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Tramblay Y.,IRD Montpellier | Bouvier C.,IRD Montpellier | Crespy A.,IRD Montpellier | Marchandise A.,SCHAPI
IAHS-AISH Publication | Year: 2010

There is a need to improve rainfall-runoff modelling of flash floods in the Mediterranean region, in order to better predict these extreme hydrological events. In this study, the efficiency of the distributed SCS-LR rainfall-runoff model is evaluated, using either the mean areal rainfall or spatially distributed rainfall over the watershed as inputs of the model. The distributed SCS-LR model is an event-based model accounting for four parameters. The efficiency of the model using either averaged or spatial rainfall as inputs is considered through the simulation of flood events, with fixed or calibrated model parameters for each event. A total of 30 flood events that occurred in the Gardon River (525 km2) located in the Cévennes region (southern France) were modelled. When both runoff and routing parameters are identical, the model is shown to underestimate the peak flows if using mean areal rainfall patterns instead of spatial rainfall patterns. Runoff volumes can also be underestimated in the case of highly variable rainfall occurring in dry soil conditions. The recalibration of the model is able to reduce some of the bias in the simulations. Nevertheless, as shown in the present study, not considering the spatial patterns of rainfall is leading to an increase in the variability of the model parameters. Thereby, the parameter estimation could be difficult with averaged rainfall in further applications of the model for operational purposes. The rainfall patterns have an impact on the parameterization of the model, depending on the rainfall spatial variation coefficient and the initial moisture of the soil. Accounting for the spatial pattern of the rainfall can improve the efficiency of the model, without increasing its complexity. Copyright © 2010 IAHS Press.

Piotte O.,SCHAPI | Pasquet F.,DREAL Center | Chaleon C.,Paris West University Nanterre La Défense | Chambon D.,DREAL Midi Pyrenees | And 4 more authors.
Houille Blanche | Year: 2016

High water marks data, in its most general definition, meaning deposit of debris, water or temporary silt markings, pictures or local residents' accounts, is a precious source of information for the many stakeholders involved in risk culture, inundation mapping, river, estuarine or coastal studies, etc. Although there have already been many initiatives to collect and exploit existing data, as well as collecting new marks after flood events, there is still a lack of harmonization and coordination. Several inventories may coexist for the same territory, post-flood field investigations can sometimes be performed twice, collected data is seldom widely shared. The French flood forecasting services, together with Cerema (research institute) and river basin districts decided to launch a process to provide technical and organizational solutions in order to set up a collaborative management approach of high water marks data. Through the work already carried out, we will present the national repository and how high water marks should be described. We will also explain the organization blue-print that is proposed, involving stakeholders ranging from the ordinary citizen to flood experts and defining their roles. Finally, we will demonstrate the dedicated tools, consisting of a post-flood field investigation guide and a collaborative and cartographic website allowing high water marks browsing, open contribution and data expertise among all stakeholders. © Société Hydrotechnique de France, 2016.

Tramblay Y.,Montpellier University | Bouvier C.,Montpellier University | Ayral P.-A.,Ecole des Mines d'Ales | Marchandise A.,SCHAPI
Natural Hazards and Earth System Science | Year: 2011

A good knowledge of rainfall is essential for hydrological operational purposes such as flood forecasting. The objective of this paper was to analyze, on a relatively large sample of flood events, how rainfall-runoff modeling using an event-based model can be sensitive to the use of spatial rainfall compared to mean areal rainfall over the watershed. This comparison was based not only on the model's efficiency in reproducing the flood events but also through the estimation of the initial conditions by the model, using different rainfall inputs. The initial conditions of soil moisture are indeed a key factor for flood modeling in the Mediterranean region. In order to provide a soil moisture index that could be related to the initial condition of the model, the soil moisture output of the Safran-Isba-Modcou (SIM) model developed by Météo-France was used. This study was done in the Gardon catchment (545 km 2) in South France, using uniform or spatial rainfall data derived from rain gauge and radar for 16 flood events. The event-based model considered combines the SCS runoff production model and the Lag and Route routing model. Results show that spatial rainfall increases the efficiency of the model. The advantage of using spatial rainfall is marked for some of the largest flood events. In addition, the relationship between the model's initial condition and the external predictor of soil moisture provided by the SIM model is better when using spatial rainfall, in particular when using spatial radar data with R 2 values increasing from 0.61 to 0.72. © Author(s) 2011.

