The force that could redraw the peninsula of India

The sense of horror Ganeshan Vasudevan felt on that warm July morning in 2010 will always remain deeply etched in his mind. A former fisherman living on the Auroville beach not far from the South Indian city of Puducherry, he recalls watching in anguish as the swirling waters of the Bay of the Bengal swallowed not just his home, but the very land it stood on.

For many years, Vasudevan ran a modest guest house out of his family home, set 1.5km (1 mile) back from the coast. Here, he took on boarders who were lulled to sleep by the soothing thrum of the ocean. When the sea swept in to claim the coast after a storm, he wasn't alone in his loss. At least 200 acres (80 hectares) of land along this coastal stretch was completely eroded, displacing at least 7,000 families, according to community reports. The storm wasn't a particularly bad one and shouldn't have caused the damage that it did, Vasudevan says.

Vasudevan's fishing village of Chinamudaliar Chavadi bore the brunt of the destruction. The village had already been badly affected in the 2004 tsunami, but at least then, when the waters receded, they could rebuild their lives, Vasudevan says. "We still had our land and could start afresh. But this time, the sea took over everything."

If we allowed this to continue unchecked, our study found that there is a danger of severe erosion possibly even altering the very shape of peninsular India – MV Ramana Murthy

The origins of the massive erosion event date back more than 20 years, to the completion of an ill-fated new harbour. The government of Puducherry had intended to develop the town's minor sea port. The project involved building a new harbour at the place where the Ariyankuppam River flows into the Bay of Bengal in the southern tip of Puducherry town. But far from rejuvenating the town, the new harbour had profound and far-reaching consequences that would redraw the shape of Puducherry's coast.

Shifting sands

Puducherry, previously known as Pondicherry, is a seaside city and a former French colony home to nearly a million people. Its satellite town, Auroville, is fondly called the City of Dawn. This 40km (25-mile) strip of coastline, divided into seven zones, used to be home to some of India's most beautiful beaches. But in the past decade, these beaches have begun to disappear.

The changes were documented and published in 2012, as part of a report called the Challenged Coast of India prepared by an environmental advocacy group, Pondicherry Citizen's Action Network (PondyCAN). The report triggered the state government agencies to act.

"We've been studying the area since 2013, attempting to find out why coastal erosion was so severe," says MV Ramana Murthy, director of the Chennai-based National Centre for Coastal Research (NCCR), part of the Indian Union Government's Ministry of Earth Sciences. "There were many factors that our study uncovered. The damming of many freshwater rivers upstream limits the water that reaches the ocean. Climate change is causing a rise in sea levels. But the most immediate cause was the blocking of the movement of the sand."

Scientists at NCCR used satellite imagery to examine 6,000km (3,700 miles) of coastline along peninsular India, and found that between 1990 and 2016, 34%-40% of this coast was facing severe erosion and 28% was experiencing accretion (where the sand was piling up). Only 34% of the coast was temporarily stable and that was because it had been fortified with man-made structures.

In Puducherry and further along the South Indian coast, groynes and seawalls had been installed as a quick-fix measure against erosion. However, these ad hoc measures weren't affording any long-term protection at all, the study noted. In fact, they were making the problem worse.

"If we allowed this to continue unchecked, our study found that there is a danger of severe erosion possibly even altering the very shape of peninsular India," says Murthy.

Fragile coasts

This loss was most acutely felt in Puducherry and especially visible along one of the city's prominent beaches, the Promenade. Once a beach filled with luxuriant sand in the 1980s, today huge rocks, boulders and gravel have completely replaced the sand, so much so that tourists started referring to it as Rock Beach.

"The grains of sand in a coastal ecosystem are like free spirits. It never stays still," says Sunaina Mandeen, environmental activist and co-founder of PondyCAN, which has been involved in coastal research and restoration since its inception in 2007. "We seldom realise this, but the sand that lies beneath our feet today on any beach is completely different tomorrow."

The shift in sand occurs as a result of natural processes, such as winds and waves that are driven by South India's monsoons. "From February to October, an estimated 300,000 to 500,000 cubic metres of sand grains move from south to north. From November to January some of it, about 100,000 cubic metres, shifts back again, moving from north to south," says Aurofilio Schiavina, co-founder of PondyCAN. This migration of sediment is known as littoral or longshore drift.

During the erosive process people are at risk of losing their homes, vegetation is destroyed, freshwater aquifers turn saline – Aurofilio Schiavina

"It's nature's way of maintaining an equilibrium and ensuring the stability of the shore," says Schiavina. But after the harbour was built in 1989, the two breakwaters, which protect anchored boats from powerful waves, were constructed as a part of this harbour, interfered with the longshore drift. "Sand began piling up on south of the harbour, and couldn't reach the northern area, which began to erode severely," says Schiavina. "This man-made erosion happens in June to September, when the littoral drift is high. It can also happen during a storm. But erosion and the loss of homes are not always because of storms and is increasingly due to poorly planned man-made structures."

This problem was anticipated when Puducherry's new harbour was built. The new harbour's design had incorporated a sophisticated sand bypass system which could dredge the accumulated sand and artificially pump it to the other side, restoring the balance. However, because of the expense, it was barely used except for a brief period from 2000-2004, says Schiavina. (The port authorities did not respond to requests for comment.)

It was a slow, steady loss. Long before the land began visibly retreating, the underwater foundation of the beach starts eroding first, says Mandeen. Within four years of its construction, the area to the north of the breakwaters had lost all of its sandy beaches.

