The relevance of mega ponds is seriously disputed by scientists

Are Basins Beneficial to Groundwater? ? A scientific battle is going on over these huge reservoirs to be built in the Marais poitevin. The latest episode in this contest between hydrological experts: the January 30 publication of a counter-report criticizing the expertise of the Bureau of Geological and Mining Surveys (BRGM) is suitable for beds.

Last July BRGM Marais Poitevin published the results of a study he conducted on behalf of the Water Cooperative, the instigator of sixteen future basins. According to this study, winter sampling to fill these reservoirs would have a negligible impact on groundwater and watercourses.

According to this paper, they can even improve groundwater levels by about 6 times during spring and summer %. Some rivers, such as the Mignon, can have a summer flow of 40 % is superior. The results were described as Thierry Boudaud, president of Coop de l’eau without recourse ».

It is important to have a solid scientific basis »

To engage in pedagogy and make it accessible to citizens, it is important to have a solid scientific base and shared knowledge. »he said Western France.

This scientific basis is disputed today by anti-basin collectives in a counter-examination by geoscientist Anne-Morwenn Pastier. This researcher, the author of a dissertation on hydrology and geology, considers the study BRGM messy ; they have methods of presenting non-serious results ».

He denounces a number of prejudices. Primarily used tool: Jurassic groundwater model. It uses unrelated algorithms to analyze hydrological data at the local scale, he said. The author of this Jurassic model notes that it is restricted to large water bodies, like all the Marais poitevin. On a smaller scale, the results are negligible »Anne-Morwenn Pastier assures.

Second bias: margin of error, estimated by 2 centimeters BRGM. Anne-Morwenn Pastier comes to a completely different conclusion. He compared the actual values ​​recorded in the field between 2000 and 2011 with the simulation data: If I had to give an indicative uncertainty value, it would be between 1.20 and 2.2 meters. ». The margin of error is no more than 2 centimeters BRGM.

The researcher also criticizes the information about the Minyon River: When they talk about improving downstream [lorsque la rivière est à son niveau le plus bas] from 40 %, this means going from 0.3 m³/s to 0.45 m³/s. However, a river is considered dry below 0.50 m³/s. Even if the mud is more liquid, we will always have a muddy bed for Mignon. »

the BRGM don’t forget global warming

The latest criticism was already mentioned this summer by the journalist Stéphane Fucard The world : failure to consider global warming in the report BRGM. This was not part of the survey »explains the organization in the email sent Reporter.

Drought episodes as recent as 2022 were highlighted in another paper BRGMcould they have implications for the relevance of these future basins? ? All this depends on the recharge of underground water during winter. ; if rainfall is sufficient in winter, the aquifers are recharged, allowing the aquifers to be supported in case of increased summer drought. In addition, without doubting the future and the impact on groundwater, climate models are now predicting more precipitation than in winter, but with higher temperatures. »concludes the email BRGM.

How does one form an opinion as a neophyte when faced with such differences between two scientific reports? ? True, it is not easy », accepts Anne-Morwenn Pastier. But the researcher hopes his work can help judges in future legal actions by opposition groups.

Especially since he is far from the only scientist who opposes these reservoirs. Many hydrologists and specialists in the water environment have taken a position in recent months. Like Magali Reghezza, a geographer and member of the Supreme Council for Climate (HCC) and Florence Habets, research director CNRS hydrometeorology hydrologists Emma Haziza and Jonathan Schuite or even Christian Amblard, emeritus director of scientific research CNRSspecialist in aquatic ecosystems.

Instead, think in balance between mediums »

A group of scientists is created within the collective Bassines non merci. “ We will try to invent a new scientific paradigm to approach agricultural issues differently. For example, rather than talking about initial volumes, why not think more about the flow and balance of environments ? » Anne-Morvenn Pastier says.

The researcher thereby hopes to put his skills at the service of anti-bass basins away from the university environment. Today, I allow myself to do this because I have given up hope of getting a job as a lecturer. Otherwise, I would be shooting myself in the foot, because in the academic world it is better not to criticize large institutions. »

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