Habert J.,DREAL Champagne Ardenne | Habert J.,European Center for Research and Advanced Training in Scientific Computation | Ricci S.,European Center for Research and Advanced Training in Scientific Computation | Le Pape E.,SCHAPI | And 5 more authors.
Journal of Hydrology | Year: 2016

This paper presents a data-driven hydrodynamic simulator based on the 1-D hydraulic solver dedicated to flood forecasting with lead time of an hour up to 24. h. The goal of the study is to reduce uncertainties in the hydraulic model and thus provide more reliable simulations and forecasts in real time for operational use by the national hydrometeorological flood forecasting center in France. Previous studies have shown that sequential assimilation of water level or discharge data allows to adjust the inflows to the hydraulic network resulting in a significant improvement of the discharge while leaving the water level state imperfect. Two strategies are proposed here to improve the water level-discharge relation in the model. At first, a modeling strategy consists in improving the description of the river bed geometry using topographic and bathymetric measurements. Secondly, an inverse modeling strategy proposes to locally correct friction coefficients in the river bed and the flood plain through the assimilation of in situ water level measurements. This approach is based on an Extended Kalman filter algorithm that sequentially assimilates data to infer the upstream and lateral inflows at first and then the friction coefficients. It provides a time varying correction of the hydrological boundary conditions and hydraulic parameters.The merits of both strategies are demonstrated on the Marne catchment in France for eight validation flood events and the January 2004 flood event is used as an illustrative example throughout the paper. The Nash-Sutcliffe criterion for water level is improved from 0.135 to 0.832 for a 12-h forecast lead time with the data assimilation strategy. These developments have been implemented at the SAMA SPC (local flood forecasting service in the Haute-Marne French department) and used for operational forecast since 2013. They were shown to provide an efficient tool for evaluating flood risk and to improve the flood early warning system. Complementary with the deterministic forecast of the hydraulic state, the estimation of an uncertainty range is given relying on off-line and on-line diagnosis. The possibilities to further extend the control vector while limiting the computational cost and equifinality problem are finally discussed. © 2015 Elsevier B.V.

Within the Thematic User Commissioning for the VHR Pléiades valorization, imagery was tasked in emergency following disaster events or user-exercise at the request of French Ministries (Ministry of the Environment, Ministry of Finance). These activities were also aimed at familiarizing French institutional users with the use of space technologies within crisis event management. One long term objective would be to set up a national capacity for these users, outside of the International Charter 'Space and Major Disasters' and Copernicus scope which did not support all the needs of the French Ministries. In March and May 2013, in coordination with CNES, SERTIT, SCHAPI, IGN and CEREMA, some Pléiades data have been tasked and processed in rush mode for the case of the Agly, Yonne and Marne 2013 flood events. In June 2013, two new rapid mapping actions have been carried out by CNES and SERTIT. The first one, liaising with the SCHAPI and the Rhin Sarre Flood Forecast Service (DREAL Alsace) for the Sarre river flooding, and the second one in coordination with the French State reinsurance company (Caisse Centrale de Réassurance) over the Gave de Pau floods. Finally, in February 2013, the exercise "SEISME 13" was performed at the request of the crisis center of the Ministry of the Environment (SG/SDSIE/CMVOA). Regarding user's needs, the objectives concerned water surface detection, dyke breaks, affected built features. In the case of rapid floods as Agly and Gave de Pau events, images analysis also included the recognition of residual flood water surfaces, mud deposits and current flows. In addition, the Agly case mapping got the benefits to flood mapping that can be derived from a Pléiades stereoscopic pair. For "SEISME 13" Exercise, the value added products took into account the specific needs expressed by the Ministries of the Environment, Transport and Health (damages to infrastructure, network, and building).

Bresson E.,Meteo - France | Ducrocq V.,Meteo - France | Nuissier O.,Meteo - France | Ricard D.,Meteo - France | de Saint-Aubin C.,SCHAPI
Quarterly Journal of the Royal Meteorological Society | Year: 2012

Northwestern Mediterranean coastal regions are frequently affected by torrential rainfall associated with quasi-stationary mesoscale convective systems (MCSs). The present work examines how the characteristics of a conditionally unstable flow impinging on the coastal complex terrain of the Northwestern Mediterranean can affect the location and intensity of quasi-stationary MCSs. The study is based on idealized simulations, but including the major ingredients of Northwestern Mediterranean heavy precipitation events: a moist conditionally unstable marine flow of about 100 km width facing the true terrain, composed of the Massif Central surrounded by the Alps and the Pyrenees. We find that MCSs are located upstream of the mountain range with a slow flow, whereas with a rapid flow the heaviest precipitation is over the Massif Central slopes. In a similar way, when the lateral environment is drier the heaviest precipitation is located upstream whereas a humid environment favours precipitation over the slopes. The dominant lifting mechanism is strongly related to the location of the system: (1) direct orographic triggering for systems over mountain slopes and (2) cold-pool triggering for upstream systems. In addition, the neighbouring mountains interplay through deflection of the flow and induced low-level convergence favoured by slow or dry lateral environments and through cold-pool blocking within valleys. © 2012 Royal Meteorological Society.