"During the erosive process people are at risk of losing their homes, vegetation is destroyed, freshwater aquifers turn saline," says Schiavina. "The net erosion or deficit doesn't seem like much and doesn't matter in the end, but the human loss does."

The government responded to this erosion by building groynes – jetty-like structures that jut out into the sea perpendicular to the coast – and seawalls constructed from rock. The objective of a groyne is to catch as much sand as possible to prevent erosion. So as sand piles up on one side of the structure, the other side is open to the ocean and prone to erosion, unless this sand is replenished.

In 2003, the government built a 7km (4.3 miles) seawall constructed of boulders along the Puducherry coast, starting at the harbour, with the intent to protect the city. It cost 400 million rupees ($5.5m/£3.9m). Individuals who could afford it started building these structures too. In 2007, Vasudevan, the former fisherman, built a concrete seawall in front of his property. Three years later, the sea still engulfed his land.

"Groynes are not built alone – they're usually a part of what we call groyne fields," says Schiavina. "Sea walls are used for armouring the shoreline, where the seawall acts as an artificial cliff. Both are only barriers and can aggravate erosion, especially on a coastline such as the one along Puducherry and neighbouring Tamil Nadu and Auroville."

The 2015 documentary India's Disappearing Beaches noted that most beaches in peninsular India are made up of sand that is transported to the sea by rivers and in all, more than one billion tonnes of sediment are discharged into the sea every year along the Indian coastline. Since beach sand is never static, like a heaving river, dealing with the problem involved a study on how to allow this movement, while still retaining the harbour.

Reef rescue

When the groynes and seawalls didn't work in Puducherry, Kerry Black, an oceanographer and former professor at Waikato University, was consulted. He discussed the issue with environmentalists, civil societies and government agencies to try to solve the problem. "We needed a structure that could act as a buffer for the coast, take the energy of the waves, while still allowing for natural sand movement."

One solution considered was to use geotextile bags that had high tensile strength and were filled with sand. These are often lined up on coastlines to lessen the impact of waves, but they are expensive and don't usually last long.

"We studied the east and west coast of India extensively, including monsoon currents, how it impacts the coastline during different times," says Joseph Mathews, a Kerala-based engineering consultant who has worked closely with Black. Their observations helped formulate the guidelines for coastal protection for climate change.

Eventually, they turned to a solution that had worked in other parts of the world, including Florida, Thailand and the Caribbean: artificial reefs. "The waves would break on top of it, providing shelter to the coastline and protection during extreme weather events. Our main aim was to protect the integrity of the coast," says Mathews.

To allow for movement of sand over the top, and to provide a space for surfers, a reef in Puducherry was constructed as a triangular wedge, like a slice of pizza, with part of it jutting out of the water. "Whether it should be made of rock or steel was debated, and steel was chosen not just for longevity but because it could be assembled onshore and then towed into the water," says Black. This was an important consideration when monsoons can often make for turbulent waters and difficulties in transport – building the reef onshore made sense, and it was cost effective too.

While it took five months to build, cost 220 million rupees ($3m/£2.1m), and weighed in at 900 tonnes, its installation 2.5m (8ft) into the water took only four hours. "The reef doesn't use any concrete or rods. It's made of carbon steel and mounted on a stone base; the bottom was quickly colonised by algae and marine organisms," says Mathews. "Over time, these recycled structures soon become habitat similar to a natural reef and provide increased saltwater fishing. It's also easy to monitor. In the case of any corrosion, it's easy to remove and refurbish."

The beach has been starved of sand for so long. We need to provide it with more sediment to nourish it – Aurofilio Schiavina

Some fishing villages, especially north of the reef, are already getting their sandy beaches back. Residents of Puducherry are overjoyed about this development, though it's been a very slow process, says Chitra Shah, director of a local school for children with special needs and intellectual difficulties, Satya Special School. She welcomes the beach back as a vital community space. "Aside from the fact that beaches are vital in protecting our coast, it is also an important space for children with special needs to learn, interact and play," she says. "There are few public spaces in India that are accessible to such children."

However, the submerged reef on its own is not a complete solution, says Schiavina. "When you don't have enough food, you tend to eat more when you do. In a similar way, the beach has been starved of sand for so long. We need to provide it with more sediment to nourish it. The reef just keeps the new sand from being lost forever." So far, 1 million cubic metres of sand have been added to the beach, in the hope the reef will help to keep it there. And until the replenishment is complete, the full benefits of the reef won't be felt.

This solution is now being used at other areas of the coast. Puducherry is far from the only part of India experiencing this issue – massive erosion has been recorded in four coastal states in India: West Bengal in the north-east, Puducherry, Kerala and Tamil Nadu in the south. Today, artificial steel reefs have been installed in four areas off coastal Karnataka as well. "We're working with state governments to reinstate these coasts," says Murthy.

However successful they are, technological fixes for erosion don't work as well as stopping the pressure or activities that are causing the erosion in the first place, says Tanvi Vaidyanathan, a researcher at the University of British Columbia working in the field of marine conservation. "Determining the success of artificial reefs to prevent coastal erosion varies on a case by case basis and requires a complete understanding of geomorphology [a study of the land] and the types of material, costs, area of the reefs as well as local conditions," she says.

For Vasudevan and many others, the new reef came a little too late to salvage his home. "Whom do I approach to compensate me?" he asks. "An ocean is wealth – no one understands this better than a fisherman." But if the artificial reef strategy proves successful, it may at least save others from the relentless ebb of the sea.