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Flood of 23 November 2019 on the French Riviera: a comparison of discharges estimated by image analysis and hydrological modelling

Etienne Robert, Gauthier Paul Daniel Marie Rousseau

The short and heavy rainfall events observed on the French Riviera often lead to flash floods on coastal catchments: during the flood of 2 October 2015, a peak discharge between 185 and 295 m(3)/s was estimated on the Brague at Biot at 8:00 PM, whereas the flow rate was about 1 m(3)/s at 5:30 PM there. While measurements of such discharges are very important (for statistical flood analysis, flood modelling, design of hydraulic structures), they are dangerous when they require an operator to handle an instrument in or near the river. Alternative methods can be used, such as video analysis. In this work, we applied two different image velocimetry (LSPIV) algorithms (Fudaa-LSPIV and OpyFlow) to several videos of the 23 November 2019 floods within the Brague catchment, in order to estimate discharge values. The discharge values obtained were then compared with the values observed on the available gauging stations, as well as to the results of rainfall-runoff modelling on the same sections. The LSPIV estimates, discharge simulations and observations are consistent across the studied sections, showing the interest of combining such different and independent techniques to estimate flood discharge values.

ROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD2022

Experimental realization and characterization of unstretched planar one-dimensional diffusion flames

Peter Monkewitz, Etienne Robert

A burner configuration that allows the creation of nearly unstretched one-dimensional diffusion flames has recently been introduced. This paper presents the first detailed characterization of flames produced in such a burner to assess how well they approach the idealized one-dimensional configuration, which is used extensively for the development of theoretical models for diffusion flame stability. Particular emphasis is directed at quantifying the remaining inhomogeneities in the burner, such as residual flame stretch or variations in the boundary conditions, and identifying possible means to minimize them. Measurements made include the velocity field, stable species concentration profiles and temperature distribution throughout the burning chamber. Additionally, the flame position in the burner is determined as a function of mixture strength, reactant transport properties and bulk flow velocity. All the measurements are found to be in good agreement with a simplified one-dimensional flame model. However, the boundary conditions and their physical location have to be determined experimentally on both sides of the flame, which complicates comparison with results from theoretical and numerical models. Despite these limitations, we conclude that this new burner type provides a good experimental approximation of the one-dimensional idealized construct. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Elsevier Science Inc2013

Thermal-diffusive instabilities in unstretched, planar diffusion flames

Peter Monkewitz, Etienne Robert

The recent development of a novel research burner at EPFL has opened the way for experimental investigations of essentially unstretched planar diffusion flames. In particular, it has become feasible to experimentally validate theoretical models for thermal-diffusive instabilities in idealized one-dimensional diffusion flames. In this paper, the instabilities observed close to the lean extinction limit are mapped in parameter space, notably as function of the two reactant Lewis numbers. Cellular and pulsating instabilities are found at low and high Lewis numbers, respectively, as predicted by linear stability analyses. The detailed investigation of these two types of instabilities reveals the dependence of cell size and pulsation frequency on the transport properties of the reactants and on flow conditions. The experimental scaling of the cell size is found in good agreement with linear stability. The comparison between experimental and theoretical pulsation frequencies, on the other hand, was hampered by the impossibility of experimentally reproducing the parameters of the stability calculations. Hence, a heuristic correlation between pulsation frequency and flow parameters, transport properties, in particular the Damkohler number, and oscillation amplitude has been developed and awaits theoretical interpretation. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Elsevier2012