OES-Environmental distributes metadata forms (questionnaires) to solicit information from developers involved in environmental monitoring around marine renewable energy project sites around the world. This page provides project descriptions, baseline assessment, post-installation monitoring, and links to available data and reports. Content is updated on an annual basis.

La Rance Tidal Barrage

Project Site

Title: La Rance Tidal Barrage
Start Date:
November 26, 1966
Technology Type:
Info Updated:
August 27, 2019
The La Rance tidal barrage
Project Status: 
Device in operation
Tidal barrage
Project Scale: 
Installed Capacity: 
240 MW

The Rance Tidal Power Station is the world's first tidal power station and also the world's second biggest tidal power station. The facility is located on the estuary of the Rance River, in Brittany, France. Opened on the 26th November 1966, it is currently operated by EDF, and is the second largest tidal power station in the world, in terms of installed capacity. With a peak rating of 240 MW, generated by its 24 turbines, it supplies 0.012% of the power demand of France. With a capacity factor of approximately 40%, it supplies an average 96 MW, giving an annual output of approximately 600 GWh. The barrage is 750m (2,461ft) long, from Brebis point in the west to Briantais point in the east. The power plant portion of the dam is 332.5m (1,091ft) long. Power is generated from 24 bulb turbines with a 5.35m (17.55ft) diameter that rotates at 93.75rpm and is rated at 10MW at a head of 5.65m (18.54ft).


The facility is located on the estuary of the Rance River near Saint Malo, Britany, France. This estuary has an average tidal range of 8.2m (13.5m maximum) with a reservoir of 184,000,000m3 over a 22km2 basin area that creates a maximum flow of 9,600m3/s.

Project Timeline: 

It took six years to complete, and was commissioned at various stages between August 1966 and December 1967. The following were the most important stages of its construction: January, 1961: commencement of work. 19th November, 1962: commissioning of the lock. 24th March, 1963: commissioning of the sluice-way section of the dam. 20th July, 1963: final closure of the dam across the estuary. 19th August, 1966: on-line connection of the first power set. 26th November, 1966: inauguration by the President of France. 1st July, 1967: inauguration of the road across the dam. 4th September, 1967: commissioning of the twenty-fourth power set. The plant is currently operating.

Key Environmental Issues: 

The barrage has caused progressive silting of the Rance ecosystem. Sand-eels and plaice have disappeared, though sea bass and cuttlefish have returned to the river. By definition, tides still flow in the estuary and the operators, EDF endeavors to adjust their level to minimize the biological impact.

La Rance Tidal Barrage is located in France.

Post-Installation Monitoring: La Rance Tidal Barrage

General Description:

The Rance Basin has undergone a full scale evaluation of the ecological impact of the tidal power station during 20 years of operation. Significant impact during the 3-year construction phases and closing of the estuary provoked disappearance of marine flora & fauna due to salinity fluctuations, heavy sedimentation and accumulation of organic matter in the basin. The new ecological equilibrium, established in the space of 10 years remains fragile and being linked to the degree of stability of abiotic conditions, dependent to a large extent on the operation conditions of the power stations. By 1976, the Rance estuary was considered again as richly diversified: a new biological equilibrium was reached and aquatic life was flourishing again.

ReceptorMonitoring Program Description Design and Methods Results Status
  • Physical Environment

Mean water level and hydrodynamic regime.


The 2.5 m rise of the mean water level has resulted in a decrease of the tidal range which includes less volume of water entering the estuary the slack period to be longer.

  • Physical Environment

Sediment dynamics.


Modification of tidal stream in the estuary, in particular during ebb has provoked more silt deposit in the low intertidal zone.

When comparing the Rance estuary with other regional estuaries, sediments dynamic processes are similar to those of natural estuaries.

  • Biological Environment

General Flora and Fauna distribution.


An increasingly diverse flora and fauna became established. The patterns of distribution of this flora and fauna, their grouping into ecological units and the nature of their interrelationships, indicate a variable degree of biological adjustment to the new environmental conditions.

  • Benthos

Distribution of benthic species and communities.


By 1980, the basin was providing habitat for 110 worm species and 47 crustacean species.

  • Fish and Fisheries

New fishery activities.


Scallops and Belon oysters are now the new fishery activities.

  • Birds

Utilization of the basin by overwintering birds.


Bird species variety is the same than before (120 species)

A well developed communities of fish-eating birds has been developed (gulls, guillemots, shags)

Birds adaptation: decrease of sand area (intertidal area)

Birds can also find food in the other Bays (mudflats)

  • Large Vertebrates

Seals distribution.


Since 2000, a seal female has been living in the basin, passing through the sluice gates or even the lock. Despite vain attempts to send her back to join seal communities, she always goes back to the Rance estuary!

Reports and Papers


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