Engineers say the next decade will decide which districts can be defended.

At low tide the mudflats in front of Tanjung Ravel stretch out for almost a kilometre, grey and shining, with fishing boats lying on their sides waiting for the water to come back. At high tide in the monsoon season, the water no longer stops at the old harbour wall. Twice last year it came over the top and into the market streets behind, flooding shops to knee height and leaving a line of silt on the walls that is still visible.

Ravel is one of a string of harbour cities along the eastern gulf that are now spending heavily on sea defences. Across the region, engineers and planners say the coming ten years will decide which neighbourhoods can be protected by walls, gates and raised land, and which will have to be gradually given up.

A wall built in sections

The biggest project is in Ravel itself. Work began in the spring on a 14-kilometre sea wall that will run in an arc around the harbour mouth, with three tidal gates allowing boats in and out. The first 2.5-kilometre section, protecting the port and the old fish market, is due to be completed in two years. The rest depends on money that has not yet been found: the full scheme is estimated at roughly four times the city’s annual budget.

Engineers have designed the wall so it can be raised by a further metre later in the century without rebuilding the foundations. That decision added around a fifth to the cost but was, the project’s lead engineer said, unavoidable.

“Every wall we build is a guess about the sea in 2080. If we guess too low, we have wasted the money. If we guess too high, we cannot afford to build anything at all. So we build for the middle and leave room to grow,” said Dewi Santoso-Hale, chief engineer of the Ravel coastal authority.

Santoso-Hale, who trained in the lowlands of another continent before returning home, spends much of her time explaining that a wall alone is not enough. Rainwater that falls behind the wall must still be pumped out, and much of Ravel’s ground is sinking by several centimetres a year because of decades of groundwater extraction. The authority has started to close illegal wells and to pipe treated river water to factories instead.

Who gets protected

The harder questions are about priorities. In Port Amaran, two hours up the coast, the first stage of a smaller wall will shelter the container terminal and the central business district. The fishing villages to the north, home to around 30,000 people, are not included in any current plan. Community leaders have accused officials of protecting cargo before people.

A planner in Amaran, who asked not to be named because she was not authorised to speak publicly, said the choice reflected where money could be raised. Port authorities and developers can contribute to defences that protect their own assets; fishing villages cannot. She said the city was considering a different approach in the north – restoring mangrove belts and raising houses on stilts – but that the funding for that was also uncertain.

  • Tanjung Ravel: 14km wall with three tidal gates, first section due in two years
  • Port Amaran: 6km wall around the port and business district, northern villages excluded
  • Sabak Lama: mangrove restoration along 20km of shoreline, no hard wall planned

The mangrove alternative

Further south, in Sabak Lama, local officials have chosen not to build a wall at all. Instead they are replanting mangroves along the shoreline, where shrimp farms cleared them in the 1990s. Mangroves slow waves and trap sediment, helping the land build up naturally. They also cost a fraction of concrete. The trade-off is time: a newly planted belt takes a decade or more to offer real protection, and it cannot hold back the sea in front of a dense city centre.

Back in Ravel, the market traders have mixed feelings. Haji Rosli, who has sold dried fish from the same stall for thirty-one years, watched the new wall’s foundations go in from his doorway. He is glad of it, he says, but doubts it will be finished in his working life. “They tell us ten years,” he said, gesturing at the line of silt on his wall. “The sea does not wait ten years.”