Flood Risk Management: Research and Practice, 2008
ABSTRACT On 22 November 2011, an exceptional rainstorm hit the North-East part of Sicily (Italy) ... more ABSTRACT On 22 November 2011, an exceptional rainstorm hit the North-East part of Sicily (Italy) producing local heavy rainfall, mud-debris flow and flash flooding. The storm was concentrated on the Tyrrhenian Sea coast near the city of Barcellona within the Longano catchment. The estimated flood peak discharge of the Longano river in the city of Barcellona (about 230 m3/s for 26 km2) is close to the highest values reported in Europe for similar watershed areas. Rainfall data from raingauge and meteorological radar were analysed and a detailed study of the hydrological response of the catchment was performed by means of rainfall-runoff modelling and flood frequency analysis. The results of the rainfall-runoff model were compared with peak discharges estimated from field observations (cross-sections survey, water marks, witnesses interviews and video recordings). Flood inundation and propagation in the city were modelled using an hydraulic model based on De Saint Venant equation equations calibrated using the data collected (water depths and flow velocities). A geomorphological survey was also conducted to ascertain the evolution of the phenomenon and related sediment processes analysis.
Ce memoire paraitra certainement un peu volumineux. Etait-il bien necessaire d'ecrire autant ... more Ce memoire paraitra certainement un peu volumineux. Etait-il bien necessaire d'ecrire autant de pages pour un memoire d'habilitation a diriger des recherches et d'infliger sa lecture aux membres du jury, alors que cela n'est pas impose par les regles non ecrites de l'exercice ? Je me suis moi-meme pose la question a plusieurs reprises au cours de cette redaction. A quoi bon depenser du temps et de l'energie pour un document qui sera peu lu et que l'on ne comptabilisera pas au rang des publications importantes ? La reponse est que j'avais besoin de mettre sur le papier ce que contient ce memoire, de reveler la logique d'un parcours de recherche diversifie mais non pas disperse qui m'a conduit des mathematiques a l'hydrologie des processus en passant par le terrain et de montrer comment cette divagation dans le monde de la recherche hydrologique nourrit une reflexion sur l'avenir de cette discipline. Trier trop severement dans les activi...
A modelling approach to assess the hydrological response of small Mediterranean catchments to the... more A modelling approach to assess the hydrological response of small Mediterranean catchments to the variability of soil characteristics in a context of extreme events C. Manus, S. Anquetin, I. Braud, J.-P. Vandervaere, J.-D. Creutin, P. Viallet, and E. Gaume LTHE, Université de Grenoble, UMR5564(CNRS, UJF, INPG, IRD), Grenoble, Cedex, France CEMAGREF, UR Hydrologie-Hydraulique, Lyon, France HYDROWIDE, Saint-Martin d’Hères, France Division Eau et Environnement, Lab. Central des Ponts et Chaussées, Bouguenais, France
In September 2002 a flash flood killed 23 human lives and generated 1.2 billion Euros of damages ... more In September 2002 a flash flood killed 23 human lives and generated 1.2 billion Euros of damages in less than 24 hours over an area of 20 000 km2 located in the south of France. The Gard river basin was hit by a storm that locally received more than 600 mm in one day. This storm triggered catastrophic flash floods on many upstream tributaries as well as the most important flood ever reported of the major rivers (Gard, Ceze and Vidourle). The distributed prediction of such extreme events remains an open question due to scarcity of observations and the unknown individual hydrological behaviour of very small basins. Due to the high spatial and temporal variability of rainfall and of the physiographic conditions, physically-based distributed hydrological models offer perspective for the simulation of such flash-floods at a regional scale, and more specifically in small ungauged basins which are recognized as the most vulnerable. However, the evaluation of model performance for such even...
The research has developed a framework, known as the FIM FRAME method, to assist stakeholders res... more The research has developed a framework, known as the FIM FRAME method, to assist stakeholders responsible for the production of emergency plans for floods to assess and improve these plans. The FIM FRAME method can also be used to assist with the development of new emergency plans for floods and other hazards. This is the final report.
