and (c) Reynolds tensor in a horizontal plane above the canopy and in the canopy (horizontal lines in figure a) reconstructed from 9 vertical planes of PIV measurements.

• Turbulent boundary layer on natural bottoms

• Non Newtonian free surface flows

• Sediment transport on complex bottoms

The “Hydrology at the catchment scale” theme includes several actions ranging from numerical rainfall-flow modeling to the estimation of the uncertainty associated with the response of a hydrodynamic model. The research work carried out is mainly dedicated to the improvement of the understanding and representation of flash flood dynamics, with in particular the identification of the dominant processes according to the characteristics of the rainfall event and the catchment area considered. Distributed modeling is the tool used to provide these elements of understanding. As a result, special attention is also devoted to the estimation of parameters in hydrodynamic models in general, as well as to the evaluation and propagation of uncertainties associated with this type of modeling. For this purpose, it was necessary to appropriate and adapt various mathematical techniques, in particular sensitivity analysis or data assimilation, in order to analyze the behavior and better constraint hydrodynamic modeling.

The research in hydrological modeling dedicated to flash floods has resulted in a high level of scientific production, while ensuring a transfer to the operational actors in the field. The SCHAPI-IMFT research agreement, renewed since 2006, is a striking example: one of the main missions of the SCHAPI (Service Central d’Hydro-météorologie et d’Appui à la Prévision des Inondations) is to support flood forecasting services at the national level. The MARINE model is part of the hydrological modeling platform PLATHYNES (PLATeforme HYdrologique pour la modélisatioN des Écoulements Spatialisés) of the SCHAPI, which is currently being tested and used for operational forecasting by several flood forecasting services. It is also registered with the Agency for the Protection of Programs. The H2O group is also very active in the international research program HyMeX – HYdrological cycle in the Mediterranean EXperiment

(http://www.hymex.org/).

The MARINE model: Modeling and Anticipation of Runoff and Flooding for Extreme Events. Schematic of the represented processes and implementation in PLATHYNES, the modeling platform with operational vocation of the SCHAPI

• Analysis and assimilation of earth observation data

• Uncertainty propagation

• Understanding and modeling of hydrological processes

Within the framework of the IMFT/OFB/PPRIME Pôle Écohydraulique, a first phase of studies has allowed to understand the flows within the fish passes, such as the macro-roughness ramps for upstream migration and the ichtyocompatible water intakes for downstream migration, and in fine to improve their design criteria. This first phase has also resulted in the design and manufacture of a tiltable flume made entirely of glass intended to evaluate the efficiency of fish passes in relation to hydrodynamic characteristics (OFB Macrorugosité 2 project). This flume allows the development of innovative optical metrology, in particular for flows with steep slopes. A second phase of studies, currently underway, consists of acquiring feedback in situ, on devices that comply with the latest recommendations, to evaluate the effectiveness of fish passes. These studies, which are already well advanced concerning downstream migration, confirm the achievement of high efficiencies (80-100% for salmon juveniles and 95-100% for silver eels), helping to reconcile hydropower, a renewable energy source, and the restoration of fish populations. These results validate the operational transfer of technical recommendations on the design of devices. Our expertise on this topic is widely recognized beyond the national level, particularly in the European programs in which the Pôle Écohydraulique is involved: H2020 FIThydro and Interreg SudoAng.

Tiltable hydraulic flume of the Environmental Fluid Mechanics Platform

• Biofilm and vegetation

• Fish upstream/downstream migration and fish passes

• Habitat