Floods

Volume 2- Risk Management

Freddy Vinet

• Editorial: ISTE Press - Elsevier
• Año: 2017
• ISBN:
  9780081023846
• Categoría: Ciencias biológicas
• Categoría: Ciencia medioambiental

The management of flood risk seems to be facing a daunting paradox. Despite increasingly effective risk knowledge tools and the efforts of international institutions to place risk reduction at the top of the agenda, the cost of disasters continues to increase. It is also increasingly difficult to avoid the urbanization or development of potential flood zones. The fundamental issue involves determining the conditions necessary for efficient prevention by focusing on adaptability to risk, which implies coping with the risk of flooding rather than directly fighting against it or simply ignoring it.

This second volume of the Floods series of books explores existing policies and tools which mitigate the impact of flooding: the construction of protective structures, the reduction of vulnerability, land use planning, the improvement of crisis management, etc. The closing chapters focus on the question of adaptation through post-flood reconstruction, integrating disaster risk reduction measures, e.g. through resilient urbanism.

• Presents the state-of-the-art surrounding flood issues, from the description of the phenomena, to the management of risk (dikes, dams, reducing vulnerability and management of crisis)
• Written by specialists, but accessible to mainstream scientists
• Exposes knowledge, methodologies, scientific locks and the prospects of each discipline on the theme of floods

Part 1

Strategic and Technical Aspects of Flood Prevention

1

Flood Management in France from 18th to 20th Centuries: A State Issue?

Denis Cœur

Abstract

The history of flood management in France forms part of the country’s broader history, marked by the affirmation and development of the State. Long treated as the primary responsibility of riparians, resident communities, cities and local authorities, this responsibility shifted in the 17th and especially the 18th Centuries as Central Government gradually took control of proceedings. This assumption of responsibility went on to follow a trajectory that involved technical, legal and administrative records. A journey which, in many ways, resembles a real conquest. Primarily it was a conquest for knowledge achieved through the development of skills and specific methods, whose implementation contributed to significant transformations of natural habitats, however this without providing definitive solutions for the prevention of catastrophic floods. Secondly, it was a political conquest as, in many ways, the fight against floods was an opportunity for the State to increase its legal and administrative jurisdiction on privately- or community-owned land and rivers.

Keywords

Crisis management; Flood Management in France; Forecast and alert; Long-term prevention; Reconstruction; Regional monitoring networks; Special navigation services; State and local authorities

1.1 Introduction

The history of flood management in France forms part of the country’s broader history, marked by the affirmation and development of the State. Long treated as the primary responsibility of riparians, resident communities, cities and local authorities, this responsibility shifted in the 17th and especially the 18th Centuries as Central Government gradually took control of proceedings [DES 95, FAV 06]. This assumption of responsibility went on to follow a trajectory that involved technical, legal and administrative records. A journey which, in many ways, resembles a real conquest. Primarily it was a conquest for knowledge achieved through the development of skills and specific methods, whose implementation contributed to significant transformations of natural habitats, however this without providing definitive solutions for the prevention of catastrophic floods. Secondly, it was a political conquest as, in many ways, the fight against floods was an opportunity for the State to increase its legal and administrative jurisdiction on privately- or community-owned land and rivers.

This chapter aims to shed light on the three main phases of public engagement: forecasting, crisis management and reconstruction and long-term prevention.

1.2 Forecast and alert: from local empiricism to regional monitoring networks

Since medieval times, river cities have sought to find answers to the questions that concern the ability to forecast floods in order to best protect people and assets at risk. Technical based monitoring and transmission methods were out of reach for a long time. Up until the early 19th Century, velocity and inevitability of floodwaters were evaluated in “real time” across affected areas as events occurred. In 1802, the Comissioner for the Seine and Marne did not integrate flood forecasting measures into his instructions directed at mayors. Measures were to be taken “as the possibility of a flood is perceived”. However, town councilors were not completely unprepared. In the first instance, they could rely on high water marks placed along river sections located in cities. High water marks not only provided a means of comparison, they also enabled thresholds to be identified which, when exceeded, indicated the dangers the city was exposed to [GAR 16].

Written flood memories also contributed to maintaining local flood culture [FAV 06]. In Lyon, during the Rhône flood in February 1711, observations provided by town councilors were supported by their knowledge of comparable events occurring between 1570 and 1602 [CHA 64]. Some evidence suggests that more sophisticated warning devices had been in existence since the 18th Century. In Grenoble, the possibility of transmitting information on horseback from an observation point along the Isère River, located several dozen km upstream of the city, was envisaged by engineers in the 1740s [COE 08]. There is also evidence that suggests this same technique was used in the Rhône Valley and mid-Loire during the same period. This was a breakthrough in the management of natural events. However, this technique was not without its limitations, both in terms of hydrological realities and practical eventualities. Technically, the device could only operate on rivers with relatively slow flow and on sections with good transportation conditions. Not to mention that it was very difficult to send the warning more than once. Before the warning signal even reached its destination, unexpected events could take place (overflows and breach formations). It was not until the mid-19th Century that more effective systems began to be implemented.

