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Keeping safe the existing road and continuing construction of the New Road

30 mars 2015

Each day, around 60,000 people use this strategic road between Saint-Denis and La Possession. This essential infrastructure consists of a road stuck between the cliff and the ocean. Around 40 years old, it is obsolete, expensive and hazardous for the people of Reunion Island.

A reminder of the precautionary measures applied to secure the existing road

The existing Coastal Road is situated the foot of a cliff and is extremely hazardous. 450,000 m² of nets have been deployed for years by the French State and the Regional Council to reduce the risks, but are inefficient against major rock falls, such as the dramatic one on 24th March 2006, that cost the lives of two Reunion Island road users. However, the measures taken to secure the road must conform to very strict rules, so as to limit the negative consequences of major events, particularly in respect of climate :

• The installation of nets to prevent and reduce the risks of rock falls on the road ;
• In the event of heavy rain, the road is partially closed to keep the users away from the cliff that has been weakened by the rain (above 30 mm of rain over 24 hours, the road is opened only on the sea side for 24 hours ; if the rain exceeds 50 mm, it remains closed for 48 hours).

It is still necessary to install, maintain, and replace the safety nets, even if the cost is very high. All the experts have concluded that it is impossible to foresee or anticipate these phenomena, which is why the existing road needs to be abandoned.

A validated solution to move the road away from the cliff

The chosen solution, which has been validated by French State, will move the road away from the cliff. Responsibility for the project, as a major road axis, was transferred by the French state to the Regional Council of Reunion on 1st January 2008. In the face of this emergency situation, in 2010 the Regional Council chose to build the New Coastal Road (NCR), with additional lanes for clean public transport (TCSP : a bus lane), the road project becoming one for a multi-function infrastructure. The choice of a road partially out at sea was made in 1999, and then confirmed in 2006. Considering the importance of this axis for the island, this solution is the one best adapted to the problem of safety. 20 years of studies, expertise, inquiries and public debates confirmed the need for a new infrastructure. The New Coastal Road responds to the different challenges of this axis, not only technically, but also financially and environmentally.

As a reminder :
Cost of upkeep and maintenance of the existing Coastal Road compared to the New Coastal Road :

Existing coastal road : €6 billion/year

New Coastal Road : €3 billion/year

HER PERSONAL EXPERIENCE :

“As in most mountain regions, the geology and the morphology of the cliff overlooking the existing Coastal Road mean that it is a natural environment subject to gravitational phenomena such as rock falls. Heavy rains, such as the ones we recently experienced, are usually the elements triggering the rock falls, notably due to the seepage and water flow that increases the pore water pressure in rocks that have already been altered and fractured.
These climatic conditions contribute to weakening the cliff, thus increasing the risks, the danger linked to this zone.
The existing protective devices (nets, fencing, ditches, gabions, etc.) secure the cliff and thus the road at its foot, deviating most of the rocks that fall to the ditch behind the gabions, thanks to the nets. These protective measures have made it possible to considerably reduce the number of rock-falls reaching the road in the last few years. However, they cannot prevent large-scale rock falls.
Most of the blocks and small rocks falling are deviated by the nets, falling into the ditch behind the gabions. Unfortunately, some parts of the road are not protected by these devices. Also, some massive rock-falls cannot be held back by the existing device. In these conditions, the road and its users are directly vulnerable to chips from rocks and rock falls.”

Séverine Bes de Berc
Head of the BRGM

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