After 15 years of existence, what impact do the basins have on natural environments in South Vendée? It is around this question that the evening organized, Thursday October 31, 2024, in Fontenay-le-Comte (Vendée), by the Confédération paysanne de Vendée, Solidaires, the Terres et rivières association and the Vite 85 collective revolved. Vendée has 25 pools under collective management, and a few private pools.
Ahead of the event, Yann Pajot, from the Confédération paysanne, explained that the union is not positioning itself against these substitution reserves, “but the samples must be determined according to the volumes available”. And since the basins are largely financed by public funds, “We believe that it is up to citizens to decide what can and should be irrigated. For example, we think that crops intended for methane digesters should be excluded and crops aimed at food self-sufficiency should be prioritized. »
The effect on waterways, “not easy to say”
Anne-Morwenn Pastier, hydrologist who works for Larouste (radical and oblique emergency laboratory in earth sciences), was invited to present a presentation on the water cycle and basins. To listen to him, more than 150 people came to the OPS room. “What effect do basins have on waterways? It is not easy to say, because there is no flow meter station downstream, to see if there is a better low flow, and if we have not reduced the level of the rivers in winter during filling”, she explained in particular. She cited Autise, “where we have dry spells which can last until beyond November. The water agency tells us that it is a river that is naturally dry. Nobody has data to say yes or no. But the testimonies of the elders tell us that this happened less often in the past. »
Thresholds too permissive?
The scientist also mentions a delay in the recharge of groundwater. It shows a graph, based on data recorded by the piezometers: “If we take the average, we can see that there is a slowdown in recharging in November-December, correlated with the start of filling of the basins,” authorized from 1is November to March 31.
She continues by talking about thresholds, too permissive according to her, “which allow the filling of basins while we are in a state of drought. » She concludes by imagining other filling criteria: “I think we should guarantee maximum recharge of the water table by setting a threshold, and guarantee satisfactory flow in the rivers. If I take these two criteria, I arrive at a cut-off threshold of 5.5 m. That would mean filling the basins every other year, or three years out of five. »
Numerous reactions in the room
Following this presentation, there were numerous discussions in the room, and the debate dragged on until 11:30 p.m. We heard all points of view, notably those of retired farmers, one of whom regretting that the speaker presents herself as an activist. “How can you not be criticized if you present yourself as an anti-watershed activist? Here, the water problem has been tackled head on for a long time. I who thought I would learn things this evening, I learn nothing. »
Others, on the contrary, have found ” bright “ the presentation. Worrying, too. “The priorities were recalled this evening: water for humans, for fauna and flora, and then for agriculture, but perhaps a different agriculture because we are heading towards a dead end,” reacted a man in the room. Another outbid: “We are not saying that we must stop everything, but can we not consider a reduction in the volumes collected? »
Tense exchanges at the end of the evening
Arnaud Charpentier and Fabrice Enon, respectively president and director of the Vendée Sèvre Autise mixed union (owner of part of the basins), were also present in the room. If they welcomed the popularization effort, they also wanted to provide other elements. “Filling only happens when we have reached a threshold, defined with all the stakeholders of the EPMP (Editor’s note: Marais Poitevin public establishment), a agricultural, environmental, community associations… It is not done at will. » They add that “the forecasts we made in 2010 were based on the knowledge we had at the time. With the hindsight we have today, we will inevitably review certain things. »
The discussions ended up taking on the air of an expert debate, on technical points that were sometimes difficult to follow. At the very end of the evening, irrigating farmers spoke, managing with difficulty to make their point of view heard over the invectives of certain people in the public. One of the participants had called, a little earlier, for a calm dialogue to “letting the world of others enter instead of listening with our biases for the sole purpose of reinforcing what we already think.”
The mission was not completely accomplished this Thursday evening.
