Archive | December, 2014

An afternoon out in The Black Mountains

24 Dec

As all is quiet here and all the shopping has been done, we decided to take a drive up into The Black Mountains to the source of the river Alzeau (called in French le prise d’Alzeau). It’s a lovely spot, very quiet, apart from the roar of the water, that is!

The river flows on but the feed-off to the right is supplying the small canal (or rigole in French) that feeds the Canal du Midi

The river flows on but the feed-off to the right is supplying the small canal (or rigole in French) that feeds the Canal du Midi

This is part of the feeder system for the Canal du Midi which is located in the south of France in the departments of Hérault, Aude, and Haute-Garonne. Its course runs for 241 kilometres between Marseillan, at a place called Les Onglous where the canal opens into the étang de Thau near Sète and Toulouse at Port de l’Embouchure (Twin-Bridges).

The Canal du Midi is a summit level canal with a slope located on the Atlantic side with a length of 57 km and the other on the Mediterranean side with a length of 189 km. The Seuil de Naurouze is the highest section (TheCanal pound).

The canal depth is 2 m on average with a minimum of 1.8 m. The draft allowed is 1.6 m although regular users advise that 1.4 m is already a lot because of mud in some places. The width on the surface is 20 m on average with variations between 16 m and 20 m. Finally, the width of the bottom of the canal is 10 m.

Compared to canals, managing rivers is difficult but only one canal is required between the Atlantic Ocean and the Mediterranean Sea. Unlike a river it is easier to manage the flow of a canal to ensure a constant flow of traffic throughout the year.

The Canal du Midi is a Summit level canal because it must pass over a height between two valleys. Indeed, the construction of this canal required passage through the Seuil de Naurouze or the Seuil de Graissens.

This is the feeder

This is the feeder

In 1660, Riquet found the solution to the main problem: the water supply to the summit point to feed both sides of the canal. His idea was to get water flowing from the Black Mountain. His important knowledge of the hydrography of the Black Mountain and Sor allowed him to imagine an ingenious irrigation system. He was inspired by the French engineer Adam de Craponne who had implemented the same system for the Craponne Canal.

The river Alzeau is flowing quite fast

The river Alzeau is flowing quite fast

For this he planned to recover the mountain waters in dams and reservoirs and then forward them to the Seuil de Naurouze through channels crossing the Seuil de Graissens. The water from the Sor passing near Revel was the main supply envisaged by Riquet. Other rivers from the Black Mountain were also part of the system such as the Alzeau, the Laudot, the Rieutort, the Bernassonne, and the Lampy.Indeed, Black Mountain is a region with twice the rainfall of the plain of Lauragais with 1400 millimetres per year at around 500 to 600m above sea level. To store the river water he planned to create three basins: the Reservoir of Lampy-Vieux, a hexagonal harbour basin at Naurouze, and the Bassin de Saint-Ferréol with a large earth dam across the mouth of the valley of the Laudot stream.

In 1664, during the study of the project, the Estates of Languedoc asked Riquet to put into practice his idea experimentally. He then built a test channel diverting water from the Sor to the Seuil de Naurouze. It was the Rigole de la plaine which he completed in 1665 and used to prove that it is possible to bring water to the highest points of the course of the canal. This was the event that reassured the Committee of Experts that the king had set up on site to inspect the choices and plans prepared by Riquet. From that moment Louis XIV knew that the canal was technically feasible.

At the age of 63, Riquet started his great enterprise in the Montagne Noire to work on the water supply. This supply system successfully fed the canal with water where it crossed the continental divide, replacing water that drained toward the two seas. The system was a masterpiece of both hydraulic and structural engineering.

Work began on the first “enterprise” on 1 January 1667 with the construction of the trough of the Rigole de la plaine then continued on 15 April 1667 with the laying of the first stone of theLac de Saint-Ferréol. No reservoir-lake of this magnitude had ever been built before.

They built a huge dam for the single reservoir, the Bassin de St. Ferréol, on the Laudot river which is a tributary of the River Tarn in the Montagne Noire some 20 km from the summit of the proposed canal at Seuil de Naurouze. It was connected to the Canal du Midi by a contoured channel over 25 km long, 3.7 m wide with a base width of 1.5 m (4.9 ft). It was eventually equipped with 14 locks in order to bring building materials for the canal down from the mountains and to create a new port for the mountain town of Revel.

In November 1667 an official ceremony laid the foundation stone of the Garonne lock in Toulouse. A first filling of water was made between the seuil de Naurouze and Toulouse during the winter of 1671-1672 and the first boat traffic could begin. In 1673 the section from Naurouze to Trèbes was completed marking the end of the first “enterprise”.

From 1671 the second enterprise began linking Trèbes to the Mediterranean Sea and to build the port of Sète (then called Cette.

In 1681 work on the canal ended at Béziers. However, in October 1680, Riquet died during construction. He did not see the end of the project.

Sorry we’ve been quiet of late

11 Dec

It’s been a really busy time what with travelling to and from the UK and organising the volunteers. But we are having a ball.

We will be blogging again soon so watch this space. Tomorrow we’re off to l’Herault for a long weekend.

Meanwhile here’s a photo of Trish with her first banana cake!

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