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Are We Sinking?

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By Eric Dasmalchi
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I saw this article in the Chronicle today: The nation’s largest cities are sinking, including San Francisco. At the top was a photo of the Treasure Island project from last year, including my building and captioned “Treasure Island, seen here in 2024, is among the locations in San Francisco that is experiencing subsidence due to the compaction of filled-in land”.

At first glance one might be rather worried about this, especially since the choice of image highlighted new development on the island. Curious, I looked up the study referenced in the article to learn more. Here it is: Land subsidence risk to infrastructure in US metropolises. Treasure Island is mentioned as a “localized zon[e] where the land is sinking faster than 5 mm per year”. Fair enough, but as the figure makes clear that’s only really true along the northwest edge of the island (the red area below).

San Francisco subsidence map. Red dots showing high subsidence are present on the northwest corner of Treasure Island, along Islais Creek, and in the southeast corner of the city.

Extended Data Fig 2, excerpt, Land subsidence risk to infrastructure in US metropolises, page 14

There is no intensive development planned for that edge of the island, though the bottom edge of the red zone could extend into a development area. Evidently quite a bit of thought (and money) has been put into geotechnical considerations. Many project documents are available online, with the Design for Development being one of the most informative.

Treasure Island development intensity chart. Development is concentrated around the intermodal hub/ferry terminal, with the northern side of the island being largely open space.

Development intensity and open space, TI YBI Design for Development, page 15

Going back to the journal article, it offers several strategies for mitigation and adaptation. Quite a few of these are already in place on TI.

Figure listing subsidence mitigation and adaptation measures. See article "Land subsidence risk to infrastructure in US metropolises linked above"

Fig. 5 | Addressing land subsidence through integrated management approaches., Land subsidence risk to infrastructure in US metropolises, page 7

The Treasure Island Development Authority’s April 16, 2025 board meeting included a report and presentation on the upcoming phase 2 major construction start. These include some insights into the geotechnical process. Also note that the northwest side of the island is… phase 8. Let’s hope it doesn’t sink too far before then.

treasure island, development
ti development climate
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