What impact will the high-speed line have on the natural environment?

Since the earliest stages of its design, the GPSO has followed the ERC (‘avoid, reduce, offset’) approach to minimise environmental damage. Impacts that cannot be avoided or reduced will be offset. The right of way of the high-speed lines covers 4,830 ha. Thanks to avoidance measures, less than 700 ha of sensitive natural areas and 250 ha of wetlands will be affected. Numerous structures (for wildlife passage and water flow) will ensure the continuity of ecological corridors. 

The environmental offsetting built into the project will restore 2,000 to 3,500 ha.

Approximately 3,000 ha of land will be returned to nature: these areas will be restored to wetlands, hedged farmland or wooded areas. “At no point will the environment lose out,” promised Alain Rousset, president of the Nouvelle-Aquitaine region.

The impact of upgrading existing lines

Several modernisation scenarios have been studied, based on the assumption that existing lines will be renovated. The environmental impacts vary according to these scenarios and it has not been possible to quantify them as precisely as for new lines. (The levels of study involving these aspects is different.)

However, in terms of rights of way and buildings, the renovation scenarios on the Bordeaux–Toulouse line have a major impact: scenario 1 (‘capacity priority’ with 5 km of shunts and sections of new line) has rights of way of 137 ha and affects 89 buildings; scenario 3 (‘journey time priority’ with 50 km of shunts) has rights of way of 664 ha and affects 360 buildings. That’s more than the new Toulouse–Bordeaux–Dax line.

The surface area of the right of way of new lines

In terms of artificialisation, not all of the rights of way of a new line should be considered artificial in accordance with the criteria of the climate and resilience act of August 2021. In fact, the proportion is very small, as the width of the platform is around 15 to 20 m (half that of a motorway, which is 28 to 35 m wide); the approaches and embankments are largely planted and do not fall into the ‘artificial’ category.

The right of way of the GPSO project covers 4,830 ha, including 1,240 has of agricultural land and 2,865 ha of forestry land. These 4,105 ha are not considered to be natural areas, but are exploited areas (forestry use with the production forest of the Landes massif, agricultural use, etc.).

The ERC approach: ‘avoid, reduce, offset.’

As far as the environment is concerned, it should be remembered that the studies have made it possible to limit the impact and define the appropriate measures to remedy it.

The ERC (‘avoid, reduce, compensate’) approach has guided the studies for the new lines project since conception, in application of the Environmental Code. The aim of the ERC approach is to avoid environmental damage, to reduce damage which cannot be sufficiently avoided and, where possible, to compensate for significant impacts.

This approach has made it possible to define avoidance and reduction measures, both in terms of the choice of route design (general measures and measures linked to site constraints) and in terms of the principles for organising the works and the operation of the infrastructure.

Avoidance measures include:

Extensive ecological inventories carried out over several biological cycles have enabled the most sensitive sectors (habitats, species) to be identified and largely avoided. As a result, only 41 ha of Natura 2000 sites have been affected, corresponding to river crossings.

The sensitive natural environments affected by the planned rights of way represents less than 700 ha and the wetlands 250 ha (mainly in the Landes forest).

Reduction measures include:

The project includes the construction of major structures to reduce impacts and ensure hydraulic and ecological continuity in sensitive areas: more than 500 structures, with a cumulative length of more than 20 km for structures over 90 m.

Additional studies have been carried out at certain sites to ensure that there are no specific impacts or to define specific measures. For example, in the Ciron Valley in Gironde (habitats and species, including the European pond turtle, surface and groundwater regime and agroclimatic issues) and in the Cros Valley in Landes (chiropterans), with an expert report carried out under the supervision of the French National Museum of Natural History. It should be noted that in the Ciron Valley, the studies concluded that there would be no impact on the production of sweet wines from the Sauternes and Barsac appellations (no impact on the Botrytis cinerea fungus).

Offsetting measures include:

Wetlands will be compensated in accordance with the provisions of the documents SDAGE (outline for the organisation of the development and management of water resources) and SAGE (outline for the development and management of water resources). 

For the 700 ha of sensitive natural areas affected, a preliminary offsetting programme of 1,000/1,750 ha have already been estimated at the pre-public enquiry study stage. The programme will be finalised in the next stages with the aim of achieving equivalence or even a net gain in biodiversity. In particular, the supplementary permits and environmental permits will set out the recommendations to be followed by the contracting authority.

The overall programme will include the most appropriate measures in terms of ecological functionality (not just surface-level approaches). By way of comparison, on the Tours–Bordeaux high-speed line, the fully implemented offsetting programme covers almost 350 sites covering 3,800 ha. (The project right of way is around 4,000 ha). As a result of the pooling of offsetting measures, the preliminary programme of 1,000 to 1,750 ha can be considered as wetland offsetting; however, it does not include land offsetting for land clearance (pine production forest), which is covered by a different logic (Forestry Code) and will be added to these figures. 

Monitoring will be introduced to ensure the long-term effectiveness of the measures (with the creation of an environmental monitoring centre).

Strong involvement of local actors

The next stages in the final design of the project and all the accompanying measures (integration, protection, restoration of networks and roads, etc.) will be accompanied by in-depth local participation, in particular through the future monitoring centres from 2024 onwards.