Case study:Reactivating river dynamics in the Vieux-Rhône River (non-navigable section) at Cornas, Roubion and Petite Île

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Location: 44° 57' 49", 4° 50' 51"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity, Hydromorphology, Monitoring
Country France
Main contact forename William
Main contact surname Brasier
Main contact user ID
Contact organisation Compagnie nationale du Rhône (CNR)
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
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Project summary

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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

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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.

Lessons learnt

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Image gallery

Old Girardon dike along the Rhône where flood debris accumulated, before the dike was opened. September 2011 (Compagnie nationale du Rhône).
Connection of flood storage zones in Cornas, during flooding. December 2012 (Juan Robert).
Opening of the Girardon dike at Cornas. October 2011 (Juan Robert).
The fallow Petite Île site prior to the work. October 2011 (Compagnie nationale du Rhône).
Vertical earthwork on the Petite Île site. The stratification (gravel layers) is clearly visible (Compagnie nationale du Rhône).

Catchment and subcatchment


WFD water body codes FRDR2007a, FRDR2007d
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body Yes
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category more than 50 m
Average bankfull channel width (m) 150
150 m
0.15 km
15,000 cm
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category more than 1000 m³/s
Mean annual discharge (m3/s) 1480
1,480 m³/s
1,480,000 l/s
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

Reach length directly affected (m) 2000
2,000 m
2 km
200,000 cm
Project started 2011/09/01
Works started
Works completed
Project completed 2011/12/01
Total cost category 500 - 1000 k€
Total cost (k€) 629
629 k€
629,000 €
Benefit to cost ratio
Funding sources ERDF (45%), Rhône-Méditerranée-Corse water agency (20%), Rhône-Alpes region (9%), Compagnie nationale du Rhône (CNR).

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance

Reasons for river restoration

Mitigation of a pressure Flood risk management
Hydromorphology Channel pattern/planform, Quantity & dynamics of flow, Continuity of sediment transport
Other reasons for the project Diversify habitats for the species on hand, Ensure lateral connections between the riverbed and side channels.


Structural measures
Bank/bed modifications Removal of lateral dikes, Reactivating river margins
Floodplain / River corridor
Planform / Channel pattern
Non-structural measures
Management interventions
Social measures (incl. engagement)


Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Monitoring documents

Additional documents and videos

Additional links and references

Link Description GB V2 Web.pdf All information on this page is copied from the AFB, The French Agency for biodiversity.

Supplementary Information

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