Restoration of the Doubs-Loue confluence

Restoring alluvial systems drivers of biodiversity

Over time, the Doubs-Loue confluence has been significantly reshaped and embanked in order to protect homes from flooding, and this has had a significant impact on the ecosystems it preserved.

As part of a contemporary approach to river development, the Syndicat mixte Doubs Loue, with the help of Artelia, has undertaken a ” reasonable ” restoration of this confluence, which aims to re-establish more natural river dynamics, raise the level of the water table and restore the ecological wealth of the site.

CONTEXT & ISSUES

Over the centuries, the confluence of the Doubs and the Loue has been subject to major development (dyking, bank protection, alluvial extraction in the minor and major beds, etc.), which reached a climax after 1950 with the industrialisation of extraction and the “domestication” of the two rivers (large-scale rectification and corseting). While the objective of controlling the “wild and uncontrolled” overflowing of the rivers was respectable, the development methods used proved to be harmful, causing major changes to the sediment dynamics of these rivers and leading to the destruction of natural environments rich in biodiversity.

The restoration of the confluence initiated by the Syndicat mixte Doubs loue is a first step in the reconstitution of alluvial areas, within an emblematic site in the region that hosts the Ile du Girard national nature reserve. The project, managed by Artelia, is based on various techniques for restoring alluvial hydro-systems, with the aim of reactivating the morpho-dynamic processes that drive alluvial biodiversity.

Our teams drew up a programme involving the removal of more than 1,500 m of riverbank, the dismantling of 1,000 m of flood traps, the removal of minor bed groynes, the dismantling of 450 m of embankment dyke and the clearing of 4.4 ha of forest. To replace these measures, erosion notches and revitalisation channels were created. An alluvial bank 38 m wide and 350 m long was also placed in the Doubs’ minor bed. Today, the confluence has recovered a certain natural flow and a number of species, particularly birds, have begun to migrate back to the river.