Intensity‐duration‐frequency (IDF) curves are one of the most common rainfall statistical models ... more Intensity‐duration‐frequency (IDF) curves are one of the most common rainfall statistical models used in hydrologic design and analysis projects. The uncertainties related to the elaboration of these IDF curves have nevertheless seldom been evaluated in the past. The article will recall the existing link between the IDF formulation and some properties of the rainfall series such as simple scaling and multifractal structure. Assuming that these properties are valid, the IDF curves formulation is then the product of a dimensionless (i.e., reduced) distribution function for the annual maximum rainfall intensities/depths and a duration‐dependent scaling factor. Its parameters can be evaluated in an integrated way (i.e., based on a unique pooled sample of peak intensities over a range of durations: from 15 min to 24 hr). The use of likelihood‐based Bayesian Markov chain Monte Carlo statistical inference methods for this evaluation provides consistent uncertainties for all the parameters ...
This paper proposes a detailed comparison of local and regional approaches for flood frequency an... more This paper proposes a detailed comparison of local and regional approaches for flood frequency analyses, with a special emphasis on the effects of (a) the information on extreme floods used in the analysis (historical data or recent extreme floods observed at ungauged sites), and (b) the assumptions associated with regional approaches (statistical homogeneity of considered series, independence of observations). The results presented are based on two case studies: the Ard eche and Argens rivers regions in southeast of France. Four approaches are compared: 1-local analysis based on continuous measured series, 2-local analysis with historical information, 3-regional index-flood analysis based on continuous series, 4-regional analysis involving information on extremes (including both historical floods and recent floods observed at ungauged sites). The inference approach used is based on a GEV distribution and a Bayesian Monte Carlo Markov Chain approach for parameters estimation. The comparison relies both on (1) available observed datasets and (2) Monte Carlo simulations in order to evaluate the effects of sampling variability and to analyze the possible influence of regional heterogeneities. The results indicate that a relatively limited level of regional heterogeneity, which may not be detected through homogeneity tests, may significantly affect the performances of regional approaches. These results also illustrate the added value of information on extreme floods, historical floods or recent floods observed at ungauged sites, in both local and regional approaches. As far as possible, gathering such information and incorporating it into flood frequency studies should be promoted. Finally, the presented Monte Carlo simulations appear as an interesting analysis tool for adapting the estimation strategy to the available data for each specific case study.
An extensive study has been conducted in the recent years on the potential flood damage costs in ... more An extensive study has been conducted in the recent years on the potential flood damage costs in the Parisian area [2]. We present here the first results of a further investigation focussed on the disturbances and the related costs for the river water users during low water periods. This study is mainly based on data given by the users themselves (drinking water and electricity producers, sewerage networks, shipping companies, fishers, administrations...). The analysis includes three steps (i) identification of the disrupting situations for each user, (ii) detailed description of the disturbances on the basis of realistic low water scenario, (iii) cost evaluation of these disturbances. The results obtained reveal no real stress on the use of water during low water periods despite the large amount of population and economical activities depending on the Seine river water : disrupting low water situations are rare and the induced costs are relatively modest. Besides, in many cases, the increase of the river discharge would not solve the problem encountered by the users and other more efficient technical solutions are available. These conclusions must nevertheless be taken with care : no severe low water period occurred during the last 3 or 4 decades. Such an event could not be studied since the users were not able to imagine it and extrapolate on its consequences.
