The Water Slope at Montech: A Technical One-Off

Pente d’eau at Montech waiting for the boat’s arrival

I recently found some photos from an outing several years ago to Montech, southwest of Montauban. The town is on the plain between the River Tarn and the River Garonne. We went to see a pente d’eau (water slope, for want of a better phrase) that was designed to bypass the existing lock system on the Canal de Garonne.

Until superseded by the railway and then by roads, the canal system in France, as in the UK, was a principal means of transporting goods. Most rivers were usually too fast-flowing, too shallow or simply too unreliable for the purpose. The problem with canals was the natural slopes that had to be negotiated by means of locks. This was time-consuming and caused long traffic jams.

The Canal de Garonne was constructed in the 19th century to connect the Canal du Midi at Toulouse with the Garonne south of Bordeaux. At Montech, five locks had to be constructed to negotiate a slope of 13m30 on the canal. They took just over an hour to get through in order to travel a few kilometres. Until about 1970, the canal was still mainly used for commercial traffic. After that, it became largely the preserve of pleasure boats and tourism.

The canal was upgraded in the 1960s to cope with larger boats. All the other locks on the canal were converted to a length of 39m (the Freycinet gauge – gabarit Freycinet) but the five at Montech retained the old gauge of 30m. At Montech, the engineers decided to experiment with a revolutionary technique to circumvent the lock system.

One of the engines

They created an artificial channel parallel to the existing lock, following the natural lie of the land. Two gigantic engines – effectively diesel locomotives – pull between them a watertight barrier that pushes a triangular wedge of water before it on the ascent and retains it on the descent. A boat or barge floats on the water and passes up or down the slope in 20 minutes, thus saving about 45 minutes on the original journey through lock system. It is reserved for boats of 40-50 metres in length. Smaller pleasure boats still have to pass through the locks.

Ringside seats to see the system in action (not us, by the way)

The system went into service in July 1974. Apparently, it is unique. When we visited, we saw it in action aboard a boat. The guide told us that other places had copied the technique but hadn’t been able to make it work. According to a local magazine, scientists the world over have visited. A delegation of Chinese engineers even came to look at it with a view to using the technique on their own waterways.

As I understand it, la pente d’eau has been out of action for a couple of years to enable repairs and maintenance to take place. But you can still enjoy a cruise on the canal and see the machinery in place. Go here to find out more.

Copyright © 2012 Life on La Lune, all rights reserved


    • I’m sorry, I don’t know. This post was written in 2012 and that was at least 3-4 years after we had visited. According to a newspaper article that I have just consulted on the internet, the pente d’eau ceased functioning in 2009 and it was still not back in service in February 2015, since funds were being sought for its repair. I would be surprised, frankly, if they had managed to get it back in service.


      • I was just curious, as I have been studying the Mississippi River and Tributaries system here at the New Orleans District Corps of Engineers and found it interesting that there hasn’t been an attempt, that I know of through my limited research, to use a gateless lock system here in the United States. I am finding the struggle between mankind and the environment very fascinating these days.

        Liked by 1 person

        • I know nothing about the technology or how it works, but, as I said in the post, it has been tried in other places but the one in Montech was the only place they could get it to work. And now, it seems, it has not been in operation since 2009. Good luck with your researches.


    • It seems like many of America’s greatest lessons have somehow involved France which is why I have started taking a look at French water control structures. Not to mention the fact that France is just slightly older than the United States. I was looking at some of the French websites and sent a text message to a colleague asking if she could read French, being that she lived in Canada for some time. I am beginning to think that it might be in the best interest of my family to start looking at choosing a second language that we can all agree on as worth learning. Maybe French is the language that I have been looking for. My family and I have certainly been enjoying the French influences here in the New Orleans area. Thank you for responding to me and if you don’t mind I would like to share some of your material with my wife and family.



      Liked by 1 person

      • Learning a foreign language is always rewarding and maybe French is a good option as you are in the New Orleans area. By all means share my posts with your family – it’s a public blog, so I have no objection.


    • It would be interesting to know if the technology is transferable. As I understand it, the mechanism has been out of action for more than 2 years for repairs, so maybe it isn’t terribly reliable in the long term.


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