User:Marc Dowling/Verdon (river)

The Verdon (Verdoun in Provençal Occitan of Mistralian standard) is a French river which rises at the foot of the Sestrière head, between the Col d'Allos and the Pic des Trois-Evêchés, and flows into the Durance, near Vinon-sur-Verdon, after having covered 166.5 kilometres.

Hydronymy
The name 'Verdon' (Virdones, Viridionis around 1030), called Vardu by the Gauls, came from the pre-celtic term vara, which refers to water.

Geography
In its upper courses, the Verdon looks like a stream and has a steep gradient: at Saint-André-les-Alpes, 45 kilometres from its source, the river's altitude is 900 metres. Downstream from this point, gradually swollen by its tributaries, the Verdon crosses over several mountain ranges through valleys, several of which have been equipped with hydroelectric dams.

The Verdon's sources
The Verdon river originates from the Southern Alps, in the Provence-Alpes-Côte d'Azur region (Alpes-de-Haute-Provence department).

The Verdon is formed by the confluence of three rivers :


 * the Verdon de la Foux, which originates from the Trois-Evêchés mountain;
 * the Bouchier river, from the Mont Pelat mountain range;
 * the Chadoulin, an emissary of the lake of Allos.

Communes crossed
In the three departments of Alpes-de-Haute-Provence, Bouches-du-Rhône and Var, the Verdon crosses thirty-two communes.

Departments that the Verdon flows through
The Verdon mainly flows through the Alpes-de-Haute-Provence department; however, sections of its course serve as a border between the Alpes-de-Haute-Provence department and the Var department (in the Provence-Alpes-Côte d'Azur region of Southeastern France) as the end of the river runs into the Var. The confluence with the Durance is in the Bouches-du-Rhône near Cadarache.


 * Allos, Colmars, Saint-André-les-Alpes, Castellane, Les Salles-sur-Verdon, Aiguines and Sainte-Croix-du-Verdon through the lake of Sainte-Croix, Quinson, Esparron-de-Verdon, Gréoux-les-Bains, Vinon-sur-Verdon (Var), and in the immediate vicinity : Moustiers-Sainte-Marie.

Toponyms
The Verdon has given its hydronym to the following communes, Les Salles-sur-Verdon, Sainte-Croix-du-Verdon, Esparron-de-Verdon, Vinon-sur-Verdon, Artignosc-sur-Verdon, Saint-Laurent-du-Verdon, La Palud-sur-Verdon et Baudinard-sur-Verdon.

Catchment area
The catchment area is 2 218 km2 or 2 294 km2.

Managing body
The managing body is the Parc naturel régional du Verdon, a mixed syndicate and carrier structure of the SAGE of the Verdon watershed.

Main Tributaries
(From upstream to downstream)


 * The Lance (rgnote 1), 12.5 km on the commune of Colmars without tributary.
 * The Issole (rd), 28.7 km at Saint-André-les-Alpes
 * The Jabron (rg), 31.2 km at the Carejuan clue
 * The Bau or Baou (rd), at the entrance to the Verdon Gorges
 * The Artuby (rg), 53.8 km at the Mescla
 * The Colostre (rd), 36.2 km shortly before Gréoux-les-Bains



Hydrology
The Verdon is a very large river, like all the rivers in the Alps. Its hydrological regime is called naive-pluvial.

The Verdon at Vinon-sur-Verdon
Its flow has been observed over a period of 38 years (1969-2006), at Vinon-sur-Verdon, at its confluence with the Durance. The river's catchment area is 2,218 km.

The modulus (the inter-annual (multi-annual) average hydrological flow of a river: it is a summary of the average annual flows ( Q MA ) of a river over a reference period (at least 30 years of consecutive measures) of the river at Vinon-sur-Verdon is 26.8 m3/s. Keep in mind that the river profile has been changed by the series of reservoir dams built on its course.

