350 years after it was designed, the system created by Riquet still remains a masterpiece in hydraulic engineering!
To supply a summit-level canal such as the Canal du Midi, significant water resources are needed. These resources need to be at a higher altitude than the highest point of the waterway.
All the earlier projects for a canal ran into this tricky problem, and none of them found a solution. They all proposed to use the big rivers that flowed down from the Pyrenees (Garonne and Ariège) to provide water for the canal.
This solution seemed viable, but it was not an easy task to channel the water collected to the Col de Naurouze, the highest point of the canal, at an elevation of 189 metres. The various projects were abandoned because they were either technically impossible or extremely costly.
In the 1650s, two people looked into the advantage of using the smaller rivers of the Montagne Noire region, in the foothills of the Massif Central. You would be right to assume that one of these people was Pierre-Paul Riquet! The other was Thomas de Scorbiac.
They both recognised the benefit of the Montagne Noire region: the mountains were not as high as in the Pyrenees and the rivers and streams much less dense! This would make it easier to channel water resources.
Scorbiac and Riquet had learnt from earlier proposals and both planned on using the waters of the river Sor. But Riquet took this a step further and put forward a proposal that was much more comprehensive than Scorbiac's.
Riquet did not simply make do with the water from the Sor, he also planned on diverting the rivers from the Mediterranean basin in the Montagne Noire region. In his study, the waters of the Rieutort, Lampy, Bernassonne and Alzeau could easily be diverted using a man-made channel in the Sor valley, on the Atlantic basin side.
Between 1648 and 1660, Riquet and his family lived in Revel. This was most likely when Riquet explored the nearby Montagne Noire region.
Some believe that he rode the paths of this mountainous region with the son of Revel's fountain engineer, but another theory seems to be more plausible.
In the grounds of his residence, the Château de Bonrepos, near Toulouse, Riquet studied his hydraulics ideas. Using the various bodies of water on the estate, he carried out some small-scale experiments to see whether they would be feasible on a larger scale.
I'm sure you agree that rushing into such a mammoth and costly project such as the Canal du Midi without studying it in detail beforehand would be completely crazy! And Riquet was not the sort of man to risk his honour, which is why he carried out these meticulous studies. The ingenuity of the solutions Riquet came up with, combined with the complexity of the supply system topography, made the Canal du Midi a masterpiece of hydraulic engineering.
The project that Riquet presented to Colbert on 15 November 1662 was based on the creation of two sections of a man-made channel:
- The Rigole de la Montagne channel: at 500 metres above sea level, this channel diverts the waters of the Mediterranean basin in the Montagne Noire, from Alzeau to Conquet.
- The Rigole de la Plaine channel: after flowing across the watershed point between the Atlantic and Mediterranean basins, the water ends up in the Sor valley. It is then collected from the Sor, upstream from Revel, and channeled to the watershed point.
To make up for the scarce water resources in summer, Riquet planned on building a dozen small reservoirs. Riquet called them 'magasins d’eau' (water storehouses) or provision basins.
In the end, these small basins were replaced by one single, vast reservoir on the Laudot river, a tributary of the Sor, at Saint-Ferréol.
Colbert was interested in Riquet's project. He was aware that the construction of such a canal would turn France into an economic power, therefore gaining an advantage over Spain in particular. Louis XIV appointed a commission of experts to study the feasibility of the project.
This commission may have issued a favourable response as to the feasibility of the project, but there were still some underlying doubts about the possibility of getting water from the Alzeau to the Seuil de Naurouze, the highest point of the canal.
Riquet was determined to win over the commission and show them that his project was completely viable, and so he offered to build a trial channel, at his own expense. In July 1665, his excavation teams began digging a small canal. In October, the waters from the Alzeau were flowing at Naurouze. Riquet's gamble paid off. There are still some remains of this trial channel which was built just above the channel that is now used to supply the canal.
Construction work in the Montagne Noire region began with the 'Montagne' and 'Plaine' channels. In April of the same year, the foundations began for Saint-Ferréol dam
Riquet sent boats to sail along the Rigole de la Plaine channel
The water supply system was operational and the first navigation trials between Naurouze and Toulouse were carried out. Saint-Ferréol dam was filled with water for the first time, but it wouldn't be finished until 1680.
Saint-Férréol dam was raised to increase its capacity. To fill the dam, the Rigole de la Montagne channel was extended by five kilometres from Conquet to Cammazes where it crosses over a ridge line via a tunnel and then rushes down from the Laudot source.
Another reservoir was added to the Montagne Noire water supply system at the Lampy river, to supply the Canal de Jonction and the Canal de la Robine in Narbonne.
This system was made all the more complex in 1950 when new reservoirs for the production of drinking water and farming irrigation were built. These reservoirs are connected to the hydraulics network of the Canal du Midi water supply system.
Over 350 years after its creation, Riquet's water supply system is now fully integrated into a vast network of water that now has a wide range of different uses!
The Rigole de la Montagne, at an elevation of between 650 and 550 metres, collects the waters from the Mediterranean basin in the Montagne Noire region.
