“
The French nation must continue to invest in hillside retentions
”.
This technical term, used by Emmanuel Macron at the Agricultural Show, probably does not speak to many French people.
To be precise, the exact term is “hill reservoir”.
These artificial water reserves, at the bottom of hilly terrain, closed by one or more dikes (or dams), are not to be confused with the mega basins, some of which have been ransacked in recent weeks by environmental activists.
Hill reservoirs, defended by some of the farmers, are fed by runoff or by rivers, unlike mega basins, dams or lakes which are fed by pumping.
In the second case, the water is drawn from the water tables to replace the withdrawals in the summer.
This explains why "
hill reservoirs are generally better accepted than reservoirs on the plain
", according to a Senate report published last November (page 92), even if they "
come up against
(also)
opposition in principle
" from the from environmental associations.
"
Sometimes the reservoir dams up a small stream or is fed by a diversion, but most of the time it doesn't
“says Magali Reghezza, member of the High Council for Climate, lecturer at the École Normale Supérieure and geographer.
Appearing in the 90s, the "small reservoirs" of individual water used by farmers have multiplied in areas where water is scarce, particularly in Ardèche, Deux-Sèvres, Vendée and Vienne. .
No official figure circulates on their number but for thirty years, a hundred projects would have been launched.
Between 2019 and 2022, the government authorized around sixty projects for the renovation or creation of water reservoirs.
Because, according to a group of experts, “
part of the deductions is misused and has high leakage rates
”.
Farmers prefer mega-ponds
Compared to “megabasins”, hillside reservoirs therefore appear to be a more virtuous solution for coping with droughts.
However, it shows its limits "
in the event of very intense and/or very long drought
", explains Magali Reghezza.
"
It will always be necessary to meet the demand for drinking water, irrigate, water the animals and restore water to the environment to avoid the death of vegetation and fauna
", she recalls.
Read alsoHow to store water to cope with the next droughts?
For their part, the representatives of the agricultural world heard by the Senate rather militate for substitution reservoirs - the megabasins -, to the detriment of the hillside retentions encouraged by Emmanuel Macron.
"
They
aim to store more during periods of high water to draw less in the summer from rivers or groundwater
".
“
The modernization strategy for these reservoirs comes up against financing difficulties, as bringing them up to standard does not fall within the scope of subsidizable operations when there is no water saving at all.
“retorts the Senate.
To which the Deux-Sèvres Chamber of Agriculture responds that its Sainte-Soline project, contested by environmentalists, aims for a 60% drop in the volumes of water withdrawn in summer in 10 years and promises "secure
irrigation by the reserves which is a powerful lever for conversion to organic farming
".
If the impact of this work on water resources is deemed "negligible" by a report from the Bureau of Geological and Mining Research (BRGM) of New Aquitaine, the assessment for each project is on a case-by-case basis.
And the reserves of substitution encounter fierce opposition from environmental activists and part of the scientific community.
Opponents of water reservoirs believe that the best solution would be to think about an agriculture that consumes less water and is more adapted to heat.
"
Agro-ecology and agro-forestry have a triple advantage: these forms of agriculture are less emitting and more sober in energy and water, rely on the services provided by the biodiversity that it helps to protect and make it possible to face to a climate that is changing at an unprecedented speed in the history of humanity
", concludes Magali Reghezza.
The debates around water reserves have not ceased to intensify.
