Energy and Climate Change CommitteeWritten evidence submitted by Jonathan White (SEV 54)

1. Executive Summary

The Rance barrage was the first and so far the only tidal barrage constructed in Europe. Commissioned in 1966, it is the only precedent able to provide an insight into the impact of building and operating a tidal barrage over an extended period of time.

When it was built, the Rance barrage was seen as a trial for a much larger tidal barrage spanning the Baie de St Michel between Cancale and Granville in Normandy. That barrage was never built and Électricité de France (“EDF”), which operates the Rance barrage, says it has no plans to build further tidal barrages in France, instead favouring investment in off-shore wind farms as its preferred source of incremental renewable energy.

During construction of the barrage the Rance estuary was turned into a freshwater lake, leading to the eradication of all marine flora and fauna.

Following construction of the barrage, the Rance estuary became a marine basin, with water levels no longer governed by the tides but exclusively controlled by the operation of the barrage.

The marine basin is very different from the estuary that existed before the barrage. Average water levels have risen by approx. 2.5 metres and tidal range has fallen by 40%, thus reducing the intertidal area from 70% to 50%.

Following the opening of the barrage, a period of 10–12 years elapsed before a new environmental equilibrium was established. The new environmental equilibrium is quite different from the one that existed before, and is highly dependent upon the operation of the barrage.

Certain species of fish previously abundant, such as conger eels, flat fish and sand eels, have completely or largely disappeared.

As there were few if any salmon and sea trout in the Rance prior to construction of the barrage, it is not possible to assess what impact the Rance barrage would have had on salmonid migration, although some evidence suggests that larger fish of other species struggle to pass through the turbines.

The years since the construction of the barrage have seen a very significant silting up of the basin. It is probable that the barrage has contributed to this phenomenon. The operation of the barrage means that high water can be maintained for as long as eight hours and low water for as long as four hours during a given 24 hour period. Long periods of slack water and therefore low current allow sediment suspended in the water to sink and settle.

The impact of this silting is such that some heavily silted parts of the basin are being colonised by plants and transformed into salt marsh, thus removing previously fertile nursery areas for fish and feeding territory for birds.

The issue of silting, and the role the barrage may be playing in aggravating this phenomenon, is currently the subject of significant friction between the communities bordering the Rance and EDF.

For the Severn estuary, the experience of the Rance barrage shows that, even if during construction of a Severn barrage the colossal destruction of marine life caused by building the Rance barrage were to be avoided, the impact on the environment of operating a tidal barrage is likely to be very significant.

In this regard, the obvious difference between the Rance and the Severn is the scale of the rivers concerned and range of species affected. The Rance is a small river, which prior to the barrage did not have significant populations of migratory anadromous fish (salmon, sea trout, shad), with a comparatively small estuary. The rivers that flow into the Severn estuary, by contrast, cover a massive watershed, and are home, inter alia, to important populations of migratory salmonids, shad and eels.

2. Origins of the Rance Tidal Barrage

EDF started to consider the construction of a tidal barrage in the Rance in the early 1940’s, with the French Parliament finally passing a law to build a barrage in August 1956.

However, the decision to proceed with construction was delayed by financial constraints and the prospect of cheaper power generation from nuclear. Gaudez1 quotes M. Jeanneney, French Industry Minister, in early 1960 as saying “It’s true that the construction of the barrage would provide work for 2,000 workers for five or six years, but… the State would be better off paying the workers to do nothing… the future is nuclear energy… the electricity produced by the Rance would, as things stand, be more expensive than that currently distributed in Brittany”.2

The decision to proceed, finally taken on 29 December 1960 despite Jeanneney’s misgivings, reflected both the fact that the project would include a bridge between St Malo and Dinard and General de Gaulle’s priorities and vision of France’s historical destiny. As de Gaulle said at the opening ceremony on 26 November 1966, “Just as the Rance flows to the sea because her source sends her there, so France is true to herself when she advances towards progress”.3 The Rance barrage should therefore be seen in the same context as other trophy projects approved by de Gaulle in this period, such as Concorde, the liner France and the nuclear power station at Chinon.

The Rance barrage was originally viewed by EDF as a trial for a much larger barrage across the Baie St Michel between Grouin, near Cancale, and Roc near Granville in Normandy. By the mid 1960’s, however, EDF was fully committed to developing nuclear rather than investing further in tidal projects. As M. Massé, Chief Executive of EDF, said at the opening ceremony for the Rance barrage, “The advent of nuclear that we are witnessing today will possibly mean that we will not follow the path opened up by the Rance.”4 Local legend has it that, off the record, de Gaulle put it even more succinctly at the opening ceremony. He allegedly turned to an aide and said, “We have done a bloody silly thing”.5

EDF has no plans to invest further in tidal barrages, preferring instead to develop several massive off shore wind farms off the Brittany coast as it seeks to reach its goals for power generation from renewable sources.6

3. Environmental Impact of the Barrage

An assessment of the environmental impact of the barrage is made harder by the fact that no environmental study was carried out prior to construction, as building took place 10 years before passage of the Environmental Protection Act.7 In addition, it should be noted that much of the research produced on the environmental impact of the barrage since construction has been, at least in part, funded by EDF.

