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Communication Dans Un Congrès Année : 2014

Roll waves study on Acquabona watershed

Etude de la formation de roll waves dans le basin de Acquabona

Résumé

The study of muddy fluids in natural slopes has great importance to natural disasters assessment. Free surface flows of Newtonian and non-Newtonian fluids represent events such as mudflows, mud floods, floods and dam breaks which can cause great damage to nearby civil structures. More specifically, concerning mud floods and mudflows, a specific type of instability may appear on the free surface, depending on the channel steepness and fluid rheology: roll waves. These instabilities could be interpreted as an additional risk for safety structures as they lead to a non-constant flow level and fast-moving wave fronts. In order to correct predict the evolution of such kind of phenomena, mechanic and hydraulic conservations laws should be carefully employed. Flow and fluid features must also be properly gathered in order to reduce uncertainties of modeling results. As an attempt to develop risk assessment engineering tools, the work presented in this article is an application of the first-order model that represents roll waves in Herschel-Bulkley laminar fluid flows and describes their characteristics, such as profile and celerity (Maciel et al., 2013). The event from August 17th, 1998, at Acquabona watershed was chosen as the case study in order to analyze the validity of the model. During that event, many surges were detected during almost one hour rain. The surges presented long period and fast propagation velocity and seemed constitute a wave train at some point. In order to investigate whether those wave trains could have been roll waves, the work here present data exploration based on in situ measurements recorded during that mass movement event (Berti et al., 2000). Rheological properties of possible fluid matrix and dynamical characteristics of flow are estimated. Mathematical model is then used to predict waves/surges properties (amplitude, wavelength, period and celerity). The influence of rheological properties on those properties is also studied. Although many assumptions had to be made to explore the available data, results presented point out that roll waves instabilities could have occurred during that event. Since the event was triggered by an unknown disturbance source, it’s difficult to predict each wave separately. When averaging all surges, results given by the mathematical model could have predicted satisfactorily some of those waves’ properties, namely their velocity and amplitude.
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Dates et versions

hal-01189103 , version 1 (01-09-2015)

Licence

Paternité - Pas d'utilisation commerciale - Pas de modification

Identifiants

  • HAL Id : hal-01189103 , version 1

Citer

Guilherme Henrique Fiorot, Fabiana de Oliveira Ferreira, Pascal Dupont, Geraldo de Freitas Maciel. Roll waves study on Acquabona watershed: an application of mathematical modelling. International Conference Analysis and Management of Changing Risks for Natural Hazards, Nov 2014, Padoue, Italy. ⟨hal-01189103⟩
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