The level of groundwater

[Adrien (ex-nico239)]

The level of groundwater as of June 1, 2017
Full Fields source

Two-thirds (70%) of France's water tables show a moderately low to very low level, due to the lack of sufficient winter recharge, the Bureau of Geological and Mining Research (BRGM) said in its balance sheet on June 1.

Only rare sectors, particularly in the south of the Paris Basin and in Occitania, have benefited from normal recharging and present levels around the average. As summer approaches, two thirds of the points are already trending downwards, only 10% still being up. Rainfall in May was very irregular, after a generally deficient winter and precipitation late until February. During the spring, the rains were beneficial for the vegetation but ineffective in recharging the water tables.

In May, part of the country was crossed until the 20th by rainy passages, but the shores of the Mediterranean, Corsica as well as the northern border regions experienced rather dry weather. High pressure conditions then settled across France.

Among the aquifers presenting the most favorable situations, with levels close to the average, the BRGM cites the karst aquifers of the regions of Nîmes and Montpellier, the chalk aquifer of Burgundy and Gatinais (south of the Paris basin), the aquifers alluvial of Corsica (east of the island). On the other hand, the Champagne chalk table, all the tables in the Adour-Garonne basin, the aquifers of the Rhône valley (upstream and downstream), the table of Jurassic limestones in Lorraine, are in a much less favorable situation.

[Grelinette]

Hello,

In my PACA region, the subject of the water deficit in groundwater comes up every year with it seems that the water tables are losing more and more of their water level and the cause would be a drop in rainfall.

However, at my level I note for a few years changes which do not come to corroborate this cause!

There are many rainwater recovery tanks in my home for each of the roofs of all three neighboring dwellings, including a very large 3 m200 water reservoir that collects rainwater from a large roof. 'an area of ​​approximately 3 m².

Usually this large reserve of water never fills completely during the year, but for about 3-4 years this reserve regularly overflows, either during the fall, winter, or even spring!
In past years, in this month of June this reserve is usually filled to less than a quarter, or even almost empty, while this year it is still 3/4 full.

Similarly, there are 1000 liter cubic tanks for each of the small roofs of 15 to 25 m² of the other buildings and I am surprised to find that these 1000 liter tanks fill and overflow in one big rain for example during from a single night of rain, which was not the case before.

My impression (out of precise measurement), is therefore that the rainfall is more important each year but very irregular: more quantity of water but with less episodes of rain, and very abundant rains for very short periods.

In addition, I attended a presentation meeting a few years ago. Flood Risk Prevention Plan in a town in the Durance valley towards Manosque in the Alpes de Haute Provence; the Durance is a river that crosses the PACA region and is subject to impressive floods: its level can rise by several meters in a few hours.

Until today we were talking about a Centennial flood of the Durance which was exceptional, now this exceptional flood is decennial and even more frequent.
Experts explain these changes by the fact that:
1 °) very rapid urbanization seals the soil producing a runoff of rainwater up to the rivers of the valley bottoms,
2) anarchic deforestation of forest areas means that rainwater is no longer retained by natural vegetation and trickles to the surface without penetrating the ground.

These two cumulative causes partly explain why rainwater no longer passes into the groundwater despite the fact that quantities of water can be more abundant.

[Christophe]

Good topic thank you!

Yes, global warming is seriously starting to affect ... the water cycle ...

Some link the heat waves and the low level of the water tables ... which are today quite similar to 1976 and 2005 (but not 2003 ??)

And AMHA, overall it will not work out ... but it is obviously not enough for the ecology to take precedence (or at least at the same level) as the economy for our dear golden leaders (a). ..

[Adrien (ex-nico239)]

Sacred pool that you have ....

For the rest of the memory, the Durance never got out of bed again since the hydraulic improvements made on its course ...

For deforestation or rather deforestation it is on that it is a catamaran.

But it was not yesterday ...


http://www.persee.fr/doc/geo_0003-4010_ ... _237_10533

Our elders of the last centuries have managed the forest in an haphazard manner until the alarm signal is raised and the law of 1882 on the restoration of mountain terrains is promulgated.

