Arles-Tarascon dike: A lone to preserve the site's biodiversity

01/26/2021

The creation of a lône (dead arm of a river) is one of the major developments carried out as part of the project to meet the hydraulic and environmental compensation measures. 

Within the framework of the Rhône Plan and more specifically the programme to secure structures against flooding of the Rhône, Egis, in partnership with Safège Suez, is providing, on behalf of SYMADREM (Syndicat Mixte Interrégional Interrégional d'Aménagement des Digues du Delta du Rhône et de la Mer), full project management for the construction of a first-rank dike of about 10 km, on the left bank of the Rhône, between Tarascon and Arles.

A large-scale operation costing more than €56 million, accompanied by the implementation of measures to cancel and reduce the hydraulic impacts linked to the creation of the dike and environmental compensatory measures. 

Ecological compensation, a major challenge for our worksites​

The creation of a lône (dead arm of a river) is one of the major developments carried out as part of the project to meet the hydraulic and environmental compensation measures. 
 

Our engineer, Mathilde Letourneux, explains the actions implemented in this project:


After an initial phase of excavation more than 4m deep in order to exploit the materials for filling the dyke (watertight silt, draining gravel, vegetal earth), the lône has been modelled over the last few months in order to create different environments in the excavated right-of-way: various bank profiles, vertical slopes, temporary pools, wet meadows, etc.

The renaturation of these environments and the riparian zone continues this winter with various plantations, seedlings and the creation of artificial shelters for wildlife.
This hydraulic and ecological annex, directly linked to the river bed and the alluvial groundwater table, will double the width of the river's working area. 
 

Why create an Ione?


Iones are calm water ecosystems that result from the natural or artificial crossing of river channels. They can be permanently connected to the river either by their downstream end, or by both ends, or only during floods. Some are fed by groundwater. In periods of flooding, they play a role in the flow of water or the draining of the plains.

They are home to an important plant and animal biodiversity, and serve as breeding and feeding grounds for many species of fish in the main river. The vegetation of the lônes participates in the self-purification of aquatic environments by absorbing nitrates and phosphates.