Wet start to year in France fills water tables but restrictions still possible

Experts have warned that more rain is needed to maintain water levels in certain areas of France to avoid restrictions later in the year.

This is despite very wet spells in January and February, including flooding in some departments, which saw water tables rise across most of the country.

Hydrologists divide France into areas with very reactive aquifers – those which fill up and discharge quickly – and inertial aquifers, which fill more slowly but also take longer to dry up.

Reactive aquifers are generally composed of sand, gravel, karst limestone or weathered granite formations.

“Recent limestone geology absorbs water easily, but it is also much more porous than areas where limestone was laid down in the Jurassic era, when dinosaurs were around, which is more compacted,” said Violaine Bault, a hydrologist with the national geological service BRGM.

“This means that in reactive areas there is space for the water to rise quickly into gaps and cavities, but also that it drains away if there is not constant replenishment with rain.”

Ms Bault said that groundwater levels which were found to be just above or just below average at the start of March were mainly in areas with old limestone geology, and included the Paris Basin up to the north.

“Before the four weeks of rain in January and February, the winter had been relatively dry, and so just one month of heavy rain is not enough for these slowly reacting water tables to fill up,” she said.

Ms Bault said there were no concerns about groundwater levels for the next couple of months, but to avoid possible shortages in August and September regular rain was needed through April.

After that time, most rainfall does not reach the water table because it is absorbed by growing vegetation.

Around two-thirds of the country’s drinking water comes from underground sources, and one third from rivers, lakes and dams.

The latest bulletin from BRGM, published in early March, reported that 84% of water tables were rising.

There was a marked difference between the south of the country, with very high water tables, and the north-east, where inertial aquifers were at an average level for the season, or even lower than normal.

Overall, 67% of water tables were above average for February, and 18% were below average.