The correction of the Rhône upstream of Lake Geneva concerns the Rhône River located in the Swiss Alps. In its Swiss section, the Rhône has undergone several modifications designed to control its course and reduce the harmful effects of flooding. In 1860, a flood caused extensive damage throughout the Rhône valley. This event triggered the decision to build the first Rhône correction between 1863 and 1894. A second correction was carried out between 1930 and 1960. In September 2000, the Valais Grand Council decided to undertake the third correction of the Rhône from Gletsch to Lake Geneva, in collaboration with the Canton of Vaud. In 2008, the Swiss Confederation announced that it was raising funds for the third correction, which is expected to take between 25 and 30 years to complete.
Geographical location
The Rhône rises in the St. Gotthard massif in the Swiss Alps. It is formed by the melting of the Rhône glacier, and flows through the long valley of the same name through the canton of Valais, marking the border with the canton of Vaud in the Chablais region before joining Lake Geneva in the commune of Port-Valais. The Rhône, between Saint-Maurice and the lake, marks the border between the cantons of Valais and Vaud. Upstream of Lake Geneva, the Rhône runs for some 170 kilometers, receiving water from around two hundred torrents (from Vaud and Valais).See Figure 1 in
The Rhône's main tributaries upstream of Lake Geneva are the Massa, fed by the Aletsch glacier, the Lonza in the Lötschental valley, and the Grande Eau, which rises in the Diablerets massif. On the left bank of the Rhône, from its source to Lake Geneva, its main tributaries are the Vispa, the Navizence in the Val d'Anniviers, the Borgne in the Val d'Hérens, the Drance joining the Rhône at Martigny, and the Vièze passing through Monthey. Due to its numerous torrents and tributaries originating from the Alpine peaks, the Rhône's hydrological regime is strongly influenced by melting glaciers and snow, resulting in significant seasonal variations in flow and water level (high flow in summer, low flow in winter).
The Rhône before the corrections Today, the people of the Valais hear most about the Third River correction project. However, two other large-scale corrections preceded it, and recent research has shown that dikes protected parts of the land as early as the Middle Ages.
Measures before the first correction Documents preserved in the communal archives held by the Valais State Archives provide an insight into the life of residents before the first Rhône correction. Far from the stereotype of a marshy, unusable valley floor, far from the cliché of a frightening river to be avoided, their existence was punctuated by agro-pastoral practices that perfectly integrated the varied resources of the Rhône plain. Shepherds led their flocks to pastures near the river or between its branches. This practice continued until the early 20th century.
Neolithic and Antiquity Land along the banks of the Rhône has probably been farmed since Neolithic times. In fact, according to Théodore Kuonen, "the practice of grazing livestock dates back to the time of the first settlers, which is attributed to the Neolithic period."
As far as the construction of river defense systems is concerned, we have no sources or archaeological finds to prove the construction of this type of development. Nevertheless, the construction of large Roman villas on the plain suggests the existence of barriers (from the Latin words barra or barreria) as early as Antiquity.
Middle Ages and Ancien Régime In the 14th century, the Count of Savoy maintained the section of the Great St. Bernard route around the Saint-Maurice d'Agaune toll station, some 20 km from Bex to Martigny. This included the maintenance of bridges over the Rhône, its right-bank tributaries downstream of Saint-Maurice and its left-bank tributaries upstream, and the construction of dykes to protect the main crossings. The work is well known, particularly through the series of accounts of the toll collector Jacques Wichard and his son Guillaume, preserved at the Archivio di Stato di Torino and digitized by the Archives du Valais.
In the 15th century, the landscape of the plain between Martigny and Saillon, dotted with tree-covered islands, meadows, and, here and there, fields, is fairly well documented. They reveal that the farmers had a precise knowledge of the land's potential. Primarily intended for cattle grazing, they also provide wood, hay, and stones, and can even be sown with cereals. The land thus represents a major economic stake, prompting riverside communities to fight over it and restrict the river's freedom to extend meadows and crops. They built dykes, or barriers, using stakes, intertwined branches, and piles of stones and gravel. The first step was to define the limits of the Rhône so that certain areas of the plain could be used. The second phase involves maintaining the structures created for this purpose. The scale of the work did not frighten the inhabitants, who were more concerned about the damage caused to their possessions. As the land along the Rhône is mainly communal property, the construction and maintenance of the dikes is the responsibility of the communities. This work was carried out in the form of drudgery by the men of the villages, in proportion to their use of the communal land.
