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Braud I.,IRSTEA | Roux H.,CNRS Fluid Dynamics Institute of Toulouse | Roux H.,CNRS Institute of Fluid Mechanics of Toulouse | Anquetin S.,University Of Grenoble Cnrs | And 7 more authors.
Journal of Hydrology | Year: 2010

This paper presents a detailed analysis of the September 8-9, 2002 flash flood event in the Gard region (southern France) using two distributed hydrological models: CVN built within the LIQUID® hydrological platform and MARINE. The models differ in terms of spatial discretization, infiltration and water redistribution representation, and river flow transfer. MARINE can also account for subsurface lateral flow. Both models are set up using the same available information, namely a DEM and a pedology map. They are forced with high resolution radar rainfall data over a set of 18 sub-catchments ranging from 2.5 to 99km2 and are run without calibration. To begin with, models simulations are assessed against post field estimates of the time of peak and the maximum peak discharge showing a fair agreement for both models. The results are then discussed in terms of flow dynamics, runoff coefficients and soil saturation dynamics. The contribution of the subsurface lateral flow is also quantified using the MARINE model. This analysis highlights that rainfall remains the first controlling factor of flash flood dynamics. High rainfall peak intensities are very influential of the maximum peak discharge for both models, but especially for the CVN model which has a simplified overland flow transfer. The river bed roughness also influences the peak intensity and time. Soil spatial representation is shown to have a significant role on runoff coefficients and on the spatial variability of saturation dynamics. Simulated soil saturation is found to be strongly related with soil depth and initial storage deficit maps, due to a full saturation of most of the area at the end of the event. When activated, the signature of subsurface lateral flow is also visible in the spatial patterns of soil saturation with higher values concentrating along the river network. However, the data currently available do not allow the assessment of both patterns. The paper concludes with a set of recommendations for enhancing field observations in order to progress in process understanding and gather a larger set of data to improve the realism of distributed models. © 2010 Elsevier B.V.

Anquetin S.,University Of Grenoble Cnrs | Braud I.,IRSTEA | Vannier O.,University Of Grenoble Cnrs | Vannier O.,IRSTEA | And 4 more authors.
Journal of Hydrology | Year: 2010

In the general context of field experiment design, this paper presents a modeling study that quantifies the respective impact of rainfall estimation and soil variability on the simulated discharge for an extreme event in southern France. The CVN distributed hydrological model, built within the LIQUID® modeling platform is used. The method is illustrated for two medium sized catchments, Saumane (99km2) and Uzès (88km2) using raingauges and two radar estimates. The soil properties are extracted from an existing soil database provided for the whole region. The model parameter specification uses available observation and a priori hydrological knowledge. No parameter adjustment is performed. For model evaluation on the regional scale, simulated maximum peak discharges are compared with post-flood estimations for 32 catchments. The area of these catchments ranges from 2.5 to 99km2 and model results are satisfactory. Then, the study focuses on the Saumane and Uzès catchments. A sensitivity analysis highlights the role of the Manning roughness coefficient on the simulated hydrographs dynamics. The impact of the bottom boundary condition of the infiltration and water redistribution module is also shown for the gauged Saumane catchment. Then the impact of rainfall input and soil spatial variability is presented. The results show that (i) the use of radar data is necessary to properly simulate the flood dynamics; (ii) although radar volume-scanning strategy has been shown to give more accurate results on a pixel/gauge comparison of the rainfall estimations, it is not necessarily the case when catchment averaged amounts are considered, especially for catchments in mountainous areas; (iii) the impact of the variability in soil properties on the simulated discharges is of the same order of magnitude as the impact of differences in rainfall estimation; (iv) the flood dynamics presents two phases: the first one, mainly controlled by the soil properties and the second one, since the soils are saturated, controlled by the rainfall variability. Therefore, uncertainties on both observations need to be mitigated in order to improve flash-flood understanding. © 2010 Elsevier B.V.