The Verdon shows seasonal fluctuations typical of a hydrological regime dominated by snow or a snow-pluvial regime. Indeed, two flood periods can be distinguished. The least important is that of the high water in autumn caused by the rains of this season. The average monthly flow rises to 30.9 m3/s in November. This period is followed by a slight drop in flow to 26.2 m3/s in December and 27.4 in February, with much of the precipitation retained in the high mountains from snow. This is followed by a second rise in the regime leading to a second peak - the largest - in April (38.9 m3) and especially in May (47.5 m3).

This was due to the melting of the snow combined with the spring rain. From June onwards, the recession begins, followed by the summer low-water period from July to September inclusive, which brings the average flow to its lowest point in August with a monthly average of 10.2 m3/s. In total, the seasonal oscillations thus appear to be small, since the average monthly flows are all in the range between 10 and 48 m3, but the fluctuations are much more pronounced over shorter periods, and also according to the year.

Water levels
At low water, the VCN3 (the minimum consecutive volume for 3 days, is the minimum flow or low water flow of rivers recorded for 3 consecutive days over the month in question) can drop to 0.060 m3/s in the case of a dry five-year period, which is only 60 litres per second. This is extremely low.

Floods
The floods are generally not very important, and above all they are not comparable to those of the neighbouring Durance or Var rivers. The river is now adjusted to deal with flooding thanks to the series of dams which it has. The millennial floods are estimated at 1,200 m3/s at the confluence of the Durance; however, a flood of 1,650 m3/s was recorded on  November 1st 1843. .

The QJX 2 and QJX 5 are worth 110 and 160 m3/s respectively. The QJX 10 or calculated daily flow of the decennial flood is 200 m3/s, the QJX 20 is 230 m3, while the QJX 50 is 280 m3/s. These flood flows are more or less three times lower than those of the Sèvre nantaise, for example, even though the two basins are very similar in size. However, this means that, for example, every two years a flood of about 110 cubic metres can be expected, and every five years a flood of 160 cubic metres can be expected

The maximum recorded daily discharge was 668 m3/s on 6 November 1994. Comparing this value to the QJX scale of the river, it appears that this flood was more than twice as large as the value calculated for a 50-year flood, and therefore highly unlikely and certainly very exceptional.

Water level and flow rate
All in all, the Verdon is a large river, further supplied by the large amount of rainfall in the region, especially in the upper part of its basin. The water flow in its catchment area is 466 millimetres annually, which is high, largely higher than the average for France as a whole, all catchment areas combined (more or less 320 millimetres), and also higher than the entire Durance catchment area (479 millimetres at Jouques-Cadarache). The specific flow of the river (or Qsp) reaches 14.7 litres per second per square kilometre of basin.

The Verdon has a profile without significant breaks in slope.


 * Upstream of the Foux d'Allos the Verdon has a slope of 175 per thousand.
 * Between Foux d'Allos and Thorame-Haute it is only 28 per thousand.
 * From Thorame-Haute to Rougon the slope is 8.9 per thousand. And 6.5 per thousand between Castellane and Rougon.
 * Between Rougon and the exit of the Gorges du Verdon (i.e. an average over all the gorges), at the level before the Sainte-Croix dam, the slope is 7 per thousand (compared to the previous 6.5 per thousand), admittedly low but with steeper sections.
 * Up to Quinson it is only 4.1 per thousand.
 * The Verdon has a gradient of about 3.4 per thousand from Quinson to the confluence.



Ecology of the river
Despite the segmentation of the river by dams, the Verdon is home to a lot of fish and invertebrate species. The trout densities are very reasonable, and make the Verdon one of fishermen’s favourite destinations in the Var. In addition, a population of Apron du Rhône (Zinger Asper, protected species, IUCN red list) in the Grand Canyon (Verdon Gorge) has been the subject of a Biotope Protection Order since 2012, covering 17 km of watercourse. A population of sculpins, also protected, has been discovered in the commune of Gréoux-les-Bains.

