Les observatoires du ruissellement : comprendre les processus pour améliorer les modélisations
- 1 December 2020
- journal article
- research article
- Published by Taylor & Francis Ltd in La Houille Blanche
- Vol. 106 (6), 7-16
- https://doi.org/10.1051/lhb/2020056
Abstract
Le ruissellement est un phénomène épisodique et localisé, donc difficile à mesurer. Il résulte de l'interaction de nombreux facteurs, dont les caractéristiques intrinsèques et de surface du sol, la morphologie du bassin versant, mais également les caractéristiques pluviométriques. Afin d'améliorer la compréhension de la genèse et de la propagation du ruissellement au sein de bassins versants de tête, cinq observatoires du ruissellement sont présentés, incluant 11 bassins versants. Pour chacun d'entre eux, la pluie et le ruissellement sont mesurés sur le terrain à haute fréquence (≤ 15 min) pendant des durées longues (1,5 à 11 ans). 1640 évènements pluvio-ruisselants sont extraits de ces chroniques en continu et statistiquement analysés, afin de cerner les facteurs influant significativement le ruissellement. La réponse ruisselante de chaque bassin versant est extrêmement complexe mais permet d'identifier des comportements communs. L'importance des caractéristiques des sols est montrée, ainsi que celle de leur occupation, de leurs états de surface et état hydrique. La dispersion de la relation pluie-débit observée au sein de chacun des observatoires permet par ailleurs de montrer et de quantifier l'impact des caractéristiques pluviométriques sur la lame d'eau ruisselée. Les leçons tirées de chacun des observatoires et leurs conséquences sur la compréhension et la modélisation du ruissellement dans différents contextes sont discutées. Runoff events are usually very concentrated in both space and time, and are therefore challenging to monitor. They result from the interactions of rainfall characteristics with both soil surface and intrinsic characteristics and catchment morphology. To improve our understanding of this complex process, five observatories were installed to monitor the runoff response of eleven catchments to natural rainfall events. Measurements were performed with a high frequency (≤ 15 min-time step) and over long time periods (1.5 to 11 years). 1640 rainfall-runoff events were extracted from rainfall and discharge time series. Statistical analyses were performed in order to determine significant triggering factors. The rainfall-runoff response of each catchment is highly variable, but some common features were identified across contrasted catchments. Under highly variable soil types, the catchment runoff exhibited contrasted patterns. Soil surface state, and land use were demonstrated to highly affect runoff. The scattering in the rainfall-runoff relationship demonstrated the key role of the initial soil moisture and rainfall characteristics. Lessons learnt from previous studies in these various environments, as well as their consequences on runoff understanding and modelling are discussed.Keywords
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