Desprats J.-F.,Bureau de Recherches Géologiques et Minières | Cerdan O.,Bureau de Recherches Géologiques et Minières | King C.,Bureau de Recherches Géologiques et Minières | Marchandise A.,SCHAPI
Houille Blanche | Year: 2010

Soil permeability is an important input parameter of several physical hydrological model used by Flooding Forecast Services: On the Gardon d'Anduze catchment selected by SCHAPI as experimental catchment for flash floods, permeability measurements were done between 2002 and 2007 by the French Geological Survey. A statistical analysis allowed to calculate the permeability of each unit combining information on soil and land use and so to propose a permeability map for the catchment. This map was validated using the runoff model STREAM.With this model, correlation between simulated and observed discharges (0.83) is satisfactory when using distributed soil permeability for Gardon d'Anduze catchment or Mialet and Saumane sub catchment. Correlation significantly decreases (0.66) when using STREAM with an homogeneous averaged permeability value of 30 mm/hour for the catchment. This showed clearly the importance of distributed soil permeability for runoff modelling with a hortonian model a Mediterranean catchment. © 2010 Société Hydrotechnique de France.

Today, hydrometric data in France are collected and published via two distinct information systems, initially to meet two different objectives: on one side, flood monitoring and forecasting; on the other side, monitoring of hydrological regimes of rivers and water resources. Within the framework of hydrometry unification, started in the years 1990 then enhanced in 2006, these information systems are being modernized, founded on a unique central database, in order to lead to a unified management of hydrometric and meteorological referential data, make these information systems interoperable and easier to change, upgrade their architecture and meet new or yet unsatisfied needs. This is the goal of the "HYDRO 3" project, broken down as follows, some of the steps below being possibly carried out in parallel: 1. define renovated data models for metadata and data, and build the new database (HYDRO DB) implementing these new data models; 2. initialize hydrometric and meteorological referential data in the new HYDRO DB; 3. start the real time part of the database and switch the Vigicrues website on the new database, as well as other tools of the national network which covers flood forecasting services, hydrometry teams and Schapi (FF&H); 4. develop the human interface with: the State operators, for referential data management and the link with the external tools allowing to control data and to feed the database with rating curves and water level correction curves; the measurement point managers, beyond FF&H network, through a specific access; the public, through an Internet portal; 5. develop functions for hydrological calculations and analysis, in order to provide equivalent functionality to the current Banque HYDRO system, 6. transfer all the historical records stored in the Banque HYDRO, into the new database; this last step allows to definitely move to the new environment. Today, the first and the second steps are achieved. Step 3 should follow between 2013 and 2014. Step 4 is well underway. Many obstacles were overcome; there is still some way to go during the coming years, for this complex and long-term task. © 2014 Société Hydrotechnique de France.

In 2003, under the impetus of the French Ministry of ecology, the national flood observation system progressively evolved towards a flood forecasting system. The French national forecasting centre (SCHAPI) was created to coordinate this evolution and the improvement of anticipation tools, in collaboration with regional flood forecasting services (SPC). This national flood forecasting network developed collaborations with scientists and consultancies, among which Irstea. The interannual collaboration with Irstea yielded the GRP model, today widely used in SPCs. This collaboration has several important aspects: the support to the operational implementation of the forecasting tool, the evaluation of its performance comparatively to other tools, the analysis of feedbacks, or the training of professionals. It gives the opportunity to raise important scientific questions, and to propose concrete solutions to improve the efficiency of the GRP model. The article describes the partnership that supports the overall development approach, and illustrates its advantages through a few examples. © Société Hydrotechnique de France, 2016.

Coustau M.,Meteo - France | Rousset-Regimbeau F.,Meteo - France | Thirel G.,Meteo - France | Thirel G.,IRSTEA | And 5 more authors.
Journal of Hydrology | Year: 2015

A Hydrological Ensemble Forecasting System (HEFS) known as SIMPE has been run over France in real time by Météo-France since 2004. The system combines the 51-member, 10-day ECMWF EPS atmospheric forcing at a 1.5° resolution with the ISBA-MODCOU physically-based distributed hydrological model to provide streamflow forecasts over France. The initial conditions for all the HEFS runs are provided by SIM; i.e., the ISBA-MODCOU model forced by the outputs of the mesoscale meteorological analysis system SAFRAN. A previous study introduced and tested two improvements of this system over a past period. These modifications consisted of an improved representation of the profile of hydraulic conductivity and the implementation of a data assimilation subsystem. The purpose of the present study was to test the HEFS and its two modifications in operational mode, with the new higher-resolution ECMWF EPS atmospheric forcing at 0.25± resolution, available in real time on the Météo-France database, and with less observed discharge available for the data assimilation subsystem. The new ISBA physics scheme led to a notable improvement in the discharge simulation in western and northeastern France, where no aquifers were simulated by the MODCOU model. This improvement was not impacted by real-time conditions. Likewise, the improvement resulting from the data assimilation system applied over France was not significantly affected by real-time conditions. The propagation of the data assimilation correction to gauging stations located upstream or downstream of the assimilated stations limited the deterioration of forecasted streamflow due to real-time conditions. Finally, the ECMWF EPS high-resolution atmospheric forcing had a significant impact on the streamflow forecasts for small catchments, which increased with lead time. © 2015 Elsevier B.V. All rights reserved.

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