And again if you read a little you will see that it was far from unanimous since some believed that the soils and drought had always prevented the forest from growing in these corners ... which was obviously stupid. ..

But these good provisions are a little forgotten by the young generations.

For the breeder to whom I lend part of my land the forest on the opposite slope is useless and it would be much more useful to cut it to (imply) to graze quadrupeds ...

Besides, before the subject was under surveillance, some landowners who had nothing to do with it happily cut down the trees: with the results we know: soil degradation, erosion ... etc

[Grelinette]

For the rest of the memory, the Durance never got out of bed again since the hydraulic improvements made on its course ...

This is another subject, but I have experienced impressive floods in the Durance relatively recently. Moreover in 2003 following a flood, the flood zones on each side of the Durance were widened: I had a company which welcomed the public installed in one of these zones and I had to move because of the extended risks of 'flood.

One of the reasons for these floods, despite hydraulic improvements, is that when there is heavy rain the dams are forced to discharge large quantities of water causing a flood downstream.
There was even a case where during the discharge of the overflow of water, branches and trunks came to block the valves which could not close which caused an unexpected flood.

There is another little-known phenomenon which would cause flooding by floods of overflow, in particular from the Durance, and it was moreover during the PPR presentation meeting that an old peasant explained that formerly the local people used pebbles a lot to build low walls and houses, which made regular cleaning of the river bed. Now this pebble removal is prohibited and the river bed would be several meters higher than it was several decades ago, in fact, even with less water the river overflows faster!

[Adrien (ex-nico239)]

I am not informed enough to say that EDF load shedding at Serre Ponçon or Château Arnous and heavy rain are linked, similarly I do not know what is the policy for cleaning the aforementioned dam lakes.

No more info on the use of pebbles to build gabions and the influence of this on the height of the course of the river.

I don't have the impression - purely visual that for 50 years that I have frequented her every day her bed has gained a lot of weight but it is just visibly.

What is certain is that the dam of Château Arnoux quickly went from swimming lake and initiation to sailing to a vast swamp ...
At the time, people promised a seaside resort (I exaggerate )

And on this subject not on either that the zones of Pertuis and St Maurice de Manosque are not in flood zones ...

[Christophe]

An interesting drawing: I never thought that industrial purification prevents the recharge of groundwater!

nappes_eaux.jpg (87.03 KiB) Viewed 3361 times

On the other hand I knew well, and for a long time, that the EVERYTHING in the sewer (= mixing rainwater, clear, and black and gray) was an aquifer scam !!

The water companies are indeed the new mafias ...

[Christophe]

The water companies are indeed the new mafias ...

water-pumping filtration / l water-we-have-to-juliet-Duquesne-and-stone-rabhi-t15841.html # p348062

Pollution prevention measures could cost Juliette Duquesne 87 times cheaper than treating polluted water

CQFD!!

[to be chafoin]

I do not quite understand the diagram: why there is no infiltration? Rainwater does not infiltrate artificial soils, where it may evaporate again and / or flow further to finally infiltrate into the aquifers ... Treated wastewater released into the rivers return well in the aquifers ...

Regarding the water tables, the problem of pollution by pesticides and nitrates, which are still so present thanks to farmers, remains to be seen!
https://www.actu-environnement.com/ae/news/alsace-nappe-phreatique-pollution-pesticides-nitrates-30293.php4

[Moindreffor]

the level of the water table mainly depends on the type of water table
with me it is fractured limestone, so the water table recharges very quickly, but also empties very quickly in waterways
so big risk with pollution, but if pollution, it is quickly evacuated

the second problem with the aquifers, it is their overexploitation, if you have 2 pumping too close, their proximity can make appear a false deficit, the first pumping, taking the water of the second

At my place, an average city came to pump into the water of the neighboring city, but with the increase in consumption, the latter came to install a pumping in my commune, going up more and more towards the source of the course water, the average city does not have a river

therefore a pumping maybe dry, but not the tablecloth ...

namely that we often measure the level of groundwater at pumping places