Journée Anniversaire des 50 ANS de mesures des bassins versants du Réal Collobrier - Recueil des communications

National audienceThe Real Collobrier research basin is located at the western end of the Maures mountain range on the Mediterranean coast. Its purpose is to study the hydrological functioning of small Mediterranean woodland basins located on a metamorphic base. This basin is characterized by a Mediterranean situation characterized by high intensity precipitation and fast kinetic floods. This research basin is not only a hydrometeorological database, it is above all a field laboratory around which multidisciplinary teams work together to carry out research on targeted themes. This research has evolved over time according to the operational needs (water resources, desertification, flooding, flood forecasting) and the scientific community to improve the understanding of the functioning of Mediterranean systems. It represents an essential link in the development of hydrological knowledge.Le bassin de recherche du Real Collobrier est situé à l'extrémité ouest du massif montagneux des Maures sur la bordure côtière méditerranéenne. Il a comme finalité l'étude du fonctionnement hydrologique de petits bassins forestiers méditerranéens situés sur socle métamorphique. Ce bassin est caractérisé par une situation méditerranéenne marquée par des précipitations de fortes intensités et des crues à cinétique rapide. Ce bassin de recherche n'est pas qu'une banque de données hydrométéorologiques, c'est avant tout un laboratoire de terrain autour duquel des équipes pluridisciplinaires s'associent pour mener à bien des recherches sur des thématiques ciblées. Ces recherches ont évolué au cours du temps en fonction des besoins opérationnels (ressource en eau, désertification, inondation, prévision des crues) et de la communauté scientifique pour améliorer la compréhension du fonctionnement des systèmes méditerranéens. Il représente un maillon indispensable dans le développement des connaissances hydrologiques

Bassin versant de recherche du Réal Collobrier, informations générales sur la pluviométrie et les écoulements

The Real Collobrier research basins are a privileged site for the observation and study of the water cycle in the Mediterranean forest environment. Studied since 1967, they are a reference site for the regional hydroclimatology. The observation network is a source of a very fine knowledge of the phenomena, which makes it an ideal laboratory for the design of a method which can be directly used in operational hydrology. The multidisciplinary approach applied to it, along with specific tests, help obtain a more detailed understanding of the soil-water-atmosphere interactions. / Les bassins de recherche du Réal Collobrier constituent un site privilégié pour l'observation et l'étude du cycle de l'eau en milieu forestier méditerranéen. Observés depuis 1967, ils constituent un site repère de l'hydroclimatologie régionale. Le réseau d'observation permet une connaissance des phénomènes à une échelle particulièrement fine, ce qui en fait un laboratoire privilégié pour la mise au point de méthodologies directement applicables en hydrologie opérationnelle. L'approche multidisciplinaire dont il fait l'objet, associée à des expérimentations spécifiques, permet un approfondissement de nos connaissances sur les interactions sol-eau-atmosphère

Comparaison d'indices pluviométriques sur les bassins versants du réal Collobrier pour caractériser les périodes sèches et humides.

International audienceRainfall and hydrology study of catchment makes it possible to better understand the climate change impact on water resources. Rainfall and flow chronics begin in 1966 and end in 2015, these data are collected and exploited by IRSTEA. The aim is to analyse these data using indices characterizing severity and duration of rainfall droughts and hydrological droughts. Trend tests are performed on these indices to highlight the evolution during the last fifty years.L'étude des précipitations et de l'hydrologie du bassin versant permet de mieux comprendre l'impact du changement climatique sur les ressources en eau. La chronologie des précipitations et des débits commence en 1966 et se termine en 2015, ces données sont collectées et exploitées par l'IRSTEA. L'objectif est d'analyser ces données à l'aide d'indices caractérisant la sévérité et la durée des sécheresses pluviométriques et hydrologiques. Des tests de tendances sont réalisés sur ces indices pour mettre en évidence l'évolution au cours des cinquante dernières années

Modélisation régionale des indices d'étiage sur les bassins jaugés et non-jaugés

International audienceEstimating low-flow indices is of paramount importance to understand low flows and to manage water resources and risk assessments. These indices are derived from time-series of river discharges which are measured at gauged sites over long periods. However, the indices must be estimated at ungauged sites. Different estimation methods exist to estimate these low-flow indices from observed discharges in neighbouring catchments and from catchment characteristics. Regression or geostatistical methods performed on the low-flow indices are the most common types of methods. Another less common method consists in regionalizing rainfall-runoff model parameters, from catchment characteristics or by spatial proximity, to estimate low-flow indices from simulated hydrographs. We developed a conceptual daily rainfall-runoff model, LoiEau, combined with a regionalized model of snow storage and melt, to simulate low-flow indices at daily or longer time intervals. This model relies on two free parameters, which is sufficient to provide accurate enough estimates of low-flow indices, yet making easier the regionalization of the model. The model is flexible in the sense that it is designed to fit to a wide variety of catchments and hydro-meteorological behaviors, including Mediterranean catchments. The aim of this work is to regionalize the two parameters of the LoiEau model in order to estimate any low-flow indices at ungauged sites. Two regional methods are tested and are based on geostatistical and regression models. The first method is the inverse distance weighting to estimate the parameter sets from the neighbouring catchments and the second one is the regional regression method. This last method is based on relationships between the parameter sets and optimal sets of catchment characteristics established using forward stepwise linear regression for homogeneous regions. The chosen regions are hydro-eco-regions that are homogeneous in terms of geology, relief and climate. The analysis is carried out on 700 French catchments that are representative of various hydro-meteorological behaviours, with a focus on the Mediterranean hydro-eco-region. The results are validated with a cross-validation procedure and are compared, on the one hand, with the ones obtained with a regional regression model performed on a specific low-flow index and, on the other hand, with the ones obtained with a regionalized monthly rainfall-runoff model to show the advantage of a daily time step to account for the temporal variability of precipitations

Comparaison d'indices pluviométriques sur les bassins versants du réal Collobrier pour caractériser les périodes sèches et humides.

