Last Sunday, while walking along the canals in the old town of Annecy, you could see that the water flow of the Thiou river (the river that goes through the old town) was very active ! Indeed, large quantities of water were flowing at a very fast pace.
This is simply because the level of the lake had risen in recent days due to the rains and the gates that regulate the flow of water in the Thiou River were wide open to evacuate this overflow of water. In this way, possible flooding on the banks of the lake can be avoided.
We often don’t know how the level of the lake is regulated and what the Thiou floodgates are used for in the old town, so here are some informations for your general knowledge 🙂
A bit of history :
It was in 1874 that the Thiou floodgates system was set up.
The engineer Sadi CARNOT was its creator. A small anecdote about him : he became President of the French Republic on December 3rd 1887 !
How it works :
The floodgates allow the regulation of the lake level. For example, if the level rises after heavy rainfall, the gates can be opened to release water more quickly and thus prevent flooding. The installation allows 45m3 of water to be discharged per second if necessary. In normal periods, the flow rate is around 8m3 per second.
There are 3 main gates which are essential for regulating the level of the lake, the one on the Perrière bridge, the one on the Albert Lebrun bridge and the one near the Vincenza quay.
There are also other valves, but these are mainly esthetic and less practical. For example, the one located in front of the restaurant l’Auberge du Lyonnais.
Walking tour :
Do not hesitate to walk along the Thiou, it’s a very nice walk to do. It will take you through the old town and through wooded paths that make you forget that you are in town !