Date:27/01/2005 URL: http://www.thehindu.com/2005/01/27/stories/2005012711970300.htm

Tamil Nadu - Chennai

Rebuilding beaches the French way

By M. Dinesh Varma

A geotextile Stabiplage unit which weighs anywhere between six to ten tonnes is a widely used beach protection mechanism in France.

CHENNAI, JAN. 26. A French technology, which uses geo-textile tubes to stave off sea erosion, offers an alternative strategy for littoral States that have conventionally been building seawalls and groynes to protect their coastline.

The Stabiplage system designed in France has gained acceptance as a coastal protection measure over the past eighteen years across the once storm-ravaged shorelines from Fort Bloque in France to Getxo in Spain.

`More effective'

"The advantages vis a vis conventional structures are that this system is much more effective in tackling erosion, does not restrict access to the beach, is aesthetically pleasing and virtually maintenance-free," says technology consultant, A. A. Dass.

He says the recent tsunami should serve as a wake-up call for putting in place more effective coastal protection mechanisms.

The technology is the invention of Jean Cornic, who has since founded the firm, Group Espace, which deals with coastal and environmental protection.

The Stabiplage system consists of large diameter ellipsoidal units formed like a sausage and laid across the beach (similar to groynes in some respects). These tubular rolls are made of geo-textile fabrics of polyester and polypropylene filaments of sound strength and durability. It is woven into tightly knit fabric, giving it a special textured surface and rolled into large diameter tubes.

The tubes are filled with beach sand and laid across the shoreline at suitable intervals. Usually, a standard stretch will have six stand-alone rolls laid at every 200 m intervals, either parallel or perpendicular to the shoreline. The construction allows the water to seep in and out but prevents the sand inside from escaping. These sand-filled tubes weigh between six to ten tonnes per metre length.

Strong adhesive bond

In storm conditions where a groyne wall could collapse, these tubes have been found to develop a strong adhesive bond with the seabed by harnessing and holding the sand in place. It is also equipped with an anchoring system, which fortifies it against the force of the high seas.

The system absorbs almost the entire wave energy and arrests the away-flow of sand from the beach, while retaining deposits within the boundaries of two consecutive units laid across the beach.

Once the process of sand deposition is established, the trapped sand helps accumulation leading to a build-up of the beach (the height of fill is raised several metres above sea level).

Further, by reducing the depth of water along the seabed over which it is laid, the system induces breaking of waves and widening the berth of beach formation.

The maximum depth up to which the system extends into the sea is only about 4 m. Since the system lies below the water level, it allows sand-transporting waves to pass above it and break into the shoreline.

A delegation of officials from Karnataka has already visited sites in France in 2003 for a first-hand appraisal of the technology.

A French delegation is likely to visit India later this year to persuade Governments in Tamil Nadu, Karnataka and Kerala to consider launching pilot projects with Stabiplage.

Mr. Dass said pilot projects for a 2-km length can be put in place in a period of five months. The cost works out to around Rs. 4 crore per km length.