L'aménagement des trois plus grands fleuves européens : Rhin, Rhône et Danube. Problèmes et méfaits - article ; n°561 ; vol.100, pg 668-713

Annales de Géographie - Année 1991 - Volume 100 - Numéro 561 - Pages 668-713
Peri-alpine Rhine, Rhone, and Danube : their management, its environmental impacts. — Although the Danube is only in part a peri-alpine stream through its right bank tributaries in Bavaria and Austria, these three rivers, the biggest of the whole E.E.C., are characterized by warm season high waters, important seasonal variations of discharge, and resulting bed instability. From one side, settlement along them is turned dangerous, but, on the other, it is a source of abundant natural resources, which have attracted men during hundreds of years : fishing, hunting, wood for building and handicrafts, and very fertile loam sedimented during the floods. Management attempts to both village protection and a better use of resources have been made in Hungary during the Middle Ages. A system of channels and dykes has been built in order to control floods, draining cultivated land and flooding during a longer period the meadows and marshes for better fishing and game and to protect the settlements. All has been abandonned with the Turkish invasion and the resulting Ottoman rule.
Along the Rhine, and to a lesser degree along the Rhone, political division hampered such a systematic management. After the annexion of most of Alsace to the French Kingdom, the Rhine became considered, during the second half of the xvnth and during the whole xvmth centuries, as a natural defence combined with the fortifications of Strasbourg and of the new town of Neuf- Brisach. The peasants have been left to their own initiatives. The defences they built lacked any coordination, so that, not unfrequently , what was constructed in a place turned into a danger for the neighbouring ones. Nevertheless, an important experience has been gained in the application of some technics, such as groins edified using long tree-stems in combination with heavy stones. In the 1780' s General d'Arçon established a first comprehensive management scheme, but the Revolution and the Empire wars gained a much greater priority. Nothing has been made during these decades. After Waterloo, France was not in a diplomatic situation enabling her to make proposals. These came from a Colonel of the Baden Dukedom, von Tulla. They were finally accepted by France after the 1830 Revolution and applied until First World War. Their purpose, initially to reduce flood extension, turned, with the emergence of Prussia and the unification of the German Empire, to transform the Rhine into a navigable river. Von Tulla management consisted in a channel rectification combined with two systems of lateral embankments, an inner one, discontinuous, containing the low floods, and an outer one, continuous, protecting arable land and settlements. Channelization increased the bed slope, which was foreseen as resulting into a river bed incision which would reduce the extension of flooded areas and enhance the effects of embankment. The Rhine ought to cut its bed deeper. It did, and much beyond any hope... The result turned catastrophic: 500 000 t/year of gravel became transported in Middle-Alsace and, a few km downstream Basel, a surimposition into solid limestones occurred, generating rapids which completely blocked any shipping. At the beginning of the present century, schemes for by-passing these rapids by a lateral canal, on the left bank, have been proposed by alsatian engineers. Of course, the governement of Baden opposed them. When France became victorious of Germany, in 1918, the political situation changed completely and after delays resulting of the obliged consultation of international commissions, Istein Rapids became by-passed by a canal and a hydraulic power plant operated in Kembs. After Second War, the Grand Canal d'Alsace project has resumed. Other problems emerged... A staircase of hydraulic plants coupled each one with a big sluice obliged to dig deep in the pervious alluvium of the Rhine upstream of every plant and sluice, and it drained very efficiently the land along the incision. It destroyed completely the original ecological conditions. Fields and meadows suffered from drought. Tentatives of irrigation were to be made ! In the meantime, Germany recovered and from a beaten ennemy turned into a precious ally in the Cold War. The B.R.D. proposed to abandon the Grand Canal d'Alsace and to manage the Rhine bed itself, each couple power-plant/ sluice being edified on a short derivation from the Rhine. This program is now completed Nevertheless, damage resulted to the biocenosis. Ecotopes have been deprived of any flooding outside the outer embankments since more than a hundred years. Rhine bed incision drained the ground-water, increasing the impact. Many endemic species are deseappering. Ecologists protest...
The management of the Rhine has served as a model for the Rhone and the Danube, with only slight differences. On the Rhone, the production of hydraulic electricity has been the first purpose for the management, at the end of the xixth century, and navigation waited until the creation of the Compagnie Nationale du Rhône, between the two world wars, to become an objective for an integrated management program. On the Danube, political division turned any management more troublesome. Austrian monarchy imposed an austrian monopoly on shipping. After World War Two, the S.S.S.R., according to its political tentatives to subjugate central Europe, imposed a management for shipping of the Iron Gates, in Roumania. Germany dug canals to link together Rhine and Danube. Ecological protests became strong in Austria and obliged to abandon any channelization in the Marchfeld, near Vienna. A huge project for a big reservoir for producing electric energy, in Gabcikovo, at the border between Slovakia and Hungary, raised too a strong opposition... Political changes which occurred during the very recent years turn investments more difficult and change completely the situation. What will be their impacts ?