Marie-Noëlle Bouin (2)) , Brice Boudevillain (7) , Olivier Bousquet (2) , Christophe Bouvier (8) ... more Marie-Noëlle Bouin (2)) , Brice Boudevillain (7) , Olivier Bousquet (2) , Christophe Bouvier (8) , Isabelle Braud (9) , Jean-Christophe Calvet (2) , Cédric Champollion (10) , André Chanzy (11) , Martin Claude (12) , Philippe Cocquerez (13) , Laurent Coppola (14) , Sylvain Coquillat (15) , Dominique Courault (11) , Eric Defer (16) , Julien Delanoë (3) , Guy Delrieu (7) , Alexis Doerenbecher (2) , Nathalie Dorfliger (17) , Michel Estèves (7) , Claude Estournel (15) , Cyrille Flamant (3) , Nadia Fourrié (2) , Olivier Garrouste (2) , Eric Gaume (18) , Hervé Giordani (2) , Laurent Gomes (2) , Gregory Roberts (2) , Hervé Jourde (8) , Laurent Labatut (2) , Dominique Lambert (15) , Jérôme Le Coz (9) , Wolfgang Ludwig (19) , Céline Lutoff (20) , Jean-François Mahfouf (2) , Eric Martin (2) , Laurence Mastrorillo (21) , Nicole Mathys (22) , Yann Michel (2) , Mathieu Nuret (2) , Françoise Orain (23) , Sandra Perez (12) , Catherine Prigent (16) , Olivier Radakovitch (24) , Karim Ramage (25) , Evelyne Richard (15) , Jean-Louis Roujeau (2) , Odile Roussot (2) , Isabelle Ruin (7) , Frédérique Saïd (15) , Alfons Schwarzenboeck (26) , Karine Sellegri (26) , Samuel Somot (2) , Isabelle Taupier-Letage (27) , Pierre Testor (28) , Joël Van Baelen (26) et Jean-Pierre Vandervaere (7) Les affiliations des auteurs se trouvent à la fin de l'article. Résumé D'initiative française, le projet international HyMeX a pour objectif d'améliorer la compréhension du cycle de l'eau en Méditerranée, de sa variabilité, de l'échelle de l'événement météorologique aux échelles saisonnières et interannuelles, et de ses caractéristiques sur une décennie, dans un contexte de changement global. Le projet est motivé par le rôle déterminant des processus de mésoéchelle, couplés entre l'atmosphère, la mer et la terre, sur la variabilité du système climatique et sur le déclenchement d'événements hydrométéorologiques extrêmes (précipitations et inondations, vents forts et convection océanique, canicules et sécheresses). Le projet vise enfin à évaluer les conséquences de ces événements extrêmes sur la vulnérabilité sociale et économique de cette région et sa capacité d'adaptation.
On the 8th and the 9th of September 2002 the Gard region received rainfall amounts locally exceed... more On the 8th and the 9th of September 2002 the Gard region received rainfall amounts locally exceeding 600 mm over 48 hours. This extreme rainfall event induced the most important flood of the Gard river of the century : its peak discharge is estimated between 5000 and 7000 m^3/s for a watershed area of 1700 km^2. It also produced remarkable
ABSTRACT The extreme dryness of the 2003 summer period in France as well as the pessimistic forec... more ABSTRACT The extreme dryness of the 2003 summer period in France as well as the pessimistic forecasts of the climate evolution (GIEC, 2001) have raised public concern about draughts and river low waters. Discussions, press articles, questions of representatives and technicians indicate that there is a certain confusion concerning the real significance of both terms "draughts” and “low waters” and the link between these two phenomena. This paper aims at clarifying these notions, from the hydrologist’s point of view, through some comments and illustrations. L’été 2003 et ses fortes chaleurs ainsi que les prévisions assez pessimistes d’évolution du climat en Europe publiées par le Groupe d’Experts Intergouvernemental sur l’évolution du Climat (GIEC, 2001) ont provoqué un regain d’intérêt général pour les phénomènes de sécheresse et d’étiage. Les nombreuses discussions, articles de presse, questions d’élus et de techniciens sur ce sujet démontrent cependant qu’il existe une certaine confusion sur la signification même des termes « sécheresse » et « étiage » et sur les liens qui existent entre ces deux phénomènes. Les pages qui suivent visent à préciser ces notions, du point de vue de l’hydrologue, au travers de quelques réflexions et illustrations.
Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 2001
ABSTRACT Urban drainage systems usually equip small size catchments, with a response time as shor... more ABSTRACT Urban drainage systems usually equip small size catchments, with a response time as short as a few tenth of minutes. Hydrological simulation of these urban catchments requires rainfall time series at a very fine temporal resolution. Most of the time, available rainfall data consist of daily or hourly measurements. It is then appealing to design rain simulation models able to disaggregate observed data into rain rate series at shorter time steps. Random cascade models are candidate tools for performing this disaggregation process. The objective of this study is to evaluate the ability of cascade model for performing realistic and robust rain series suited for needs of urban hydrology.
