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The Rhône, a river shaped by man Known as the Rotten in its upper reaches, the source of the Rhône is meltwater from the Furka glacier in the Swiss canton of Valais. It runs for 300 km before reaching Lake Geneva. The French section of the Rhône, from Lake Geneva to the River Saône, winds its way through the mountains of the Jura and the pre-alps before it reaches the Ain plain. At Lyon, the river meets the rocky obstacle that is the Massif Central, forcing it to change direction to run down a northsouth axis all the way to its delta, the Camargue. The Rhône basin is noteworthy for the diversity of climates - mountainous, The Furka glacier, like most other Alpine glaciers, has retreated a great deal over the last 150 years because of climate change. oceanic, continental, Mediterranean - influencing how the river functions. The Rhône is a major communication channel, engineered to optimise navigability, work on which started in the first half of the 19th century. Since 1934, navigability works, hydro-electricity, and the use of its waters for irrigation have all expanded. The Rhône is a river shaped by man with dykes and channels, deviated from its natural course long ago. DID YOU KNOW? The French portion of the Rhône now features 22 hydro-electric power plants, 16 nuclear reactors and 19 locks enabling the river to be navigated along some 300 km of its length. ATLANTIC OCEAN IDENTITY CARD Mouth of the Rhône carrying glacier sediment into Lake Geneva, on the Swiss side. Source: Furka glacier, Swiss Alps Mouth: Mediterranean Sea Length: 810 km (just over 500 miles) Discharge rate at mouth: 1,700 m 3 /s Catchment area: 0.1 million sq. km. Countries: Switzerland, France A cut-off (lône) is an abandoned or secondary branch of the Rhône. Most of them are the result of man-made changes to the river s direction. They are supplied with water by groundwater or directly by the river in times of flooding. The rivers Ain, Saône, Isère and Durance, the Rhône s four major tributaries, receive 60% of the catchment area s water. Confluence of the Rhône (right) and Saône (left) in Lyon. The temperature of the Rhône and its tributaries has risen substantially over the last 40 years. These changes are caused by climate change, a slower rate of flow, and discharges of hot water from the power plants. The Rhône discharges 54 billion cubic metres of water, which is 20% of the river water that flows into the Mediterranean 22
A complex river The Rhône tributaries show highly disparate monthly flow rates. Some, supplied by melting snow, have a strong flow in summer; others, mainly supplied by rainfall, have a greater hydrological regime in autumn and winter. The inflows from these rivers have different effects on Rhône s flow rate, floods and low water levels, depending on the location and the season. Different types of flood may occur in the Rhône basin in winter and autumn, i.e. oceanic towards the north, and Cévennes and extensive Mediterranean in the south, The Rhône basin receives heavy precipitation, some 1,100 mm on average per annum. In the Alps, precipitation of over 3 metres per annum has been measured, mainly in the form of snow. the latter two being extreme and sudden. If they occur at the same time or a few days apart, a general flood arises, often with devastating effects, as in 2003. According to researchers, the impact of climate change on the Rhône basin is difficult to assess. Separating the influence of this factor from others such as human activities and changes brought about to the environment is no easy matter. It is however proven that temperatures are rising, that evaporation is greater and that snow is melting earlier. Scientific organisations (IRSTEA France s National Research Institute of Science and Technology for Environment and Agriculture, CNRS - French National Centre for Scientific Research, France s meteorological office Météo-France, universities) have been working together for years on a whole range of programmes studying water resources and the impact of climate change. These hydroclimatic modelling projects, ranging from Gewex-Rhône to the current Modelling the Rhône programme, show the system s sensitivity to fluctuations brought about by man-made and natural causes. Average monthly flows Source: banque hydro The Isère is a tributary supplied by meltwater from snow and glaciers; the waters of the river Saône are essentially rainwater. The flows of each river will differ a great deal depending on the season. Owing to the varying hydrological regimes of the various sub-catchment areas and the various climates the river passes through, the Rhône has a complex flow pattern, which can experience episodes of flooding or low water at different times of the year. Downstream from Valence, the Rhône and its tributaries are affected by the Mediterranean climate, with autumn downpours resulting in frequent flooding, as here at les Gardons. The banks of the Rhône in Lyon in 2003. This general flood caused more than a billion euros of damage, making it one of the most costly floods ever to occur in France. Researchers anticipate an increase in air temperature of 1 to 3 C, unpredictable changes to winter precipitation (from -10% to 10%) and a 5% drop in summer rainfall. They have not, however, uncovered any clear trend in changes to floods. The Camargue is extremely vulnerable to Rhône floodwaters as its topography is flat and low-lying. It can become flooded if a dyke is breached, as here in December 2003. The river hit a rare peak flow of 11,500 m 3 /s in December 2003 23
