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    -Nathalie Dörfliger \ BRGM
    "Since 2008 and the signature of the collaboration agreement with BRGM, Onema has assisted in funding the WFD monitoring network on the quantitative status of groundwater, operated on the national level by BRGM..."

Combined efforts for the hydrological monitoring of the 2011 drought

The year 2011 was confronted with an early dry period and a severe water shortage. In response to the exceptional situation, calls went out to Onema on both the local and national levels. In the field, Onema personnel monitored lowflow levels and the impact of the water shortage on aquatic environments. The resulting information was presented to the hydrological-monitoring commission of the National water committee.

The year 2011 was the sixth driest in the past 50 years with a hydrological “balance sheet” 10% lower than normal levels over virtually the entire country. Severe low-flow situations started in the spring and ended only in late November in certain areas. In response to this situation, the hydrological-monitoring commission of the National water committee met five times between May and September to assess the status of water resources in continental France and in particular effective rainfall, river flow rates, aquifer levels, aquatic environments and reservoir levels behind dams. This data was collected and processed by Météo France, river-basin environmental agencies, BRGM, Onema and other experts involved in regularly providing quantitative water data. All the data was published by Onema in the national hydrological-monitoring bulletin, put out by the Ecology ministry.

Early activation of ROCA (monitoring network for crisis-level river flows)

The difficult hydro-climatic conditions incited the Ecology ministry to activate the ROCA network over virtually the entire country for the first time on 16 May 2011. This network, which was replaced in 2012 by the ONDE observatory (see article on page 18) provides quantitative information on water resources in addition to the standard data (flow rates and piezometric data). On the basis of visual observations carried out in the field by Onema personnel, ROCA data is used to calculate an indicator for each department informing on the seriousness of the local situation. Almost 90 departments (out of 100 in France) mobilised the network in 2011.

The effects of the drought

In addition to collecting ROCA data, Onema also observed the consequences of the hydro-climatic conditions on habitats and on the operation of aquatic environments. The results were impatiently awaited by the various stakeholders in the water sector. For the year 2011, Onema noted abnormal gradients in the temperature rise of water and an acceleration of all hydro-biological processes. These conditions encouraged the massive development of aquatic plants in rivers and affected the migration of some fish, e.g. salmonids, thus provoking delays in their reproductive cycle.

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Activation of the ROCA network in the spring of 2011

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