Japan Built an Airport on the Sea. Now It's Sinking.
The Sinking Island
Watch the documentary 'Japan Built an Airport on the Sea. Now It's Sinking.' — the filmed companion to our Kansai International Airport investigation. The written analysis works through three decades of settlement data; the film shows what those numbers look like on the ground: a terminal held level on hydraulic jacks, runways repaved to flex with a still-moving island, and an airport that has kept operating while slowly descending towards the sea. Production notes and a viewing guide are below.
What Happened
Osaka needed an airport its neighbourhoods could not host, so engineers built one on two man-made islands in the bay. The engineers knew the seabed clay would compress; nobody knew by how much. The first island went down further during reclamation than forecasts allowed for decades of operation, and the gap between prediction and measurement never closed. The airport opened in 1994 and has flown ever since — held up by jacks, raised seawalls and constant surveillance.
Inside the Documentary
The written investigation dissects the geotechnical record in detail. The documentary adds the dimension text cannot carry: the scale of two islands raised from roughly 400 million cubic metres of reclamation fill, the jacking operation that keeps a working terminal level, and aerial context for what settling towards sea level means for a runway ringed by water. It also reconstructs the September 2018 night when Typhoon Jebi flooded the airfield and a drifting tanker cut the only bridge — the moment an engineering footnote became an operational emergency.
Every figure on screen comes from the same record as the written piece: operator settlement data, the peer-reviewed Mesri and Funk analysis published in 2015, and contemporaneous reporting. Where Japanese engineers contest the long-range projections, the film says so. No scene claims the airport is closing — settlement has never shut it for a day.
If you are choosing between the two: read the investigation for the numbers, the sources and the executive lessons; watch the film for a physical sense of a megaproject slowly negotiating with the sea. Both end at the same question — how do you price a forecast you cannot test?
Read the Full Investigation
Investigation PIA-INV-015 — the complete written forensic analysis, key facts, executive lessons and FAQs.
Frequently Asked Questions
The first island was down about 8.2 metres by 1990 — before opening — against a prediction near 5.7 metres. By December 2012 the averages stood at 12.9 metres for Island I and 14.2 metres for Island II; operator data quoted in 2025 reporting puts them around 13.7 and 17.5 metres.
The islands rest on deep beds of soft clay beneath Osaka Bay. The weight of the reclaimed fill squeezes water out of that clay — consolidation — and the clay compressed far quicker than pre-construction laboratory tests suggested. Millions of vertical sand drains sped the process up but could not cap how far it would go.
The 2015 peer-reviewed projection has parts of the second island at sea level around 2056 and the first around 2067, with a key safety threshold on Island II passed around 2023. Japanese engineers contest elements of that outlook and countermeasure work continues. What is not in dispute: the design's safety margin was consumed decades ahead of plan.
Phase 1 is generally quoted near ¥1.45 trillion — roughly US$14 billion at historical rates — and cumulative outlay including the second island and settlement countermeasures reached about US$20 billion by 2008. Jacking, seawall and monitoring work continues to add to the bill.
When Typhoon Jebi struck in September 2018, floodwater covered the runways and reached underground plant rooms, and a tanker torn from its moorings rammed the airport's sole road-and-rail link. Thousands of travellers were stranded — a demonstration that a sinking island's real exposure is the shrinking gap between runway and sea.
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