From a distance it looks like a corrugated astro-turf, adding a shade of green on a small patch of a rather long and dusty embankment (or dyke) for protection from swirling waters of the mighty Brahmaputra. Called geo-textile tube (or geo-tube), it comprises of high-strength woven geo-textile that is filled with sand slurry under high-pressure. The geotextile fabric allows consolidation of the sand to create a long sausage-like gravity structure. As grass takes root on this surface over time, the tubes are expected to provide strength and stability to the embankment.
The positive experiences with geo-tubes for shoreline protection in some parts of Malaysia brought the technology to India, ostensibly to stop the recurrence of embankment erosion. A pilot project, utilising geo-tubes installed as submerged dykes, was undertaken in 2006 to protect shoreline erosion at many vulnerable sites along the Malaysian coast. Encouraged by the success of the pilot initiative, a similar project was undertaken two years later to protect a five-km-stretch of the beach at Pantai Batu Buruk.
Buoyed by the success stories emanating from the Far East, 146 geo-tubes were laid at Matmara in Majuli, the biggest river island in Assam, amidst fanfare and optimism. Since the original embankment was breached at this site by the Brahmaputra in 2008, geo-tubes were installed to strengthen a five-km-stretch of the weakened dyke. But the river had little regard for the geo-tubes laden 3.5 km stretch (which could only be completed) and swept it away the following year. It not only meant loss of materials worth Rs. 100 crore but the consequent damages caused by surging waters were several times over.
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The story didn’t end here though. The Malaysian executing agency — Emaskiara — faced flak for the dyke failure but recreated geo-tubes on a small stretch for future reference. The project seems suspended for the time but the equipments and materials are still being guarded at the site. Local people apprehend that despite being a failure the project will be revived to serve vested interests. “But it is unlikely to stop erosion and protect our villages,” opines Sunil Kumar Pgn, a resident of nearby Ruptoli village and a member of the local students union.
Reports indicate that some 93 per cent of all the dykes are well past their effective lifespan of 25 years. Erected way back in the 1950s and 1960s, the length of earthen embankments in Assam is an incredibly 4,463 km. Not only have breaching of embankments and consequent flash floods been a consistent problem for the past couple of decades, a parallel economy of flood control for repair and maintenance of dykes has come into being as well. Capital expensive geo-tubes have only contributed value to the political economy of flood management.
Interest in new mechanisms to control embankment breach is beginning to grow, oblivious of the price the exchequer may have to pay. As many as 354 cases of breach of embankments were registered in 2004, which till then was the highest for the preceding two decades. As many as 114 breaches in embankments have officially been recorded during the last four years, making a strong case for search for alternatives to the conventional system of flood moderation. No wonder, geo-textile tubes and its close cousin, geo-fabric bags, have been in the news.
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Akin to conventional sand-bags, geo-fabric bags have also been tried at erosion-prone Rohmoria, upstream of the town of Dibrugarh. As was the fate of the geo-tubes, so has been the case with the geo-fabric bags. Laid along 2.6 km stretch of the Brahmaputra river bank under an Rs. 52 crore erosion control project, the geo-fabric bags have either been washed away or dislocated in the first surge of monsoon flow in the river itself. Will the geo-fabric last another season in its present form is a million-dollar question.
It goes without saying that the Brahmaputra river bed has risen significantly on account of increased silt flow due to forest clearance and infrastructure development along its course in recent decades, leading to flood waters spilling over large areas in the floodplains. “Unlike other rivers, the Brahmaputra has strong current which needs cost-effective techniques of flood moderation,” says Ravindranath of Rural Volunteers Centre, a flood relief and rehabilitation centre in flood-prone Dhemaji district.
(The writer is with the Ecological Foundation, New Delhi)