By David Saint-Sernin
Long gone are the days of the historic flooding of the Garonne last January. In this year 2022 of extremes, the river has now been under tension for several weeks in Haute-Garonne, like many of the rivers that feed it.
A Toulouse, the images impress passers-by, especially on the Bazacle side.
The Garonne under perfusion
If the low level of the river challenges, its flow has nevertheless been artificially maintained under perfusion for several weeks thanks to the daily releases of water from Pyrenean lakes.
These releases of water “represent up to 40% of the water in the crossing of Toulouse”, recall the authorities. Without this low water policy, the Garonne would therefore be in much worse shape than it appears today.
These releases allow the river to stay above its heightened alert thresholdthe one that could tip our Toulouse noon into much tougher water consumption restrictions than they are today.
Reserves are falling in the lakes
Except that after several weeks of releases and rains reduced to a bare minimum in the former Midi-Pyrénées for many months, the situation is clearly tense.
The photos from the Pyrenean dams are relentless. The reserves of the deductions are visibly decreasing, as here at Soulcem dam in Ariège, one of the many Ariège lakes which feed the Garonne upstream of Toulouse.
More than half of the water broth consumed
The authorities confirm: “A volume of 39 million cubic meters of water, i.e. more than half of the available stock, has already been released from the Ariège river to join the Garonne upstream of Toulouse”, they indicate in a statement.
stay the Lake Ôo in Haute-Garonne, whose reserves remain intact according to the latest bulletin from Smeag, the joint study and development union for the Garonne in charge of managing the river’s low-water level support policy since 1993.
A low water level never seen in 30 years…
The prefecture of Haute Garonne does not hide his concern:
“The releases compromised the prefectural measures of restriction, thus safeguarding an entire economy dependent on water from the river, from the Pyrenees to the Gironde estuary. Without it, withdrawal bans would have been ordered by the prefects since mid-July and total bans at the beginning of August downstream of the river. This exceptional effort, never encountered in 30 years of existence of low water supportbears witness to the intensity of the drought we are experiencing”.
The adjusted strategy
Thursday August 18, 2022, she, who has constantly taken restrictive measures since the beginning of August to save water resources, is once again sounding the alarm…
“The situation requires increased vigilance from all: saves every drop of water, because there are still two and a half months of low water campaign and it is in September-October that the situation is likely to be the most tense. In order to avoid a premature depletion of water resources, possible around mid-September at the current rate of low water supportto guarantee the safety of vital activities in the Garonne, including the supply of drinking water, and to conserve one million cubic meters in solidarity with the Neste-Gascogne sub-basin which is encountering a particularly difficult low water level, the committee (which brings together the State and the Smeag, Editor’s note) decided to adjust the water release strategy”.
What’s going to happen
Very clearly, the Smeag will readjust the amount of water released week after week. After the rains of the past few days, the level of releases has been lowered to 3 m3/second in the Garonne against 11 m3 last week.
With the return of good weather and heat expected next week, we will have to step up this effort.
“We are going to readjust the low water support at the rate of 6 m3/second to try to keep the river flowing so that it can maintain priority uses such as the consumption of drinking water and the maintenance of agricultural and industrial activities. But the flow of the river will be lowered. Until now we had held a flow between 40 and 45 m3/s in Toulouse. Next week, we will rather be at 35 meters3/s, Explain Nicolas Cardot, low water management engineer at Smeag.
As a reminder, in Toulouse, the crisis threshold, where drinking water cuts could occur, is 27 meters3/s.
Sufficient reserves to last until October
In the longer term, without rain, the Smeag estimates that it will be able to hold the flows above the crisis thresholds until the end of the low water policy, which should take place in October.
The union then expects releases of 4 m3/s on average. This still required switching the Toulouse noon to stronger restrictions.
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