The main objective of this paper is to evaluate a threshold-based flash flood warning method, by ... more The main objective of this paper is to evaluate a threshold-based flash flood warning method, by considering a wide range of climatic and physiographic conditions, and by focusing on ungauged basins. The method is derived from the flash flood guidance (FFG, hereafter) approach. The FFG is the depth of rain of a given duration, taken as uniform in space and time on a certain basin, necessary to cause minor flooding at the outlet of the considered basin. This rainfall depth, which is computed based on a hydrological model, is compared to either real-time-observed or forecasted rainfall of the same duration and on the same basin. If the nowcasted or forecasted rainfall depth is greater than the FFG, then flooding in the basin is considered likely. The study provides an assessment of this technique based on operational quality data from 11 mountainous basins (six nested included in five larger parent basins) located in northeastern Italy and central France. The model used in this study is a semi-distributed conceptual rainfall-runoff model, following the structure of the PDM (probability distributed moisture) model. Two general questions are addressed: (1) How does the efficiency of the method evolve when the simulation parameters can not be calibrated but must be transposed from parent gauged basins to ungauged basins? (2) How sensitive are the results to the method used to estimate the initial soil moisture status? System performances are evaluated by means of categorical statistics, such as the critical success index (CSI). Results show that overall
This paper presents some analytical results and numerical illustrations on the asymptotic propert... more This paper presents some analytical results and numerical illustrations on the asymptotic properties of flood peak distributions obtained through derived flood frequency approaches. It confirms and extends the results of previous works: i.e. the shape of the flood peak distributions are asymptotically controlled by the rainfall statistical properties, given limited and reasonable assumptions concerning the rainfall-runoff process. This result is partial so far: the impact of the rainfall spatial heterogeneity has not been studied for instance. From a practical point of view, it provides a general framework for analysis of the outcomes of previous works based on derived flood frequency approaches and leads to some proposals for the estimation of very large return-period flood quantiles. This paper, focussed on asymptotic distribution properties, does not propose any new approach for the extrapolation of flood frequency distribution to estimate intermediate return period flood quantiles. Nevertheless, the large distance between frequent flood peak values and the asymptotic values as well as the simulations conducted in this paper help quantifying the ill condition of the problem of flood frequency distribution extrapolation: it illustrates how large the range of possibilities for the shapes of flood peak distributions is.
Spatial and temporal scales of occurrence of flash floods, combined with the space and time scale... more Spatial and temporal scales of occurrence of flash floods, combined with the space and time scales of conventional measurement networks of rain and discharge, make these events particularly difficult to observe. The effective documentation of flash floods requires post‐flood survey strategies encompassing accurate radar rainfall estimation, field observations of the geomorphic processes associated with the flood, indirect reconstruction of peak discharges and interviews of eyewitnesses. This paper describes the methods applied and the results achieved in the survey of a flash flood that occurred on 18th September 2007 in the Selška Sora watershed (Western Slovenia). Hydrometeorological analyses of the storm are based on radar reflectivity observations. The documentation of the flash flood reveals high peak flood discharges and a complex flood response. Peak discharges were estimated at 22 cross sections, with drainage areas ranging from 0·2 to 147 km2. Among the lessons learned from...
ABSTRACT Flash floods are one of the most significant natural hazards in Europe, and can cause da... more ABSTRACT Flash floods are one of the most significant natural hazards in Europe, and can cause damage to buildings and infrastructure and pose a high risk to life. Existing inventories of past floods give information for other geographical regions or lack quantitative information on the meteo-hydrological and hydraulic characteristics of the event. The lack of centralised national and international databases for storing meteo-hydrological, hydraulic and socio-economic data relating to past flood (and particularly flash flood) events within Europe means that it is difficult to calibrate and validate research results on a range of previous floods from different climatic regions. To address this apparent gap in availability of centrally stored, high quality data and with the aim of supporting research on risk assessment and ?ash flood forecasting, a data base has been developed that collates flash flood data from seven European hydrometeorological regions and that could be extended in the future to other areas. Compilation of the database required the development of a data template and flood event selection rules. Initial analyses of the data highlight spatial variations of flood hazard magnitude, with highest speci?c peak discharges in the Mediterranean region. There is a strong seasonality to the occurrence of events, with events occurring mostly in the autumn in the Mediterranean region and in the summer in middle and eastern European regions. There have been flash floods in France and Spain on a basin scale of greater than 500 km2 . This work has been carried out for HYDRATE, which is a currently ongoing EC funded project that is aiming to improve techniques for flash flood forecasting. The work presented here represents some of the first outputs from this project.