International audienceRainfall and hydrology study of catchment makes it possible to better understand the climate change impact on water resources. Rainfall and flow chronics begin in 1966 and end in 2015, these data are collected and exploited by IRSTEA. The aim is to analyse these data using indices characterizing severity and duration of rainfall droughts and hydrological droughts. Trend tests are performed on these indices to highlight the evolution during the last fifty years.L'étude des précipitations et de l'hydrologie du bassin versant permet de mieux comprendre l'impact du changement climatique sur les ressources en eau. La chronologie des précipitations et des débits commence en 1966 et se termine en 2015, ces données sont collectées et exploitées par l'IRSTEA. L'objectif est d'analyser ces données à l'aide d'indices caractérisant la sévérité et la durée des sécheresses pluviométriques et hydrologiques. Des tests de tendances sont réalisés sur ces indices pour mettre en évidence l'évolution au cours des cinquante dernières années

Modélisation régionale des indices d'étiage sur les bassins jaugés et non-jaugés

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUInternational audienceEstimating low-flow indices is of paramount importance to understand low flows and to manage water resources and risk assessments. These indices are derived from time-series of river discharges which are measured at gauged sites over long periods. However, the indices must be estimated at ungauged sites. Different estimation methods exist to estimate these low-flow indices from observed discharges in neighbouring catchments and from catchment characteristics. Regression or geostatistical methods performed on the low-flow indices are the most common types of methods. Another less common method consists in regionalizing rainfall-runoff model parameters, from catchment characteristics or by spatial proximity, to estimate low-flow indices from simulated hydrographs. We developed a conceptual daily rainfall-runoff model, LoiEau, combined with a regionalized model of snow storage and melt, to simulate low-flow indices at daily or longer time intervals. This model relies on two free parameters, which is sufficient to provide accurate enough estimates of low-flow indices, yet making easier the regionalization of the model. The model is flexible in the sense that it is designed to fit to a wide variety of catchments and hydro-meteorological behaviors, including Mediterranean catchments. The aim of this work is to regionalize the two parameters of the LoiEau model in order to estimate any low-flow indices at ungauged sites. Two regional methods are tested and are based on geostatistical and regression models. The first method is the inverse distance weighting to estimate the parameter sets from the neighbouring catchments and the second one is the regional regression method. This last method is based on relationships between the parameter sets and optimal sets of catchment characteristics established using forward stepwise linear regression for homogeneous regions. The chosen regions are hydro-eco-regions that are homogeneous in terms of geology, relief and climate. The analysis is carried out on 700 French catchments that are representative of various hydro-meteorological behaviours, with a focus on the Mediterranean hydro-eco-region. The results are validated with a cross-validation procedure and are compared, on the one hand, with the ones obtained with a regional regression model performed on a specific low-flow index and, on the other hand, with the ones obtained with a regionalized monthly rainfall-runoff model to show the advantage of a daily time step to account for the temporal variability of precipitations

Impact d'un incendie de forêt sur les débits de référence d'un petit bassin versant méditerranéen

The forest fire that recently hit the Rimbaud watershed - 146 ha -, that belongs to the Real Collobrier Experimental Research Watershed, has noticeably changed the hydrological behavior of the watershed. The current study looks, on the basis of a rain-flow modelling, at the fire impact on the model parameterization. The distribution functions of production and transfer parameters, estimated on samples taken before and after the fire, are significantly different. A random simulation procedure, based on scenarii of hourly rains changed into flow, permits the estimation of the number of flood peaks before and after the fire. The study concludes that, for a same apparition probability, the reference flows are twice as important. / L'incendie de forêt qui a affecté le bassin versant du Rimbaud - 146 ha - BVRE du Réal Collobrier a sensiblement modifié le comportement hydrologique du bassin. La présente étude examine, sur la base d'une modélisation pluie-débit, l'impact de l'incendie sur la paramétrisation du modèle. Les fonctions de distribution des paramètres de production et de transfert, estimées sur les échantillons avant et après incendie, sont significativement différentes. Une procédure aléatoire de simulation, basée sur des scénarios de pluies horaires transformées en débit, permet d'estimer les quantités de débits de pointe de crue avant et après incendie. L'étude conclue qu'à même probabilité d'apparition les débits de référence sont doublés

Uncertainties of low-flow indices estimation based on continuous simulation hydrological using data resampling.

International audienceThe study focus only on the uncertainties stemming from the sampling of calibration data (flow observations), to determine the variability of the hydrological parameter set and their impact on the estimation of the flow indices (low-flows, annual and monthly flows). For comparison, the uncertainties obtained under the same sampling conditions by fitting classical probability distributions were also investigated. These approaches are tested on 644 gauged catchments set on French territory, representative of all hydrological regimes in France.L'étude se concentre uniquement sur les incertitudes découlant de l'échantillonnage des données de calage (observations de débit), afin de déterminer la variabilité de l'ensemble des paramètres hydrologiques et leur impact sur l'estimation des indices hydrologiques d'étiage, de bilan et de saisonnalité. Aux fins de comparaison, les incertitudes obtenues dans les mêmes conditions d'échantillonnage en ajustant les distributions de probabilités classiques sur les observations ont également été étudiées. Ces approches sont testées sur 644 bassins versants jaugés situés sur le territoire français, représentatifs de l'ensemble des régimes hydrologiques en France