Bien que le Danube ne soit un fleuve périalpin que par ses affluents bavarois et autrichiens de rive droite, les trois fleuves ont les mêmes caractéristiques, en particulier les hautes eaux de saison chaude, très favorables écologiquement puisqu'en été, la végétation dispose, en abondance, d'eau et de chaleur, et posent les mêmes problèmes d'aménagement. Le dépôt de limons fertiles lors des inondations rend les abords de ces fleuves fort attractifs, car on y trouve les ressources de la chasse, de la pêche, de l'exploitation des forêts, des prairies et des terres cultivables, mais leurs divagations constituent un grave danger. On a tenté, très tôt, dès le Moyen Age en Hongrie, d'améliorer les conditions d'exploitation du milieu et la protection des terres, des prairies, des villages. Mais tout fut abandonné avec la conquête turque. Le Rhin est alors devenu le prototype de l'aménagement après une période où les villageois n'ont pu faire que des interventions locales, isolées et inefficaces, car la Monarchie utilisait le fleuve comme une « défense naturelle ». Von Tulla colonel badois, proposa et fit adopter, sous la Monarchie de Juillet, un programme comportant la construction de digues extérieures, distantes de quelques kilomètres seulement, protégeant totalement contre les inondations la majeure partie de l'ancien lit majeur, de digues intérieures, n'arrêtant que les crues faibles, et la rectification du lit mineur, concentré en un seul bras et fortement raccourci. La pente en fut donc augmentée. Comme prévu, le Rhin incisa, ce qui accrut l'efficacité des digues. Mais l'incision dépassa de beaucoup les prévisions. Ses effets se firent sentir après l'unification allemande, qui fit passer l'amélioration de la navigation comme objectif prioritaire à la place de la lutte contre les inondations. Avant la Première Guerre mondiale, une incision de 7 m, par surimposition dans un chicot calcaire, créa la Barre d'Istein, bloquant l'accès des bateaux à Bâle. Le projet de Grand Canal d'Alsace fut adopté à la suite de la défaite de l'Allemagne. La Barre d'Istein fut contournée par un canal alimentant la centrale de Kembs et comportant une écluse. Après 1945, les travaux reprirent, selon le même schéma. Mais le canal était fortement entaillé dans les alluvions en amont de chaque centrale. Il draina donc la nappe phréatique, ce qui assécha champs et prairies. L'Allemagne demanda et obtint que chaque couple écluse-centrale ne soit construit que sur une dérivation locale, partant du Rhin et le rejoignant sur la plus courte distance possible. Cet aménagement se termine. Mais d'importants dégâts écologiques se sont produits. Ils provoquent la protestation, justifiée, des écologistes. En effet, depuis un siècle, il n'y a plus d'inondations à l'extérieur des digues et le creusement a provoqué l'abaissement du toit de la nappe. Les biocénoses dont l'existence était conditionnée par l'abondance estivale de l'eau et les apports de limon par les inondations disparaissent, et, avec elles, diverses espèces endémiques. Le modèle d'aménagement rhénan a été copié sur le Rhône, mais les priorités se sont succédées là dans un ordre inverse : d'abord l'hydroélectricité sur le haut Rhône, ensuite, entre les deux guerres, la navigation avec la fondation de la Compagnie nationale du Rhône. Sur le haut Rhône, les interventions ayant été réduites, les biotopes ne sont pas en péril. Par contre, ils le sont le long du Danube, où l'opposition de l'opinion a fait renoncer à la canalisation dans le Marchfeld, près de Vienne et où un gigantesque projet de retenue et de centrale hydraulique, à Gabcikovo, sur la frontière Slovaquie-Hongrie, inquiète fortement les hongrois car il modifierait la dynamique des eaux dans leur plaine. Les changements politiques récents en Europe centrale vont probablement remettre en question l'aménagement du Danube, conçu, antérieurement, en fonction des intérêts soviétiques...
46 pages
Source : Persée ; Ministère de la jeunesse, de l’éducation nationale et de la recherche, Direction de l’enseignement supérieur, Sous-direction des bibliothèques et de la documentation.