Towards the end of 2023, the San Francisco Bay Area faced an unprecedented onslaught of rain, with atmospheric rivers pouring hundreds of inches across the region. However, this excessive rainfall is just one facet of our city's challenges. Much of San Francisco's infrastructure is built on artificial fill—land created by piling up soil, mud, rocks, rubble, and dirt—posing an alarming question for the people of San Francisco: are our buildings literally sinking into the ground? This phenomenon, known as soil liquefaction, has developers scrambling for solutions.
The Leaning Tower of Pisa serves as an excellent example, demonstrating that buildings with foundations on landfill can sink. The construction process often disregards landfill ground, assuming the foundation alone provides sufficient stability. Post-construction, the building's weight exerts pressure on the landfill soil, displacing water and inducing instability, a process accelerated by earthquakes or, as seen in the Bay Area with recent atmospheric rivers, heavy rainfall.
On average, Downtown San Francisco receives 2 to 7 inches of rain in December. However, December 2023 shattered records with over 33 inches of rainfall. This remarkable precipitation is not just an anomaly; it's intricately linked to the city's vulnerability to the climate crisis. Massive atmospheric rivers lingering over San Francisco and intensified weather patterns, driven by climate change, contributed to this extreme event. Scientists warn that such instances are likely to become more frequent, with projections indicating a two-thirds increase in precipitation by the century’s end, further challenging the city's infrastructure to cope with these escalating weather extremes.
Given the impact of soil liquefaction and persistent rainfall, it's unsurprising that numerous areas in San Francisco have experienced these effects. The Millennium Tower, a prominent example, has been sinking at a rate of 3 inches per year for the past decade, resulting in a total westward tilt of 30 inches. However, this issue extends beyond the city's tallest skyscraper to affect a significant portion of the ground supporting San Francisco’s foundations. Approximately 56% of the city’s land sits on landfill, rendering it particularly susceptible to the effects of soil liquefaction. As the city sinks, rising sea levels and coastal flooding, exacerbated by climate change, further threaten San Francisco's infrastructure.
The history of filling in marshlands in the Bay Area adds complexity to these challenges. Centuries ago under the stewardship of the Ohlone and Miwok peoples, the Bay Area's coastline looked vastly different, featuring marshlands and wetlands that served and continue to serve as vital ecosystems. However, during the late 1800s and early 1900s, much of these marshlands were stolen by settlers-colonists who enacted drainage efforts. Levees were constructed, and the land was “reclaimed” for agriculture and urban expansion. The mid-1800s U.S. Swamp Land Acts facilitated this trend by allowing individuals to claim wetlands or marshlands for agricultural purposes by draining them. In the late 1950s, a study by the Army Corps of Engineers revealed a staggering 243 square miles of land had been reclaimed, representing former marshlands and wetlands filled for human settlement and economic activities.
The consequences of these historic measures on the natural environment are evident. Marshland alterations disrupted ecosystems, led to biodiversity loss, and eliminated natural barriers against coastal erosion. The filling in of marshlands removed the buffer against rising sea levels and storm surges, exacerbating the challenges faced by San Francisco today.
BAYCS in collaboration with the South Bay Salt Pond Restoration Project for a Workshop on Saturday, September 9th, 2023.
In recent times, there's a growing awareness of the environmental consequences of these practices. Organizations such as The Watershed Project in Richmond, CA, Save The Bay, and Turtle Island Institute are actively working towards restoration efforts. The Watershed Project focuses on community-based environmental education and habitat restoration, addressing the impacts of historic practices on the Bay Area's natural landscapes. Save The Bay is dedicated to protecting, restoring, and celebrating the San Francisco Bay, actively engaging in marshland restoration projects. Turtle Island Institute contributes Indigenous perspectives and knowledge to ecological restoration efforts, emphasizing the importance of holistic approaches to environmental justice.
Understanding the historical implications of marshland alterations provides a crucial perspective on San Francisco's current predicaments, emphasizing the need for sustainable development practices prioritizing environmental conservation and resilience. Addressing soil liquefaction and marshland restoration requires collective action, necessitating swift and organized efforts to implement strategies that mitigate these issues and build a more resilient urban environment.
*Author's note: if you are interested in taking an active role in stewarding resilience between our local marshlands and human communities, please check out this list of organizations and collectives.
Beckett, Lois. “Sinking Feeling: San Francisco’s Millennium Tower Is Still Leaning 3in Every Year.” The Guardian, 11 Jan. 2022, https://www.theguardian.com/us-news/2022/jan/10/san-francisco-millennium-tower-sinking.
Griggs, Troy. “More of the Bay Area Could Be Underwater in 2100 than Previously Expected.” The New York Times, 7 Mar. 2018, https://www.nytimes.com/interactive/2018/03/07/climate/san-francisco-sinking-land-flooding-climate-change.html.
Kahramaner, Deniz. “Soft Soil: The Untold Problem with 56% of San Francisco’s Properties.” Atlasa, 26 May 2018, https://medium.com/atlasa/liquefaction-the-untold-issue-with-56-of-san-franciscos-properties-dfc8ad291681.
O’Mara, Kelly. “Large Parts of the Bay Area Are Built on Fill. Why and Where?” Kqed.org, https://www.kqed.org/news/11799297/large-parts-of-the-bay-area-are-built-on-fill-why-and-where. Accessed 31 Jan. 2024.
Romero, Ezra David. “San Francisco’s Aging Infrastructure Isn’t Ready for Its Wetter Future.” Kqed.org, https://www.kqed.org/science/1983299/san-franciscos-aging-infrastructure-isnt-ready-for-its-wetter-future. Accessed 31 Jan. 2024.
“San Francisco Bay Area Cities Built on Landfill Are Sinking Faster, Study Finds.” CBS San Francisco, 7 Mar. 2018, https://www.cbsnews.com/sanfrancisco/news/san-francisco-bay-area-cities-built-landfills-sinking-faster-study-finds/?gclid=Cj0KCQiA-62tBhDSARIsAO7twba61ukg7FQbA6e8Oqtkg7A81xcoOPcqMJGn4z0LG2GY-is5iFjEqLsaAqblEALw_wcB.
Sfchronicle.com, https://www.sfchronicle.com/projects/weather/california-rain-totals/. Accessed 31 Jan. 2024.