Flood Risk Management: Research and Practice, 2008
ABSTRACT On 22 November 2011, an exceptional rainstorm hit the North-East part of Sicily (Italy) ... more ABSTRACT On 22 November 2011, an exceptional rainstorm hit the North-East part of Sicily (Italy) producing local heavy rainfall, mud-debris flow and flash flooding. The storm was concentrated on the Tyrrhenian Sea coast near the city of Barcellona within the Longano catchment. The estimated flood peak discharge of the Longano river in the city of Barcellona (about 230 m3/s for 26 km2) is close to the highest values reported in Europe for similar watershed areas. Rainfall data from raingauge and meteorological radar were analysed and a detailed study of the hydrological response of the catchment was performed by means of rainfall-runoff modelling and flood frequency analysis. The results of the rainfall-runoff model were compared with peak discharges estimated from field observations (cross-sections survey, water marks, witnesses interviews and video recordings). Flood inundation and propagation in the city were modelled using an hydraulic model based on De Saint Venant equation equations calibrated using the data collected (water depths and flow velocities). A geomorphological survey was also conducted to ascertain the evolution of the phenomenon and related sediment processes analysis.
Ce memoire paraitra certainement un peu volumineux. Etait-il bien necessaire d'ecrire autant ... more Ce memoire paraitra certainement un peu volumineux. Etait-il bien necessaire d'ecrire autant de pages pour un memoire d'habilitation a diriger des recherches et d'infliger sa lecture aux membres du jury, alors que cela n'est pas impose par les regles non ecrites de l'exercice ? Je me suis moi-meme pose la question a plusieurs reprises au cours de cette redaction. A quoi bon depenser du temps et de l'energie pour un document qui sera peu lu et que l'on ne comptabilisera pas au rang des publications importantes ? La reponse est que j'avais besoin de mettre sur le papier ce que contient ce memoire, de reveler la logique d'un parcours de recherche diversifie mais non pas disperse qui m'a conduit des mathematiques a l'hydrologie des processus en passant par le terrain et de montrer comment cette divagation dans le monde de la recherche hydrologique nourrit une reflexion sur l'avenir de cette discipline. Trier trop severement dans les activi...
A modelling approach to assess the hydrological response of small Mediterranean catchments to the... more A modelling approach to assess the hydrological response of small Mediterranean catchments to the variability of soil characteristics in a context of extreme events C. Manus, S. Anquetin, I. Braud, J.-P. Vandervaere, J.-D. Creutin, P. Viallet, and E. Gaume LTHE, Université de Grenoble, UMR5564(CNRS, UJF, INPG, IRD), Grenoble, Cedex, France CEMAGREF, UR Hydrologie-Hydraulique, Lyon, France HYDROWIDE, Saint-Martin d’Hères, France Division Eau et Environnement, Lab. Central des Ponts et Chaussées, Bouguenais, France
In September 2002 a flash flood killed 23 human lives and generated 1.2 billion Euros of damages ... more In September 2002 a flash flood killed 23 human lives and generated 1.2 billion Euros of damages in less than 24 hours over an area of 20 000 km2 located in the south of France. The Gard river basin was hit by a storm that locally received more than 600 mm in one day. This storm triggered catastrophic flash floods on many upstream tributaries as well as the most important flood ever reported of the major rivers (Gard, Ceze and Vidourle). The distributed prediction of such extreme events remains an open question due to scarcity of observations and the unknown individual hydrological behaviour of very small basins. Due to the high spatial and temporal variability of rainfall and of the physiographic conditions, physically-based distributed hydrological models offer perspective for the simulation of such flash-floods at a regional scale, and more specifically in small ungauged basins which are recognized as the most vulnerable. However, the evaluation of model performance for such even...
The research has developed a framework, known as the FIM FRAME method, to assist stakeholders res... more The research has developed a framework, known as the FIM FRAME method, to assist stakeholders responsible for the production of emergency plans for floods to assess and improve these plans. The FIM FRAME method can also be used to assist with the development of new emergency plans for floods and other hazards. This is the final report.