The Rigole de la Montagne originates from the streams on the south side of the mountain, and then flows into a waterway on the north side, the Sor, in the hamlet of Le Conquet, at 'Le Saut du Sor'. Once the Sor has been filled with the waters from this channel, the waters are deviated to the Rigole de la Plaine channel at the town of Sorèze, supplying water to the town of Revel and the Seuil de Naurouze.
In 1689, Vauban improved the canal and the water supply system. He connected the Rigole de la Montagne to Laudot stream via an underground route he called the Voûte Vauban in today's town of Cammazes.
Saint-Ferréol reservoir is at an elevation of 350 metres and has the capacity for 6,300,000 m3 of water!
This unique reservoir lake is used to supply water to the canal in periods of drought.
Saint-Ferréol reservoir lake gets its water supply from Laudot stream, and is then joined onto the Rigole de la Plaine channel, to supply water if needed at a place called 'Les Thoumazés'.
Did you know?
In the 19th century, an ornamental garden was created at the foot of the dam, and the highlight of this garden was a water jet that used the waters from the reservoir. This jet and a waterfall are still popular attractions here today.
The Rigole de la Plaine (at an elevation of between 245 and 189 metres) is used to carry water to the Seuil de Naurouze.
The channel begins at Pont-Crouzet and then collects the waters of the Sor, then the Laudot and channels this water as far as Naurouze. The total length of the Rigole de la Plaine is 38.120 km, and it is approximately 2 metres wide.
Upstream, a second channel then takes the water up to the highest point of the Canal du Midi, the Seuil de Naurouze. At this watershed point, using the force of gravity, water flows west towards Toulouse, and east towards the Mediterranean.
In 1672, after 5 years of construction work, the system was almost completed. Water from the Montagne Noire could be channeled as far as Naurouze, the canal's watershed point.
(1) Alzeau water inlet.
(2) Lampy: The engineer Garripuy created the Lampy Neuf dam (reservoir with a capacity of 1.6 million m3 of water) upstream from the former Lampy Vieux dam, to increase the water reserves. This 2nd reservoir was created in 1782 to supply the Canal de Jonction which connects the Canal du Midi to the Canal de la Robine de Narbonne, providing a second access to the sea.
(3) Le Conquet: Passage from the Mediterranean basin to the Atlantic basin. There is a sluice gate to control the flow from the Rigole de la Montagne, and excess water is directed towards the Sor.
(4) Cammazes Dam on the Sor, was built in 1956 by the 'Institution Interdépartementale d’Aménagement Hydraulique de la Montagne Noire'. It has a storage capacity of 20 Mm3. It is supplied with water from the Sor and the channel at the Conquet weir. By decree, VNF holds the rights to the water of Cammazes Dam to supply the Canal du Midi. Its main purpose is to store water for domestic consumption and for crop irrigation.
(5) Les Cammazes: the Voute de Vauban or Cammazes tunnel was created by Vauban. It allows the Rigole de la Montagne channel to reach Laudot stream in another basin.
(6) Saint-Ferréol Lake supplied by the Laudot, which in turn is supplied by the waters of the Rigole de la Montagne channel.
(7) Pont Crouzet, in the foothills of the Montagne Noire, is where the water inlet for the Sor is located.
(8) Les Thoumasés: The Rigole de la Plaine channel and Laudot stream merge here. There is a spillway to evacuate excess water into the Laudot towards the Atlantic basin. The water needed to supply the Canal du Midi is directed to the Rigole de la Plaine channel towards the Mediterranean basin.
(9) Seuil de Naurouze: This is the highest point of the canal route. The Rigole de la Plaine flows into the Canal du Midi here.
The Montagne Noire network supplies water to the section of the Canal du Midi between Toulouse (Ponts-Jumeaux) and Carcassonne (Villedubert lock), covering a distance of 109 km (52 km for each basin and 5 km for the summit pound). The total capacity of the canal pounds is 3.65 Mm3.
It should be noted that the Montagne Noire channels are not the only water source for the canal. As I'm sure you're aware, this wouldn't be enough bearing in mind the water needed for the section that leads towards the Mediterranean (downstream from Carcassonne).
There are four extra water inlets from rivers, to supply water to the canal from Carcassonne to Béziers (99 km) as well as for the Canal de Jonction (5 km).
The capacity of the canal pounds is 3.3 Mm3, for this part of the Canal du Midi and 0.165 Mm3 for the Canal de Jonction.
- Lachaux water inlet on the Fresquel in Villemoustoussou, now abandoned.
- Villedubert water inlet on the Aude, in Villedubert
- Orbiel water inlet on the river Orbiel in Trèbes
- Cesse water inlet on the river Cesse in Mirepeisset
These water inlets are the finals additions to the water supply system:
The water inlet at Pont-Rouge dam in Béziers
On the left banks of the Orb, this water inlet provides any additional water needed from Béziers onwards.
Agde water inlet at the Prades lock
On the left banks of the Hérault, this water inlet provides water for the section from Agde to Thau Lagoon.
Moussoulens water inlet
On the right banks of the Aude, this water inlet supplies the Canal de La Robine.