Consequently,
Drize again placed under infusion:
ThoseDrought in Geneva –
The Drize is again placed under infusion
Since August 5. Moreover, the state has bombarded the river with drinking water. However, The measure is supposed to be exceptional. Nevertheless, Are there not other more sustainable means to save our rivers?
Since August 5, some 30,000 m³ of drinking water have been injected into the Drize, as in 2023 and 2022. Furthermore, (Illustration photo of the operation on the Drize in 2022).
Lucien fortunate
- The canton injects drinking water into the Drize to maintain its drize again placed under infusion biodiversity.
- An important water leak has been identified in the Grange-Collomb sector.
- The rivers of the right bank retain an acceptable flow thanks to the precipitation.
- Solutions such as recharge of water tables are being developed.
The Drize is thirsty. Consequently, Since August 5. Similarly, to save the fauna, the canton had to place the river under infusion and inject it cubic meters of drinking water. Therefore, The operation, interrupted Tuesday against the rain, is expected to resume next week. For example, This measure, already established in 2022 et 2023is however supposed to be “exceptional”. However, While the heat wave episodes will multiply, what lasting solutions are planned?
Especially since the Drize should, in a few years, snap in the pav and become its aquatic “spine” … Therefore, We take stock with Guillaume Marsac, Deputy Managing Director of theCantonal drize again placed under infusion water office.
In 2022, the flow of the Drize only reached 1 liter per second. Similarly, What state is it currently?
In recent times, its low water flow (the lowest) has been ten to twenty times lower than the average flow. Consequently, On August 5. Consequently, its flow, measured at a measurement station where the fish fauna is important, amounted to 7 liters/second, below the alarm level of 10 liters/second. Additionally, Consequently, It was therefore decided to inject drinking water to avoid a fishery disaster.
This ensures a minimum flow over 4 kilometers downstream of the injection and preserves a refuge for biodiversity. Some 30,000 m³ of water have already been injected (Editor’s note: 60,000 m³ in 2023).
A section was however completely dry Tuesday past… Where has the injected water disappeared and what drize again placed under infusion impact on fauna?
From 2022, we had suspected infiltration, without being able to locate it. However, we have just identified him, in a sector of 100 meters long in Grange-Collomb, not far from Bachet. Almost all of the injected flow flow into it.
The cause has not yet been established. It could be natural – a bed of gravel not guaranteeing sealing -. the fact of man – impact of work for the creation of a channel. Fortunately, the consequences on fish fauna seem to be limited, we have not picked up dead fish on this section. Most were able to fall back in gouilles or go up upstream.
What is the situation in other Geneva rivers?
Those on the right bank – Allondon. Versoix – retain a low but rather correct flow, unlike those on the left bank – Drize drize again placed under infusion and Aire -, who suffer more. This difference is mainly due to the weather and the hydrogeological context.
The snow cover. the rains were more abundant on the French Jura, which recharged the Karst (limestone rock) and which partly explains the preserved flow of the Allondon and the Versoix. This phenomenon did not take place on the Salève and the left bank.
As for the Seymaz. its flow remains satisfactory thanks in particular to the waters selected in a marsh which acts as support. Hermance. the nant of Aisy or the nant of paradise are generally dry, but it is naturally the case during the summer.
Guillaume Marsac is the deputy director general of the Cantonal Water Office.
DR
In 2023, the state declared that feeding the drize with drinking water was an exceptional measure. However, it has just been renewed. Isn’t there any alternatives?
Solutions are being studied and some are even in progress. We end a classification of rivers in order to identify the most sensitive. “important”, that is to be those whose fauna is the richest. We cannot act everywhere. For the Allondon. cross -border measures are already deployed, especially in the Pays de Gex, where the agglomeration is working to revalue drize again placed under infusion its wetlands and limit pumping that can influence its flow.
For the area, work will start by the end of the year in order to recharge its superficial water table. A derivation channel will take water between November. April, to increase its recharge, before it comes out in the area naturally a few months later. We hope to win 20 to 50 liters/second on its flow. The same process will be applied to the Drize.
With the difference that for the Drize, you also plan to use water dripping on agricultural greenhouses and Genilac. How?
The water will be recovered via a pipe in Troinex greenhouses. in addition to the water from the Marsh stream, thanks to a partnership with a farmer, then redirected in a marsh connected to a water table near the Drize. These works could be implemented next year.
In the PAV perimeterthe water used by Genilac to heat. cool the neighborhood will be valued – rather than being thrown into the arve – and injected into a network of raw water which will be used to supply the Drize, but could also be used for watering and water hunts. We hope to stabilize a 30 -liter/second flipper.
Why not install tanks or retention basins?
It is difficult to find areas to install tanks, you cannot afford to use convenient surfaces. As for the pools, they promote losses, because of evaporation, and water sometimes reaches up to 25 degrees. Injecting water at this temperature into a river would be harmful to biodiversity. The use of tablecloths allows us to favor a natural, underground solution.
We often hold the catchments, made in France, for responsible drize again placed under infusion for the low water levels in our rivers. What about?
The quantities withdrawn for drinking water have decreased. even if some catchments persist, in particular at the foot of the Salève. This is not what dries up rivers but each drop counts. and we work closely with the French to diversify their supply.
The new agreement signed recently on the exploitation of the Geneva tablecloth is one of them: the community of municipalities of Genevois (which includes in particular Archamps. Saint-Julien) and Annemasse will be able to double the samples in this tablecloth, provided that you no longer pump in the sources.
Until now, the French have little used this tablecloth, judging the rates too high. The canton has revised them downwards-they remain competitive and interesting for Geneva and the GIS-hence a win-win agreement.
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Drize again placed under infusion
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