Intensity‐duration‐frequency (IDF) curves are one of the most common rainfall statistical models ... more Intensity‐duration‐frequency (IDF) curves are one of the most common rainfall statistical models used in hydrologic design and analysis projects. The uncertainties related to the elaboration of these IDF curves have nevertheless seldom been evaluated in the past. The article will recall the existing link between the IDF formulation and some properties of the rainfall series such as simple scaling and multifractal structure. Assuming that these properties are valid, the IDF curves formulation is then the product of a dimensionless (i.e., reduced) distribution function for the annual maximum rainfall intensities/depths and a duration‐dependent scaling factor. Its parameters can be evaluated in an integrated way (i.e., based on a unique pooled sample of peak intensities over a range of durations: from 15 min to 24 hr). The use of likelihood‐based Bayesian Markov chain Monte Carlo statistical inference methods for this evaluation provides consistent uncertainties for all the parameters ...
This paper proposes a detailed comparison of local and regional approaches for flood frequency an... more This paper proposes a detailed comparison of local and regional approaches for flood frequency analyses, with a special emphasis on the effects of (a) the information on extreme floods used in the analysis (historical data or recent extreme floods observed at ungauged sites), and (b) the assumptions associated with regional approaches (statistical homogeneity of considered series, independence of observations). The results presented are based on two case studies: the Ard eche and Argens rivers regions in southeast of France. Four approaches are compared: 1-local analysis based on continuous measured series, 2-local analysis with historical information, 3-regional index-flood analysis based on continuous series, 4-regional analysis involving information on extremes (including both historical floods and recent floods observed at ungauged sites). The inference approach used is based on a GEV distribution and a Bayesian Monte Carlo Markov Chain approach for parameters estimation. The comparison relies both on (1) available observed datasets and (2) Monte Carlo simulations in order to evaluate the effects of sampling variability and to analyze the possible influence of regional heterogeneities. The results indicate that a relatively limited level of regional heterogeneity, which may not be detected through homogeneity tests, may significantly affect the performances of regional approaches. These results also illustrate the added value of information on extreme floods, historical floods or recent floods observed at ungauged sites, in both local and regional approaches. As far as possible, gathering such information and incorporating it into flood frequency studies should be promoted. Finally, the presented Monte Carlo simulations appear as an interesting analysis tool for adapting the estimation strategy to the available data for each specific case study.
An extensive study has been conducted in the recent years on the potential flood damage costs in ... more An extensive study has been conducted in the recent years on the potential flood damage costs in the Parisian area [2]. We present here the first results of a further investigation focussed on the disturbances and the related costs for the river water users during low water periods. This study is mainly based on data given by the users themselves (drinking water and electricity producers, sewerage networks, shipping companies, fishers, administrations...). The analysis includes three steps (i) identification of the disrupting situations for each user, (ii) detailed description of the disturbances on the basis of realistic low water scenario, (iii) cost evaluation of these disturbances. The results obtained reveal no real stress on the use of water during low water periods despite the large amount of population and economical activities depending on the Seine river water : disrupting low water situations are rare and the induced costs are relatively modest. Besides, in many cases, the increase of the river discharge would not solve the problem encountered by the users and other more efficient technical solutions are available. These conclusions must nevertheless be taken with care : no severe low water period occurred during the last 3 or 4 decades. Such an event could not be studied since the users were not able to imagine it and extrapolate on its consequences.
