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An example of environmental upgrading of roads and highways

In 2009, ASF (Southern France Highways) launched a study on creating ecological corridors in the Drôme department. Contacted by ASF, Onema took part right from the very beginning by participating in the scientific committee. Once the priority sites requiring restoration had been selected, ASF started work on a structure that blocked the continuity of a river under the A7 highway. In just two years, a fish pass and a lateral passageway were built and put into service, thus enabling many species to overcome the obstacle.

Contacted by ASF, the Onema Rhône-Alpes regional office identified an existing structure on the Roubion river that had been classified as a priority project by the eel-management plan because work was required to restore continuity. Made of smooth concrete, the two-metre high weir blocked the passage of not only aquatic species, but also mammals such as beavers, otter, fox, deer and micro mammals.

Development of a multi-species project
The goal was to carry out a multi-species project. Onema provided technical support to ASF and the Ginger engineering firm in selecting a technical solution to meet the stated needs. The weir could not be removed or reduced in size, so a ramp with an uneven surface was selected. Onema approved the project in the summer of 2010 and the work was programmed for the summer of 2011. After cutting into the weir, ASF created a ramp (less than 3° angle) with concrete studs regularly arranged on a stone surface to slow the flow of water to a speed compatible with the swimming speed of the fish. A passageway over a dry section was also set up for land animals.

Two monitoring systems to check the results
Two monitoring systems, funded by ASF, were set up to measure the effectiveness of the new installation. For eels, the Naturalia engineering firm, commissioned by ASF, ran nocturnal counting operations one kilometre upstream and downstream of the installation. No eels were found upstream prior to the work, which confirmed that the structure was an effective barrier. The monitoring results after completion of the project are expected this year.
For the other aquatic species, approximately 100 fish will be equipped with transponders that two antennas in the fish pass will automatically detect. A double photographic trap equipped with a motion sensor was installed to monitor the passage of land animals.
This rapid and effective collaborative effort made it possible to put the fish pass into service only two years after the initial contacts between ASF and Onema.

Contacts: pascal.roche@onema.fr

 

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