Hydrol. Earth Syst. Sci., 19, 4149–4164, 2015 www.hydrol-earth-syst-sci.net/19/4149/2015/ doi:10.5194/hess-19-4149-2015 © Author(s) 2015. CC Attribution 3.0 License. Reconstruction of flood events based on documentary data and transnational flood risk analysis of the Upper Rhine and its French and German tributaries since AD 1480 I. Himmelsbach1, R. Glaser1, J. Schoenbein1, D. Riemann1, and B. Martin2 1Physical Geography, Albert-Ludwigs Universität Freiburg, Freiburg, Germany 2CRESAT, University of Haut-Alsace, Mulhouse, France Correspondence to: J. Schoenbein ([email protected]) Received: 1 December 2014 – Published in Hydrol. Earth Syst. Sci. Discuss.: 7 January 2015 Revised: 11 September 2015 – Accepted: 23 September 2015 – Published: 14 October 2015 Abstract. This paper presents the long-term analysis of flood the small rivers in Alsace compared to those on the Baden occurrence along the southern part of the Upper Rhine River side – an interesting fact – especially if the modern European system and of 14 of its tributaries in France and Germany Flood directive is taken into account. covering the period starting from 1480 BC. Special focus is given on the temporal and spatial variations of flood events and their underlying meteorological causes over time. Ex- 1 Introduction amples are presented of how long-term information about flood events and knowledge about the historical aspect of The knowledge about the occurrence of floods in histori- flood protection in a given area can help to improve the un- cal times, their meteorological causes and their distribution derstanding of risk analysis and therefor transnational risk within the (hydrological) year does provide a deeper under- management. Within this context, special focus is given to standing of the natural variability of the severity of flood flood vulnerability while comparing selected historical and events by providing long-term knowledge about changes in modern extreme events, establishing a common evaluation the causes, frequencies and gravity of the floods as it had scheme. recently been discussed in detail, e.g., by Seidel and Bár- The transnational aspect becomes especially evident ana- dossy (2010) or Grünewald (2010). Pursuing the ideas from lyzing the tributaries: on this scale, flood protection devel- Glaser et al. (2010) to research climate responses of rivers oped impressively different on the French and German sides. and creeks with small catchments, this paper focusses on the We argue that comparing high technological standards of tributaries of the Rhine within the Upper Rhine Rift. Flood flood protection, which were initiated by the dukes of Baden research on smaller rivers as presented in this paper com- on the German side starting in the early 19th century, misled plements the research related to larger river systems for two people to the common belief that the mechanical means of main reasons. Creeks and small rivers show a more direct re- flood protection like dams and barrages can guarantee the se- sponse to the atmospheric forcing. Similarly, they are much curity from floods and their impacts. This lead to widespread more susceptible to changes of land use or alterations of the settlements and the establishment of infrastructure as well as floodplain due to an increase of settlements and infrastruc- modern industries in potentially unsafe areas until today. The ture, as those alternations also directly affect discharge. legal status in Alsace on the French side of the Rhine did not From a perspective of transnational risk research, those allow for continuous flood protection measurements, leading creeks and small rivers are equally interesting to look at. to a constant – and probably at last annoying – reminder that The flood risk management of these smaller catchments lies the floodplains are a potentially unsafe place to be. From a within the responsibility of smaller communities while the modern perspective of flood risk management, this leads to large river systems are under control of larger and stronger a significant lower aggregation of value in the floodplains of administrative units. This however sums up the similarities Published by Copernicus Publications on behalf of the European Geosciences Union. 4150 I. Himmelsbach et al.: Reconstruction of flood events based on documentary data between the French and German sides: due to its roots in the modified through the Belfort Gap. This however might only Roman jurisdiction, the state of France had no rights on the happen in less than 10 % of the year. The westerly winds and non-navigable rivers and therefore could not develop plans of approx. 