Marie-Noëlle Bouin (2)) , Brice Boudevillain (7) , Olivier Bousquet (2) , Christophe Bouvier (8) ... more Marie-Noëlle Bouin (2)) , Brice Boudevillain (7) , Olivier Bousquet (2) , Christophe Bouvier (8) , Isabelle Braud (9) , Jean-Christophe Calvet (2) , Cédric Champollion (10) , André Chanzy (11) , Martin Claude (12) , Philippe Cocquerez (13) , Laurent Coppola (14) , Sylvain Coquillat (15) , Dominique Courault (11) , Eric Defer (16) , Julien Delanoë (3) , Guy Delrieu (7) , Alexis Doerenbecher (2) , Nathalie Dorfliger (17) , Michel Estèves (7) , Claude Estournel (15) , Cyrille Flamant (3) , Nadia Fourrié (2) , Olivier Garrouste (2) , Eric Gaume (18) , Hervé Giordani (2) , Laurent Gomes (2) , Gregory Roberts (2) , Hervé Jourde (8) , Laurent Labatut (2) , Dominique Lambert (15) , Jérôme Le Coz (9) , Wolfgang Ludwig (19) , Céline Lutoff (20) , Jean-François Mahfouf (2) , Eric Martin (2) , Laurence Mastrorillo (21) , Nicole Mathys (22) , Yann Michel (2) , Mathieu Nuret (2) , Françoise Orain (23) , Sandra Perez (12) , Catherine Prigent (16) , Olivier Radakovitch (24) , Karim Ramage (25) , Evelyne Richard (15) , Jean-Louis Roujeau (2) , Odile Roussot (2) , Isabelle Ruin (7) , Frédérique Saïd (15) , Alfons Schwarzenboeck (26) , Karine Sellegri (26) , Samuel Somot (2) , Isabelle Taupier-Letage (27) , Pierre Testor (28) , Joël Van Baelen (26) et Jean-Pierre Vandervaere (7) Les affiliations des auteurs se trouvent à la fin de l'article. Résumé D'initiative française, le projet international HyMeX a pour objectif d'améliorer la compréhension du cycle de l'eau en Méditerranée, de sa variabilité, de l'échelle de l'événement météorologique aux échelles saisonnières et interannuelles, et de ses caractéristiques sur une décennie, dans un contexte de changement global. Le projet est motivé par le rôle déterminant des processus de mésoéchelle, couplés entre l'atmosphère, la mer et la terre, sur la variabilité du système climatique et sur le déclenchement d'événements hydrométéorologiques extrêmes (précipitations et inondations, vents forts et convection océanique, canicules et sécheresses). Le projet vise enfin à évaluer les conséquences de ces événements extrêmes sur la vulnérabilité sociale et économique de cette région et sa capacité d'adaptation.
On the 8th and the 9th of September 2002 the Gard region received rainfall amounts locally exceed... more On the 8th and the 9th of September 2002 the Gard region received rainfall amounts locally exceeding 600 mm over 48 hours. This extreme rainfall event induced the most important flood of the Gard river of the century : its peak discharge is estimated between 5000 and 7000 m^3/s for a watershed area of 1700 km^2. It also produced remarkable
ABSTRACT The extreme dryness of the 2003 summer period in France as well as the pessimistic forec... more ABSTRACT The extreme dryness of the 2003 summer period in France as well as the pessimistic forecasts of the climate evolution (GIEC, 2001) have raised public concern about draughts and river low waters. Discussions, press articles, questions of representatives and technicians indicate that there is a certain confusion concerning the real significance of both terms "draughts” and “low waters” and the link between these two phenomena. This paper aims at clarifying these notions, from the hydrologist’s point of view, through some comments and illustrations. L’été 2003 et ses fortes chaleurs ainsi que les prévisions assez pessimistes d’évolution du climat en Europe publiées par le Groupe d’Experts Intergouvernemental sur l’évolution du Climat (GIEC, 2001) ont provoqué un regain d’intérêt général pour les phénomènes de sécheresse et d’étiage. Les nombreuses discussions, articles de presse, questions d’élus et de techniciens sur ce sujet démontrent cependant qu’il existe une certaine confusion sur la signification même des termes « sécheresse » et « étiage » et sur les liens qui existent entre ces deux phénomènes. Les pages qui suivent visent à préciser ces notions, du point de vue de l’hydrologue, au travers de quelques réflexions et illustrations.
Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 2001
ABSTRACT Urban drainage systems usually equip small size catchments, with a response time as shor... more ABSTRACT Urban drainage systems usually equip small size catchments, with a response time as short as a few tenth of minutes. Hydrological simulation of these urban catchments requires rainfall time series at a very fine temporal resolution. Most of the time, available rainfall data consist of daily or hourly measurements. It is then appealing to design rain simulation models able to disaggregate observed data into rain rate series at shorter time steps. Random cascade models are candidate tools for performing this disaggregation process. The objective of this study is to evaluate the ability of cascade model for performing realistic and robust rain series suited for needs of urban hydrology.