A subdued river Matter in motion in rivers can be split between alluvium and clay in suspension, and sand, gravel and pebbles washed along the river bed. In the Rhône s case, the transport of fine sediment in suspension and sand has been in decline for a century, but is still substantial. Gravel and pebbles being carried along the river bed has almost stopped. Consequently, only sand, alluvium and clay shape the plain and currently reach the mouth of the Rhône. The Girardon engineering structures designed to increase the depth of the navigable channel, together with large reservoir dams, hold back a large proportion of the sediment in suspension and the sand. The inflow of pebbles and gravel from tributaries is stopped by large-scale extraction of aggregates. With the scarcity of gravel inflows and the channelling of the river, it is now subdued and sluggish, its bed and banks no longer change and no longer rebuild themselves. The river s managers are currently working on dismantling the Girardon structures so as to limit the level of floods, increase the sediment carried by the river, and boost ecosystems by rehabilitating the Rhone s dead offshoots, the lônes, and adjoining land environments. The Rhône Sediment Observatory (OSR) is a multi-partner research platform, aiming to generate cross-disciplinary scientific knowledge over the long term delivering better understanding of the river system s dynamics and improved information for public operators. Partners include the Rhône Basin Long-term Environmental Research Observatory (ZABR), Rhône Valley Environmental Observatory (OHM-VR), river management bodies, government departments, French Water Agency, Compagnie Nationale du Rhône, EDF (electricity generating company), local governments of regions through which the river passes, and research institutes. Digues basses longitudinales Accumulation des galets Digue basse Epis plongeants From Lyon onwards, the Rhône has been gradually altered to improve flood protection and navigability, and generate hydro-electric power. These alterations have changed the river s transport of sediment, its geometry, and how the river works in general. Fine sediment carried through Arles is estimated at 10 million tonnes per annum, compared with 20 million in the 1950s and perhaps 30 million tonnes per annum at the end of the 19th century. Put in place between 1880 and 1920, the Girardon system, consisting of groynes, cross members and low dykes, reduced the river s width while making it deeper. The consequence of these engineering works was not only to lengthen the period when navigation was possible, but also to cut substantially into the river bed, reduce the diversity of depths, increase deposits of alluvia and sand on the banks, worsen the effects of floods and to cut off the Rhône s secondary branches. The Camargue coast is retreating because river s load of solid matter is taken directly out to sea by the outer branches of the delta, the Camargue being contained by dykes and isolated. Tributaries inflows of solids have been divided by 5, mainly from the removal of aggregates, especially at their mouths, certain HEP facilities, and the reduction of flow speed, which reduces the amount the river can carry. At Saintes-Maries de la Mer, in the Camargue, the German bunker originally built at the top of the beach is now submerged, which provides a measure of how far the coastline has retreated. The Génissiat dam is holding back over 12 million m 3 of various types of sediment 24
Back to the source After more than a century of development work, the Rhône has changed from a multiplecourse system to a channelled river. The remediation work has a number of aims, including to reintroduce and improve the transport of larger sediments, to reconnect and re-supply the cut-off branches (the lônes ), increase the flow in short-circuited sections, rehabilitate river habitats, and to restore fish migration routes. The lônes, cut off from the main river by dykes and flow regulators, fill with sand and silt, leading to the formation of separate bodies of water, ponds and ditches. Dredging the beds and removing some of the dykes improves water flow, recreating the diversity of habitats that is typical of alluvial plains. Other branches of the old Rhône river bed now receive just a fraction of the water they used to. The flow in these short-circuited sections has been increased to improve the ecological system and make a Rhône a swift flowing river once again. These measures are helping to re-establish ecological continuity and encourage fish to spread over a wider area of the basin. It is essential to monitor and analyse the effects of this restoration work to extend it to other sites in the Rhône basin, while taking account of the effects of human activities and climate change on these newly-created habitats. RhônEco (the scientific monitoring of the Rhone rehabilitation work) is a programme run by the aforementioned ZABR as part of the wider Rhône Plan. RhônEco focuses on ecological monitoring of the Old Rhône and its rehabilitated offshoots. It is a long-term research programme that aims to analyse the ecological impact of the rehabilitation, assess their predictability, and in so doing help to determine the river s ecological potential. Before After Since 1995, a hydraulic and ecological remediation programme has been underway, to recreate habitats and to attempt to restore the biodiversity that is characteristic of major central European rivers (Rhine, Rhône and Danube). Since the increase in reserved flow speed from 10 to 100 m 3 /s in 2000 in the Old Rhône around Pierre-Bénite, the relative abundance of some fish species (common bleak, beaked carp, dace) has increased significantly (42% on average). The cut-off branches ( lônes ) are remediated by dredging sediment and opening the channel downstream, and sometimes upstream. Before and after pictures of the Ciseland Iône in the Pierre Bénite area, south of Lyon. The flow in the old Rhône was cut (by 80 to 98%) to supply water to hydro-electricity plants through diversion channels. Old Rhône at Chautagne on the right, diversion channel on the left. Engineering structures and dams on the river have fragmented the water space. The travel of migratory fish is curbed, as in the shad of the Rhône. The Migratory Fish Management Plan implemented in 1993 allows the progressive reopening of migration routes. The zingel asper, the only species endemic to the basin, is no longer recorded in the Rhône itself, being found only in a few tributaries. The remediation of the Old Rhône is helping to safeguard hundreds of other animal and plant species 25