Kirstetter P.-E.,University of Versailles | Delrieu G.,University Of Grenoble Cnrs | Boudevillain B.,University Of Grenoble Cnrs | Obled C.,University Of Grenoble Cnrs
Journal of Hydrology | Year: 2010

Characterisation of the error structure of radar quantitative precipitation estimation (QPE) is a major issue for applications of radar technology in hydrological modelling. Due to the variety of sources of error in radar QPE and the impact of correction algorithms, the problem can only be addressed practically by comparison of radar QPEs with reference values derived from ground-based measurements. Using the radar and raingauge datasets of the Bollène-2002 experiment, a preliminary investigation of this subject has been carried out within a geostatistical framework in the context of the Cévennes-Vivarais Mediterranean Hydrometeorological Observatory. First, raingauge measurements were critically analysed using variograms to detect erroneous squared differences between pairs of raingauge values. The anisotropic block kriging technique was then used to compute and select the most reliable reference values. The statistical distribution and the spatial and temporal structure of the residuals between radar and reference values was established and analysed. The error variance separation concept was also tested to estimate the variance of the residuals between the radar estimates and the true unknown rainfall. A preliminary version of the radar QPE error model was established for 1-km2 domains and time steps ranging from 1 to 12h using the limited data sample of the Bollène-2002 experiment. The error model is dependent on the time scales considered and needs to be conditioned on the rain rate and rainfall type as well as on the radar range. © 2010 Elsevier B.V.

Branger F.,IRSTEA | Braud I.,IRSTEA | Debionne S.,HYDROWIDE | Viallet P.,HYDROWIDE | And 4 more authors.
Environmental Modelling and Software | Year: 2010

Distributed hydrological models are valuable tools that can be used to support water management in catchments. However, the complexity of management issues, the variety of modelling objectives, and the variable availability of data require a flexible way to customize models and adapt them to each individual problem. Environmental modelling frameworks offer such flexibility; they are designed to build and run integrated models on the basis of reusable and exchangeable components. This paper presents the LIQUID® framework, developed by Hydrowide since 2005. The purpose of developing LIQUID® was to provide both easier integration of hydrological processes and preservation of their characteristic temporal and spatial scales. It suits a wide range of applications, both in terms of spatial scales and of process conceptualisations. LIQUID® is able to synchronize different time steps, to handle irregular geometries, and to simulate complex connections between components, in particular involving feedback. The paper presents the concepts of LIQUID® and the technical choices made to meet the above requirements, with focuses on the simulation run system and on the spatial discretization of process components. The use of the framework is illustrated by five application cases associated with contrasted spatial and temporal scales. © 2010 Elsevier Ltd.

Branger F.,IRSTEA | Debionne S.,HYDROWIDE | Viallet P.,HYDROWIDE | Braud I.,IRSTEA | And 4 more authors.
Modelling for Environment's Sake: Proceedings of the 5th Biennial Conference of the International Environmental Modelling and Software Society, iEMSs 2010 | Year: 2010

Environmental modelling frameworks are valuable and increasingly used tools for building customized models, in a context where the complexity of management issues and the availability of data require much flexibility. The LIQUID ® framework has been developed since 2005. It is mostly dedicated to hydrological modelling. It aims at easily integrating hydrological processes while preserving their characteristic temporal and spatial scales. LIQUID ® allows the user to build and run integrated models on the basis of reusable and exchangeable modules. It provides templates for easy development of new modules, connections to databases and GIS for data input and output, and module coupling mechanisms, that synchronize different time steps and handle irregular geometries. LIQUID ® suits a wide range of applications, involving various spatial scales and process conceptualisations. The framework is also able to simulate complex interactions between modules, in particular including feedback. The paper will present the recent advances of LIQUID ®, in terms of concepts as well as in terms of technical specifications, and a brief overview of the ongoing main applications. Those deal with the assessment of landscape management impact on hydrology in agricultural and suburban areas, and with the analysis of hydrological responses in the context of flash floods.

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