The main objective of this paper is to evaluate a threshold-based flash flood warning method, by ... more The main objective of this paper is to evaluate a threshold-based flash flood warning method, by considering a wide range of climatic and physiographic conditions, and by focusing on ungauged basins. The method is derived from the flash flood guidance (FFG, hereafter) approach. The FFG is the depth of rain of a given duration, taken as uniform in space and time on a certain basin, necessary to cause minor flooding at the outlet of the considered basin. This rainfall depth, which is computed based on a hydrological model, is compared to either real-time-observed or forecasted rainfall of the same duration and on the same basin. If the nowcasted or forecasted rainfall depth is greater than the FFG, then flooding in the basin is considered likely. The study provides an assessment of this technique based on operational quality data from 11 mountainous basins (six nested included in five larger parent basins) located in northeastern Italy and central France. The model used in this study is a semi-distributed conceptual rainfall-runoff model, following the structure of the PDM (probability distributed moisture) model. Two general questions are addressed: (1) How does the efficiency of the method evolve when the simulation parameters can not be calibrated but must be transposed from parent gauged basins to ungauged basins? (2) How sensitive are the results to the method used to estimate the initial soil moisture status? System performances are evaluated by means of categorical statistics, such as the critical success index (CSI). Results show that overall
This paper presents some analytical results and numerical illustrations on the asymptotic propert... more This paper presents some analytical results and numerical illustrations on the asymptotic properties of flood peak distributions obtained through derived flood frequency approaches. It confirms and extends the results of previous works: i.e. the shape of the flood peak distributions are asymptotically controlled by the rainfall statistical properties, given limited and reasonable assumptions concerning the rainfall-runoff process. This result is partial so far: the impact of the rainfall spatial heterogeneity has not been studied for instance. From a practical point of view, it provides a general framework for analysis of the outcomes of previous works based on derived flood frequency approaches and leads to some proposals for the estimation of very large return-period flood quantiles. This paper, focussed on asymptotic distribution properties, does not propose any new approach for the extrapolation of flood frequency distribution to estimate intermediate return period flood quantiles. Nevertheless, the large distance between frequent flood peak values and the asymptotic values as well as the simulations conducted in this paper help quantifying the ill condition of the problem of flood frequency distribution extrapolation: it illustrates how large the range of possibilities for the shapes of flood peak distributions is.
Spatial and temporal scales of occurrence of flash floods, combined with the space and time scale... more Spatial and temporal scales of occurrence of flash floods, combined with the space and time scales of conventional measurement networks of rain and discharge, make these events particularly difficult to observe. The effective documentation of flash floods requires post‐flood survey strategies encompassing accurate radar rainfall estimation, field observations of the geomorphic processes associated with the flood, indirect reconstruction of peak discharges and interviews of eyewitnesses. This paper describes the methods applied and the results achieved in the survey of a flash flood that occurred on 18th September 2007 in the Selška Sora watershed (Western Slovenia). Hydrometeorological analyses of the storm are based on radar reflectivity observations. The documentation of the flash flood reveals high peak flood discharges and a complex flood response. Peak discharges were estimated at 22 cross sections, with drainage areas ranging from 0·2 to 147 km2. Among the lessons learned from...
ABSTRACT Flash floods are one of the most significant natural hazards in Europe, and can cause da... more ABSTRACT Flash floods are one of the most significant natural hazards in Europe, and can cause damage to buildings and infrastructure and pose a high risk to life. Existing inventories of past floods give information for other geographical regions or lack quantitative information on the meteo-hydrological and hydraulic characteristics of the event. The lack of centralised national and international databases for storing meteo-hydrological, hydraulic and socio-economic data relating to past flood (and particularly flash flood) events within Europe means that it is difficult to calibrate and validate research results on a range of previous floods from different climatic regions. To address this apparent gap in availability of centrally stored, high quality data and with the aim of supporting research on risk assessment and ?ash flood forecasting, a data base has been developed that collates flash flood data from seven European hydrometeorological regions and that could be extended in the future to other areas. Compilation of the database required the development of a data template and flood event selection rules. Initial analyses of the data highlight spatial variations of flood hazard magnitude, with highest speci?c peak discharges in the Mediterranean region. There is a strong seasonality to the occurrence of events, with events occurring mostly in the autumn in the Mediterranean region and in the summer in middle and eastern European regions. There have been flash floods in France and Spain on a basin scale of greater than 500 km2 . This work has been carried out for HYDRATE, which is a currently ongoing EC funded project that is aiming to improve techniques for flash flood forecasting. The work presented here represents some of the first outputs from this project.
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Papers by E. Gaume