Case study:Reactivating river dynamics in the Vieux-Rhône River (non-navigable section) at Cornas, Roubion and Petite Île
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- 1 Project overview
- 2 Image gallery
- 3 Catchment and subcatchment
- 4 Site
- 5 Project background
- 6 Reasons for river restoration
- 7 Measures
- 8 Monitoring
- 9 Additional documents and videos
- 10 Additional links and references
- 11 Supplementary Information
|Project web site|
|Themes||Habitat and biodiversity, Hydromorphology, Monitoring|
|Main contact forename||William|
|Main contact surname||Brasier|
|Main contact user ID|
|Contact organisation||Compagnie nationale du Rhône (CNR)|
|Contact organisation web site||http://www.cnr.tm.fr/en/|
|Parent multi-site project|
| This is a parent project
encompassing the following
In order to improve the functioning of the river system and facilitate the passage of flood waters, it was decided to directly address the cause of habitat degradation and lateral disconnection by removing the structures created during the 1800s.
The experimental work undertaken was intended to reverse the trend toward aggradation of the banks and the river margins, still in progress even today, in order to restore the hydraulic and ecological dynamics of the river. The study of historic aerial photos in June 2005, pertaining particularly to the morphological evolution of the Rhône around the city of Montélimar, revealed that certain sites:
• had a number of favourable characteristics for work to reactivate the river margins;
• did not appear to have any major vulnerabilities concerning their ecological value or any heritage issues.
The mobilisation of sediment (self-dredging) by the current appeared to be sufficient. Consequently, three sites (Cornas, Roubion and Petite Île) were selected for removal of the lateral dikes.
Monitoring surveys and results
A brief ecological characterisation study was carried out prior to the work. Following the work, a complete ecological monitoring programme (vegetation, birds, amphibians, odonata, fish) was initiated as part of the overall authorisation procedure. The year 2012, the year following the end of the work, was selected as a reference point. In September 2012, the Compagnie nationale du Rhône initiated monitoring of the fish compartment in the three pools on the Cornas site. The monitoring will continue until 2016. Birds, odonata, amphibians as well as the terrestrial and aquatic vegetation are monitored by a consulting firm. The annual campaigns will also be pursued from 2012 to 2016.
For the time being, only preliminary results have been published because the available data concerns only the first year of monitoring. The general idea behind the work to reactivate river dynamics is to initiate a hydraulic and geomorphological process using the energy of the river and its floods. The desired ecological changes and improvements will become visible following floods and over a fairly long time span. The data from the geomorphological monitoring are still being analysed, however some changes are already visible. For example, signs of river dynamics have been observed on two sites (Cornas and Petite Île) during annual floods.
The fish community in the pools is the product of the fish trapped by the floods in May and June 2012 and that survived over the summer. The most common are smaller fish (carp, bitterling, etc.) and juvenile bleak, roach and bream.
In terms of terrestrial and aquatic vegetation, a strip of helophytes has developed on the exposed banks, where a number of indigenous species (Ranunculus sceleratus, Najas marina, etc.) have appeared.
At Cornas, wetland vegetation has developed in conjunction with pioneer species and undesirable species (Japanese knotweed) along the channel.
Studies on odonata revealed the presence of a dozen species, including Gomphus simillimus and Coenagrion mercuriale, the latter being protected nationwide. There are indications of amphibian reproduction and various species (natterjack toads, common toads and midwife toads) have been observed.
Catchment and subcatchment
Cost for project phases
Reasons for river restoration
Hydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Additional documents and videos