The last stretch of the A89 highway between Lyon and Bordeaux has been launched in 2009 by ASF (Autoroutes du Sud de la France). This stretch, 80 kms long between Balbigny (Loire county) and la Tour de Salvagny (Rhone county), has been opened at the end 2012.
Within the Rhone region between Violay (42) and Tour de Salvagny (69), the A89 intercepts 16 streams.
At every stream crossing, a watercourse diversion has been implemented .Then ecological restoration and environmental integration measures have always been carried out on the river parts impacted by the works.
The implementation of technical measures has mainly taken into account the longitudinal profile of the diverted segments of watercourses, the flow type and the hydraulic regime of the streams as well as their geomorphological and ecological conditions.
Moreover the constraints relative to river development can be listed as follows:
- Comply with the course of the river and slopes of watercourses required by the location of the hydraulic structures and properties required by the highway construction
- Keep the hydraulic capacities of the diverted river resulting from the hydraulic studies linked with the A89 construction project.
- Check the flow speeds and stabilize the longitudinal profile of the watercourses in order to reduce the risk of potential regressive erosion and lateral erosion near hydraulic structures.
- Promote an environmental restoration of high quality while preserving ecological continuity.
Every watercourse has benefited of a specific development project well adapted to his intrinsic physical and ecological characteristics.
In each case, the implemented techniques were as follows:
- Temporary diversion of the watercourse and construction of an hydraulic structure
- Earthmoving of the new river bed according to a sectional profile matching the various natural formations seen on the sections free of works
- Possible stabilization of the watercourse longitudinal profile by installing rip rap structures
- Reconstitution of an alluvial soil by bringing biogenic materials with a well-fitted granulometry
- Reshaping of the riverbanks and spreading topsoil.
- Possible stabilization of the riverbanks bottom by using bioengineering techniques, such as planting well-suited native species with ramified dead and living branches.
- Covering the riverbanks with a biodegradable coir geotextile canvas, seeding and planting some willow stem cuttings and bushes consisting of well-suited native species.
Since the achievement in 2011, the follow-up of the landscaping developments by the various technical stakeholders, mainly the Federation de Pêche du Rhône (Fishing Federation)has shown that all the techniques implemented have limited the impacts due to the infrastructure and preserved the ecological continuity on each crossed streams.
These promising results have shown a high level of commitment and have been carried out thanks to the involvement of a project manager specialized in ecological landscaping development and stream restoration from the design phase until the completion.This early involvement has ensured a positive cooperation with the technical and administrative units and has allowed the concern about river-crossings to be considered as one of the main features of the motorway project
crossing of river, barrier effect, fauna passages, wildlife mitigation, vegetation, compensation