The ecological balance of the river is however strongly affected by the hydroelectric works of the Verdon itself, but also of the Durance. This prevents the upstream migration of anadromous species such as salmon or eels, and fragment the populations of other species. Also, the control of the flow limits the solid transport and the remodelling of the bed of small and medium amplitude floods. However, the increase in 2012 of the instream flows downstream of the Chaudanne and Gréoux reservoirs has improved the dynamism of the Verdon's aquatic ecosystems.

The white-footed crayfish, formerly present on all the waterways of the catchment area, has seen its range greatly reduced following the introduction of exotic species, which are more competitive and sometimes healthy carriers of aphanomycosis (or crayfish plague). However, it is still present in some tributaries.

From a plant point of view, the Verdon riparian zone has a wide variety of facies, with Alpine and Mediterranean influences.

The pronounced green colour of the Verdon is due to the fluorine and micro-algae it contains. However, in the reservoirs (Sainte-Croix or Quinson, in particular), its waters have a turquoise colour due to the clayey bottom.

History
The Verdon, whose course is mainly marked by the existence of narrow and deep gorges, has generally played a role as a border rather than a transport route throughout history, like the Durance of which it is a tributary. As such, the river still marks the boundary between the departments of Alpes-de-Haute-Provence and Var. Finally, it is notable that part of the Grand canyon du Verdon was only explored in the 20th century.

Prehistoric times
Nevertheless, like many rivers, the Verdon has attracted man since prehistoric times: traces of human occupation from the Paleolithic era were found on the lower Verdon, it is especially the Neolithic era that has delivered large quantities of material now mainly preserved in the Museum of Prehistory of the Gorges du Verdon, in Quinson.

During protohistory, the upper Verdon was part of the Alpine area, while the middle and lower Verdon were part of the Mediterranean area of Provence.

Antiquity
Some names of peoples from this period are known: the Gallitae or Gallites (literally "little Gauls") in Allos (at the sources of the Verdon), are probably Gaul s from Cisalpine Gaul - Umbrians -; the Sueters populate the Verdon valley in the Alpes-de-Haute-Provence; the Reii, who gave their name to Riez, their capital, are the most commonly found ethnic group north of the lower Verdon.

It is especially on the course of the Colostre, a tributary of the Verdon, and from this last oppidum that an important human occupation seems to have developed: not far from Saint-Martin-de-Brômes, the oppidum of Buffe-Arnaud dominates the strategic confluence of the Colostre and the Verdon. The latter site was excavated during the rectification of the departmental road 952 in 1992 and has notably revealed a fragment of a Latin bracelet in the plastic style. Riez remained an important city in Roman and early Christian times: the ruins of a Roman temple and an octagonal baptistery bear witness to the past splendour of this city, which was then linked to Aix-en-Provence by the via sextiana.

Middle Ages
In the Middle Ages, the Provençal noble families of Simiane, Pontevès and Sabran shared the ownership of the Verdon villages with the bishops of Riez.

Tourist Economy
L The Verdon territory saw significant economic change in the second part of the 20th century. The construction and impoundment, between the Second World War and 1975, of the five hydroelectric dams that form two sets upstream and downstream of the gorges, coupled with the advent of mass tourism, caused a sudden shift from a rural economy based on agriculture (breeding/trufficulture) to an economy focused on tourism. The Maison-Musée du Haut-Verdon, in Colmars, presents tourists with the life and objects of the Haut-Verdon, from the 17th to the 19th century.

Main tourist activities: Haut-Verdon/Val d'Allos: high winter attendance (winter sports), hikers in summer Moyen-Verdon: Outdoor activities: Hiking, Rafting, Kayaking, Water hiking, Hydrospeed on the Verdon; Canyonning in the tributaries (Bau)), Hiking, Camping-car, Motorbike. Lac de Sainte Croix : Swimming, sailing, pedal boats Bas-Verdon : Fishing, spa.

The Gorges du Verdon
The Gorges du Verdon is a major tourist attraction in Provence. Its most prominent course, the "Grand canyon of Europe", is between Castellane and the lake of Sainte-Croix.

Hydroelectric development
The Verdon is now called the  of the Bouches-du-Rhône and Var departments by Électricité de France: five dams were built on its course to supply water to lower Provence for irrigation and drinking water production.