1000 m of mean height difference between the rims flood protection. The German tributaries, however, stood un- and the valley floor account for a heterogeneous distribution der the undisputed sovereign territory of the Dukes of Baden of precipitation between the Vosges Mountains and the Black since the 18th century, who opted for technical flood protec- forest as well as within the Upper Rhine Valley. Precipitation tion with dams and barrages to protect the floodplains. varies greatly from as little as 550 mm a−1 at Colmar lee- This administrative difference concerning flood control ward of the Vosges Mountains to more than 2200 mm a−1 at and management plays an important role in modern flood the summits. Two precipitation maxima can be identified in risk management. In France flood risk management on non- the course of the year: one in July and another in December. navigable rivers is handled by PPRIs (Plan de prévention du The July maximum is generated mainly by convective rain- risque d’inondation) which are negotiated by the commu- fall, resulting usually from thunderstorms. nities and the responsible parts of the administration. Their Large parts of the study area belong to the European re- goal is to determine the area with a risk of being flooded gion “Regio TriRhena” and nearly the whole study area is along the examined rivers and to discriminate between zones also part of the Trinational Metropolitan Region Oberrhein where different human activities can be allowed or have to be (TMO-MRO) forming a multicore, trinational conurbaniza- forbidden. tion combining more than six million people and industrial In Germany (especially in Baden-Württemberg) the flood hot spots. Both concepts try to improve the transnational col- risk management of smaller tributaries (water bodies of cate- laboration on the fields of science, commerce, technology gory II) resides with the legal responsibility of communities and politics as well as civil societies. Strasbourg is one of the while the large non-navigable rivers (water bodies of cate- European capitals. Historically, the researched area has been gory I) are under control of stronger administrative units like affected by many territorial conflicts since the 17th century. regional councils. Still, the category of water body changes Between 1871 and 1919 and again from 1940 to 1945 Al- from category II (the upper parts of the river) into category sace was occupied by Germany. As far as flood control man- I at positions which were specified according to the master agement is concerned, those different administrations tried to plan of Johann Gottfried Tulla (1770–1828) in the 19th cen- realize their own concepts and ideas; however, both admin- tury. istrations were not been able to come up with and enforce This study presents the results from the project TRAN- a master plan for flood protection due to traditional water SRISK, which was realized between 2008 and 2011 in rights (see below). collaboration between CRESAT (Centre de Recherche sur les Economies, les Sociétés, les Arts et les Techniques) of the University de Haute Alsace in Mulhouse funded 3 Methods and data by the French Agence Nationale de la Recherche (ANR- 07-FRAL-025) and the Department of Physical Geography Within the TRANSRISK project, the Rhine between Basel of the Albert-Ludwigs-Universität Freiburg founded by the and Strasbourg and 14 of its tributaries have been analyzed: Deutsche Forschungsgemeinschaft (DFG-Gl 358/5-1). in Alsace the rivers Largue, Ill, Doller, Thur, Fecht and Lauch; and in Baden the rivers Wiese, Klemmbach, Kander, Neumagen/Möhlin, Dreisam, Elz, Schutter and Kinzig. 2 Study area For none of those tributaries had hitherto a flood research or a comparative survey regarding flood protection measures The study area is located within the Upper Rhine Rift and been conducted. So the first interest was to reconstruct the stretches approx. 110 km between Basel, Switzerland, and flood events between 1480 and 2007 as detailed as possible, Strasbourg, France, including the edges of the Black For- their underlying meteorological causes together with their est and Vosges Mountains (Table 1). The elevation of the spatiotemporal variation. Our approach followed the method Upper Rhine Rift ranges from about 250 m a.s.l. in Basel to of critical source analysis, which can be regarded as well es- 130 m a.s.l. at Strasbourg. The highest mountaintops of the tablished in the field of historical climatology (Pfister, 1985; region are the Feldberg (1493 m a.s.l.) in the Black Forest Glaser and Stangl, 2003; Jacobeit et al., 2006; Glaser et al., and the Grand Ballon d’Alsace (1424 m a.s.l.) in the Vos- 2010; Wetter et al., 2011; Himmelsbach, 2014). Following ges. The area is located in the midlatitudes, a zone of pre- these well-established principles of critical source analysis, dominant westerly winds and in the transition of maritime the multitude of information gathered had been critically re- too continental climate. The climate is moderately mild due viewed in a hermeneutic approach due to their informational to its location around 48◦ N and decent protection against content mainly analyzing diction of the source as well as ad- cool air masses from the surrounding low mountain ranges. ditionally information about the author like level of educa- Warm southwesterly winds which originate from the West- tion or social environment, intention, etc., which might have ern Mediterranean region can reach the area only moderately influenced or motivated the writings.