13 Oct 2011

New La Réunion coastal highway built on the sea

A road highly exposed to the sea as well as to falling rocks from the near-by cliff connects the two major towns on the island of La Réunion in the Indian Ocean.

A road highly exposed to the sea as well as to falling rocks from the near-by cliff connects the two major towns on the island of La Réunion in the Indian Ocean. To make transport and trade safer and more reliable, it is planned to build a new coastal highway, a combination of viaducts and dikes. DHI is part of the team designing the road, using model tests and wave studies to reveal the safest and most cost-efficient solution.

A scenic road, 13 km long and widely known as the Route du Littoral, connects La Réunion’s two largest cities – Saint Denis and La Possession. Crouched at the bottom of steep volcanic cliffs, the road closely follows the coastline. Even though one might get some astonishing views, this exposition mainly means a big hassle and even danger to the estimated 80,000 travellers using the Route du Littoral every day: Rocks falling from the cliffs provoke regular accidents on the road or block it. Moreover, during cyclonic swell the road often inclines, resulting in the closure of several lanes – which happens on average on 64 days a year and results in serious traffic congestion. The effect on trade is dramatic, as 60% of the island’s freight is transported on the Route du Littoral.

Video - La nouvelle route de La Reunion

The current Route du Littoral is highly exposed to rocks falling
from the nearby cliff. The Nouvelle Route will keep a safe distance.

Click above to follow the course of the Nouvelle Route du Littoral.

The public authority in charge, the Conseil Régional de la Réunion, therefore decided to build a new, safer and more reliable road – La Nouvelle Route du Littoral. This causeway will be a combination of dikes and viaducts, sufficiently distant from the cliffs to avoid falling rocks to hit it. The French consultant EGIS will design the structures to be built. DHI, as a sub-consultant to EGIS, will carry out physical hydraulic model tests supporting the design of the structures - to ensure that it is safe and reliable. Construction works are planned to commence by the end of 2013 and be completed by 2020.

Previously, DHI investigated the preliminary design of the road. These investigations included a wave hindcast study of cyclonic waves as well as physical model tests in a wave flume. The current physical model tests will take a closer look at five specific parts of the dikes and viaducts, and include both flume tests (2D tests) and tests in wave basins (3D tests). DHI will document the hydraulic stability of the marine structures and allow EGIS to further optimise their design.

Thereby, DHI’s model tests will help the client to find the right balance between the necessary investment and efficiency of the road structure. In 2009, the construction costs were estimated at 1.6 billion EUR. But the benefits of the Nouvelle Route du Littoral will surely outbalance the investment, as it averts the loss of life through falling rocks and landslides. And maybe the scenic views of the cliffs are even more impressive from a safe distance.

 Physical Model Tests