Upper Verdon
The Verdon upstream from Saint-André-les-Alpes. This corresponds to the current canton of Colmars-Allos (and the Communauté de communes du Haut Verdon-Val d'Allos); the Verdon rises in the commune of Allos, and, up to Thorame-Haute, the limit of the Haut Verdon, crossing Villars-Colmars, Colmars-les-Alpes, Beauvezer, the hydraulic installations have remained modest, compared to those set up downstream. There were mainly a few sawmills which were also used to produce electricity at certain times or to drive a grain mill. These installations disappeared completely with the appearance of the nationalised public service company EDF.

Middle Verdon
The Middle Verdon begins in the communes of Allons and La Mure-Argens (canton of Saint-André-les-Alpes) and corresponds to the Communauté de communes du Moyen Verdon.

The development of the Middle Verdon was the first to take place: it was done gradually.

Between 1928 and 1932, the Société hydroélectrique du Verdon (SHV) was responsible for the Castillon and Chaudanne worksites and benefited from the reparations owed by Germany after the World War 1 for this task. Following the bankruptcy of the company in 1932, the work was interrupted until 1938, when it was resumed, first temporarily under the leadership of the Énergie électrique du littoral méditerranéen (EELM), then definitively from 1942.

Finally, the Castillon dam, the furthest upstream, was impounded in the spring of 1949: it created a reservoir of 5 square kilometres and 150 million cubic metres, 85 of which were reserved for agriculture.

Downstream, the Chaudanne dam, was built during the winter of 1952 by Électricité de France (EDF): located in a lock of the Victoire massif, it is mainly used to regulate the water flow.

Lower Verdon
On the lower Verdon, the planning phase began in 1926. The development of the river is inextricably linked to that of the Durance in which the Verdon ends its course. .

In 1957, the Société du Canal de Provence (S.C.P.) was created: from 1963, a power station was built by E.D.F. at Vinon-sur-Verdon and a dam was built upstream of the commune of Gréoux-les-Bains. The Gréoux dam is useful for hydroelectric production, but also for supplying water to the Provence canal.

It gave birth to the Gréoux reservoir, commonly known as "Lac d'Esparron", which was impounded in 1967.

Finally, the construction of the Sainte-Croix dam, in the Baudinard-sur-Verdon valley, began in 1970: the reservoir of the same name (the "Sainte-Croix lake") was impounded in 1975 and covers a surface area of 22 square kilometres to store 760 million cubic metres of water, 140 of which are reserved for agriculture.

Sainte-Croix is the second largest artificial lake in France (after Serre-Ponçon). Under its waters are the Fontaine-l'Evêque spring (the first spring in France), a number of archaeological sites (the results of emergency excavations undertaken before the water was put in can be seen at the Musée de la Préhistoire des Gorges du Verdon in Quinson) and the village of Les Salles-sur-Verdon, which was rebuilt further up. Twenty-five additional kilometres of road and two bridges had to be built to facilitate traffic on both sides of the reservoir.

Also in 1975, a final dam was completed at Quinson: it replaced a previous 15-metre high structure that had been completed in 1869 to irrigate the plain of Aix-en-Provence via the old Verdon canal and gave rise to the Quinson reservoir, sometimes called the "Lac de Montpezat". The main role of the latter is that of a compensation basin for the Sainte-Croix dam.

The Verdon: Water from Marseille, Aiz and Toulon
The Canal de Provence brings together all the hydraulic works that participate in the supply, mainly with raw water captured in the Verdon, of 110 municipalities in the Bouches-du-Rhône and Var regions, including Aix-en-Provence, Marseille, and Toulon, for a total population of over 2,000,000 inhabitants. It irrigates 70,000 hectares of agricultural land and supplies more than 8,000 industrial sites in the region. With a length of 270 km, 140 of which are underground, the canal, designed and built progressively from the 1960s onwards, has avoided the effects of drought in the departments it serves, thus contributing to their economic development.