What is this “ticklous” river from Loire-Atlantique which measures only 52 km?

The commune of Machecoul-Saint (Loire-Atlantique) is crossed by a river … and yes, it is the Falleron.

If the Falleron is not listed in the smallest French rivers, the shortest making 1 km, it only travels 52 km away. It takes its source at an altitude of 59 meters in the town of Grand’Landes (Vendée) and it flows into the Atlantic Ocean at the wearing of the Collet in Baie de Bourgneuf. He is the main outlet for the Breton marsh.

In Machecoul, the 3.3 km of the brought channel connect the right bank of the Falleron to the left bank of the outfit. Thanks to pumps and locks, water levels can be held in the Breton marsh during dry periods.

The slope of the outfit is so weak that fresh water can be diverted from the Loire at high tide as far upstream.

The pumping station From Pommeraie, built in the 1960s, raised the water from the last three meters of the hold at Falleron. But the brought channel also serves to evacuate Machecoul water during the periods of intense rains.

A very fluctuating flow

For its part, the Falleron has the distinction of “reacting” to the slightest drop of water. Falleron’s “tickling” character requires a anticipation From the management of water levels in the marshes to the collar.

This small river could even be described as “milk soup”. At the slightest rain, he quickly rushes into flow and the next moment (in a few hours), he finds a normal flow at low.

As emphasizes Olivier FandardCoordinator Territorial Contract Water Finished: “After 15 months of rain and floods at more than 30 m3/second in Saint-Etienne de Mer De de de de de de de de de de de de de de Merne De de de de de de de de de de de de de de Mémie. »»

These figures are even more telling by converting them: from 30,000 liters per second, the volume of water in flow rose to only 200 liters per second.

Already close to the alert threshold

Knowing that the rain stopped at the end of February 2024 (in March, only 13 mm were recorded and 13 mm for early April), the Falleron flow is already approaching alert threshold which is 120 liters per second.

Obviously, the Falleron lives according to rainfallbut with the particularity of having very sensitive levels.

“Rainwater arrives very quickly in the river,” explains Olivier Fandard. A river is fueled by its sources and wetlands. Spatial planning of recent decades has impacted more than 65 % our wetlands thus depriving the capacity to retain water and to return it to the river. »»

The fifteen months of rain do not make sure to have water in the Falleron in sufficient quantity and the flows of the river remain under surveillance.

To find out more, conference “L’Eau à Machecoul-Saint-Saint” Tuesday April 20 at 8 pm at Espace en Retz.

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