THE RHÔNE DELTA a Case Study

THE RHÔNE DELTA – A Case Study

The Rhône River is one of the major rivers in Europe. It rises as an effluent of the Rhône Glacier in Valais, Switzerland, before passing through Lake Geneva and running through south-eastern France. 4 km north of Arles, near its mouth on the Mediterranean Sea, the river divides into two distributaries, known as the Grande Rhône and Petite Rhône. The eastern branch - Grande Rhône is larger and carries 85% of the Rhône’s water into the north-western Mediterranean. At Arles, the river is only 2 metres above sea level and takes almost 50 km to reach the sea. The resulting delta, located between the 2 branches, constitutes the Camargue region. The Rhône as it flows from Valais into Lake Geneva

The delta is criss-crossed by numerous small islands, abandoned channels and active levees. Most of the settlements and transport are located close to the river, where the land is slightly higher. Further away from the river the land is lower, swampy, and frequently covered with water. The same pattern exists along the western branch - the Petite Rhône.

Between these two limbs of the Rhône is a flat region characterised by many marshes and salt water lakes (étangs), known as the Camargue. This is the main part of the delta – a marshy island bounded by the two branches of the Rhône and the Mediterranean Sea. To the west of the Petite Rhône is the Petite Camargue - a smaller but similar area. The largest lake is the Étang de Vaccares, which is less than 1 m deep. The étangs receive most of their water from rainwater that becomes trapped between the slightly higher riverine locations and the sand bars and dunes at the coast.

Deltas are geologically young landforms. Present-day deltas began forming no more than 7,000 years ago, when sea levels stopped rising after the last ice age ended. Over Earth's history, as sea levels have risen and fallen in response to glacial periods, deltas have formed and have been covered over. The current deltas of some rivers are built on the remains of numerous deltas stretching back millions of years. Yet their surface can change rapidly and significantly. The Rhône delta is believed to be less than one million years old. The key to the creation of a delta, and its continual formation, is a river and the sediment it transports. Deposition by the river is estimated to be 17m³annually (about 50 tonnes per minute). As the Mediterranean Sea has a small tidal range, there are no currents to carry away these deposits. In addition, the Mediterranean is very saline. Thus, flocculation occurs with clay and mud particles coagulating and sinking to the bottom. Thus, there is rapid deposition at the mouth of the delta. There are a number of stages in the formation of a delta. The first is the development of sandbanks in the original mouth of the river. This causes the river to divide into distributaries. Following this is a phase of repeated subdivision until there are a large number of distributaries flowing towards the sea. Each of the channels develops its own set of levees, which has an impact on the human environment (settlement and transport) as well as the physical environment (affecting the development of étangs between the main branches of the river). The étangs may slowly accumulate sediment to form marshes, or they may be drained and reclaimed to form farmland or used by people in other ways.

Importance of the Rhône Delta

With an area of over 930 km² (360 sq. miles), the Camargue is Western Europe's largest river delta, with exceptional biological diversity, and home to unique breeds of Camargue Horses and Camargue Bulls, and to more than 400 species of birds including Pink Flamingoes.

One part of the delta has been set aside for a nature reserve, thereby protecting the feeding and nesting grounds of flamingos, egrets, ibis, and other rare species. Since 1962 the left bank of Fos has been transformed into a vast industrial complex consisting of port facilities, refineries, oil-storage tanks, and steel mills.

In the past, the étangs used to collect water from regular flooding of the River Rhône (before a sea dike was built). Today it collects the runoff from the surrounding rice paddies. Its exposure to sun and wind make it an efficient water purification system. The area is important for avifauna like coots, diving ducks and fishing birds such as grebes, terns, seagulls. Other Ponds and marshes cover a large part of the river delta. Marshes are subject to the vagaries of the Mediterranean Climate and may dry up in summer. Ponds are the habitats of choice for migratory and sedentary birds including egrets, night herons, bitterns, mallards and wagtails as well as numerous insects.

The north of the Camargue is mainly agricultural land. After the Second World War, the northern marshes of the Camargue were drained and then irrigated with fresh water. The main crop planted, rice, was so successful was it that by the 1960s the Camargue was supplying three-quarters of French demand for rice.

Vines were also reintroduced after the war. They are unique in France in surviving the Phylloxera pandemic that destroyed all the other vineyards in France in the nineteenth century. (So all other existing French vines are derived from rootstocks re-imported into France). The reason that these vines survived the disease is that their roots and stems were under water. Other crops include wheat, rapeseed, grapes and fruit orchards.

The centre and south of Camargue is a more natural area, characterised by a brackish saline ecosystem. Flora of the Camargue is adapted to these conditions. Sea lavender and glasswort flourish along with tamarisks, reeds, juniper trees, wild irises wild rosemary. The juniper trees growing to a height of 6m form the woodland on the islands between the Étang du Vaccarès and the sea (Bois des Rièges). The salt water lagoons are surrounded by sand dunes. Originally sculpted by the wind they are now man- made and are where salt is produced - dried by the sun and wind in immense spaces called "salins". This salt was a source of great wealth for the so-called "salt abbeys" of Ulmet and Psalmody in the Middle Ages. The salt industry started up again in the nineteenth century and large chemical companies founded the salt extraction city of Salin-de-Giraud. Today, evaporation pans at Salin-de-Giraud - the largest in Europe - extend over 11,000 hectares and produce some 1,000,000 metric tons a year,

Those aalt marshes near Salin-de-Giraud in the southeast corner of the Camargue are famous for their salt production, producing up to 15,000 tons a day in the summer. Salt is produced along the final stretch of the Grand Rhône, an industry that dates back to Romans times (first century AD). This is one of the biggest salt works anywhere in the world. Some is used as table salt. Fleur De Sel de Camargue ("flowers of salt") is hand raked and harvested. Only the premium, top layer of the salt bed is used for this. The name Fleur De Sel comes from the aroma of flowers - violets in particular - that develops as the salt dries.

Sodium and chlorine from the salt are used in many chemicals and pharmaceuticals. Low-lying salt plains (sansouires) dry out and crack in summer. They are carpeted with glasswort (grazed by the wild bulls and Camargue horses). These plains are submerged in winter but in the spring they re-emerge as wetlands for marsh birds such as black-winged stilts, godwits, and sandpipers.

Tourism is a major source of income. The Camargue is visited by over one million tourists each year.