Significant climatic changes occurred during the Little Ice Age, a cold period that hit Europe from around 1350 to 1860. The most spectacular result was the rapid advance of the Alpine glaciers. In the Valais, episodes of violent rainfall caused numerous floods and a significant increase in the amount of material that the Rhône struggled to transport. As the bottom of the riverbed rises, the river weaves new arms, in the middle of which islands multiply, and takes up more and more space on the plain. During periods of high water, the river rises out of its bed, deposits alluvial deposits on the valley floor, destroys crops, and feeds the wetlands in the lowlands. This mobility, which implies a displacement of the riverbed, is incompatible with the extension of pastures, crops, and communication routes. As early as the 15th century, the river's inhabitants realized that the Rhône had to be straightened to increase the force of the current, to protect bridges, roads, and access paths to farmland, and to guarantee the boundaries of communes and properties.
Numerous conflicts arose between communes as a result of changes to the riverbed or works undertaken to constrain it. This was also the case between the Bernese, who dominated the Pays de Vaud, and the Valaisans. In 1756, Bern and Valais decided "to draw up an exact plan of the Rhône in its present state, with all the barriers and the old and new limits", to put an end to the incessant conflicts caused by the delimitation of the riverbed. The river forms the border between the Valais and Bernese Chablais.
Three examples of flooding
The first recorded flood occurred in 563, during the Tauredunum disaster. A landslide created a dam in the Rhône valley, and a body of water formed upstream of this natural dam, which eventually gave way. The breaking wave caused damage both downstream and on the shores of Lake Geneva. According to Vischer, the site of the landslide was located in the Saint-Maurice region. The latest studies locate the landslide further down the Rhône, not far from where the Rhône now flows into Lake Geneva.
Devastating floods in 1545, caused by heavy rains, were reported at the Diet of February 26, 1546: "This session, decided on at the last Christmas Council, is being held today in connection with the terrible flooding of the Rhône, as a result of which the route du Pays downstream from the Morge, the property owned and leased, the routes, the common pastures, and other places still, could be entirely lost, wiped out by the waters, if appropriate and indispensable measures are not taken, and if the Rhône is not led in a straight line." This passage proves that the authorities feared a recurrence of such events. It was important to them to safeguard the royal road and the land used by their subjects.
Other floods are caused by glaciers. Glacial flooding occurs when the movement of a glacier obstructs the course of a river, causing the river to impound water behind the glacier, and the glacier to break up under the weight of the water, causing major damage. In 1818, the Giétro glacier obstructed the course of the Drance (a tributary of the Rhône), creating a lake containing 18 million m3 of water. The glacier gave way on June 16, 1818, causing 44 deaths and destroying numerous buildings in the valley.
Modern state During the period of French domination, the canton of Vaud was formed in 1803, taking over the Bernese territory below Saint-Maurice. The canton of Valais joined the Swiss Confederation in 1815. These political changes led to a determination to develop the Valais, in particular by strengthening agriculture. Roads and bridges were built throughout the canton. In 1850, a railroad line was built between Lake Geneva and Sion. Protection of the Rhône Valley from the river's floods was increasingly under consideration.
As early as 1803, the Valais State Council convened the communes of Riddes, Saxon, Martigny, Fully, Saillon, and Leytron to decide on a joint plan to give the river a specific course. Tired of the ruinous and interminable formalities of the courts, certain communes had asked the cantonal government to find a solution to the crisis that had been going on since the catastrophe of 1782 (when a terrible flood had caused the river to change course in the area between Saillon and Saxon, causing damage as far away as Vernayaz). Thanks to this new willingness to compromise, a project was drawn up against the "common enemy": the Rhone, demonstrating the company's long experience with the river. Although the actual implementation of the program would take several years, it was a major step forward.
From 1830 onwards, work began on rectifying the course of the Rhône, notably in the Rarogne plain and between Riddes and Martigny. Here, engineer Ignace Venetz developed the system of groins protruding into the Rhone bed, which was adopted for the first Rhone correction. In addition to this work, the riverbed was also lowered and the material clogging it cleared, a process already tried and tested by residents as early as the end of the 16th century. The cantonal law of 1833 allowed the Conseil d'État to order riverside communes to carry out work on the banks of the Rhône, without however providing subsidies for the work, even though these major financial burdens exceeded communal resources. Some communes were obliged to sell bourgeois land when they were unable to pay for the work. The situation was particularly serious in the mid-19th century. An upsurge in flooding from 1834 onwards was compounded by the political unrest and revolutions that paralyzed the state between 1839 and 1852.
In 1860, Karl Culmann was commissioned by the Swiss Federal Council to draw up a "report to the Swiss Federal Council on the study of Swiss torrents". In his opinion, the structures were not properly combined, and only two stretches of the Rhône were well corrected: a 3.5 km section at Rarogne and a stretch at Martigny.
First correction During the 19th century, many floods were the result of heavy precipitation during a mild spell, when river flows were already high due to melting snow. 1855 and 1857 were particularly noteworthy. However, it was the flood of 1860 that "probably surpassed all events of modern times in its magnitude between the Goms Valley and Martigny."