In the early years of the barrage’s operation, environmental issues did not enjoy a high priority. Characteristic is Gaudez’ book on the Rance barrage,8 which contains only one sentence on the environmental impact: “The ecological impact appears to be hard to assess, and even more difficult to measure.” 9

During construction of the barrage the estuary was completely cut off from the sea for three years between 1963 and 1966. During this period the estuary was stabilised at a constant level of 8.5 metres above sea level, salinity dropped to around 10% and significant silting occurred. According to Retière10 the transformation of an estuary characterised by a high tidal range into a basin with a constant level led to the almost total destruction of marine flora and fauna within the basin.

Following construction of the barrage, water levels in the basin are dictated by the operation of the barrage in order to optimise the generation of electricity, and are no longer governed by the tide. As a result, water levels are on average 2.5 metres higher than before the barrage, the tidal range has been reduced by 40% and the intertidal area has been reduced from 70% to 50% of the area of the basin.

According to Retière, it took 10 to 12 years after the commissioning of the barrage to establish a new ecological balance within the basin.

After the 10 to 12 year stabilisation period, the new ecological balance that emerged in the Rance basin was entirely different from the environment that had existed prior to construction of the barrage. As Retière notes, the Rance had been “profoundly altered”.11

Certain species that had been abundant in the Rance estuary substantially or completely disappeared from the basin following commissioning of the barrage. Mauffret’s12 study of the commercial fishery in the Rance estuary prior to the barrage shows the historical abundance of flat fish, conger eel and sand eels. As Stratakis13 and Bregeon14 have noted, these species have substantially disappeared from the Rance basin.

Retière and Stratakis both highlight the extent to which the ecology of the basin is dependent on the functioning of the barrage, with fish populations being vulnerable to sudden changes in water level. For example, they note instances of high fish mortality caused by abrupt drops in water level exposing previously inundated nursery areas for fish.

The extent of fish mortality caused by migration through the barrage is unclear, as very little scientific research has been carried out. Stratakis believes that there is selection by size, with larger fish being more vulnerable to being killed or wounded by the turbine blades, and points to the fact that fish caught within the basin are of smaller size than prior to construction of the barrage. This conclusion is based on oral testimony given the absence of any environmental study prior to construction.

Lockwood,15a member of MAFF Directorate of Fisheries Research, observed over 150–200 dead fish in the lock and lock pits of the barrage during an informal visit to the barrage in August 1989. This gave rise to a study carried out in the summer of 1991 that had inconclusive results, in part due to difficulty in catching enough fish to conduct a tagging programme.

Retière and Stratakis both point to indirect fish mortality caused by the turbines, for example as a result of fish shoals being broken up by the extremely strong currents caused by the turbines and therefore becoming vulnerable to predation by birds. In this regard, they note the high concentration of gulls and cormorants in the vicinity of the barrage, a phenomenon that is still apparent today.16

It is not possible to assess the impact of the barrage on migratory salmonids, as these were not present in any significant numbers in the Rance prior to construction of the barrage, probably having disappeared as a result of the canalisation of the Rance upstream of La Hisse in the first half of the nineteenth century.17

4. Silting of the Rance Marine Basin

One of the most important developments since the construction of the barrage has been the very high degree of silting that has occurred within the basin. This has become an extremely controversial issue between EDF and the communities on the banks of the Rance basin.

It has been estimated18 that currently 30,000 m3 of silt are being added each year to the marine basin and that, for example, the level of silt at Mondreuc is now eight metres above sea level.

François Lang, Chargé de Mission, Mer et Littoral, at Coeur Emeraude, a local environmental protection agency, looked in detail at water levels in the marine basin for the years 1980, 1981 and 198219 and found that, in order to optimise power generation, slack water at high water was being maintained for up to 8 hours and at low water for up to 4 hours in a 24-hour period. The long periods of immobile water favour the deposition of sediment, as does the fact that low water seldom drops below 3.5 metres above sea level.

The effect of this has been to silt up to a great extent the bays within the basin as well large parts of the central channel, covering previously sandy areas of the bottom with a thick layer of silt. Lang has observed that in many areas silting has become so extreme that plants have colonised zones that were previously flooded at high water. This has had the effect of turning parts of the basin into salt marsh, thus eliminating areas that were previously valuable nursery areas for fish and feeding territory for birds.

Appendices 1, 2 and 3 illustrate the remarkable extent to which silting has occurred within the Rance marine basin.

5. Lessons for the Severn

Clearly the ecological effects of the Rance barrage are unlikely to be directly transposable to other potential sites for tidal barrages such as the Severn estuary. For example, the level of silting that would occur would depend on the amount of sediment in the water and the way in which a barrage in the Severn would be operated. Equally, the extent of mortality caused by the barrage will depend on the size and fragility of the organisms present and the speed of rotation of the turbines. Given the complexity of the systems involved, modelling and predicting the precise impact is unlikely to be feasible.

What can be observed, however, is that the experience of the Rance demonstrates that construction and operation of a tidal barrage causes a permanent fundamental change to the ecology and geomorphology of an estuary.

The obvious difference between the Rance and the Severn is one of size. The Rance is a small river, which prior to construction of the barrage did not have significant population of migratory salmonids or eels. By contrast, the Severn is the longest river in the UK and the rivers Severn, Wye and Usk that flow into the Severn estuary are home to significant populations of migratory salmonids, eels and shad. As a result, the environmental impact of a barrage in the Severn would, in absolute terms, be much greater.

APPENDIX 1

Viaduc de Lessard in the 1930’s (above) and in September 2012 (below).

APPENDIX 2

Pointe du Chêne vert in the 1930’s (above) and in 2011 (below).

APPENDIX 3

Plage de la Ville-Ger in the 1950’s (above) and in 2012 (below).

December 2012