High spatial resolution mapping of surface velocities and depths for shallow overland flow
2012
Legout , Cédric (Université Joseph Fourier (Grenoble 1), Grenoble(France). Laboratoire d'études des Transferts en Hydrologie et Environnement (LTHE) UMR 5564 CNRS-INPG-IRD-UJF) | Darboux , Frédéric (INRA , Ardon (France). UR 0272 Unité Science du Sol) | Nédélec , Yves (Centre d'Etudes Techniques de l'Equipement du Sud-Ouest, Bordeaux(France). Département Laboratoire de Bordeaux; Groupe Géotechnique, Risques et Bâtiments) | Hauet , Alexandre (Electricité de France, Toulouse(France). Centre Hydrométéorologique Pyrénées Massif Central) | Esteves , Michel (Institut de Recherche pour le Développement, Grenoble(France). Laboratoire d'études des Transferts en Hydrologie et Environnement (LTHE) UMR 5564 CNRS-INPG-IRD-UJF) | Renaux , Bernard (INRA , Ardon (France). UR 0272 Unité Science du Sol) | Denis , Hervé (Centre National de la Recherche Scientifique, Grenoble(France). Laboratoire d'études des Transferts en Hydrologie et Environnement (LTHE) UMR 5564 CNRS-INPG-IRD-UJF) | Cordier , Stéphane (Centre National de la Recherche Scientifique, Orléans(France). Laboratoire de Mathématiques - Analyse, Probabilités, Modélisation - Orléans (MAPMO), UMR 6628 CNRS-Université d'Orléans)
Point measurements of flow rate, depth or velocity are not sufficient to validate overland flow models, particularly when the interaction of the water with the soil surface creates a complex flow geometry. In this study, we present the coupling of two techniques obtaining spatial data of flow depths and surface velocity measurements for water depths as low as 1 mm. Overland flow experiments were performed in the laboratory at various flow rates and slopes on two surfaces. The first surface was 120cm by 120cm showing three undulations of sinusoidal shape with an amplitude of 1 cm and a wavelength of 20 cm, while the second was a 60cm by 60 cm moulded reproduction of a seedbed with aggregates up to 2 cm in size. Large scale particle image velocimetry (LSPIV) was used for velocity measurements with a sub-centimetre spatial resolution. An instantaneous-profile laser scanner was used to map flow depths with a sub-millimetre spatial resolution. A sensitivity analysis of the image processing of the LSPIV showed good robustness of the method. Comparison with measurements performed with hot film anemometer and salt velocity gauge showed that LSPIV surface velocities were representative of the flow. Water depths measured with the laser scanner were also in good agreement with single-point measurements performed with a dial indicator. Spatially-distributed flow rates could be computed by combining both presented techniques with a mean relative error less than 20%.
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