This was made possible thanks to the combination of a series of scientific, technical and administrative developments, primarily brought about by State engineers, Roads and Bridges engineers and the engineers within the Head Engineering Office. French river hydraulics experienced major developments as of 1740 thanks to the distribution of work carried out by Italian hydrologists (Castelli, Guglielmini and Venturi) but also thanks to progress made in the field of Mathematics (Bernoulli). From this perspective, the work of Forest de Belidor (1737–1739), Dubuat (1779), Riche de Prony (1802), Pitot and Woltman, mark a decisive step in the measurement of flow velocity and evaluation of river discharge [COE 00]. Calculation of maximum flood depth propagation was solved half a century later, notably by engineers Sainjon and Belgrand; Sainjon conducted experiments in the Loire basin and Belgrand in the Seine. To do this, they relied on the existence of perennial observation sites from which water depths could be observed, including during floods. These hydrographic observations, originally established to meet the needs of navigation, continued to multiply after 1800 as part of the development of regional navigation services. This observation and daily recording model was used on the Tournelle Bridge located in the Seine basin in Paris from 1730, before being used across the entire basin, then also on the Loire, Rhône and Garonne basins [COE 02b].

However, up until the 1840s, emerging regional networks were only able to record information but were unable to send this information towards watersheds downstream. Two factors contributed to resolving this issue. The first was of both an economic and administrative nature. Severe flooding of the Loire in Autumn 1846, reoccurring from May–June 1856, as well as in a significant part of the Rhône and Garonne basins and, to a lesser extent, the Seine basin, were the catalysts for an unprecedented mobilization of State services in terms of improving knowledge of watershed operation, particularly flood events, their impacts, and the preventive steps that could be taken (see section 1.4 below). Structural solutions (retention dams, dikes) were widely advocated, however they failed to systematically resolve the issue. Solutions of a more innovative nature were also discussed, such as incorporation with daily State-lead administrative tasks (concerning water or shipping policy) specifically designed to develop knowledge of the river itself. This “special service” essentially involved maintaining a network of hydrometric stations, ensuring water depths were recorded regularly, preserved and published and using this information to further develop knowledge and understanding of flood events and also to improve the service. The official creation of water supply services in 1848 handled some of these expectations. The service was supplemented by special navigation services present on the Loire in 1853 and on the Seine in 1854 – under the auspices of the engineer Belgrand – and even on the Rhône and the Saone (1844).

The second factor is of a technical origin. Rapid expansion of railways as of 1850 also marks the creation of one of the first telegraph networks. Before long, every large river valley had one. Thanks to this expansion, the Roads and Bridges Authority was provided with an inexpensive solution concerning transmission of flood-related information downstream. “Now that electric telegraphy enables us to communicate almost immediately from one end of our largest rivers to the other, notifying people of the danger long enough in advance is easy”¹.

Moving on from the first achievements brought on by the will of a few great visionary engineers, autonomous services monitoring rivers and sending out flood alarms emerged in the second half of the 19th Century. Catastrophic flooding of the Garonne in June 1875 reinforced the process. The Flood Alarm Commission based within the Department of Public Works was set up as early as July 1875. It was responsible for supervising implementation of alarm systems designed to alert people living in every one of the large catchment areas in models of the Loire and the Seine². Specific regulations were established in order to manage hydrometric stations as well as a “routing system”, organizing the transmission of information between different departments (prefect, sub-prefect, mayor and police). As this took place, hydrological knowledge of rivers also continued to progress, highlighting the importance of gathering and publishing data. There were 35 flood alarm offices in place in Metropolitan France in 1876, confirmed following an official count (Decree of 21st August). Due to a lack of adequate observational data required to calibrate processes, it was a further 15 years before all services were operational. However, with limitations on fast-flowing river channels, the Chief Engineer of the Aude region in France in 1889 recalled “we cannot predict anything ahead of time, and to do so would risk leading people into a false state of security”³. At the turn of the 20th Century, the number of services reached 51 for a total of 675 observation stations responsible for sending out flood alarms [MAI 08].

Associating knowledge of flood events and flood management with ever-growing cohesion, the system never ceased to be tweaked and...