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Abstract. Risk Flood protection involves works which reduce the hydraulic hazard in protected areas in terms of frequency, duration, water level, water velocity or flood arrival time. These works are parts of protection systems. In this paper, we discuss and compare three structure-based solutions that contribute to flood protection but seem to oppose one another in the mind of general opinion: levees based protection systems, whose purpose is to prevent water from spreading in protected areas; diversion channels that aim to decrease the flow at their downstream; flood expansion areas, whose purpose is to temporary store water, reduce flood peak and spread flow duration. The article also deals with weirs which can be found in addition to dikes in the three types of solutions on which the paper focuses. For each type of these flood protection solutions, the paper describes their functions and limits, details how these solutions are similar, opposite or complementary, and in the end shows that they are globally complementary and not mutually exclusive. It also demonstrates the interest of a multi-scale analysis and of an integrated design and management of these arrangements, taking into account flood risk, morphological changes and associated environmental objectives.

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In December 2007, a French decree related to hydraulic structures (levees and dams) has introduced for owners the necessity to produce a hazard study for each levee system. On the river Loire, three major class A* state levee systems are present and protect three main urban areas, Orléans, Tours and Authion representing some 240 000 inhabitants. Around 40 class B* and C* levee systems are also present on the river Loire and its tributaries representing 600 km of levees and requiring such hazard studies. In order to have a homogenous method to do these specific risk assessment studies on river Loire levees, a new model named CARDigues (for Levee Breach Hazard Calculation) was developed in a partnership with DREAL Centre-Val de Loire, Cerema and Irstea. This model enables to approach the probability of failure on every levee sections and to integrate and cross different "stability" parameters (topography, embedded structures, geology), hydraulic solicitations and observations from visual inspections or instrumentation results considered as disorders (seepage, burrowing animals, vegetation, pipes, etc.). This model and integrated tool CARDigues enables to check for each levee section, the probability of appearance and rupture of five breaching scenarios initiated by: overflowing, internal erosion, slope instability, external erosion and uplift. It has been recently updated and has been applied on several levee systems by different contractors. The article presents the CARDigues model (V28.00) with examples on river Loire and how it is currently used for a relevant and global levee system diagnosis and assessment. Levee reinforcement or improvement management is also a perspective of applications for this model CARDigues. (* levee classes are function of levee height and protected population)

Les historiens d'autres périodes sont souvent déconcertés par les travaux des antiquisants. La rareté des sources, la pauvreté des documents dont ceux-ci disposent, l'extraordinaire déploiement d'érudition dont ils font usage pour établir de minces certitudes, la fréquence des questions qui restent, faute de moyens d'investigation, sans réponse, font que l'histoire ancienne paraît, vue de l'extérieur, plus souvent imitatrice qu'initiatrice, et qu'elle semble adapter à son champ de recherche des méthodes ou des formes d'étude qui ont fait leurs preuves ailleurs. Il est cependant un domaine, la prosopographie, où l'histoire romaine a, sinon servi de modèle, du moins présenté des réalisations qui ont ensuite été imitées pour d'autres périodes. C'est elle, à tout le moins, qui a donné ce nom à une forme d'invention et d'étude de documents. En quoi consiste cette démarche ? Pourquoi s'est-elle affirmée de la sorte dans ce domaine particulier de l'histoire romaine ?